(You don't need to read this whole thread. This first post is regularly updated with all the available information we can find.)
CEDIA and the CTA have taken a few decades of best practices about dedicated theater design and construction (the audio half in this case) and summarized it in one document. It is available for free to anyone with an interest in reading it:
cedia.org
They have organized it around 21 design goals, and four levels of performance for each goal. The traditional "reference" level is level 3. But for many of us, level 1 would be more than enough to be satisfied. So it's great they have put rigor into not just a single level of performance.
At first blush, this list might seem like a recipe book.
A closer look at the details behind each performance parameter reveals a very articulate explanation of the performance goal, and relatively little detail about how to achieve it. That's fine: The document was not designed to tell you HOW to achieve these goals in a comprehensive manner. (And there will be a second document about measurement details or how to assess a room.)
This post tries to collect additional "how to" guidance for enthusiasts. Results are not guaranteed, but hopefully we can help each other up level and better predict what factors will make the most improvement to our personal screening rooms.
IMO, this guide produces better results than some of the traditional tools like: The academic, technically correct, allocentric speaker layout ,as well as Dolby's official (and free) design tool that uses angles to position speakers for a single listener in a mastering suite.
![Image]()
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Some are easy to understand how to implement: Parameter One says that a reference level (3) theater will have no seats within 4 feet of a wall. That tells you the goal AND how to achieve it.
Some are difficult to achieve: Parameter Fifteen is that a reference level (3) theater will ideally have a background noise level of NCB 18. That's super non trivial. And RP22 does not explain how to achieve that in enough detail that you could direct a contractor in the building process (or do it yourself) without additional knowledge.
The additional knowledge, in most cases, is "out there."
Intrepid enthusiasts can use this post to help in finding that additional knowledge. This post is not "complete" and if you have additions that will help make it more complete and or accurate, please share them.
The goal here is a guide to how to achieve the performance levels outlined in RP22 when the methods are not self evident or explained in actionable detail in RP22. This thread is not intended as a place to debate RP22 itself.
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1. Seating/Room Wall Distance
Self explanatory.
2. Decoder Channels
Self explanatory.
3. Screen wall speaker locations
Self explanatory.
4. Maximum SPL differences between screen wall speakers
This is achieved not just through speaker sensitivity/power handling/output but also through amplification and through distance differences, as well. Use a calculator to assess the speakers, such as the Peak SPL Calculator to see whether the speakers are within the correct range of one another. Example from RP22 doc.
5. Maximum horizontal angle between adjacent surround speakers
On an accurate drawing, use a protractor. In the room, the “compass” app on a smart phone can aid in the visualization.
6. Maximum SPL differences between surround speakers
This is achieved not just through speaker sensitivity/power handling/output but also through amplification and through distance differences, as well. Use a calculator to assess the speakers, such as the Peak SPL Calculator to see whether the speakers are within the correct range of one another. Example from RP22 doc.
7. Wide speaker deviation from median angle.
On an accurate drawing, use a ruler and then a protractor. In the room, a measuring tape, and then the “compass” app on a smart phone, can aid in the visualization.
8. Upfiring speakers allowed
Self explanatory.
9. Allowable vertical angle.
On an accurate drawing, use a protractor. In the room, there may be some “level” apps on a smart phone can aid in the visualization, but I use a laser level/distance device.
10. Max spl difference between upper level speakers
This is achieved not just through speaker sensitivity/power handling/output but also through amplification and through distance differences, as well. Use a calculator to assess the speakers, such as the Peak SPL Calculator to see whether the speakers are within the correct range of one another. Example from RP22 doc.
11. Number of speakers allowed outside of zonal recommendations
Self explanatory.
12. Screen speakers spl capability
This is achieved not just through speaker sensitivity/power handling/output but also through amplification and through distance differences, as well. Use a calculator to assess the speakers, such as the Peak SPL Calculator to see whether the speakers can reach sufficient output levels. Example from RP22 doc.
13. Non screen speakers spl capabilities
This is achieved not just through speaker sensitivity/power handling/output but also through amplification and through distance differences, as well. Use a calculator to assess the speakers, such as the Peak SPL Calculator to see whether the speakers can reach sufficient output levels. Example from RP22 doc.
14. Bass spl capabilities
CEDIA hasn't defined how this is modeled, but it can be measured after the fact. However, other folks have done the modeling part. More than a decade ago, Audioholics published their room sizing guide, which translated CEA2010 subwoofer measurements into "X sub can play at Y level in room volume Z" but their guide focused on output at 31hz. THX has done something similar (though more opaque) that appears to target 20hz output. A thread at AVForums started by MR Wolf in the UK published the following info, which is the best modeling approach available to the public at present:
![Image]()
15. Background Noise Floor
From: Soundproofing does not exist... but Isolation can:
16. Seat to seat frequency response variance among screen wall speakers.
REW measurement, or similar, once room is built -- but that would be too late. Method for predicting ahead of time is not defined by CEDIA nor the CTA at present.
