Small Bedroom Theater Acoustic Panel Advice Needed (2 Viewers)

[siles1991]

This is a rough layout of my bedroom. I missed out on some surrounds that are mounted on the rear walls. I don't have much space but I want to try to make the best of it. As you can see I have a wardrobe and windows on the left and right side of the room which doesn't allow me to mount any acoustic panels on the sides but I made do with some thick acoustic foam I command stripped to the window sill and wardrobe doors. They're large enough to not get in the way but I definitely can't really fit panels there, they've helped enough so far for first reflections albeit not ideal but Audyssey is doing a good job on that front and I'm currently happy.

So now I'm planning to DIY some 4" acoustic panels with 4" 60kg/m3 Rockwool. 60x120cm sized but effectively it'll be taking up 90x150cm. I'm starting off with 3 panels which will be put on my rear walls above my computer table(horizontal mount), and to the side of my bed when I change to a smaller single bed. The third one I'm still wondering if I should hang it on my door or to the wall in between the door and wardrobe. There's just enough space there for a panel there and not to get in the way of the door opening.

The other 3 panels would be placed on the front wall one each behind the speakers and one above the TV(horizontal). With the lack of space you can see I have no corners I can place bass traps and I have some bass issues so I'm hoping that 4" panels will help with it.

My question is whether 3-6 panels would be too much or too little for bass and echo and is there any advice you can give me? I could probably fit another acoustic panel above the TV and possibly pull my computer table forward to add another panel and change the mounting to vertical instead. I can't add acoustic panels to both the door and the wall next to it at the same time so I have to choose either one or make 2x 2"acoustic panels and straddle because the gap from the door open to the wall is 4" so I could do that but I believe thinner panels don't do well with absorbing lower freqs.

EDIT: I could also possibly add a cloud panel on the ceiling.

 

[Nathan_H]

I’d probably place several at ear height on the wall opposite the tv, ie, behind where you sit.

 

[siles1991]

I’d probably place several at ear height on the wall opposite the tv, ie, behind where you sit.

Thanks for the reply! Will keep that in mind!

 

[Nathan_H]

Thanks for the reply! Will keep that in mind!

Sure.

If you want to get more into the weeds, here is a draft of a guide I am working on:
Acoustic panels are typically used to improve the reverberation time in the room -- how much sound is reflected and echoed around the space. (They can also have an impact on some aspects of frequency response in some specific use cases, but that's a topic for another thread.) This impact can be measured, and there are industry standards for what that measurement should look like in a good sounding room.

The usual measure is called RT60. There have been many mentions of RT60 (the reverberation time in a room) over the years on AVS. How to estimate it (tough), How to measure it (now pretty easy), and What a good result looks like (depends a bit).

(Note that I am using the term "RT60" as a catch all. Purists and pedantic rightly call it RDT -- reflection decay time -- since RT60 makes more sense as a concept in a concert hall and not in a home theater. But the measurement and evaluation process is actually the same.)

One of many examples of working through this topic: https://www.avsforum.com/threads/rt60-what-is-a-good-value.332289/

---

This post describes two objective methods for assessing and treating a room.

BUT: If you just want a TLDR method that doesn't involve measurement, instead, that's simple and very effective, here it is:

Cover about 15% to 20% of your walls / ceiling with acoustic panels that are at least 2" thick, ideally 4" thick, evenly spaced around the room, from companies like the following, and enjoy.

Custom Art Panels & Bass Traps - GIK Acoustics

https://www.gikacoustics.com/product/gik-acoustics-242-acoustic-panel/

These are good too but not as thick so therefor not as useful:

Acoustic ART panels, Decorative Acoustic Art sound Panels - The Perfect ...

https://www.acoustimac.com/acoustic...anels/executive-422-acoustic-panels-48x24x2-1

These would not be as good but perhaps the look makes them a better choice for you:

https://www.gikacoustics.com/product-category/impression-series/

And of course there are very good DIY options for those who are so inclined:

https://www.avsforum.com/threads/di...-panels-cheap-version-2-0-discussion.3221663/

---

But now for the more scientific/engineering based approaches:


FIRST:

You can measure the RT60 in your room with a free piece of software (REW) and a hundred dollar microphone (eg, the UMIK 1).

