# Sticky  Ask Me Anything with Peter Aylett



## VerticalScope

Hello AVS!

Welcome to the Ask Me Anything with Peter Aylett!

An integrator of over 30 years and now a partner at HTE Acoustic Interior Design, Peter currently chairs the CTA/CEDIA R10 Standards Committee as well as one of its workgroups currently re-writing best practice for entertainment space/cinema/theatre audio design.

If you have any questions concerning industry standards for designing and setting up home theaters, or want the perspective of an experienced engineer then Peter is your guy to ask for robust answers that are highly detailed and product-agnostic.

This thread is now open, and will run until Sunday, Nov. 28th! We can't guarantee that every question will be answered, but even if not, you'll still be seeing some interesting responses.

Looking forward to seeing your questions!

Welcome Peter!

All the best,
Dan


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## AmishAnarchist

Why aren't manufacturers in this industry held to higher standards? There's no excuse for making TVs with only 1 full speed HDMI port in the 21st century. Yet, most manufacturers did it with HDMI 2.0, and now they're doing it again with 2.1. It's ridiculous.

Second. Why does the industry refuse to move on from IR remotes? Nobody offers BT or RF all these years even on premium models of HT equipment.


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## J. Atkinson

AmishAnarchist said:


> Why aren't manufacturers in this industry held to higher standards? There's no excuse for making TVs with only 1 full speed HDMI port in the 21st century. Yet, most manufacturers did it with HDMI 2.0, and now they're doing it again with 2.1. It's ridiculous.
> 
> Second. Why does the industry refuse to move on from IR remotes? Nobody offers BT or RF all these years even on premium models of HT equipment.


You understand he is an Acoustics expert right? CEDIA standards for acoustics.


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## Peter Aylett

J. Atkinson said:


> You understand he is an Acoustics expert right? CEDIA standards for acoustics.


No worries. I'll play!

1. Cost. In a REALLY competitive market, it costs manufacturers far more money to implement that latest tech as the silicon is more expensive. By the time that silicon cost comes through the supply chain, even $10 extra at retail can send a marketing department into a spin
2. 'Higher Standards' - Interesting phrase. As a professional, I will choose the equipment that best meeds the needs of my customer, and what I promised them. Generally, all my sources are connected to an AVR/processor so a single HDMI socket is enough! Different scenarios need different levels of functionality. Why pay for something you don't need...
3. We're beginning to see a shift towards RF remotes in all their different flavours. AppleTV, Amazon Fire TV Stick already use BT. Many TV remotes that use gyro motion sensing to move a cursor around the screen use RF remotes. Agin, it comes down to cost. IR is cheap, simple and zero config for most people.


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## nathan88

From an acoustically point of view, in home cinemas that are normal rooms and not dedicated spaces, is it better to have a lot of stuff (like shelves with books, furniture, etc) or it's usually better to keep the room less crowded?

Does a room filled with stuff makes audio calibration tougher?


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## robav1

I have questions regarding construction of riser. I am trying to build a bass trap and have some questions. Room is The platform is 10'3" wide by 6 with a 2" landing. I am constructing it with 2x6 (10x8). On top I am running 2x8 for the 6' platform. I am either going with sandwich of roofing paper with 1/2 inch, or just 3/4 osb subfloor. Fill with pink or rockwool.???

The basement flooring is laminated flooring with moisture barrier underneath. I was planning on building the platform on top of a piece of carpet padding that I had laying around. Note back of riser goes to wall. It was a very quick sketch!

Ceiling is low (7'6") but need platform to be approx 14" up to see over front chair.
Not really clear by my "drawing" , but there will be an approx 2' landing behind front row as a step and path to riser chairs. That makes platform approx 10x8 (6x8 where top chairs will be located). Platform will overhang by 2" and will be carpeted.









Questions: Thank you in advance!

1- Does this build make sense? Should platform extend wider than 10 feet wide?
2- Where should bass trap vents go? How many vents and what size? I understand they should be back against wall and on side. However, platform is approx 2 feet from one side wall (and 4 feet on other side). So unsure about side locations.
3- Room is in basement and planning on using black,lined curtains on sides and to just next to screen. This will help cover the side alcove where a future snack bar may go. Not sure if will curtain the rear as there are 2 AC vents. If no curtains in rear would consider acoustical panels. However, don't use ac in basement too often and can open curtains to allow air prior to watching (or have cutouts made in the curtains. There is currently no door to room. May add a hidden bookcase door in future.
4- Should rear sub go on platform next to chair or on floor between platform and wall?


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## ARROW-AV

Hello Peter,
First and foremost I want to say thank you for taking the time to do this and answer peoples questions and for all of your hard work regarding industry standards.

For the benefit of those who are not in the know please can you kindly explain what is the CTA/CEDIA R10 Standards Committee, and what is RP23, RP22, and RP1, why these matter, and how will these affect the home theater market moving forwards?


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## Peter Aylett

nathan88 said:


> From an acoustically point of view, in home cinemas that are normal rooms and not dedicated spaces, is it better to have a lot of stuff (like shelves with books, furniture, etc) or it's usually better to keep the room less crowded?
> 
> Does a room filled with stuff makes audio calibration tougher?


Great question.

A reply detailing all the facets of the way speakers, rooms, stuff in rooms and listeners interact would take a year. Probably the most important aspect, and one that's quite straightforward to explain and measure is RdT - Reflection decay Time. You'll usually see this stated as 'RT60', and one of the great acoustics myths is that it is a single number. RdT is usually stated over an octave band (an octave being a doubling of frequency). The most common octave band to see it stated is 500Hz to 1KHz. The RT60 time is how long it takes for sound to decay by 60dB and is a measure of how reverberant a space is (an echo is a discrete sound, reverberation is a combination of all the decaying echos). Sound is absorbed by stuff to different degrees and dependent on frequency. High frequencies (Above 4KHz) are REALLY easy to absorb. Carpet and its underlay do an excellent job. Midrange frequencies (Around 400Hz to 4KHz) are easy to absorb at the top end of the frequency range getting increasingly harder as the frequency goes down. Bass (Below 400Hz) is REALLY hard to absorb.

The 'correct' RdT time is hotly debated. Around 0.3s to 0.35s is a good number to aim for without doing a complex calculation. Others may disagree (-:
The trick is to consider all frequencies, and to have your absorption as linear and even as possible across the audible frequency spectrum (With a pragmatic, but not massive allowable rise in the RdT below around 150Hz in most room sizes). So, use some inexpensive software, an inexpensive measurement microphone, and a free tone generator to measure the RdT time of your room from 62.5Hz up to 8KHz. That will then tell you where you are and what you may need to do next. The mistake most people make is to over absorb high frequencies (Using lots of 25mm / 1" Absorption material), but barely touch low frequencies. This ends up in a dead and boomy room -YUK!

The great Floyd Toole talks about 'The acoustical treatments of life' such as carpet, curtains, sofas, people, chairs, beanbags etc. You may well find that in a normally furnished room, you don't need much extra material at all to achieve good and linear RdT times at high/mid frequencies. At bass frequencies, however, you may need to do some work. 

To answer your calibration question - A room with lots of broadband bass absorption is far easier to calibrate as the room mode and null extremes are flattened, thus leading to a far more even bass frequency response across the room. Having stuff in a room is generally much better than having a bare room.


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## Peter Aylett

ARROW-AV said:


> Hello Peter,
> First and foremost I want to say thank you for taking the time to do this and answer peoples questions and for all of your hard work regarding industry standards.
> 
> For the benefit of those who are not in the know please can you kindly explain what is the CTA/CEDIA R10 Standards Committee, and what is RP23, RP22, and RP1, why these matter, and how will these affect the home theater market moving forwards?


Great questions, and very close to my heart...

The CTA (Consumer Technology Association) has long been a standards development organisation. Since most of their members are manufacturers, their standards focus on product and component level ones. Around 15 years ago, CEDIA (Custom Electronic Design and Installation Association) created the R10 Standards Committee with The CTA (The CTA already had 1 to 9...) to focus on standards and recommended practices related to the installation of technology into residential environments. Last year, CEDIA itself became an ANSI Accredited Standards Organisation and has now taken over the running of R10 though it absolutely remains a joint CEDIA/CTA effort.
The key with R10 (and all the other CTA 'R' committees) is industry consensus. R10 is the only totally product and commercially agnostic standards committee within the installed residential technology space. Any member of either The CTA or CEDIA has the right to participate - The working groups are not, and cannot be selective so to ensure there is no bias. There are rules for conducting meetings with respect, and 'lurkers' may be asked to either contribute occasionally or withdraw from the workgroup. Prices, products and brands are NEVER discussed and the Chairs ensure that everyone can have their say, and their position debated. 

Under R10, there are a number of workgroups. The current active ones are - 
WG1 - Audio
WG3 - Video

WG1 is currently working on - 
RP22 - Recommended Practice for Multichannel Audio Room Design (Though this title will likely change). This will be the definitive recommended practice on the design of the room and system for private cinema/theatre/screening room/media room design. We hope to finish by February next year.
RP1 - Performance Facts. A recommended practice for manufacturers to give us engineers the objective facts we need to make informed specification decisions. As an example, we are likely removing Watts as a recommendation for both amplifier and speaker specifications, and replacing it with short and long term voltage capacity (At 2,4,6 & 8 Ohms for amps, and with an impedance curve for speakers).
RP??? - When RP22 is done, we'll move onto a recommended practice for the measurement and verification of audio systems.
WG3 is currently working on - 
RP23 - Recommended Practice for Video System Design. Both projection and flat panel.

As part of RP22 and RP23 we are introducing four different levels of overall objective system performance. The metrics will be predictable at the design stage, and measurable/veifable at commissioning. Level one is the baseline for what we feel reproduces a basic level of artistic intent. Level four is at the bleeding edge of what is achievable and is draconian in its requirements.

PLEASE don't ask me any more specifics about performance levels as we've not yet finished and I can't share the information as it's not mine to share (-:

My belief is that these works, when complete and looked at as a whole, will shift the conversation away from 'what brand or product do you recommend', and towards performing engineering design to ensure consistency of performance BEFORE then specifying the correct product to meet the engineering need.


