Back Wall Treatment for Home Theater

[CK.]

Greetings to all,

Guys I would really appreciate your input on the following questions that I have with regards to acoustic treatment.

First off, let's set the scene:

• Due to budget constraints I can only treat my back wall at this point (attached photo)
• I would only like to use safe materials with no toxic components or any breathable fibers, dust, etc.
• Idea is to replace existing canvasses (60cmx60cm each) with art panels
• Attached some measurement from one of my front speakers (FR, RT60, Waterfall graph).

Questions:

1. anyone knows of the EcoCore material from acoustimac is safe and absolutely risk free to be around? (attaching their claim)
2. If I was to choose between having 3 panels 60cmx60cmx10cm (i.e. 4" thick) and having 3 panels 120cmx60cmx5cm (i.e. 2" thick but more surface area) for the back wall which should I go for?
3. Is the area covered by my art canvasses as shown in the photo with respect to the back wall generally enough for acoustic treatment?

Many thanks guys!

 

[Mishaiger]

Hi, i cant recommend you any specific products, but about other questions.
I'm no expert or anything. First about panel depth. Here is absorption coefficient of some rockwool:
As you can see, 5 cm will absorb frequencies about 300 hz and higher. 10 cm will absorb about 150 hz and higher. Will do very little to frequencies below that.

In my opinion, 3 60x60x10 panels wont provide much impact, if at all, audially. 3 120x60x5 will cover more area and, i suspect, will provide some minor differences audially.

That being said, i see in your rt60 and waterfall graphs that you have very lively room, about 800 ms of reverberation time. I see surround speakers, so this is your movie room. For movies recommended rt60 is about 200ms. For stereo music recommended rt60 is about 300ms.
At most 3 120x60x5 panels will reduce reverberations by, idk, few ms, but only in panel working frequencies, i.e. 300hz and above. This will align reverberations more to your high end frequencies, 10 khz and above. Since your high end have lower reverberations than the rest of spectrum. But low end, 200 hz and lower, will not change at all.
Something like that:


So, in summary, adding panels will at most reduce some reverberations, but not in bass region, so it might emphasize bass, which is not a good thing. On the other hand, since your high frequencies rt is lower, panels will bring mid frequencies more close to high frequencies.
In reality though, i dont think so little quantity of panels will provide any meaningful difference in sound.

 

[CK.]

Hi, i cant recommend you any specific products, but about other questions.
I'm no expert or anything. First about panel depth. Here is absorption coefficient of some rockwool:View attachment 325507
As you can see, 5 cm will absorb frequencies about 300 hz and higher. 10 cm will absorb about 150 hz and higher. Will do very little to frequencies below that.

In my opinion, 3 60x60x10 panels wont provide much impact, if at all, audially. 3 120x60x5 will cover more area and, i suspect, will provide some minor differences audially.

That being said, i see in your rt60 and waterfall graphs that you have very lively room, about 800 ms of reverberation time. I see surround speakers, so this is your movie room. For movies recommended rt60 is about 200ms. For stereo music recommended rt60 is about 300ms.
At most 3 120x60x5 panels will reduce reverberations by, idk, few ms, but only in panel working frequencies, i.e. 300hz and above. This will align reverberations more to your high end frequencies, 10 khz and above. Since your high end have lower reverberations than the rest of spectrum. But low end, 200 hz and lower, will not change at all.
Something like that:View attachment 325512


So, in summary, adding panels will at most reduce some reverberations, but not in bass region, so it might emphasize bass, which is not a good thing. On the other hand, since your high frequencies rt is lower, panels will bring mid frequencies more close to high frequencies.
In reality though, i dont think so little quantity of panels will provide any meaningful difference in sound.

First of all thank you for your input. This is my living room where I also watch movies yes. I do not have a dedicated home theater so unfortunately very little flexibility. Having said that, my goal was to reduce reverb to about 500ms which is the upper end for home theaters. I am not expert my self but all the posts I have seen state a target reverb for HT of about 200-600ms.
However, since acoustic panels are expensive (or at least the ones I am considering) I wouldn't want to spend that money for marginal at best improvement. So would you say that placing the panels on the wall behind my head would have very little impact on the overall clarity and definition of the sound?

 

[Mishaiger]

I am not expert my self but all the posts I have seen state a target reverb for HT of about 200-600ms.

Yes, i was just thinking about lower end of target reverb, because i don't like reverberations...

However, since acoustic panels are expensive (or at least the ones I am considering) I wouldn't want to spend that money for marginal at best improvement. So would you say that placing the panels on the wall behind my head would have very little impact on the overall clarity and definition of the sound?