How do you measure RT60 with REW? At present the steps are:

Here's the process:

1. Open up an mdat with full range measurements of your L+R
2. Select a measurement on the left, then go to "RT60 Decay" window
3. The graphs will (probably) be empty
4. Hit the "Generate" button in the bottom left of the bottom graph
5. Hit the "Controls" gear
6. Hit "Calculate RT60 Model"

Now, go to the regular RT60 window. The measurement you used above will now have an RT60 graph.


SECOND:

What is a good RT60? In the past people often talked about a single RT60 value for a room. This is a fudge. As you can see from the graph you created in REW, there is an RT60 value for every frequency you measure.

What's the target? Well, reasonable people can disagree. One can argue that the smaller a room, the lower the RT60 target will be. And there is some amount of taste that can come to bear. But if one's room is relatively linear from the transition frequency up to above 10k, and between .2 and .4, you are probably in the realm of "quite good."

So check two things: Is the RT60 graph for your room consistent from around 125hz up to 10khz? If so, that is good.

Then, is that line roughly centered on .3 seconds (with .2 acceptable if the room is under 200 square feet, and .4 acceptable if the room is over 1000 square feet)?

If the answer to both those questions is YES then you are golden. Set aside your measurement gear, stop adding acoustic panels, and enjoy your state of the art system.

---


Do you want to go further down the rabbit hole?

Okay, if you want to try to follow a specific target, something like an industry standard, for critical listening, I find the Dolby specification for mastering suites to be a good goal. The Dolby Atmos Home Entertainment Studio Technical...
It is buried in their Room Design Tool:

Now, this is a studio guideline, and some of us like to dial in our room as close as possible to the ideal for a mastering suite both for video and for audio.

But while for video there is a very specific agreed upon guideline for most measured responses (in fact maybe all, perhaps other than some aspects of tone mapping HDR EOTF), on the audio side, there is a slightly more generous range for RT60.

Typically, getting below .5 across the frequency range is considered a good room. And some traditionally furnished rooms with couches, curtains, rugs, book cases, and so on get close to that on their own for some of the octaves, which is nice.

And many people consider .3 or .35 to be a more comfortable target than the Dolby mastering suite guidlines

(And almost everyone who has compared such rooms to one that measures .2 or lower agrees that that is really unpleasant and overkill once you hit .2.)

The ITU has a nuanced document about target RT60 numbers for rooms that is based on their size, as well, discussed here:

https://www.avsforum.com/threads/re...-is-what-your-room-should-sound-like.3261875/

which can be downloaded here:

https://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1116-1-199710-S!!PDF-E.pdf

called:

"Rec. ITU-R BS.1116-1 1
RECOMMENDATION ITU-R BS.1116-1*
METHODS FOR THE SUBJECTIVE ASSESSMENT OF SMALL IMPAIRMENTS IN AUDIO SYSTEMS INCLUDING MULTICHANNEL SOUND SYSTEMS"

which gets into how room size can make the targets a little different, to achieve the desired effect.

Decades of testing different size rooms and different amounts of decay with many many people, who were then asked what rooms sounded best, resulted in such consistent preferences that there is an equation to get it "right" or best. The ITU paper listed above is highly technical.

Grimani talks about this (and other topics) in detail in this video from the AVS YouTube channel.

https://www.youtube.com/live/nEhyajMyoXw?feature=share

But to jump to the spoiler:

And while we are watching YouTube, it's worth noting that Matt Poes makes some interesting points in his video. Among other things, he notes that the lower the RT60 time, the more you hear issues with your speakers, in the source material, and your setup, so ultimately measurements aren't the goal, but just a way to get in the ballpark. Then he does what most eperienced professionals do: He listens critically to a wide range of material, draws on years of experience in a multitude of state of the art -- and real world comprised -- rooms, and adjusts.




--



TLDR:

1. Consistency: If your REW RT60 measurements vary widely across the frequency range, that is likely worth correcting. You can see how Dolby targets a slightly downward slope in terms of RT60, for example.

2. Amount: If in general your numbers (line/graph) are above .4 seconds, then it is likely that adding panels or traps (ideally a minimum of 4" in depth but even 2" can help) to your room will make marked improvement in the clarity of your system. If you get down to .2 seconds, you should stop. Often, covering 15% of all the surface area (floor, ceiling and walls added to together) with panels spread evenly around the room will do the trick, if this is a dedicated room with otherwise empty walls. (If this is a living room with lots of stuff in it, you may not need as many panels.)