17. Seat to seat frequency response variance among non screen wall speakers.
REW measurement, or similar, once room is built -- but that would be too late. Method for predicting ahead of time is not defined by CEDIA nor the CTA at present.
18. In Room bass extension -3db frequency cutoff point.
Covered under #14, though the table only goes down to 20hz.
19. Frequency response below the room's transition frequency.
REW measurement, or similar, once room is built -- but that would be too late. Method for predicting ahead of time is not defined by CEDIA nor the CTA at present.
20. Seat to seat frequency response variant from the RSP below the room's transition frequency.
REW measurement, or similar, once room is built -- but that would be too late. Method for predicting ahead of time is not defined by CEDIA nor the CTA at present.
21. Level of early reflections relative to direct sound.
Dolby, many rooms designers like Erskine and Grimani, and countless top level room on AVS have used RT60 or reflected decay times to assess room acoustics. That approach can still produce excellent results: How Many Panels and Traps Do I Need?: RT60, RDT, REW... It is NOT the complete answer to achieving the results specified in RP22, but it is a big step in that direction.
CEDIA and the CTA have taken a few decades of best practices about dedicated theater design and construction (the audio half in this case) and summarized it in one document. It is available for free to anyone with an interest in reading it:
RP22 Thanks
cedia.org
They have organized it around 21 design goals, and four levels of performance for each goal. The traditional "reference" level is level 3. But for many of us, level 1 would be more than enough to be satisfied. So it's great they have put rigor into not just a single level of performance.
At first blush, this list might seem like a recipe book.
A closer look at the details behind each performance parameter reveals a very articulate explanation of the performance goal, and relatively little detail about how to achieve it. That's fine: The document was not designed to tell you HOW to achieve these goals in a comprehensive manner. (And there will be a second document about measurement details or how to assess a room.)
This post tries to collect additional "how to" guidance for enthusiasts. Results are not guaranteed, but hopefully we can help each other up level and better predict what factors will make the most improvement to our personal screening rooms.
IMO, this guide produces better results than some of the traditional tools like: The academic, technically correct, allocentric speaker layout ,as well as Dolby's official (and free) design tool that uses angles to position speakers for a single listener in a mastering suite.
Some are easy to understand how to implement: Parameter One says that a reference level (3) theater will have no seats within 4 feet of a wall. That tells you the goal AND how to achieve it.
Some are difficult to achieve: Parameter Fifteen is that a reference level (3) theater will ideally have a background noise level of NCB 18. That's super non trivial. And RP22 does not explain how to achieve that in enough detail that you could direct a contractor in the building process (or do it yourself) without additional knowledge.
The additional knowledge, in most cases, is "out there."
Intrepid enthusiasts can use this post to help in finding that additional knowledge. This post is not "complete" and if you have additions that will help make it more complete and or accurate, please share them.
The goal here is a guide to how to achieve the performance levels outlined in RP22 when the methods are not self evident or explained in actionable detail in RP22. This thread is not intended as a place to debate RP22 itself.
------
Implementation Guide
1. Seating/Room Wall Distance
Self explanatory.
2. Decoder Channels
Self explanatory.
3. Screen wall speaker locations
Self explanatory.
4. Maximum SPL differences between screen wall speakers
This is achieved not just through speaker sensitivity/power handling/output but also through amplification and through distance differences, as well. Use a calculator to assess the speakers, such as the Peak SPL Calculator to see whether the speakers are within the correct range of one another. Example from RP22 doc.
5. Maximum horizontal angle between adjacent surround speakers
On an accurate drawing, use a protractor. In the room, the “compass” app on a smart phone can aid in the visualization.
6. Maximum SPL differences between surround speakers
This is achieved not just through speaker sensitivity/power handling/output but also through amplification and through distance differences, as well. Use a calculator to assess the speakers, such as the Peak SPL Calculator to see whether the speakers are within the correct range of one another. Example from RP22 doc.
7. Wide speaker deviation from median angle.
On an accurate drawing, use a ruler and then a protractor. In the room, a measuring tape, and then the “compass” app on a smart phone, can aid in the visualization.
8. Upfiring speakers allowed
Self explanatory.
9. Allowable vertical angle.
On an accurate drawing, use a protractor. In the room, there may be some “level” apps on a smart phone can aid in the visualization, but I use a laser level/distance device.