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## dschulz

If you live in an area with a stable electric grid and very low danger of lightning strikes, how much should you worry about power? Just get whole-house surge suppression and call it day? Or should one look into isolation transformers, power conditioning, balanced power, additional surge suppression at the rack, etc?


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## cricket9998

How do I know if a speaker has SBIR issues, particularly my LCR front stage?

I was thinking of making 6” thick safe n sound acoustic panels and put them right behind each tower since there will be a small gap I can’t remove and even though this would push them out more, it should absorb reflections right?


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## dcowboy7

Why cant i change my tvs screen aspect ratio when watching 4K ??
For example if im watching something thats 2.35 2K i can switch it to 16x9 to fill the screen.
Yea yea i like it that way sometimes. 
But if im watching something thats 2.35 4K i cant switch it to 16x9.
Tried on amazon 4K fire stick & 4K bluray....no dice.


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## JonasHansen

Peter Aylett said:


> To answer your calibration question - A room with lots of broadband bass absorption is far easier to calibrate as the room mode and null extremes are flattened, thus leading to a far more even bass frequency response across the room. Having stuff in a room is generally much better than having a bare room.


A follow up question here:

In more and more newer designs, I see much less use of the typical bass traps (either OC703 triangles in the corner or various pressure based absorbers in high-pressure zones). Instead the bass is optimized by placing seats and multiple subs accordingly and seat-to-seat variation and modes are close to being eliminated. (<80-100hz only though)

What is your treatment design principles when it comes to managing the bass in a home theater?


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## nathan_h

cricket9998 said:


> How do I know if a speaker has SBIR issues, particularly my LCR front stage?


Every speaker in a room unless the walls are far away has SBIR....

I am curious where Peter prioritizes dealing with SBIR versus room modes, decay time, etc. and whether he subscribes to the approach of using in wall speakers (baffle wall design) as a way to remove SBIR from that direction?


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## nathan_h

dcowboy7 said:


> Why cant i change my tvs screen aspect ratio when watching 4K ??
> For example if im watching something thats 2.35 2K i can switch it to 16x9 to fill the screen.
> Yea yea i like it that way sometimes.
> But if im watching something thats 2.35 4K i cant switch it to 16x9.
> Tried on amazon 4K fire stick & 4K bluray....no dice.


Typically this ability to ZOOM is a feature of the TV/display, and not the source (though some video processors can do it, too) -- though of course some TV's these days don't include this feature, either.

I am curious about Peter's view on constant image height setups, though I understand he is more on the acoustics side than the display side.

So perhaps Peter can share his view about angles of spread for left and right speakers -- such as "behind the screen" in a constant image height setup, and "aside the screen" for a 16x9 screen?


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## robav1

robav1 said:


> I have questions regarding construction of riser. I am trying to build a bass trap and have some questions. Room is The platform is 10'3" wide by 6 with a 2" landing. I am constructing it with 2x6 (10x8). On top I am running 2x8 for the 6' platform. I am either going with sandwich of roofing paper with 1/2 inch, or just 3/4 osb subfloor. Fill with pink or rockwool.???
> 
> The basement flooring is laminated flooring with moisture barrier underneath. I was planning on building the platform on top of a piece of carpet padding that I had laying around. Note back of riser goes to wall. It was a very quick sketch!
> 
> Ceiling is low (7'6") but need platform to be approx 14" up to see over front chair.
> Not really clear by my "drawing" , but there will be an approx 2' landing behind front row as a step and path to riser chairs. That makes platform approx 10x8 (6x8 where top chairs will be located). Platform will overhang by 2" and will be carpeted.
> View attachment 3200731
> 
> 
> Questions: Thank you in advance!
> 
> 1- Does this build make sense? Should platform extend wider than 10 feet wide?
> 2- Where should bass trap vents go? How many vents and what size? I understand they should be back against wall and on side. However, platform is approx 2 feet from one side wall (and 4 feet on other side). So unsure about side locations.
> 3- Room is in basement and planning on using black,lined curtains on sides and to just next to screen. This will help cover the side alcove where a future snack bar may go. Not sure if will curtain the rear as there are 2 AC vents. If no curtains in rear would consider acoustical panels. However, don't use ac in basement too often and can open curtains to allow air prior to watching (or have cutouts made in the curtains. There is currently no door to room. May add a hidden bookcase door in future.
> 4- Should rear sub go on platform next to chair or on floor between platform and wall?


Follow up... my ceiling is Ceilume ceiling tiles with fiberglass ins in the joists above. Is this going to be an issue? ...especially if using Atmos??? If so, do you have an acoustical suggestion to remediate?


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## nathan88

We read a lot about the benefits of dual subwoofer vs one subwoofer in home cinema. Most modern AV receivers and audio processors have two sub outputs, for using dual subwoofer.

But I have seen a lot of guys that are using more than two, 3, 4, 5 even 6 subwoofers and not in large rooms but in regular size rooms. Moreover, they also buy the largest and most powerfull subwoofers they can afford.

My question is, when it comes to number and size of subwoofer, when do we stop? Is it too many and too big something that is not only unnecesary but it is actualy detrimental?


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## imagic

Hi @Peter Aylett 

AVS Forum is, of course, full of members who worship at the altar of deep bass, done right. I count myself among them.

I am curious about the whole topic of infrasonic bass and seek your opinion on a couple of things:

1. If cost is no object, what's roughly the lowest frequency (in Hz) that's worth chasing after for home theater, in your opinion? 

2. While there are lists that cover deep bass in movies, so we know where to find it, I am wondering how much content below 16 Hz is truly intentional? How about single-digit Hz content, already very rarefied, how much of that is intentional? And if it is intentional, under what conditions are frequencies like that being mixed and monitored? How does the viewer know they are honoring "artist's intent"?


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## Reddig

How much space should be between my compression loaded horn speakers and my .8 gain AT weave screen? Right now I’m at about 6 inches of space between the front of speaker and back of screen material roughly. Thanks.


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## Worf

I have a simple question related to the first - why isn't there a standard for RF remotes? IR remotes are great because they all adopted the NEC protocol so it's easy to design a remote to do it all. But with the annoying shift to RF remotes, it means I back to having a half dozen devices on my table and a ream of paper explaining how to configure the settings on every device. Back when the Harmony remote was a thing, this was easy, but now it's back to being an annoyance.

How in the world is this moving forward? Going from a mess of remotes down to one programmed to do it all and now back to a million remotes again. What does an installer do - surely you don't tell your customer that they have to live with a table full of remotes? Is there a potential standard in the works to make it so it's possible to consolidate?

Also, we generally know things like CEC are flaky - are there plans to improve and standardize things so it becomes more reliable? In many cases it works, until it doesn't, and in other cases it just doesn't work at all.


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## niterida

What are your thoughts on using a soft baffle wall. A few of us have been discussing the benefit of just have the front wall filled with insulation and the speakers flush with the face of the insulation. So no hard MDF wall - just the insulation (covered with AT material of course). My thoughts are that the absorption by the insulation would have the same effect as the reduction of reflections with a hard baffle, but the open faced insulation will provide much better bass / lower frequency trapping/absorption. It is much simpler, easier and cheaper than building a proper baffle wall. 
We have done some internet searching and can't find any research or even any other in-depth discussions on this.
Thanks for your time and effort in helping out AVS Forum


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## ereed

@Peter Aylett I have a question about testing subwoofers. As far as I know of the 3rd party data-bass.com is where it shows full measurements in complete detail. I'm starting to see companies only providing basic measurements and not full shown measurements for consumers. What are your thoughts of testing methods beyond CEA and if compression and distortion will be included in that?


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## Sheeraz Khan

VerticalScope said:


> View attachment 3198911
> 
> 
> Hello AVS!
> 
> Welcome to the Ask Me Anything with Peter Aylett!
> 
> An integrator of over 30 years and now a partner at HTE Acoustic Interior Design, Peter currently chairs the CTA/CEDIA R10 Standards Committee as well as one of its workgroups currently re-writing best practice for entertainment space/cinema/theatre audio design.
> 
> If you have any questions concerning industry standards for designing and setting up home theaters, or want the perspective of an experienced engineer then Peter is your guy to ask for robust answers that are highly detailed and product-agnostic.
> 
> This thread is now open, and will run until Friday, Nov. 26th! We can't guarantee that every question will be answered, but even if not, you'll still be seeing some interesting responses.
> 
> Looking forward to seeing your questions!
> 
> Welcome Peter!
> 
> All the best,
> Dan


Hello Dan,

I'm planning to get a subwoofer for my Home theater system. My room is 284 Sq. ft/2,272 Cubic ft., and it will be open on one side. I'm really interested in SVS- PB 2000, but it's price point is higher. My budget is around $500, so can you recommend any other subwoofer with similar specs in that price range ? Thanks!


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## veeracs

Hello Peter,

My home theater is 16'Wx24'L with two rows of 3 seats each. I have a wall on the left side and I installed heavy blackout curtains on the right side (no wall and two pillars). I've installed three 6"ng (2'x4') bass absorbers on the ceiling and alternate bass absorbers (6' - 2'x4') and diffusers (2D) on the left wall. I have a 6' (2'x4') bass absorber on the rear wall between Back Left and Back Right speakers and a diffuser (3D - 2'x4') on the outside of these speakers. On the front wall, I have a 6' (2'x4') base absorber behind the center channel. I'm planning to install corner bass absorbers sometime in the future.

Is there anything else I can do to improve sound quality in my room? Are curtains good enough or should I build a wall on the right side for better sound?
Also, when I build the riser platform (12'x6'x12"), should add holes of various sizes on the front (facing frontwall) and backside (facing backwall)?

Appreciate your advice. Thank you!

P.S. I haven't really measured the room at the moment as I want to do it once I install the riser platform with second row seating. But it sounds really good at the moment for what I've done. I have RMC-1L as a preamp and Parasound A51 and PS Audio M700 as power amps, SVS Ultras, and PB-16 subwoofer.


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## TheUO

Peter Aylett said:


> RP22 - Recommended Practice for Multichannel Audio Room Design


I see the concept of levels as a goal that you've specifically identified. Are there other overarching goals that are driving the development of RP22 and RP23 that you can share with us?



Peter Aylett said:


> Level one is the baseline for what we feel reproduces a basic level of artistic intent.