My guess is that it will sound a little better, even with still high decay time of bass.
I can tell you my experience. I started with empty room that had about 350 ms of reverberation time. I treated it little by little, measuring each time. I started with 4 100x60x15cm panels: 2 front, 2 back. I don't have measurements anymore, but rt dropped to, maybe, 300-320ms. I remember sound became a little different, it wasn't better or worse, room just became a little bit more dead. I couldn't hear any additional clarity or something. Then i treated room more and more, and when half of my room was in panels.. about 12 panels, my room is very small... RT was about 200ms and from there i could definitely hear more clarity and definition. Still not as much as in headphones, but i was getting there. Then i fully treated my ceiling, that was great improvement for me. I continued to add panels until there was no more space for them... If we count ceiling as panels, then there was about 33 100x60x15cm panels. RT in such room was about 60ms:




Sure, i had more rt time in bass region, but i was totally fine with it. In this room i was able to hear all definition and clarity there is in my tracks. As if i were listening in headphones.

All in all, based on all this, i think that 3 panels wont provide desired effect. You can also consider DIY panels. You simply need to build a frame, fill it with material of your choice and close it with fabric of your choice. All my panels were DIY, all 33 costing about 500$, but your materials could be pricier.

 

[CK.]

Yes, i was just thinking about lower end of target reverb, because i don't like reverberations...

My guess is that it will sound a little better, even with still high decay time of bass.
I can tell you my experience. I started with empty room that had about 350 ms of reverberation time. I treated it little by little, measuring each time. I started with 4 100x60x15cm panels: 2 front, 2 back. I don't have measurements anymore, but rt dropped to, maybe, 300-320ms. I remember sound became a little different, it wasn't better or worse, room just became a little bit more dead. I couldn't hear any additional clarity or something. Then i treated room more and more, and when half of my room was in panels.. about 12 panels, my room is very small... RT was about 200ms and from there i could definitely hear more clarity and definition. Still not as much as in headphones, but i was getting there. Then i fully treated my ceiling, that was great improvement for me. I continued to add panels until there was no more space for them... If we count ceiling as panels, then there was about 33 100x60x15cm panels. RT in such room was about 60ms:

View attachment 325696


Sure, i had more rt time in bass region, but i was totally fine with it. In this room i was able to hear all definition and clarity there is in my tracks. As if i were listening in headphones.

All in all, based on all this, i think that 3 panels wont provide desired effect. You can also consider DIY panels. You simply need to build a frame, fill it with material of your choice and close it with fabric of your choice. All my panels were DIY, all 33 costing about 500$, but your materials could be pricier.

Thanks for sharing your experience. From what I read thus far, it seems that RT60 is not a valid metric when it comes to smaller rooms. From what I understand your room must be quite small, based also on the fact that you started off with 350ms. Also, I came across a few forum posts stating that too much treatment can cause over-damping with the sound being lifeless.

In any case, my constraint is that the panels I use must be art panels in order to be placed in the living room and thus I cannot DYI them. Also the materials used are a bit expensive (no fiberglass, no mineral wool) and this is why I am now debating whether I should spend something like 600$ for 3 panels.

 

[Mishaiger]

Also, I came across a few forum posts stating that too much treatment can cause over-damping with the sound being lifeless.

Sound will become just like in headphones. Its not lifeless or anything, simply there is very little interactions with room. I personally like it.

Another thought, maybe instead of absorbing sound you'd be better off diffusing it? I have no experience with it, but in theory it can add some clarity and definition.

Once again, i'm not sure diffusion will help you.
But my experience tells me that 3 absorbing panels wont improve sound by much.
Also, my listening position was far from walls, your, however, is close to back wall, so treating it might have bigger effect than when you are far from walls.

Maybe you can purchase cheap non eco panels, second hand even, place them on wall and check for any difference in sound. If you will hear any improvement, then go ahead and buy eco panels. If not, well, you can try the same with diffusing panels or give up on idea of treating back wall and save money... Alternatively, consider buying more than 3 panels, say, 10 absorbing panels across the room and about 6 bass absorbing membrane panels will surely bring RT to about 500ms across whole spectrum. This requires considerable amount of space though.

 

[CK.]

Sound will become just like in headphones. Its not lifeless or anything, simply there is very little interactions with room. I personally like it.

Another thought, maybe instead of absorbing sound you'd be better off diffusing it? I have no experience with it, but in theory it can add some clarity and definition.
View attachment 325883
Once again, i'm not sure diffusion will help you.
But my experience tells me that 3 absorbing panels wont improve sound by much.
Also, my listening position was far from walls, your, however, is close to back wall, so treating it might have bigger effect than when you are far from walls.

Maybe you can purchase cheap non eco panels, second hand even, place them on wall and check for any difference in sound. If you will hear any improvement, then go ahead and buy eco panels. If not, well, you can try the same with diffusing panels or give up on idea of treating back wall and save money... Alternatively, consider buying more than 3 panels, say, 10 absorbing panels across the room and about 6 bass absorbing membrane panels will surely bring RT to about 500ms across whole spectrum. This requires considerable amount of space though.