10. Max spl difference between upper level speakers
This is achieved not just through speaker sensitivity/power handling/output but also through amplification and through distance differences, as well. Use a calculator to assess the speakers, such as the Peak SPL Calculator to see whether the speakers are within the correct range of one another. Example from RP22 doc.
11. Number of speakers allowed outside of zonal recommendations
Self explanatory.
12. Screen speakers spl capability
This is achieved not just through speaker sensitivity/power handling/output but also through amplification and through distance differences, as well. Use a calculator to assess the speakers, such as the Peak SPL Calculator to see whether the speakers can reach sufficient output levels. Example from RP22 doc.
13. Non screen speakers spl capabilities
This is achieved not just through speaker sensitivity/power handling/output but also through amplification and through distance differences, as well. Use a calculator to assess the speakers, such as the Peak SPL Calculator to see whether the speakers can reach sufficient output levels. Example from RP22 doc.
14. Bass spl capabilities
CEDIA hasn't defined how this is modeled, but it can be measured after the fact. However, other folks have done the modeling part. More than a decade ago, Audioholics published their room sizing guide, which translated CEA2010 subwoofer measurements into "X sub can play at Y level in room volume Z" but their guide focused on output at 31hz. THX has done something similar (though more opaque) that appears to target 20hz output. A thread at AVForums started by MR Wolf in the UK published the following info, which is the best modeling approach available to the public at present:
THX and Audioholics room size ratings
A home cinema system's subwoofer output requirement is, to a greater extent, a function of listening level, room volume and the low frequency content of the movies being played. Two information sources currently exist that advise on a specific subwoofer model's suitability for particular room sizes. These are THX and Audioholics.
THX has its Select, Ultra and Dominus programmes under which it tests and certifies subs as being capable of achieving cinema reference level in 2,000Ft3, 3,000Ft3 and 6,500Ft3 rooms respectively.
THX’s certification method isn’t published but a requirement is widely believed to be that frequency response must be flat to 20Hz. So to be THX certified, a sub must be able to hit 115dB reference level peaks with minimal distortion at 20Hz. Very few manufacturers choose to participate in this programme these days so unfortunately very few THX certified subwoofers exist. You will however find THX certified subwoofer models from Monoprice, Perlisten and M&K.
In contrast, AV guru website Audioholics (“AH”) assign room size ratings to the many subs it reviews and measures based on its estimate of their ability to hit 115dB at 31.5Hz (and 109dB at 25Hz) in rooms of different volumes from under 1,500Ft3 to over 5,000Ft3.
This is a significantly easier performance target to hit than THX’s as most subs have far more output capability at 31.5Hz than they do at 20Hz. AH’s rating method is simply to add 9dB to CEA-2010 RMS@2M output at 31.5Hz and adjust this result by +/-6dB per halving/doubling of room volume from a 3,000Ft3 baseline due to a change in sound pressure, e.g. 1,500Ft3/6000Ft3 rooms add/subtract 6dB from the result due to doubling/halving of volume.
My maximum listening level ratings
The main limitation of the THX/AH subwoofer ratings is the fact that almost nobody listens at cinema reference level in their homes. As listening between 10dB and 20dB below reference level can require only 1% to 10% of the amplifier power, the THX/AH ratings can lead to seriously over-specifying the subwoofer output needs of some systems.
In order to address this, using THX’s tougher 20Hz lowest frequency hurdle and AH’s CEA-2010 to in-room output adjustment method, I’ve estimated various subwoofers’ abilities to support different listening levels (relative to reference) in room sizes from 1,250Ft3 to 5,000Ft3. The maximum listening level capability is calculated simply by subtracting 115dB from the subwoofer’s estimated in-room output at 20Hz and these are the figures that are shown in the table.
Apparently, due to psycho-acoustics in smaller spaces, listening at -10dB sounds about as loud as cinema reference level (i.e. 0dB) does in large commercial cinemas. This is why I have referred to the silver highlighted >-10dB ratings as "home reference level".
Why I used a 20Hz low frequency hurdle and not 31.5Hz like AH
AH’s rating system is based on 31.5Hz output due to the bass content of >90% of movies being >30Hz. While this is probably correct, I chose to use THX’s more challenging 20Hz standard for the following reasons:
Alternatively, refer to the table at the end of this post which shows maximum listening level capability on the basis of 31.5Hz output.
A home cinema system's subwoofer output requirement is, to a greater extent, a function of listening level, room volume and the low frequency content of the movies being played. Two information sources currently exist that advise on a specific subwoofer model's suitability for particular room sizes. These are THX and Audioholics.
THX has its Select, Ultra and Dominus programmes under which it tests and certifies subs as being capable of achieving cinema reference level in 2,000Ft3, 3,000Ft3 and 6,500Ft3 rooms respectively.