Can we actually understand the artist's intent in a way that allows us to measure equipment against? Perhaps it's just me but the concept of an artist's intent seems too subjective for anyone else but the artist to ever truly understand. I feel I'm being too philosophical about this and would like to know if there's some science behind it.



Peter Aylett said:


> As an example, we are likely removing Watts as a recommendation for both amplifier and speaker specifications, and replacing it with short and long term voltage capacity (At 2,4,6 & 8 Ohms for amps, and with an impedance curve for speakers).


That seems like quite the undertaking to get the industry as a whole to make those changes. How might such changes be facilitated or am I overthinking it?


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## nathan_h

TheUO said:


> Can we actually understand the artist's intent in a way that allows us to measure equipment against?


In this context, this means the artist created the material in a calibrated reference mastering studio. Chasing a similar standard Ed reference playback system lets the viewer see and hear what the artist saw and heard….what they INTEND audiences to see and hear….the “artist’s intent”.



> That seems like quite the undertaking to get the industry as a whole to make those changes. How might such changes be facilitated or am I overthinking it?


I would love to hear more about this too but basically when selling into the custom installer marketplace, manufacturers will either share this data or be at a disadvantage. Another member of the working group has described it like the nutritional label on food. Failure to provide it will be a barrier to sales channels and markets.


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## Holmz

VerticalScope said:


> … or want the perspective of an experienced engineer then Peter is your guy to ask for robust answers that are highly detailed and product-agnostic.
> …


Here I go:
We have a living room, and I am intending on putting the 65” TV in front of the window in a table with a TV lift.
(Currently it is on the hearth above the fireplace)

The 2.0 is not in the room yet.
The sound is finally somewhat usable out of the LG OLED 65” with a lot of futzing around with various settings.
However I did order a used AVR preprocessor, which has arrived, but has not yet been set up.
I am intending on have the front left and front right go into the 2.1 system and using a fixed (marked) volume setting so that the AVR room correction can work. Then those two channels will go through the 2.0 side.

I picked up some wall mount surround speakers for the RR and LR, as well as a Center channel… which are from the same manufacturer as the 2.1 speakers.

I am intending on powering the LF and RF with the tube amp, and the center and surrounds with Class-D.

There is a sub with the 2.1, and i have another couple of 12 subs which I will make boxes for either as sealed or maybe 4th or 6th order bandpass.

I have access under the house, and a bunch of Neutrik XLR connectors and wiring, and chassis mounts to put into the floor in order to run signal wires closer to the speakers (under the floor). 
Should I even consider 5.2.2 or 5.2.4 with the 11 foot high ceilings? And if so which?
What general wisdom should be paying attention to?

The Haus-Boss does not want it to become a home theatre room, so it will have to remain somewhat stealthy and tasteful.

We normal stream NetFlix from the TV or from a NUC as the source. The AVR-Processor will require the NUC (I think) to separate the audio(? And delay the video), but maybe the OLED outputs the ARC for the AVR-Processor to do its thing. 

Kindergartener sketch (speaker location I am considering are marked in red, and the sketch is a bit lopsided… sofa and door are a bit further to the right hand side.):


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## Peter Aylett

1.


dschulz said:


> If you live in an area with a stable electric grid and very low danger of lightning strikes, how much should you worry about power? Just get whole-house surge suppression and call it day? Or should one look into isolation transformers, power conditioning, balanced power, additional surge suppression at the rack, etc?





dschulz said:


> If you live in an area with a stable electric grid and very low danger of lightning strikes, how much should you worry about power? Just get whole-house surge suppression and call it day? Or should one look into isolation transformers, power conditioning, balanced power, additional surge suppression at the rack, etc?


The only actual input into your system is power. I know many top private cinema designers who will ALWAYS use an isolation transformer on every project. The results will depend on - 
1. How clean the power is coming into your home
2. What devices you may have plugged in creating noise and harmonics. Some switched-mode power supplies are very bad at this.
3. The sensitivity of the components you use to power issues

I would always use an AV-specific (as opposed to stuff made for the I.T. world) power conditioner/surge protector on racks of stuff purely for protection. I've never seen or heard a quality difference, but the peace of mind in terms of protecting expensive equipment is worth it. I HAVE, however, heard the sonic benefits of using AV specific isolation transformers on systems. Whatever you do, ensure that the product does not raise the impedance of the line and thus prevent power amplifier power supplies from drawing dynamic power.


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## CP850-CLED

I was pleasantly surprised by this video featuring Peter on HTE's philosophy to find such a strong parallel with my life's work working in technical and architectural acoustics development of form facilitates function in a team leadership capacity with top Italian architects Gian Enrico Fabro, Michele Bonan and my personal favorite Massimo Iosa Ghini, Italian Craftsmen are among the best in Europe although the Turks you will find have honed these fine crafts for much longer, but also in carte blanche collaborations with Zaha Hadid and Jacques Grange out of which the Inspiration for the prototype Dolby Cinema concept was sparked.

Peter and I also have similar life experiences when he mentions that one defective piece of equipment (in my case a stereo minijack which's cable was stapled by the drywall people in a remote never used 95 sq ft. reading Loft accessible only by a long narrow spiral staircase ) in a secondary zone can take down a job with a brilliantly performing cinema. That clicked, as it is the very same reason I stopped doing multiroom in 1999. Although I admit now being tempted to delve into distributed Atmos music.

Motivated by what I hear to be Peter's intent in his committees and what the Raison D Etre at HTE is I will share my findings and observations but also my objecting reservations, much of of which will sound conflicting and iconoclastic to many of the generally accepted (ie. THX 80 hz cutoff) in the hope that some of it sticks with his new committees that hopefully will espouse broader views moving forward.

I will thus post my mini manifesto of what constitutes a great immersive space and I look forward to his impressions.


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## Peter Aylett

cricket9998 said:


> How do I know if a speaker has SBIR issues, particularly my LCR front stage?
> 
> I was thinking of making 6” thick safe n sound acoustic panels and put them right behind each tower since there will be a small gap I can’t remove and even though this would push them out more, it should absorb reflections right?


SBIR (Speaker Boundary Interference Response) happens with EVERY speaker that is not soffit/flush-mounted. It occurs when the audio reflection off a surface returns to the speaker 180º out of phase thus creating cancellation at that frequency. As an example, the wavelength of 94Hz (around the frequency that gives a kick-drum its weight) is 12'. So, if your speaker is 3' from a back wall, the reflection at 94Hz will be 180º out of phase and thus result in a (partial) cancellation.

Get yourself an inexpensive USB Mic, and a free piece of audio measurement software and see for yourself if you are suffering from it, and if so, at what frequency.
Check the specs on whatever absorbing product or material to see what its absorption coefficient is at the frequency that you have an SBIR issue. 6" of conventional foam/fibreglass will have little effect at bass frequencies, but will totally absorb upper midrange/treble. Be VERY careful about using too much as you'll end up with a dead but still boomy room.

It sounds like your speakers are close to the wall, so any SBIR will be higher in frequency so 6" (if you have a problem) Will do the trick but again, take care not to reduce the RdT (Reflection decay time) at upper midrange/treble too much.


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## Peter Aylett

dcowboy7 said:


> Why cant i change my tvs screen aspect ratio when watching 4K ??
> For example if im watching something thats 2.35 2K i can switch it to 16x9 to fill the screen.
> Yea yea i like it that way sometimes.
> But if im watching something thats 2.35 4K i cant switch it to 16x9.
> Tried on amazon 4K fire stick & 4K bluray....no dice.


You should always watch content in its native aspect ratio. if you stretch 2.35 to fit 1.78. you'll end up with everything distorted vertically. If you crop the picture to only show the middle part of the picture, you'll miss out on much of the beautiful work of the cinematographer.


----------



## Peter Aylett

JonasHansen said:


> A follow up question here:
> 
> In more and more newer designs, I see much less use of the typical bass traps (either OC703 triangles in the corner or various pressure based absorbers in high-pressure zones). Instead, the bass is optimized by placing seats and multiple subs accordingly and seat-to-seat variation and modes are close to being eliminated. (<80-100hz only though)
> 
> What is your treatment design principles when it comes to managing the bass in a home theater?


Yikes! This is a 3 hour seminar to discuss, not something I can describe here. The fundamentals, however, are - 

1. RdT (Usually stated as an RT60 time) should be linear through the frequency range. Big bits of foam in corners may have limited effect on bass, but still absorb midrange and treble.
2. It's REALLY difficult to model a room for bass. The model depends on inputting the construction of the room in terms of a surface's impedance to bass. Good luck with that in a home, though with a REALLY expensive build it can be done. So, it's very difficult to predict the high pressure zones to use a pressure absorber, and the room's modal response to predict where seats should go.
3. We build rooms using a system that effectively turns every wall into a big broadband bass trap. The more depth we are given, up to around 15", the lower in frequency it's effective to. The construction is done in a way that does NOT over absorb mid and high frequencies so we end up with very linear RdT.
4. Multiple subs (locate in specific positions) - Usually 2 or 4 identical ones, works really well to mitigate modal issues. Lots of bass absorption combined with multiple subs delivers the best results and most flexible seating locations.


----------



## Peter Aylett

nathan_h said:


> Every speaker in a room unless the walls are far away has SBIR....
> 
> I am curious where Peter prioritizes dealing with SBIR versus room modes, decay time, etc. and whether he subscribes to the approach of using in wall speakers (baffle wall design) as a way to remove SBIR from that direction?


If possible, I would always advocate baffle wall or flush mounting every speaker including subs. This eliminates SBIR, and also increases the efficiency at bass frequencies. Room modes and decay time/impulse response go hand in hand. The energy in the room must be dissipated somehow. If there is little to absorb bass energy, no amount of clever DSP will deliver good bass.


----------



## jamin

Peter Aylett said:


> If possible, I would always advocate baffle wall or flush mounting every speaker including subs. This eliminates SBIR, and also increases the efficiency at bass frequencies. Room modes and decay time/impulse response go hand in hand. The energy in the room must be dissipated somehow. If there is little to absorb bass energy, no amount of clever DSP will deliver good bass.


A question here for clarification please. Admittedly with no absorption there is no decay. And the increase of broadband damping a la Gedes or as perhaps you utilize is wonderful:


Peter Aylett said:


> We build rooms using a system that effectively turns every wall into a big broadband bass trap. The more depth we are given, up to around 15", the lower in frequency it's effective to. The construction is done in a way that does NOT over absorb mid and high frequencies so we end up with very linear RdT.