Yeah I agree with your comments. I placed a couple of thick cushions behind the listening position on the wall and also moved the measuring microphone away from the wall to try and simulate somewhat an acoustically treated back wall. The result was a bit smoother RT60 but only 30-50ms lower.

Also, since I've never listened to HT in a treated room I really cannot appreciate what a well treated room sounds like. I cannot say I am bothered by the high RT60 and the sound in my room but then again I do not know how a much lower RT60 sounds like. So yeah I would need to rethink this a bit, the idea was to treat the back wall, then replace the back speaker stands with bass trap tubes and then treat the front wall but now I am not so sure if this is worth it.

 

[HiMu]

In any case, my constraint is that the panels I use must be art panels in order to be placed in the living room and thus I cannot DYI them.

One possibility could be custom 4-6" deep frames from a local hobbyist woodworker, you could design them in a way that you can just swap the art print on the front, so you don't have to discard the acoustic treatment if the art has to go.

A good selling point to your family/SO is that treating the living room slightly bit more than 3 small panels might have overall beneficial effect on the coziness and calmness of the room, speech clarity etc.. Everyone who visits my place says that this room is "so quiet", the background noise level is almost the same all around our house, only difference is the heavy acoustic treatment of my music room.

I know this sounds quite crazy practical experiment. If you live near Ikea or other store like that, you can demonstrate the effect of (too much) acoustic treatment by going to the rug department where they have large rugs hanging on the walls. It's so damped that just talking in there you'll notice how "quiet" or calm it sounds because of the amount of absorbing material. That is way overboard for a living room and that rug department experiment might make some feel a bit claustrophobic, but the phenomena that is almost impossible to describe can be experienced.

 

[CK.]

One possibility could be custom 4-6" deep frames from a local hobbyist woodworker, you could design them in a way that you can just swap the art print on the front, so you don't have to discard the acoustic treatment if the art has to go.

A good selling point to your family/SO is that treating the living room slightly bit more than 3 small panels might have overall beneficial effect on the coziness and calmness of the room, speech clarity etc.. Everyone who visits my place says that this room is "so quiet", the background noise level is almost the same all around our house, only difference is the heavy acoustic treatment of my music room.

I know this sounds quite crazy practical experiment. If you live near Ikea or other store like that, you can demonstrate the effect of (too much) acoustic treatment by going to the rug department where they have large rugs hanging on the walls. It's so damped that just talking in there you'll notice how "quiet" or calm it sounds because of the amount of absorbing material. That is way overboard for a living room and that rug department experiment might make some feel a bit claustrophobic, but the phenomena that is almost impossible to describe can be experienced.

Thank you HiMu, these are all very valid and interesting points! I actually live near an Ikea and would consider checking the rug department out.
As an update, I have manage to convinced my SO to actually put 3 or 4 4" (1200mmx600x100mm) solid color panels on the back wall on slightly different heights to offer a modern decoration. I am hoping that these could make an audible difference, fingers crossed. These panels offer 50% absorption (0.7 coefficient) at 150Hz and 100% absorption > 300Hz. What do you think?

 

[Timcognito]

Acoustic Panels Archives

Our acoustic panels are sound absorbing, reduce noise, and control sound. We have the largest collection of sizes, types, and colors to meet any requirement.

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Professional Grade Acoustic Panels, Sound Absorbing Panels | Acoustimac.com

Acoustimac has produced Professional Grade panels for over a decade. Used for acoustical sound absorption in walls and ceilings. Effective at elimination slap echo and reverb from any space. All panels made to order and are ASTM-E84 Class A Fire Rated. Best for use in churches, studios, home...

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[CK.]

Acoustic Panels Archives

Our acoustic panels are sound absorbing, reduce noise, and control sound. We have the largest collection of sizes, types, and colors to meet any requirement.

acousticalsolutions.com

Professional Grade Acoustic Panels, Sound Absorbing Panels | Acoustimac.com

Acoustimac has produced Professional Grade panels for over a decade. Used for acoustical sound absorption in walls and ceilings. Effective at elimination slap echo and reverb from any space. All panels made to order and are ASTM-E84 Class A Fire Rated. Best for use in churches, studios, home...

www.acoustimac.com

There are more companies, search acoustic panels

Thanks! I was actually considering acoustimac but then found ekustik.eu and I was just in love with their quality...not so much with the price.
Also, many companies are classifying their 4" panels under bass traps. Is that right?

 

[Timcognito]

Thanks! I was actually considering acoustimac but then found ekustik.eu and I was just in love with their quality...not so much with the price.
Also, many companies are classifying their 4" panels under bass traps. Is that right?