TLDR of th TLDR: Spending money on acoustic panels to tune your room will make a far bigger impact than spending that extra two thousand dollars on a step up AVR or amplifier.



__


And a bonus, where to put them? I prioritize the rear wall, the ceiling, the front wall, and the side walls.......rather than "just the side wall first reflections"......because especially if you have a wide room and speakers with even consistent dispersion, the main audible issues aren't coming from the side wall first reflections at that point......and no matter how good the speakers are, reflections from the rear wall almost always smear the sound in the room.

And this illustration of "bass traps" is a useful guide, but when they call them "Bass Traps" what they apply to are thick broadband absorption panels in general.

image is from How to Fix Speaker Boundary Interference (SBIR) Issues

 

[siles1991]

Sure.

If you want to get more into the weeds, here is a draft of a guide I am working on:
Acoustic panels are typically used to improve the reverberation time in the room -- how much sound is reflected and echoed around the space. (They can also have an impact on some aspects of frequency response in some specific use cases, but that's a topic for another thread.) This impact can be measured, and there are industry standards for what that measurement should look like in a good sounding room.

The usual measure is called RT60. There have been many mentions of RT60 (the reverberation time in a room) over the years on AVS. How to estimate it (tough), How to measure it (now pretty easy), and What a good result looks like (depends a bit).

(Note that I am using the term "RT60" as a catch all. Purists and pedantic rightly call it RDT -- reflection decay time -- since RT60 makes more sense as a concept in a concert hall and not in a home theater. But the measurement and evaluation process is actually the same.)

One of many examples of working through this topic: https://www.avsforum.com/threads/rt60-what-is-a-good-value.332289/

---

This post describes two objective methods for assessing and treating a room.

BUT: If you just want a TLDR method that doesn't involve measurement, instead, that's simple and very effective, here it is:

Cover about 15% to 20% of your walls / ceiling with acoustic panels that are at least 2" thick, ideally 4" thick, evenly spaced around the room, from companies like the following, and enjoy.

Custom Art Panels & Bass Traps - GIK Acoustics

https://www.gikacoustics.com/product/gik-acoustics-242-acoustic-panel/

These are good too but not as thick so therefor not as useful:

Acoustic ART panels, Decorative Acoustic Art sound Panels - The Perfect ...

https://www.acoustimac.com/acoustic...anels/executive-422-acoustic-panels-48x24x2-1

These would not be as good but perhaps the look makes them a better choice for you:

https://www.gikacoustics.com/product-category/impression-series/

And of course there are very good DIY options for those who are so inclined:

https://www.avsforum.com/threads/di...-panels-cheap-version-2-0-discussion.3221663/

---

But now for the more scientific/engineering based approaches:


FIRST:

You can measure the RT60 in your room with a free piece of software (REW) and a hundred dollar microphone (eg, the UMIK 1).

How do you measure RT60 with REW? At present the steps are:

Here's the process:

1. Open up an mdat with full range measurements of your L+R
2. Select a measurement on the left, then go to "RT60 Decay" window
3. The graphs will (probably) be empty
4. Hit the "Generate" button in the bottom left of the bottom graph
5. Hit the "Controls" gear
6. Hit "Calculate RT60 Model"

Now, go to the regular RT60 window. The measurement you used above will now have an RT60 graph.


SECOND:

What is a good RT60? In the past people often talked about a single RT60 value for a room. This is a fudge. As you can see from the graph you created in REW, there is an RT60 value for every frequency you measure.

What's the target? Well, reasonable people can disagree. One can argue that the smaller a room, the lower the RT60 target will be. And there is some amount of taste that can come to bear. But if one's room is relatively linear from the transition frequency up to above 10k, and between .2 and .4, you are probably in the realm of "quite good."

So check two things: Is the RT60 graph for your room consistent from around 125hz up to 10khz? If so, that is good.

Then, is that line roughly centered on .3 seconds (with .2 acceptable if the room is under 200 square feet, and .4 acceptable if the room is over 1000 square feet)?

If the answer to both those questions is YES then you are golden. Set aside your measurement gear, stop adding acoustic panels, and enjoy your state of the art system.

---


Do you want to go further down the rabbit hole?

Okay, if you want to try to follow a specific target, something like an industry standard, for critical listening, I find the Dolby specification for mastering suites to be a good goal. The Dolby Atmos Home Entertainment Studio Technical...
It is buried in their Room Design Tool:

View attachment 190397

Now, this is a studio guideline, and some of us like to dial in our room as close as possible to the ideal for a mastering suite both for video and for audio.