We have seen that decreasing the amount of energy put into a system at a problematic pesky frequency can result in purportedly acceptable steady state response for bass frequencies. Further that ostensibly we respond favorably to steady state magnitude smoothness in the bass region, see Olive and Toole.

Does this mean that, for example, the Harman SFM and subsequent PEQ is just clever DSP and does not work ?

edit : added subsequent PEQ — duh


----------



## Venue

@Peter Aylett

1) Are corner bass traps a myth, are you better of using DSP and 4 subwoofers, 1 in each corner?
2) In contrast to the above, isn't it true that the less DSP, the better, the more physical acoustic treatment, the better?
3) Can diffusers be recessed into a wall, or does the whole wall need to be recessed for this to work, covered by cloth?
4) Would you rather place diffusion on rear side walls instead of the rear wall, with bipole surrounds on the rear wall, 5.1?
5) Any benefit having 2" absorption behind a non-AT fixed frame screen, mounting the screen flush or 1-2" from the wall?
6) How important is it to seal off an archway leading out to another room, can this be done with somewhat of a thick cloth?
7) Do you know any acoustically transparent carpets that could be used covering pits in front of the screen?

About question #1, Anthony Grimani advocates using bass traps in power corners, and ceiling/wall corners, is this a bad approach, is it a general rule of thumb within the industry to use these, if not, could you explain why, I think lots of members could use the correct information on this, appreciated.

Thanks!


----------



## Wayne Z

The room where I listen to a lot of music has a door that leads into the furnace room. Although the door is weather-stripped, lower pitch (under 500hz) sounds come through the door. What material could I attach the to the back (furnace side) of the door to deaden the sound?


----------



## Albsroses

What should I clean my preamps jacks with if they’re dirty?

Also,

ifni have a preamp, and amp, a phono preamp, a equalizer, a sound processor and a passive isolating device and a receiver what would be the best way to plug them?


----------



## confinoj

Mark Henninger said:


> Hi @Peter Aylett
> 
> AVS Forum is, of course, full of members who worship at the altar of deep bass, done right. I count myself among them.
> 
> I am curious about the whole topic of infrasonic bass and seek your opinion on a couple of things:
> 
> 1. If cost is no object, what's roughly the lowest frequency (in Hz) that's worth chasing after for home theater, in your opinion?
> 
> 2. While there are lists that cover deep bass in movies, so we know where to find it, I am wondering how much content below 16 Hz is truly intentional? How about single-digit Hz content, already very rarefied, how much of that is intentional? And if it is intentional, under what conditions are frequencies like that being mixed and monitored? How does the viewer know they are honoring "artist's intent"?


Mark these are great questions that I’m sure many of us have wondered about as well and hope Peter gets a chance to offer his opinion.


----------



## markus767

Peter Aylett said:


> WG1 is currently working on -
> RP22 - Recommended Practice for Multichannel Audio Room Design (Though this title will likely change). This will be the definitive recommended practice on the design of the room and system for private cinema/theatre/screening room/media room design. We hope to finish by February next year.
> RP1 - Performance Facts. A recommended practice for manufacturers to give us engineers the objective facts we need to make informed specification decisions. As an example, we are likely removing Watts as a recommendation for both amplifier and speaker specifications, and replacing it with short and long term voltage capacity (At 2,4,6 & 8 Ohms for amps, and with an impedance curve for speakers).
> RP??? - When RP22 is done, we'll move onto a recommended practice for the measurement and verification of audio systems.
> WG3 is currently working on -
> RP23 - Recommended Practice for Video System Design. Both projection and flat panel.


Will these "recommended practices" documents be made available to the general public once finalized?



Peter Aylett said:


> My belief is that these works, when complete and looked at as a whole, will shift the conversation away from 'what brand or product do you recommend', and towards performing engineering design to ensure consistency of performance BEFORE then specifying the correct product to meet the engineering need.


I hope you succeed as the consumer is bombarded with subjective product reviews online and offline, pushing them in the opposite direction – unfortunately successfully so.


----------



## Peter Aylett

nathan88 said:


> We read a lot about the benefits of dual subwoofer vs one subwoofer in home cinema. Most modern AV receivers and audio processors have two sub outputs, for using dual subwoofer.
> 
> But I have seen a lot of guys that are using more than two, 3, 4, 5 even 6 subwoofers and not in large rooms but in regular size rooms. Moreover, they also buy the largest and most powerfull subwoofers they can afford.
> 
> My question is, when it comes to number and size of subwoofer, when do we stop? Is it too many and too big something that is not only unnecesary but it is actualy detrimental?


There are multiple strategies for delivering great bass in rooms. This is another one of those questions where the answer could be a one week long course. When we say 'great' bass, we want - 

Great seat to seat consistency. Every seat has a similar (Identical is a futile exercise) experience.
Deep - Can reproduce everything on the content material, intentional or not.
SPL - To maintain the same SPL when you halve the frequency requires four times the amount of air to be moved. This is a combination of cone/piston size and excursion. Keep this in mind - If our LCR speakers can deliver a constant 105dB at the reference position, you need to add +10dB for the LFE channel, if you are using the subs for bass management then add another 5dB, and if in your calibration you want a +10dB contour as subwoofer frequencies then add another 10dB. That equals 130dB.
Low distortion. Included in this is thermal compression (as more power gets put through a voice coil, it heats up. As it heats up its resistance increases)
Good impulse response. Often called haow 'fast' a sub is. This is a combination of sub design, and room acoustics.
In any speaker design for bass, you are balancing efficiency vs max SPL vs frequency extension. For instance, a sealed subwoofer will go lower than a ported one, but will not generally be as efficient.

So, to answer the question. Multiple subs (This is a great reference on the subject - https://www.harman.com/documents/multsubs_0.pdf ) are used for - 


If positioned correctly, multiple subs can be used to effectively cancel out some room modes thus giving better seat to seat consistency.
Multiple subs working together deliver more SPL. If each sub isn't working as 'hard', then they are likely (depending on the design of the sub) to be able to deliverlower frequencies at a similar SPL.
Some people believe that it's best to bass manage speakers to subs located close to the speaker being bass managed.

It is said that smaller subs are 'faster' than larger ones. This is not inherantly true, but unfortunately there are some inexpensive large subs that perform poorly. It's MUCH harder and more expensive to make a large sub than a small one.

When adding more subs, ask yourself why you are doing this. Usually, I design rooms with a minimum of two, and preferably four identical subs. These reproduce LFE and are used for bass management. For higher end projects, I'll add an infra-sub or two.

Yes, adding more subs ust for the sake of it CAN be detrimental. In every case, though the modal response of a room is extremely difficult to predict, it is possible to predict SPL capacity and LF extension.


----------



## Chuck Miller

Peter, I’m interested in your comments on stage and riser construction. I’m currently designing them for my HT (in progress; hanging drywall next week) and have read extensively the discussions on the AVS forums regarding both. And I come away with no clear approach. I understand that ‘best practice’ for stages is to fill them with sand to absorb sound and prevent vibration of the stage and the surrounding structure. I also understand that many like to design risers as ‘broadband absorbers’ using vents to allow sound waves to enter the structure and be deconstructed by the insulation filling the large cavity. I see both as sound (pun intended) approaches, but have the following questions about my design that includes large LCR speakers and two subwoofers on a 17’ x 6’ x 10” stage and the equipment rack and two large subwoofers on the 10’ x 10’ x 10” riser:

Do you agree that the stage should be filled with sand? If not, what do you recommend instead?
Do you promote the design of a riser as a broadband absorber? If not, what do you recommend?
In thinking about the applications of each, if the broadband absorber is desirable in the riser, why shouldn’t the stage be designed as a broadband absorber as well? It will have similar impact from and equal number of subwoofers as the riser, right? Conversely, if sand is more beneficial, why not use it as fill in the riser as well?
Do you recommend use of corner bass traps in both front and rear (both will be concealed in my design), regardless of construction of riser (and stage?) as broadband absorbers?
Thanks so much. You have the opportunity to help clear my indecision related to the design of these two critical HT features.

Chuck


----------



## ereed

@Peter Aylett 
Being that you are an audio industry guy, I'm surprised that you didn't jump on my previous question about making the audio standard more inclusive by actually including distortion types like: total harmonic, component harmonic, sub harmonic, intermodulation, and on into compression and normalized compression. After all, this is what reproduced audio contains plus more. If you're producing a "bleeding edge" profile of audio performance, will it include these aspects of audio? Or will it be another "output only" metric?


----------



## Peter Aylett

Hi Everyone,

Apologies for my tardiness over the past few days. I had a 3rd (Booster) COVID jab yesterday morning that has floored me. Dan has gratiously agreed to keep this thread open over the weekend which should allow me to write the replies you all deserve.

Cheers,

Peter.


----------



## ARROW-AV

Peter Aylett said:


> Hi Everyone,
> 
> Apologies for my tardiness over the past few days. I had a 3rd (Booster) COVID jab yesterday morning that has floored me. Dan has gratiously agreed to keep this thread open over the weekend which should allow me to write the replies you all deserve.
> 
> Cheers,
> 
> Peter.


Hope you feel better soon Peter!


----------



## EdgarQ

@Peter Aylett I got my jab too, and it's also taking me a couple of days to process it. While also lurking here and reading your thoughtful and educational replies. The other members are asking about all the things many of us think about, so your replies are hugely beneficial to all of us. Thank you for giving us more of your time and experience!