THX’s certification method isn’t published but a requirement is widely believed to be that frequency response must be flat to 20Hz. So to be THX certified, a sub must be able to hit 115dB reference level peaks with minimal distortion at 20Hz. Very few manufacturers choose to participate in this programme these days so unfortunately very few THX certified subwoofers exist. You will however find THX certified subwoofer models from Monoprice, Perlisten and M&K.
In contrast, AV guru website Audioholics (“AH”) assign room size ratings to the many subs it reviews and measures based on its estimate of their ability to hit 115dB at 31.5Hz (and 109dB at 25Hz) in rooms of different volumes from under 1,500Ft3 to over 5,000Ft3.
This is a significantly easier performance target to hit than THX’s as most subs have far more output capability at 31.5Hz than they do at 20Hz. AH’s rating method is simply to add 9dB to CEA-2010 RMS@2M output at 31.5Hz and adjust this result by +/-6dB per halving/doubling of room volume from a 3,000Ft3 baseline due to a change in sound pressure, e.g. 1,500Ft3/6000Ft3 rooms add/subtract 6dB from the result due to doubling/halving of volume.
My maximum listening level ratings
The main limitation of the THX/AH subwoofer ratings is the fact that almost nobody listens at cinema reference level in their homes. As listening between 10dB and 20dB below reference level can require only 1% to 10% of the amplifier power, the THX/AH ratings can lead to seriously over-specifying the subwoofer output needs of some systems.
In order to address this, using THX’s tougher 20Hz lowest frequency hurdle and AH’s CEA-2010 to in-room output adjustment method, I’ve estimated various subwoofers’ abilities to support different listening levels (relative to reference) in room sizes from 1,250Ft3 to 5,000Ft3. The maximum listening level capability is calculated simply by subtracting 115dB from the subwoofer’s estimated in-room output at 20Hz and these are the figures that are shown in the table.
Apparently, due to psycho-acoustics in smaller spaces, listening at -10dB sounds about as loud as cinema reference level (i.e. 0dB) does in large commercial cinemas. This is why I have referred to the silver highlighted >-10dB ratings as "home reference level".
Why I used a 20Hz low frequency hurdle and not 31.5Hz like AH
AH’s rating system is based on 31.5Hz output due to the bass content of >90% of movies being >30Hz. While this is probably correct, I chose to use THX’s more challenging 20Hz standard for the following reasons:
- 20Hz is the frequency at which subwoofers can produce the least output in their typical 20-120Hz audible range of operation in a home cinema system. A sub’s maximum clean SPL output at 20Hz is therefore the limiting factor on maximum volume capability if a flat, undistorted, response down to 20Hz is desired on dynamic peaks.
- A 31.5Hz hurdle is likely to be too high for movies with very low frequency content. As 20Hz is the lowest audible frequency, if a soundtrack contains 20Hz content, then distortion might be audible if a sub lacks sufficient output capability here. Also, <31.5Hz content is not just reserved for minority interest sci-fi movies as even naturally occurring deep bass sound effects (e.g. thunder) can be as low as 20Hz.
- THX uses 20Hz for its certification programme so this method, in effect, provides THX style ratings that are adjusted for different room sizes and listening levels. This also provides a useful source of validation by looking at THX rated subs for which CEA-2010 output data is available.
Alternatively, refer to the table at the end of this post which shows maximum listening level capability on the basis of 31.5Hz output.
15. Background Noise Floor
From: Soundproofing does not exist... but Isolation can:
16. Seat to seat frequency response variance among screen wall speakers.
REW measurement, or similar, once room is built -- but that would be too late. Method for predicting ahead of time is not defined by CEDIA nor the CTA at present.
17. Seat to seat frequency response variance among non screen wall speakers.
REW measurement, or similar, once room is built -- but that would be too late. Method for predicting ahead of time is not defined by CEDIA nor the CTA at present.
18. In Room bass extension -3db frequency cutoff point.
Covered under #14, though the table only goes down to 20hz.
19. Frequency response below the room's transition frequency.
REW measurement, or similar, once room is built -- but that would be too late. Method for predicting ahead of time is not defined by CEDIA nor the CTA at present.
20. Seat to seat frequency response variant from the RSP below the room's transition frequency.
REW measurement, or similar, once room is built -- but that would be too late. Method for predicting ahead of time is not defined by CEDIA nor the CTA at present.
21. Level of early reflections relative to direct sound.
Dolby, many rooms designers like Erskine and Grimani, and countless top level room on AVS have used RT60 or reflected decay times to assess room acoustics. That approach can still produce excellent results: How Many Panels and Traps Do I Need?: RT60, RDT, REW... It is NOT the complete answer to achieving the results specified in RP22, but it is a big step in that direction.