But while for video there is a very specific agreed upon guideline for most measured responses (in fact maybe all, perhaps other than some aspects of tone mapping HDR EOTF), on the audio side, there is a slightly more generous range for RT60.

Typically, getting below .5 across the frequency range is considered a good room. And some traditionally furnished rooms with couches, curtains, rugs, book cases, and so on get close to that on their own for some of the octaves, which is nice.

And many people consider .3 or .35 to be a more comfortable target than the Dolby mastering suite guidlines

(And almost everyone who has compared such rooms to one that measures .2 or lower agrees that that is really unpleasant and overkill once you hit .2.)

The ITU has a nuanced document about target RT60 numbers for rooms that is based on their size, as well, discussed here:

https://www.avsforum.com/threads/re...-is-what-your-room-should-sound-like.3261875/

which can be downloaded here:

https://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1116-1-199710-S!!PDF-E.pdf

called:

"Rec. ITU-R BS.1116-1 1
RECOMMENDATION ITU-R BS.1116-1*
METHODS FOR THE SUBJECTIVE ASSESSMENT OF SMALL IMPAIRMENTS IN AUDIO SYSTEMS INCLUDING MULTICHANNEL SOUND SYSTEMS"

which gets into how room size can make the targets a little different, to achieve the desired effect.

Decades of testing different size rooms and different amounts of decay with many many people, who were then asked what rooms sounded best, resulted in such consistent preferences that there is an equation to get it "right" or best. The ITU paper listed above is highly technical.

Grimani talks about this (and other topics) in detail in this video from the AVS YouTube channel.

https://www.youtube.com/live/nEhyajMyoXw?feature=share

But to jump to the spoiler:

View attachment 190398

View attachment 190399


And while we are watching YouTube, it's worth noting that Matt Poes makes some interesting points in his video. Among other things, he notes that the lower the RT60 time, the more you hear issues with your speakers, in the source material, and your setup, so ultimately measurements aren't the goal, but just a way to get in the ballpark. Then he does what most eperienced professionals do: He listens critically to a wide range of material, draws on years of experience in a multitude of state of the art -- and real world comprised -- rooms, and adjusts.




--



TLDR:

1. Consistency: If your REW RT60 measurements vary widely across the frequency range, that is likely worth correcting. You can see how Dolby targets a slightly downward slope in terms of RT60, for example.

2. Amount: If in general your numbers (line/graph) are above .4 seconds, then it is likely that adding panels or traps (ideally a minimum of 4" in depth but even 2" can help) to your room will make marked improvement in the clarity of your system. If you get down to .2 seconds, you should stop. Often, covering 15% of all the surface area (floor, ceiling and walls added to together) with panels spread evenly around the room will do the trick, if this is a dedicated room with otherwise empty walls. (If this is a living room with lots of stuff in it, you may not need as many panels.)

TLDR of th TLDR: Spending money on acoustic panels to tune your room will make a far bigger impact than spending that extra two thousand dollars on a step up AVR or amplifier.



__


And a bonus, where to put them? I prioritize the rear wall, the ceiling, the front wall, and the side walls.......rather than "just the side wall first reflections"......because especially if you have a wide room and speakers with even consistent dispersion, the main audible issues aren't coming from the side wall first reflections at that point......and no matter how good the speakers are, reflections from the rear wall almost always smear the sound in the room.

And this illustration of "bass traps" is a useful guide, but when they call them "Bass Traps" what they apply to are thick broadband absorption panels in general.

View attachment 190400

image is from How to Fix Speaker Boundary Interference (SBIR) Issues

Thank you for such an informative reply, I skimmed a bit since I'm out but will definitely read everything properly when home. I'm actually waiting for a UMIK1 to arrive sometime this following week so I'm looking forward to do proper measurements. Your time and effort in giving this info is very appreciated. Thank you!!!

 

[smithbrad]

Sure.

If you want to get more into the weeds, here is a draft of a guide I am working on:
Acoustic panels are typically used to improve the reverberation time in the room -- how much sound is reflected and echoed around the space. (They can also have an impact on some aspects of frequency response in some specific use cases, but that's a topic for another thread.) This impact can be measured, and there are industry standards for what that measurement should look like in a good sounding room.