----------



## ToddDavid

Peter Aylett said:


> There are multiple strategies for delivering great bass in rooms. This is another one of those questions where the answer could be a one week long course. When we say 'great' bass, we want -
> 
> Great seat to seat consistency. Every seat has a similar (Identical is a futile exercise) experience.
> Deep - Can reproduce everything on the content material, intentional or not.
> SPL - To maintain the same SPL when you halve the frequency requires four times the amount of air to be moved. This is a combination of cone/piston size and excursion. Keep this in mind - If our LCR speakers can deliver a constant 105dB at the reference position, you need to add +10dB for the LFE channel, if you are using the subs for bass management then add another 5dB, and if in your calibration you want a +10dB contour as subwoofer frequencies then add another 10dB. That equals 130dB.
> Low distortion. Included in this is thermal compression (as more power gets put through a voice coil, it heats up. As it heats up its resistance increases)
> Good impulse response. Often called haow 'fast' a sub is. This is a combination of sub design, and room acoustics.
> In any speaker design for bass, you are balancing efficiency vs max SPL vs frequency extension. For instance, a sealed subwoofer will go lower than a ported one, but will not generally be as efficient.
> 
> So, to answer the question. Multiple subs (This is a great reference on the subject - https://www.harman.com/documents/multsubs_0.pdf ) are used for -
> 
> 
> If positioned correctly, multiple subs can be used to effectively cancel out some room modes thus giving better seat to seat consistency.
> Multiple subs working together deliver more SPL. If each sub isn't working as 'hard', then they are likely (depending on the design of the sub) to be able to deliverlower frequencies at a similar SPL.
> Some people believe that it's best to bass manage speakers to subs located close to the speaker being bass managed.
> 
> It is said that smaller subs are 'faster' than larger ones. This is not inherantly true, but unfortunately there are some inexpensive large subs that perform poorly. It's MUCH harder and more expensive to make a large sub than a small one.
> 
> When adding more subs, ask yourself why you are doing this. Usually, I design rooms with a minimum of two, and preferably four identical subs. These reproduce LFE and are used for bass management. For higher end projects, I'll add an infra-sub or two.
> 
> Yes, adding more subs ust for the sake of it CAN be detrimental. In every case, though the modal response of a room is extremely difficult to predict, it is possible to predict SPL capacity and LF extension.


How do you then make the decision between sealed and ported?

… which begets the question: in a small HT [12x14x8] with carpeted concrete & doubled up padding and where you really only care about your own listening position, would you still do multiple subs _(currently I have 3 sealed 15’s — an HSU ULS15MK2 and a pair of older Velodyne)_… or would you go with a single high performance sub, perhaps something like an 18” PSA or Rythmik F18?… or just stick with what I have and add tactile transducers. 

Additional question: if I try to go heavy with bass traps, does that mean I can then turn my subs up louder for greater tactile response?

Thanks for your time.


----------



## loader963

Hey Peter, thanks for the Q and A! My questions are for my future case, a 26’x16’x10’ dedicated HT in a fully open basement that can be framed any way I want it. 

1) if a customer wanted all in wall speakers, for subs would you recommend them to use an infinite baffle or ported/sealed enclosures encased in wall? 

2) And following that, would it be better for all of them to be in one row in one wall, split symmetrically placed on opposing walls, or split asymmetrically placed on opposing walls?

3) Should in wall subs ( especially multiple) be closer to the middle of walls or rather in the corners?


----------



## GalvatronType_R

What was in that briefcase from _Pulp Fiction_?


----------



## Peter Aylett

Mark Henninger said:


> Hi @Peter Aylett
> 
> AVS Forum is, of course, full of members who worship at the altar of deep bass, done right. I count myself among them.
> 
> I am curious about the whole topic of infrasonic bass and seek your opinion on a couple of things:
> 
> 1. If cost is no object, what's roughly the lowest frequency (in Hz) that's worth chasing after for home theater, in your opinion?
> 
> 2. While there are lists that cover deep bass in movies, so we know where to find it, I am wondering how much content below 16 Hz is truly intentional? How about single-digit Hz content, already very rarefied, how much of that is intentional? And if it is intentional, under what conditions are frequencies like that being mixed and monitored? How does the viewer know they are honoring "artist's intent"?


Hi Mark,
The importance of reproducing infra bass was hotly debated during the CEDIA/CTA RP22 meetings when we were discussing objective performance metrics. The consensus was split down the middle. I suspect that those that had the opinion that it is not necessary, have never actually heard a system that truly delivers it.

I doubt many/any dubbing stages/mixing suites have the ability to genuinely reproduce infra-bass frequencies at meaningful SPLs (if anyone knows of any, i'd love to know!). Even if they did, the rooms where the content will be reproduced will in 99.999999% of cases not be able to reproduce those frequnecies so it's highly unlikely there are there on purpose. But, those frequencies are definitely present.
The rooms I've heard that genuinely reproduce infra-bass (and we're currently involved in the construction of three rooms that definitely will) were incredible in the sense of space they created. Impact, rumble, trouser flapping bass were also present, but that's not what was special. I suspect this is because in real life, especially when outside, we are exposed to infra-bass every day. Next time you are in a busy city, close your eyes and 'feel' the soundscape. It is absolutely just as much about the way it feels as the way it sounds. 

The other advantage to implementing infra-subs is how much they releive the burden on the 'conventional' subs at really low frequencies. If crossed over at 24dB/Octive at around 35Hz, the conventional subs will be able to deliver higher SPLs because they do not have to deliver the cone/piston excursions required for frequencies below 35Hz (Of course, a 24dB/Octave crossover is not a brick wall so they will still need output below that crossover frequency)

I've not done enough research to answer the 'how low do you go' question. Certainly, when I design rooms with the request that they be 'the best', I will aim for meaningful SPL output at 10Hz - The calculations for this to be predictable (Bare in mind that in 99% of projects I work in, once the subs have been positioned at the design stage, i'ts almost impossible to move them once built) are complex and need to allow for room gain below the lowest modal frequency.

If/when you have the opportunity to experience a system that truly delivers infra-bass, listen to it, then ask for the infra bass subwoofer(s) to be switched off and just allow the other subs to go as deep as they can, as loud as they can. This demo is really compelling but will likely be extremely detremental to your bank balance 😉

PS. I'm going to be teaching a course on Infra-bass at CEDIA Expo 2022 with someone who I consider to be at the bleeding edge of product development in this area. 👍🏻


----------



## Peter Aylett

Reddig said:


> How much space should be between my compression loaded horn speakers and my .8 gain AT weave screen? Right now I’m at about 6 inches of space between the front of speaker and back of screen material roughly. Thanks.


The recommendation in RP22 will state (paraphrased) - 

Increasing the distance of loudspeakers from the screen will reduce the severity of acoustic artifacts effects. –

A minimum of150mm when the speaker employs point source dome tweeter(s).
When the speaker employs horn or waveguide coupled tweeter(s), it can be brought closer to the screen.
Some loudspeakers can be fitted with absorptive materials on their front baffle to mitigate comb filtering effects.

It is suggested to treat the area behind the screen with absorptive materials to reduce the level of reflected sound and in-turn reduce acoustic artifacts. These materials need to be effective – 

At frequencies down to a minimum of 500Hz
To fit into the overall acoustic treatment plan for the room


----------



## Peter Aylett

GalvatronType_R said:


> What was in that briefcase from _Pulp Fiction_?


CEDIA/CTA RP666 Recommended Practice for Treatement of individuals who apply too much high frequency absorption to their cinema rooms.


----------



## Peter Aylett

niterida said:


> What are your thoughts on using a soft baffle wall. A few of us have been discussing the benefit of just have the front wall filled with insulation and the speakers flush with the face of the insulation. So no hard MDF wall - just the insulation (covered with AT material of course). My thoughts are that the absorption by the insulation would have the same effect as the reduction of reflections with a hard baffle, but the open faced insulation will provide much better bass / lower frequency trapping/absorption. It is much simpler, easier and cheaper than building a proper baffle wall.
> We have done some internet searching and can't find any research or even any other in-depth discussions on this.
> Thanks for your time and effort in helping out AVS Forum


Interesting question. Without data on the exact method, and its in-room results, I can't give a firm answer. Part of the job of a baffle wall is reflections! As bass frequencies, one of the jobs of a baffle wall is to increase efficiency. Either way, 6" of absorptive material on a wall will do little at bass frequencies, but could end up over-absorbing mid and high frequencies if not part of an overall room treatment plan. The material will allow the majority of bass energy straight through it to the hard wall behind, which will then reflect back and still end up with comb filtering from SBIR. Sure, this reflected wave will be attenuated a bit (Dependent on the thickness of material), but this effect will be nowhere near as mitigated as if using a hard baffle wall. Keep in mind that to absorb sound completely, the absorbing material (When used as a velocity absorber) needs to be as thick as a quarter of the wavelength you are absorbing. At 50Hz, this would need 1.7m depth of material, or constructed using a method that employs other clever acoustic tricks...


----------



## Peter Aylett

markus767 said:


> Will these "recommended practices" documents be made available to the general public once finalized?
> 
> 
> 
> I hope you succeed as the consumer is bombarded with subjective product reviews online and offline, pushing them in the opposite direction – unfortunately successfully so.


Yes, they will be available to all. For CTA and CEDIA members, they will be free of charge. To everyone else, there will be a small fee.


----------



## markus767

Peter Aylett said:


> Yes, they will be available to all. For CTA and CEDIA members, they will be free of charge. To everyone else, there will be a small fee.


Great news! Looking forward to read through them and discuss the contents. Hope this helps to bring an end to the plethora of useless subjective equipment reviews with purchase recommendations devoid of any meaningful information.


----------



## Peter Aylett

jamin said:


> A question here for clarification please. Admittedly with no absorption there is no decay. And the increase of broadband damping a la Gedes or as perhaps you utilize is wonderful:
> 
> We have seen that decreasing the amount of energy put into a system at a problematic pesky frequency can result in purportedly acceptable steady state response for bass frequencies. Further that ostensibly we respond favorably to steady state magnitude smoothness in the bass region, see Olive and Toole.
> 
> Does this mean that, for example, the Harman SFM and subsequent PEQ is just clever DSP and does not work ?
> 
> edit : added subsequent PEQ — duh


Harman SFM (Sound Field Management) is a very clever measurement process that ends up relatively simple PEQ and delay settings for multiple subwoofers to mitigate room modes and deliver much better seat to seat consistency (flatter frequency response as bass frequencies). Whilst SFM is unique, all the other manufacturers of electro-acoustic optimisation (EQ) systems have/are making great strides with how they deal with bass. I know that two of them have major announcements on the horizon. So, clever DSP absolutely does work! It is not, however, a panacea to cure all ills. The strategy that every competent cinema designer uses is to optimise the acoustics in the physical domain, and then let EQ put the icing on the cake. As bass/modal frequencies, the more absorption you have, the flatter the peaks and nulls and thus the easier time any EQ has. It's impossible to remove room modes using acoustic treatments (well, maybe not impossible, but in the real world totally impractical) so in EVERY system, EQ is necessary.