Not an expert. Other opinions?

 

[HiMu]

These panels offer 50% absorption (0.7 coefficient) at 150Hz and 100% absorption > 300Hz. What do you think?

In my absolutely non scientific measuring I get about 2-3dB softer reflections with 100mm Rockwool panels in the 0.6-0.7 region. Coefficient values are from multi-layer absorber calculator for GFR 8.8k material.

Here is the spec sheet from the material manufacturer Retex: https://en.retex.cz/assets/uploads/...IZOL-TB-OH-50_Material-specification_EN-2.pdf

Most likely you'll hear a noticeable effect with 4 panels, but don't expect miracles below upper bass/low mids region.

 

[HiMu]

Did you get any panels for the back wall? Would be interesting to hear any follow up on those.

 

[CK.]

I have already ordered them and should be arriving in a couple of weeks but will be sure to update you with my impressions and measurements. I opted for 4 panels 100mm thickness with absorption down to 125Hz (0.7).

 

[ozzy9832001]

I have 16 6", 2'x4' panels in my room and 8 18" deep bass traps. Still the room has some minor issues.

4 panels will be a starting point but its not going to provide the sort of results you're looking for.

 

[Trdat]

It is often maintained that if your sitting on the back wall then absorbtion is super important otherwise back wall in generally not recommended. This is due to the possibility of receiving late reflections from the back wall which are healthy, however, this is all up for debate and depends on your goals so don't quote me. In your case obviously the recommendation would be to cover back wall.

Secondly, you already have a sofa there that will perfrom some absorbtion and although it would be hard to simulate absorbtion with a sofa and a panel behind it my guess would be that an absorber panel behind the sofa can provide significantly more reduction in RT times than if you just simulate the back wall covered.

Lastly, the entire back wall will need to be covered not just two or three panles, I mean from top to bottom at least the same width as the sofa.

In terms of audible improvement, its hard to say but you will get some RT60 reduction times..

I would also recommend say half the back wall perhaps behind the sofa rockwool that targets the lower frequencies while the top portion say something that targets mid bass frequencies.

 

[CK.]

I have 16 6", 2'x4' panels in my room and 8 18" deep bass traps. Still the room has some minor issues.

4 panels will be a starting point but its not going to provide the sort of results you're looking for.

Thats a lot of treatment indeed, now I guess it depends which frequency range you may want to treat. I have given up on low bass treatmenets because that is unrealistic in my space and more focused on midrange and highs. However I agree that 4 panels are just too few. I am hoping that since my couch is against the wall, panels there might improve things noticably but not sure

 

[CK.]

It is often maintained that if your sitting on the back wall then absorbtion is super important otherwise back wall in generally not recommended. This is due to the possibility of receiving late reflections from the back wall which are healthy, however, this is all up for debate and depends on your goals so don't quote me. In your case obviously the recommendation would be to cover back wall.

Secondly, you already have a sofa there that will perfrom some absorbtion and although it would be hard to simulate absorbtion with a sofa and a panel behind it my guess would be that an absorber panel behind the sofa can provide significantly more reduction in RT times than if you just simulate the back wall covered.

Lastly, the entire back wall will need to be covered not just two or three panles, I mean from top to bottom at least the same width as the sofa.

In terms of audible improvement, its hard to say but you will get some RT60 reduction times..

I would also recommend say half the back wall perhaps behind the sofa rockwool that targets the lower frequencies while the top portion say something that targets mid bass frequencies.

I have never thought that panels behind the sofa would be that much beneficial but is an interesting idea. I guess the advantage with the sofa is that it has a few inches space from the wall and can do double absorption.

With regards to the panels, the 4 that I ordered have a surface area of 5m x 2.5m (16 ft x 8ft) which covers about 80 per cent of the naked wall.

I know that you need to do a lot of treatment to fix the room but I am hoping to at least have a noticable improvement especially in midrange clarity

 

[Trdat]

I have never thought that panels behind the sofa would be that much beneficial but is an interesting idea. I guess the advantage with the sofa is that it has a few inches space from the wall and can do double absorption.

The advantage with sofa is that bass frequencies need deep absorbtion to actually have an effect due to their longer wavelenghts, the sofa adds to the thickness(depth). How much it helps is another matter, in theory it makes sense though often sofa's have foam or other materials that are not great absorbers however, the wavelenghts would travel through that then hit your panel hence why some panels plus the couch might not be so bad. So in this case the panel needs to be behind the sofa, hence why I suggested the whole back wall covered. The space behind the sofa wont play much of a role.

The rear wall is only a good pace for absorbtion if your sitting up on it, otherwise it is not a priority spot it all depends on the arrival of the reflection from the back wall and what you want to do with them and what you're trying to achieve overall.