Great information, I'm glad I viewed this thread. I will be building my next HT in two years when we build a new house. For the new house I was thinking of using various prebuilt 2" wall panels and bass traps in the corners from GIK Acoustics. For my existing theater that I built back in 2004, without measuring, I did 1" rigid fiberglass floor to ceiling on the front wall and ear-level down for the back and side walls.

 

[siles1991]

FIRST:

You can measure the RT60 in your room with a free piece of software (REW) and a hundred dollar microphone (eg, the UMIK 1).

How do you measure RT60 with REW? At present the steps are:

Here's the process:

1. Open up an mdat with full range measurements of your L+R
2. Select a measurement on the left, then go to "RT60 Decay" window
3. The graphs will (probably) be empty
4. Hit the "Generate" button in the bottom left of the bottom graph
5. Hit the "Controls" gear
6. Hit "Calculate RT60 Model"

Now, go to the regular RT60 window. The measurement you used above will now have an RT60 graph.


SECOND:

What is a good RT60? In the past people often talked about a single RT60 value for a room. This is a fudge. As you can see from the graph you created in REW, there is an RT60 value for every frequency you measure.

What's the target? Well, reasonable people can disagree. One can argue that the smaller a room, the lower the RT60 target will be. And there is some amount of taste that can come to bear. But if one's room is relatively linear from the transition frequency up to above 10k, and between .2 and .4, you are probably in the realm of "quite good."

So check two things: Is the RT60 graph for your room consistent from around 125hz up to 10khz? If so, that is good.

Then, is that line roughly centered on .3 seconds (with .2 acceptable if the room is under 200 square feet, and .4 acceptable if the room is over 1000 square feet)?

If the answer to both those questions is YES then you are golden. Set aside your measurement gear, stop adding acoustic panels, and enjoy your state of the art system.

I finally received my UMIK and did the measurements as follows.

LEFT:

RIGHT:

CENTER:

LEFT + RIGHT:

SUB:

So with these measurements my decay is about .33 at the lowest and .467 at it's highest (125hz-10khz)
I should add acoustic panels until I can get these down to around .2 since my room is under 200sqf. Am I on the right track? Though anything below 125hz looks pretty long reaching .7.

 

[Nathan_H]

I would try for .3 seconds, and not worry too much about the bass.

If you can get down the .3 or .35 seconds in the 200 hz and above region that is going to be very nice.

To do better in the bass, especially the subwoofer region of 100 hz and below, you would use a second subwoofer set up carefully.

Here is a draft of a guide I am working on: https://www.avsforum.com/threads/su...distance-setup-crossover-selection-eq.940684/ which currently reads:

There are five main steps to subwoofer setup after you have set all your speakers to "small," and are sending the subwoofer signal out of your AVR or pre-pro as a single mono signal**:

1. Placing the subs in the most favorable positions.
2. Aligning the subs with one another (often called ”time alignment.”)
3. Then, aligning the subs with the mains (often called the “distance tweak”.)
4. And, selecting the crossover points for your speakers. (Repeating steps 3 + 4 iteratively since they interact, if you don't hit upon something you like the first time.)
5. Then, running EQ.

First, one needs to place the subs in the most favorable positions.

The concept is that you place the subs as best you can for your given room.

If you have multiple rows of seats, you likely want to place one sub in each corner of a rectangular room. You might be able to get by with two subs, likely in katty corner locations, or the center of two opposing walls. But four subs will give you a more consistent result.

If you have only one row of seats, you can usually manage with just two subs if:

• you have some placement flexibility on the front wall or the back wall, and
• you have the ability to move the seating forward or back to avoid dips along the length of the room.

Often, putting those two subs at 1/4 and 3/4 of the front wall or of back wall (both in front or both behind), or in both the corners at the front of the room, or in both of the rear corners, will give you good left/right consistency across seats.

Of course, rooms are not symmetrical even when they measure that way with a tape measure. Different construction, door jambs, etc, make them acoustically not quite symmetrical especially in the bass.

Some subwoofer placement options give you a big head start in terms of getting consistent bass response across multiple seats, typically with fewer dips in response to deal with.

Todd Welti did some great research at Harman on this. https://www.harman.com/documents/multsubs_0.pdf

Then, one needs to (time) align the subs with one another.


This creates a single virtual subwoofer, with positive summation (ie, fewer dips and better peaks) and more seat to seat consistency than a single subwoofer can generate.