Please don't ask me what EQ is best! My answer will probably be 'the one that you understand the best, and know how to get the best results from'. The more sophisticated ones perform correction in the time domain as well as in the frequency domain.


----------



## imagic

Peter Aylett said:


> Hi Mark,
> *The importance of reproducing infra bass was hotly debated during the CEDIA/CTA RP22 meeting*s when we were discussing objective performance metrics. The consensus was split down the middle. I suspect that those that had the opinion that it is not necessary, have never actually heard a system that truly delivers it.
> 
> *I doubt many/any dubbing stages/mixing suites have the ability to genuinely reproduce infra-bass frequencies at meaningful SPLs (if anyone knows of any, i'd love to know!)*. Even if they did, the rooms where the content will be reproduced will in 99.999999% of cases not be able to reproduce those frequnecies so it's highly unlikely there are there on purpose. But, those frequencies are definitely present.
> 
> The rooms I've heard that genuinely reproduce infra-bass (and we're currently involved in the construction of three rooms that definitely will) were incredible in the sense of space they created. Impact, rumble, trouser flapping bass were also present, but that's not what was special. I suspect this is because in real life, especially when outside, we are exposed to infra-bass every day.* Next time you are in a busy city, close your eyes and 'feel' the soundscape. It is absolutely just as much about the way it feels as the way it sounds.*
> 
> The other advantage to implementing infra-subs is how much they releive the burden on the 'conventional' subs at really low frequencies. If crossed over at 24dB/Octive at around 35Hz, the conventional subs will be able to deliver higher SPLs because they do not have to deliver the cone/piston excursions required for frequencies below 35Hz (Of course, a 24dB/Octave crossover is not a brick wall so they will still need output below that crossover frequency)
> 
> *I've not done enough research to answer the 'how low do you go' question.* Certainly, when I design rooms with the request that they be 'the best', I will aim for *meaningful SPL output at 10Hz* - The calculations for this to be predictable (Bare in mind that in 99% of projects I work in, once the subs have been positioned at the design stage, i'ts almost impossible to move them once built) are complex and need to allow for room gain below the lowest modal frequency.
> 
> *If/when you have the opportunity to experience a system that truly delivers infra-bass*, listen to it, then ask for the infra bass subwoofer(s) to be switched off and just allow the other subs to go as deep as they can, as loud as they can. This demo is really compelling but will likely be extremely detrimental to your bank balance 😉
> 
> PS. I'm going to be teaching a course on Infra-bass at CEDIA Expo 2022 with someone who I consider to be at the bleeding edge of product development in this area. 👍🏻


Thanks, Peter.

I did figure, nobody is mastering that infrasonic content on a soundstage. Beyond system capability, it's hard to imagine producers paying to pursue something neither movie theaters nor the vast majority of home viewers would have the ability to recreate. Maybe some crazy engineers are taking material home and working on it in their own systems? I agree, 'it's there" and that a really good mic is likely to pick up infrasonics with a good balance vs. the rest of the sound, and that's valid information if reproduced properly. But in audio land, it does have the allure of undiscovered country. 

Maybe infrasonic sound will be the next big thing like Atmos, lol.

Personally, yeah I've experienced some wild systems over the years. The very *first Home Theater of the Month* by @popalock had 16 18" sealed subs and when playing the "**cking Irene" helicopter scene from Black Hawk Down (8 Hz I think) the closet doors all around the house were opening and closing like Poltergeist. The *second-ever HToM* by @notnyt was an 8X LMS5400 equipped 18" ported subwoofer system, which could make the whole house "breathe" as it cracked the drywall in every room. More interesting of course is how they sounded properly tuned and at (or maybe a bit below) reference level, which is to say effortless.

I count Keith Yates as a friend, so yeah... deep bass! Seems to me @KeithYates is a bit of a pioneer in this category. And, I got into DIY sub building so I could master my own music with infrasonic elements in it, and in turn, learned a lot about subs.

Yup, I make recordings of cityscapes and when listened to in isolation the depth of the layering of sounds, and the importance of bass in making it feel real, are tangible! I've come to the conclusion that the _ultimate_ "you are there" effect is listening to binaural recordings through great open-back headphones, but with a powerful deep-playing subwoofer integrated (need to add delay to the headphones), so (for example) the infrasonic undertone of a diesel engine comes through with proper "feel." That's the good stuff!

So, I'm sold on Infrasonics and its worth, or at least entertainment value, and know well the cost (in material and physical space) of buying that much horsepower and displacement. But as I suspected, if you get it all "just right" it's all "cherry on top" or "icing on the cake" because at least from a production standpoint, it's serendipitous when it exists in the right amounts, and is associated with the right sounds, rather than picking up random thuds and vibrations or putting useless, speaker-destroying tones at the beginning of a movie! The other issue, of course, is how rapidly the number of movies or music tracks that dip down to a given frequency drops the moment you get into the infrasonic zone.


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## Thejasvi

Hello  this is my first post ever...appreciate any kind of feedback on below. I am.settimh up my new media room and in past have been happy with deftech series with denon. This time its a 7.2.2 set up. 2 atmos ceiling speakers.

Below is what.i am.looking at

Towers (2) : Def tech BP9060
Center(1) : Def tech CS 9080
Surrounds(4) : Def Tech SR 9080
Ceiling (2) : bowers n wilkins CCM663

Receiver : 
Denon AVR-X6700H

Question is .. I am.going with Def tech BP9080 series...except for the towers. Towers going with BP9060 for the reason that BP 9080 comes with a Atmos unit for height sounds fitted on top (it shoots at the roof and reflects it down) . But I have wired for 2 speakers in ceiling as u see in the picture for this purpose and given the size of the room.i don't need this feature of BP9080. 

Is there anything else I am missing out from not going to 9080 ?

Any suggestions on the entire set?


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## ToddDavid

Does this door-jarring drywall-cracking infra bass have any health impacts on the electronics in the room?


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## ss3740

I realize this question is not design EQ related, so maybe no response is necessary. My apologies if this is the case. But I wonder if you don't have some inside information on something that effects your systems as well as everybody else's. I remember hearing that "shiny disc are going away" and wondering what was going to replace them. I'm thinking Wow!.. They must have something fresh and GREAT in the streaming world... Wrong., we went backwards. How long do you think it will take for the streaming world to catch up to the Blu Ray world that got tossed to the side for nothing more than lazy customers that want no part of actually going to a brick and mortar store to purchase *lossless *DVR's. Peter, do you think this will ever happen? I have a fortune in this wonderful system but my only option is to purchase movies shipped through mail so that little "HDAudio" icon will light up in my Lyngdorf MF-40 processor. (And when it does it's like kicking in another 4 barrel !! ) Seems as though we take one step forward and two back to me.... I think Garbage in.... Garbage out (GIGO) is a real issue in our audio world.
I buy all my Video concerts and don't have a problem doing so, but buying all the movies on disc is just not something I'm interested in..


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## srw1000

Hi Peter, thank you for sharing your knowledge here.

Do you have any specific recommendations for home theaters constructed with ICF (Insulated concrete forms)? I've read articles and books regarding concrete block and solid concrete walls, but very little specifically about ICF, other than noise reduction ratings.

The construction is different, since there is 2.5" of EPS foam between the solid concrete walls and the drywall, which is placed snuggly against the foam. This eliminates the drywall flex you would normally get with stud construction. In addition, the EPS foam is almost invisible to the sound waves, so I would imagine some of that energy would be absorbed by the drywall, much would pass through and be reflected by the concrete, and then get partially absorbed again before coming back into the room.

I'm currently treating the room with a mixture of absorption and diffusion per the guides in Floyd Toole's guides, but wondering if there might be something else to be considered in the equation.

Thank you for any insight you might be able to share,

Scott


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## huskydriver

Peter,

Are you available for one on one fee based consultation? I was at CEDIA this year (what an unfortunate event) and saw you were planning to present. Of course, that didn't happen. Please let me know if a phone based consultation is possible. Thank you.

Tom


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## Peter Aylett

ereed said:


> @Peter Aylett I have a question about testing subwoofers. As far as I know of the 3rd party data-bass.com is where it shows full measurements in complete detail. I'm starting to see companies only providing basic measurements and not full shown measurements for consumers. What are your thoughts of testing methods beyond CEA and if compression and distortion will be included in that?


As part of the upcoming CEDIA/CTA RP1 Performance Facts recommended practice, there will be recommendations to manufacturers for the data that engineers requre to make objective engineering decisions on equipment specification. Included in this will be specifications for loudspeakers including subs.
Most current specs from manufacturers (There are exceptions...) are written by marketing departments rather than engineers. CEA 2034 will be an important part of the requested specs but we are going much further and deeper with our recommendations. 

RP1 Performance Facts will be transformational in terms of giving us the data needed to make engineering decisions. Huge kudos to Anthony Grimani for leading and chairing the work effort.


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## Peter Aylett

Sheeraz Khan said:


> Hello Dan,
> 
> I'm planning to get a subwoofer for my Home theater system. My room is 284 Sq. ft/2,272 Cubic ft., and it will be open on one side. I'm really interested in SVS- PB 2000, but it's price point is higher. My budget is around $500, so can you recommend any other subwoofer with similar specs in that price range ? Thanks!


Sorry, I never recommend specific products unless i'm responsible for the complete design, engineering and specification of a system to a specific set of user and performance requirements. I'd say it's more important to get the acoustics of the room correct, and engineer the subwoofer/room/listeners interface, than it is to worry about specific subs. At sub frequencies, you are listening more to the room than the sub.


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## Peter Aylett

Venue said:


> @Peter Aylett
> 
> 1) Are corner bass traps a myth, are you better of using DSP and 4 subwoofers, 1 in each corner?
> 2) In contrast to the above, isn't it true that the less DSP, the better, the more physical acoustic treatment, the better?
> 3) Can diffusers be recessed into a wall, or does the whole wall need to be recessed for this to work, covered by cloth?
> 4) Would you rather place diffusion on rear side walls instead of the rear wall, with bipole surrounds on the rear wall, 5.1?
> 5) Any benefit having 2" absorption behind a non-AT fixed frame screen, mounting the screen flush or 1-2" from the wall?
> 6) How important is it to seal off an archway leading out to another room, can this be done with somewhat of a thick cloth?
> 7) Do you know any acoustically transparent carpets that could be used covering pits in front of the screen?
> 
> About question #1, Anthony Grimani advocates using bass traps in power corners, and ceiling/wall corners, is this a bad approach, is it a general rule of thumb within the industry to use these, if not, could you explain why, I think lots of members could use the correct information on this, appreciated.
> 
> Thanks!