You will need to electronically time align the subs to one another. There are many good videos and explanations of this time alignment process, so I will keep this one relatively short and simple.

The simple version is with two subs.

Level or gain match then with an SPL. Yes there is a difference between these two methods. But either will work. Then time align:

Leave one sub's phase at zero. And adjust the other subs phase until the combined response of the two subs produces the fewest troughs in response and the most consistent response across your seats. If you have a rectangular room, and you can symmetrically place your subs in the room, you may not need to do anything else to time align them together......so if your response from the two subs looks fine in REW, you can skip the rest of this and proceed to steps 3 and 4.

But often, there is improvement to be had. Here is an example where alignment was necessary, because I did not place the subs symmetrically in the room:

I thought I was going to have to bust out the miniDSP for my subs and that would let me adjust the distance even more than the phase knob, but then I remembered that the phase knob on the Rythmik is also a distance knob (even tells you happily what 180 degrees is in milliseconds of delay), and found via the REW alignment tool that about 7ms was what I needed.

Green and Purple are the individual subs.
Red is the combined response without time alignment.
Yellow is the combined response with time alignment.
For simplicity, I do not show all the other traces that didn't look as good as the yellow version.

Pretty darn text book summation where the combined response meets or exceeds (especially in the critical chest slam 40 to 60hz region) the response of any individual sub by quite a margin, in many cases by more than 10db.

Note that I tried to use the REW time alignment prediction tool. It wasn't quite right. So it pays to take time to experiment with different "distances" or "phase."

If you have more than two subs, once you have dialed in two subs, consider those a single, virtual sub, and then align that single virtual sub with the third sub, and so on, for as many subs as you have.

If you have three or more subs, it can be worthwhile to use a miniDSP and to use the free Multi Sub Optimizer software.

In theory, some "room correction" systems are getting better at doing this for your subs. I'll bet if you check their work, you can improve upon them.

Finally......check your other seats. If you have significantly different response in your different seats, you mean need to move the subs, some seats, accept imperfect response for some listeners, and/or add more subs.*




The Third & Fourth steps are where one figures out the AVR distance and crossover settings.


These two steps actually interact with one another, so you will work on them iteratively.

One needs to align this single virtual subwoofer (ie, all the time aligned subs as a single sub output) with the mains. In the old days we called this phase alignment, but the normal tool here is the “distance” setting on the AVR.

This was popularized as the sub distance tweak.

To get this right is an iterative process where you measure the response in that region with different delays (distances) for the virtual single sub, and with different crossover points.

You can see quickly that that means measuring every distance from zero to 30ms, with a 60hz crossover, then all those distances again with a 70hz crossover, etc, up to 120hz or even higher. There will likely be a combination that is a little better at showing no wide dips……and that is the best alignment.

Don’t worry about peaks. You will EQ the final result.

And remember: Sometimes the best alignment is using, for example, a 120hz crossover, and that may feel weird…… and sometimes you may do almost as well at 80hz, and that’s okay……..and some people prefer 80hz and choose that lower choice even though it’s not quite as good.

Personally, since that lower frequency choice also increases seat to seat variance in the 80 to xxx region, I find in such a situation that the 120hz crossover in this example might actually be the better compromise. Better alignment with the mains and better (less) seat to seat variation due to the advantage of multiple subs covering more of the frequency range.

The verification will be the REW measurements of the final result showing a positive summation throughout the crossover region. And while it should go without saying, your auto setup software may not choose the best distance nor the best crossover for you. It doesn't actually test the speakers and subs TOGETHER nor with different real world settings. It measures them individually and tries to predict what will work best.

Here is an example of the concepts at work in a real room:

I started with 80hz and checked the distance from 10' down to 0' which is more than a 180 degree phase shift in the crossover region, so should cover most options.

2' of distance was the best compromise. Some were a tiny bit better in the 80hz region, some were a little better in the high 90s, but those involved tradeoffs in one or the other area. 2' was the best balance.

Here is a closeup showing the region a bit better:

Then I tested different crossovers to see what could be gained....And 80hz was still the winner.

Then I tested where things broke down when using the Center speaker instead of the Right speaker as the bed layer speaker I'm integrating the subwoofer with. No worries:

Finally I tested the surround speaker crossover. Going lower than ARC chose (100hz) did create a better graph, but the power handling of the Triad Bronze satellite when trying to play at 90hz was not up to the task. Its a small specialized speaker and just a temporary choice. Bumping the crossover up to 120hz didn't make it worse measuring than when at 100hz, and increased the power handling, so that is what I settled on for this speaker for now. (I'll be eager, short term, to reclaim my on wall Revels for this room, and longer term to use the Triad Bronze LCR for surround duty when I build out the false falls.)

Always remember that the measurement tools can make these differences look really big. But the truth is that audibly, just getting "in the ballpark" will often work very well. That is why the automated systems, even if they aren't as thorough as this iterative process of testing real configuration changes, often can sound good.

What do I mean?

Many of these glaring differences disappear when human hearing is taken into account.....and arguably if one completely trusts psychoacoustic smoothing, 4' might be a better distance setting for the sub than 2' by a tiny margin (ie, 1db in some places). Or, in other words, I have graphed the measurements to exaggerate as much as possible what the microphone can pick up and what the graphs can show, but if you take into account what a human can hear, things are much less stark:

And then Step Five, running your room EQ, will clean things up super well.

Add in an house curve if you like. Enjoy!


———————

Final thoughts.

There are a myriad variations to the method described here. But the concept remain very similar.

MiniDSP: A popular tool is a minidsp instead of using the phase adjustment on the subs to time align the subs. Some people also like to use the minidsp for EQ to take some of the effort off the room EQ system, or even use the minidsp to align the subs to the mains (distance tweak). And / or they use the minidsp to also apply bassEQ. I have a minidsp and I found I didn’t need to use it, and I wanted to share the process without using one.

MSO: Especially if you have three or more subs, including mismatched subs, and a miniDSP, you can use a free piece of software called the Multi Sub Optimizer to take your REW measurements and figure out optimal settings to align and EQ your subs, that you then dump into your MiniDSP…..resulting in one great measuring single virtual sub.






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**Don't fall prey to magical thinking about stereo subs, speaker level inputs, and so on. You don't need to blindly follow any theories, either. Rather, make use of the double blind studies conducted with hundreds of people, that show how a mono subwoofer signal, processed correctly, coming from the right places in the room, is seamless and transparent to the source.....even more than full range speakers, stereo subs, and other kinds of superstition left over from the 20th century, which have no support once listening tests are no longer sighted.

*In addition to my short summary at the start of this process, see also Welti's papers on this, his engineering papers in which he discusses tradeoffs between output and consistency across multiple seats, his interviews like at AVRANT on YouTube, etc.

 

[Nathan_H]

Great information, I'm glad I viewed this thread. I will be building my next HT in two years when we build a new house. For the new house I was thinking of using various prebuilt 2" wall panels and bass traps in the corners from GIK Acoustics. For my existing theater that I built back in 2004, without measuring, I did 1" rigid fiberglass floor to ceiling on the front wall and ear-level down for the back and side walls.

Glad you will be using acoustic panels in your new dedicated room.

Generally you will be better off with a little less wall coverage than the last room, but a little thicker panels when you use them. 4” is the sweet spot in terms of bang for buck.

For bass traps, if you have a screen hung on a “false wall” or a drop tile ceiling or a similar large space you can fill with cheap insulation batts, that is often more useful than corner traps.

And of course using dual subs set up correctly (see the link in my prior post) is a big benefit in “active” bass trapping.

 

[siles1991]

I would try for .3 seconds, and not worry too much about the bass.

If you can get down the .3 or .35 seconds in the 200 hz and above region that is going to be very nice.

To do better in the bass, especially the subwoofer region of 100 hz and below, you would use a second subwoofer set up carefully.

Here is a draft of a guide I am working on: https://www.avsforum.com/threads/su...distance-setup-crossover-selection-eq.940684/

Thank you. I will get on it as soon as I can!

 

[Nathan_H]

I have two layers of Linacoustic duct liner floor to ceiling behind the screen wall that wraps around the corners approximately 18”.

That is great for comb filtering that happens off the screen.

Is it not useful for SBIR nor for bass trapping.

If you have a bunch of open space behind the screen still, consider a cheap and very effective bass trap: Piles of cheap batt insulation. This will kill any SBIR and it will act like a very effective giant bass trap.

I have 21 Auralex Minifusers for diffusion that are currently unmounted (and unpainted!).

I linked to some explanations of panel layout earlier in this thread. In particular, this video is a fine place to start.