1. Kind of... There is a LOT more to predicting where the high pressure and/or velocity areas in a room are for problematic frequecies. Corners are a kind of 'if in doubt, put bass absorbers there' sort of location. Plus, it's a good place to hide the bulk of most bass absorbers...

2. Absolutely! Getting the room right in the physical domain before the application of (essential) DSP is critical. Focus on the entire audible frequency spectrum. 2" stuff all over the walls will give you a dead and boomy room. Correctly designing room acoustics is, IMHO, the single most complex aspect of private cinema design. And also usually the most abused...

3. Yes. So long as the diffuser is not covered by anything that will reduce its efficacy, it can be recessed. Just be careful to not put diffusers too close to listeners - Pay attention to manfacturers' recommendations on this.

4. Placement of diffusers is not a simple answer. Generally i would not use di/bi-poles any more. They were fine in the old days of analogue pro-logic, but now we have discrete digital channels with the additional layer of multiple objects being rendered, spatial resolution is important - Some thing that bi-poles are not the best at, and di-poles are designed to not do at all! The caveat is a 5.1 system in a small room where surrounds are relly close to listeners. In these situations, I may choose to sacrifice resolition, for non-localisation of speakers.

5. Any acoustical materials in a room must be part of the overall plan. Any materials placed behind a non AT screen will have minimal effect at mid and high frequencies. The front wall could, however, still be built as a bass absorber in which case if it were open at the top and bottom, the more depth the better.

6. Rectangular rooms are more predictable at bass frequencies than irregularly shaped rooms. Closing off another room with a thick curtain will certainly absorb mid and high frequencies, but will do nothing at bass frequencies to make the room more predictable.

7. I don't... With controlled dispersion speakers as LCR, we generally prefer hard floors to carpet. Carpets and underlays are great high frequency absorbers, but do little from midrange down. It's likely that with everything else in the room and on the walls, you don't need the additional high frequency absorptionthat carpet delivers.

Anthony Grimani is one of the finest small room acousticians around. I've learned a huge amount from him over the years. His recommendationsa re based on a 'if you want a simple recommendation that will likely do more harm than good, do this'. I'm sure if he engineered a specific room, his recommendations would likely be different from his generic ones. As a general rule of thumb, corners are good for bass traps. BUT, that's absoloutely NOT to say that in any given room that is the best solution...


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## Peter Aylett

srw1000 said:


> Hi Peter, thank you for sharing your knowledge here.
> 
> Do you have any specific recommendations for home theaters constructed with ICF (Insulated concrete forms)? I've read articles and books regarding concrete block and solid concrete walls, but very little specifically about ICF, other than noise reduction ratings.
> 
> The construction is different, since there is 2.5" of EPS foam between the solid concrete walls and the drywall, which is placed snuggly against the foam. This eliminates the drywall flex you would normally get with stud construction. In addition, the EPS foam is almost invisible to the sound waves, so I would imagine some of that energy would be absorbed by the drywall, much would pass through and be reflected by the concrete, and then get partially absorbed again before coming back into the room.
> 
> I'm currently treating the room with a mixture of absorption and diffusion per the guides in Floyd Toole's guides, but wondering if there might be something else to be considered in the equation.
> 
> Thank you for any insight you might be able to share,
> 
> Scott


Sorry, not really... Any construction material will have a set of acoustical properties. It is extremely difficult to predict the behaviour of a 'solid' surface to bass. In the amazing Room EQ Wizard, when predicting a room's modal response, there is single number for the absorption coefficient of each wall. The problems are - 

Published and as-built figures are often very different
Any 'solid' surface behaves differently at different bass frequencies. To predict the performance, you'd really need 1/6th octave data...
If you have some time, get a good measurement mic, the Gated Noise RT60 add-in on AudioTools and do some measurements. This will allow you to see where the RdT (reflection decay time, as in small rooms, it's not really true reverberation) is currently, and therefore what frequencies you want your materials to be effective at. Keep the RdT as linear as possible. This is a luxury I don't have as a cinema designer as we need to predict performance before the room is built. So, we use room build methods that largely mitigate the construction method of the room.


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## Peter Aylett

huskydriver said:


> Peter,
> 
> Are you available for one on one fee based consultation? I was at CEDIA this year (what an unfortunate event) and saw you were planning to present. Of course, that didn't happen. Please let me know if a phone based consultation is possible. Thank you.
> 
> Tom


Hi Tom,
I'm doing this Ask me Anything slot as a purely non-commercial gig to (hopefully) benefit the community. I am, however, open to being found at industry events, taken to a brewery, and for as long as i am supplied the finest beers known to humanity, happy to talk about whatever you like!

Cheers,

Peter.


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## Peter Aylett

Albsroses said:


> What should I clean my preamps jacks with if they’re dirty?
> 
> Also,
> 
> ifni have a preamp, and amp, a phono preamp, a equalizer, a sound processor and a passive isolating device and a receiver what would be the best way to plug them?


The best way to clean connectors is to unplug and plug them back in a few times... Failing that, try some isopropyl alcohol and cotton buds.


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## Peter Aylett

Wayne Z said:


> The room where I listen to a lot of music has a door that leads into the furnace room. Although the door is weather-stripped, lower pitch (under 500hz) sounds come through the door. What material could I attach the to the back (furnace side) of the door to deaden the sound?


There is really nothing you can simply attach to the door to isolate 500Hz and below. You'd need to look at the entire wall between the rooms and come up with a complete isolation strategy. For doors, it's as much about sealing them as it is about what they are made of.


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## Peter Aylett

ereed said:


> @Peter Aylett
> Being that you are an audio industry guy, I'm surprised that you didn't jump on my previous question about making the audio standard more inclusive by actually including distortion types like: total harmonic, component harmonic, sub harmonic, intermodulation, and on into compression and normalized compression. After all, this is what reproduced audio contains plus more. If you're producing a "bleeding edge" profile of audio performance, will it include these aspects of audio? Or will it be another "output only" metric?


Good question.

Within the totality of the recommendations, there will be metrics at two levels - 

An overall system performance spec. 
Recommendations for the data we need on individual components to make engineering decisions.
In my experience, too many people obsess over things like the SNR difference between two ESS Sabre DAC, but not the gross electro-acoustic and acoustic distortion that dominates. In standards, we are focussing more on things like acoustic noise floor (if your room has an acoustic noise floor of 30dBA, you will just not hear a lot of the low level distortion present), and what happens when things get loud - If an amp is pushed into clipping, all other distortion becomes irrelevant.

I totally agree that ALL specs are important. Whilst we are not ignoring the little things, we are focussing on the major mistakes made by people.


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## Peter Aylett

ToddDavid said:


> How do you then make the decision between sealed and ported?
> 
> … which begets the question: in a small HT [12x14x8] with carpeted concrete & doubled up padding and where you really only care about your own listening position, would you still do multiple subs _(currently I have 3 sealed 15’s — an HSU ULS15MK2 and a pair of older Velodyne)_… or would you go with a single high performance sub, perhaps something like an 18” PSA or Rythmik F18?… or just stick with what I have and add tactile transducers.
> 
> Additional question: if I try to go heavy with bass traps, does that mean I can then turn my subs up louder for greater tactile response?
> 
> Thanks for your time.


Sealed vs Ported is like saying Class AB vs Class D. Neither are inherantly 'better' than the other - They just have different design compromises.

What are the measurements at the only seating position you care about? What particular aspect of the sound do you feel is lacking? See my previous posts about what constitutes 'good bass'. I'm unsure what you mean by 'doubled up padding'? In planning your acoustics strategy, focus on linear absorption across the audible frequency spectrum.

Lots of bass absorption will certainly help deliver clean and 'fast' transients. It will not help deliver trouser flapping rumble -That's down to having subs able to deliver low bass at the requred SPL with little distortion. For one seating position (Positioned with consideration to be out of any significant nulls) a single sub can deliver near flat frequency response. Having multiple diffent subs, with different capabilities, can be extremely difficult to calibrate. When using multiple subs, I try and ensure that they are identical.


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## Peter Aylett

Thejasvi said:


> Hello  this is my first post ever...appreciate any kind of feedback on below. I am.settimh up my new media room and in past have been happy with deftech series with denon. This time its a 7.2.2 set up. 2 atmos ceiling speakers.
> 
> Below is what.i am.looking at
> 
> Towers (2) : Def tech BP9060
> Center(1) : Def tech CS 9080
> Surrounds(4) : Def Tech SR 9080
> Ceiling (2) : bowers n wilkins CCM663
> 
> Receiver :
> Denon AVR-X6700H
> 
> Question is .. I am.going with Def tech BP9080 series...except for the towers. Towers going with BP9060 for the reason that BP 9080 comes with a Atmos unit for height sounds fitted on top (it shoots at the roof and reflects it down) . But I have wired for 2 speakers in ceiling as u see in the picture for this purpose and given the size of the room.i don't need this feature of BP9080.
> 
> Is there anything else I am missing out from not going to 9080 ?
> 
> Any suggestions on the entire set?


Welcome to the community!

Sorry, as ive said to others on this thread, i'm not here to make equipment specific recommendations. There is very little 'bad' (modern) equipment available - It's less about WHAT is used, and more about HOW it is used. Don't under estimate the effect the room has on the way the system sounds. My advice is to buy yourself a good inexpensive measurement microphone, and use some free software (There are many amazing threads on this forum discussing these topics) to measure and learn about sound within spaces. You'll then find that your equipment upgrade choices become more driven by your needs in your room rather than other people's rooms, comments and needs.

Good luck with your journey - Every day is a school day regardless of if this is your first post, or if you have been a professional for 40 years 😊


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## darrellh44

What's your feeling on SBA or DBA bass arrays vs multiple subs, good placement, and extensive and properly tuned bass traps. Will SBA/DBAs almost always be better?