TLDR: After you place all the absorption panels, add these in between those panels EXCEPT directly behind the seats, where absorption is far more useful.

Then, if you want more, here are a series of videos, if you want to dive deep some weekend and get even more educated: https://www.avsforum.com/threads/th...eading-material-like-ceb22-and-ceb23.3274569/

Acoustimac absorption panels on the walls – I was thinking four – 2’x4’x2” panels on each side wall as well as a couple of 2’x4’ panels on the ceiling.

1. Top priority would be on the rear wall to prevent smearing of the sound in the room. Ideally, six inch thick panels there (could be 4" plus a 2" air gap if that is easier) act like a full range treatment. Basically one 2x4' panel per seat in the rear row, directly behind each seat at ear height, is the ideal.

2. Then, placing panels on the sides and ceiling is useful. A room your size would likely benefit from four or 5 2x4' panels on each side. 4" thick panels is ideal, 2" would be the minimum. Likely a similar number on the ceiling is useful too.

Some people will say to place those side wall and ceiling panels at first reflection points. This is not a steadfast requirement. Here is how I describe that thinking:

For a while it was a given that killing first reflections was "always a good thing." Then researchers actually evaluated preferences in double blind listening tests, and it turns out that that was sometimes not true at all.

Whether you kill the side walls involves key questions like:

1. How far away are the side walls? More than 2 meters = Less important to kill reflections.
2. How even (consistent) is the off axis response of the speakers? Very consistent = Less important to kill the reflections.
3. Do you like a very spacious sound, perhaps more than what is specifically intended by the recording (ie, some two channel audiophiles) = Then less side wall absorption may be called for.

On the other hand, are the side walls within 1 meter of the speakers = Absorption can be helpful at the reflection points.

Is the off axis response of the speakers inconsistent with their on axis response = Kill the first reflections to keep the sound clear. Most of what you hear are actually the reflections and if they don't have the same general response curve as the on axis sound, the experience tends of be poor.

Are you mostly playing movies and not two channel stereo recordings? Absorption is not evil even if you have lots of space and consistent dispersion. Add panels to taste.

These days, with better speakers (more consistent off axis response) and EQ, the overall RT60 time is still important, but killing first reflections completely is not usually necessary, nor necessarily preferred in blind listening tests. But it is seldom a bad practice to target the first reflection points -- it is just no longer always the recipe for success it once was.

You don't mention what speakers you are using, so I can't speculate further.



(What about first reflections behind the listener's head? Absorption behind the listeners is far more useful than a flat wall or even some diffusion there. That is why I said that was a top priority. Yes, diffusion on the back wall of a dedicated room can be useful.... just not at the first reflection points / behind listeners' heads. Diffusion works well outside the seating area, where there isn't a first reflection point.)


What about first reflection points on the ceiling and floor? Those are typically less useful that side wall reflections for creating a sense of space, and even speakers with wide even dispersion often don't have great (as in similar to on axis) off axis response vertically, so killing the ceiling first reflections and floor first reflection makes sense more of the time. (Killing the floor is hard, because getting something thick enough there to act broadband instead of as a tone control can be challenging. The old audiophile trick of a thick rug with thick padding is about as good as most of us can do.

How many panels? I have given you some rough figures, above.

If you want to get scientific and act like an engineer with measurement equipment, and follow guidelines from people like the CEDIA group, Dolby and so on, that is totally possible. Then the answer is: Enough to achieve consistent decay times throughout the frequency range of a specified target. See: Dial in your RT60 time

Should I make any of the panels 4” bass traps rather than 2” panels? If so which ones?

Yes, as many as possible. I would say "all" if possible.

Also, I am thinking of going with Acoustimac’s Eco-Core insulation as they say it outperforms Roxul or OC703

Technically it is slightly more absorptive. But the difference is about one panel's worth of absorption in a room this size with nearly 20 panels. Or less. Don't constrain yourself.

Is there any advantage between any of their three fabric options (DMD, Executive, and Suede)?

I think the suede looks the best. I have a set of their suede panels on my ceiling. However, it is slightly less acoustically transparent. That means that the insulation behind the fabric doesn't get to do quite as much work in your room. More of the sound bounces off. Not a deal breaker, but I would recommend you not worry about the acoustics of these three materials. Just get samples of all three before committing to buying anything.

Many people prefer the look of the Executive over the Suede.