Thanks,
Darrell


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## Peter Aylett

ToddDavid said:


> Does this door-jarring drywall-cracking infra bass have any health impacts on the electronics in the room?


A very interesting question, that i've never considered apart from projectors that i've seen go out of mechanical alignment/convergnce presumably from the LF energy in a room.

I'll ask around a few manufacturers of electronics as i've never heard the topic being discussed before! I know many who discuss the microphonic nature of most electronic components and consider vibration control to be critical. This is more about sound quality of than the health of components.

Hmmmm, interesting!


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## Peter Aylett

darrellh44 said:


> What's your feeling on SBA or DBA bass arrays vs multiple subs, good placement, and extensive and properly tuned bass traps. Will SBA/DBAs almost always be better?
> 
> Thanks,
> Darrell


WOW, deep question!

A DBA (Double Bass Array) especially with four subs per end is a wonderful thing and is what i'll do as and when I have the space and budget (for 8 proper subs, plus 2 infra subs...) in a future house to build a dedicated room. It's not a cure-all to every problem with bass, and needs some very carefull setup on a processor with high time domain resolution to set up correctly. You also need to keep in mind that the subs as the back of the room are there to take energy OUT of the room so don't add to the bass energy or SPL. To do it properly, you'll also need the subs located accurately, and for the room to be, ideally, sealed (difficult when ventilated...).

It's difficult to say if a DBA will also be better as every room needs to be taken as an individual case - I also know many who will never put a large output sub behind an AT screen as regardless of the screen's acoustical transparency, the surface WILL move to a degree thus compromising video resolution.

I know that some processor/electro acoustic optimisation companies are working on specific setup modes to optimise DBA setups. It's not an easy thing to 'have a go and try it out'... The rooms i've heard it implemented properly in, however, have been spectacular.


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## Peter Aylett

CP850-CLED said:


> I was pleasantly surprised by this video featuring Peter on HTE's philosophy to find such a strong parallel with my life's work working in technical and architectural acoustics development of form facilitates function in a team leadership capacity with top Italian architects Gian Enrico Fabro, Michele Bonan and my personal favorite Massimo Iosa Ghini, Italian Craftsmen are among the best in Europe although the Turks you will find have honed these fine crafts for much longer, but also in carte blanche collaborations with Zaha Hadid and Jacques Grange out of which the Inspiration for the prototype Dolby Cinema concept was sparked.
> 
> Peter and I also have similar life experiences when he mentions that one defective piece of equipment (in my case a stereo minijack which's cable was stapled by the drywall people in a remote never used 95 sq ft. reading Loft accessible only by a long narrow spiral staircase ) in a secondary zone can take down a job with a brilliantly performing cinema. That clicked, as it is the very same reason I stopped doing multiroom in 1999. Although I admit now being tempted to delve into distributed Atmos music.
> 
> Motivated by what I hear to be Peter's intent in his committees and what the Raison D Etre at HTE is I will share my findings and observations but also my objecting reservations, much of of which will sound conflicting and iconoclastic to many of the generally accepted (ie. THX 80 hz cutoff) in the hope that some of it sticks with his new committees that hopefully will espouse broader views moving forward.
> 
> I will thus post my mini manifesto of what constitutes a great immersive space and I look forward to his impressions.


Thanks!

I look forward to reading and discussing you manifesto 👍🏻


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## darrellh44

Peter Aylett said:


> I also know many who will never put a large output sub behind an AT screen as regardless of the screen's acoustical transparency, the surface WILL move to a degree thus compromising video resolution.


Thanks for the great response. Screen flutter can be a problem with well endowed bass rooms no matter where the subs are located, but maybe not as bad I guess when they are right behind the screen. Thanks again.


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## Peter Aylett

Thanks to Dan, Jacob and the AVS Forums team for giving me this opportunity. When i'm teaching, I judge people by how good the questions are - I've had some truly excellent ones here! 

My apologies if i've missed anyone's post - I'll review the thread again over the next few days and try to answer anyone i've missed privately.

If any of you are CEDIA or CTA members, let me know if you'd like to be involved in our standards efforts.

I hope to meet many of you sometime in the future at industry events.

Cheers,

Peter.


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## ToddDavid

Peter Aylett said:


> Sealed vs Ported is like saying Class AB vs Class D. Neither are inherantly 'better' than the other - They just have different design compromises.
> 
> What are the measurements at the only seating position you care about? What particular aspect of the sound do you feel is lacking? See my previous posts about what constitutes 'good bass'. I'm unsure what you mean by 'doubled up padding'? In planning your acoustics strategy, focus on linear absorption across the audible frequency spectrum.
> 
> Lots of bass absorption will certainly help deliver clean and 'fast' transients. It will not help deliver trouser flapping rumble -That's down to having subs able to deliver low bass at the requred SPL with little distortion. For one seating position (Positioned with consideration to be out of any significant nulls) a single sub can deliver near flat frequency response. Having multiple diffent subs, with different capabilities, can be extremely difficult to calibrate. When using multiple subs, I try and ensure that they are identical.


_doubled-up padding as in carpet padding_

So then since I’m only concerned with my own listening position [in a 12x14x8 room], does this mean I should scrap the three sealed 15’s and just go with a single 18”? … and in this small size of a room how would we determine between 18” sealed and 18” ported? Could we even go with a sealed 21” in a small HT if it’s treated well?

With a carpeted concrete floor with 2 layers of carpet padding, I guess what I’m looking for the most is to be able to experience greater tactile response from the front stage but without the sub actually sounding louder or boomier. 

Some info: My primary sub position is in the front right corner pulled out about 2 feet, so its driver is about 10 ft from the back wall and about 6 ft from me. The room is sealed. I have space behind the sub to do a rectangular bass trap 15” deep, 24” wide, and 48” tall. In the left corner I can do the same, but at 15” wide. In the middle of the rear wall I can do a panel as large as 6’ x 4’ that’s up to 6-8” deep, with some strips of metal tape… but I could do a thicker trap across the top of the wall up to 12-15” deep. Cant do much in the back corners but small triangular corner traps about 15” across. I have an 85” TV with about 10” of utilizable space behind it that could be fitted with a large trap as well.


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## Reddig

Peter Aylett said:


> The recommendation in RP22 will state (paraphrased) -
> 
> Increasing the distance of loudspeakers from the screen will reduce the severity of acoustic artifacts effects. –
> 
> A minimum of150mm when the speaker employs point source dome tweeter(s).
> When the speaker employs horn or waveguide coupled tweeter(s), it can be brought closer to the screen.
> Some loudspeakers can be fitted with absorptive materials on their front baffle to mitigate comb filtering effects.
> 
> It is suggested to treat the area behind the screen with absorptive materials to reduce the level of reflected sound and in-turn reduce acoustic artifacts. These materials need to be effective –
> 
> At frequencies down to a minimum of 500Hz
> To fit into the overall acoustic treatment plan for the room


 Thank you so much for your very thorough response. I indeed have my space behind the screen treated but only with 12” by 12” acoustic foam squares back there. Think I’ll work on that. Once again thank you. @Peter Aylett


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## ereed

Peter Aylett said:


> Good question.
> 
> Within the totality of the recommendations, there will be metrics at two levels -
> 
> An overall system performance spec.
> Recommendations for the data we need on individual components to make engineering decisions.
> In my experience, too many people obsess over things like the SNR difference between two ESS Sabre DAC, but not the gross electro-acoustic and acoustic distortion that dominates. In standards, we are focussing more on things like acoustic noise floor (if your room has an acoustic noise floor of 30dBA, you will just not hear a lot of the low level distortion present), and what happens when things get loud - If an amp is pushed into clipping, all other distortion becomes irrelevant.
> 
> I totally agree that ALL specs are important. Whilst we are not ignoring the little things, we are focussing on the major mistakes made by people.


But you still did not answer my question and it was a specific question that only required yes or no answer. 

In my own opinion those are very important metrics (distortion/compression) if you want to really compare high end quality product against another product rather than just output metrics or whatever other bleeding edge technology you are referring to since you did not include the specifics. So I will take this as you are avoiding my specific question due to politics and not wanting to upset certain vendors/products you may be working with.


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## sdrucker

M m.


Peter Aylett said:


> Sorry, not really... Any construction material will have a set of acoustical properties. It is extremely difficult to predict the behaviour of a 'solid' surface to bass. In the amazing Room EQ Wizard, when predicting a room's modal response, there is single number for the absorption coefficient of each wall. The problems are -
> 
> Published and as-built figures are often very different
> Any 'solid' surface behaves differently at different bass frequencies. To predict the performance, you'd really need 1/6th octave data...
> If you have some time, get a good measurement mic, the Gated Noise RT60 add-in on AudioTools and do some measurements. This will allow you to see where the RdT (reflection decay time, as in small rooms, it's not really true reverberation) is currently, and therefore what frequencies you want your materials to be effective at. Keep the RdT as linear as possible. This is a luxury I don't have as a cinema designer as we need to predict performance before the room is built. So, we use room build methods that largely mitigate the construction method of the room.


Hi Peter,
For Gated Noise RT60, do you look at the full 63 to 4000 Hz range mentioned in the Audiotools documentation or a narrow range (e.g. 250 or 300 Hz upward)? I'm referring to this:





Gated Noise RT60 | Studio Six Digital







studiosixdigital.com





FYI REW has T20 and T30 measurement, so for the enthusiast, can we generate something similar with their ETC plot, limiting where the pink noise sweep is conducted, and following their suggested methodology in this link? We generally would be using an EMM-6 or UMIK type mic with a USB connector.


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## VerticalScope

Peter Aylett said:


> Thanks to Dan, Jacob and the AVS Forums team for giving me this opportunity. When i'm teaching, I judge people by how good the questions are - I've had some truly excellent ones here!
> 
> My apologies if i've missed anyone's post - I'll review the thread again over the next few days and try to answer anyone i've missed privately.
> 
> If any of you are CEDIA or CTA members, let me know if you'd like to be involved in our standards efforts.
> 
> I hope to meet many of you sometime in the future at industry events.
> 
> Cheers,
> 
> Peter.



Thanks a bunch Peter! I'm very glad you were able to come out. On behalf of the community, thank you for your time and your detailed responses!

- Dan


----------

