The "Room Acoustics" thread

[cmsajith]

Yes I agree - it will be better to position it to the rear of the room, possibly behind the sitting position. One also has to consider blackout curtains - which are easily available fortunately in the fabric stores.
Cheers
Sid

But my understanding is that the entire back side should not be reflective, esp. linearly reflective. The reflection/diffusion should be done at the following locations (marked as Y) if you divide the back wall into 6 portions.
<Corner : BassTrap> X Y X X Y X <Corner : BassTrap>

X : Absorbers
Y : Diffusers

Also the 2 back ends of the side walls can be made reflective/diffusers leaving the basstraps for the corners.

Moreover, to make the diffusers effective you should sit atleast 8ft from the diffusers, else its always better leave the entire back wall to be sound absorbing.

 

[sidvee]

But my understanding is that the entire back side should not be reflective, esp. linearly reflective. The reflection/diffusion should be done at the following locations (marked as Y) if you divide the back wall into 6 portions.
<Corner : BassTrap> X Y X X Y X <Corner : BassTrap>

X : Absorbers
Y : Diffusers

Also the 2 back ends of the side walls can be made reflective/diffusers leaving the basstraps for the corners.

Moreover, to make the diffusers effective you should sit atleast 8ft from the diffusers, else its always better leave the entire back wall to be sound absorbing.

Typically a HT rooms hould not have any windows. Secondly if you do have windows with glass what i understand it is better to be in the section of the room wherein reflection is desired ie the rear. Regarding reflection from glass unless a large surface area is used a small section like a standard window is not going to matter. At-least this is not audible from what I have heard. Regarding placement of diffusers/absorbers there are many schools of thought:
1. LEDE - wherein absorbers are towards the front and diffusers are to the rear.
2. What you have stated with a mix of both.
3. I read a recent paper by Dr. Toole of Harman International wherein he states that for HT's/music listening no need to treat first reflection points with absorption but place absorbers behind the speakers and place geometric diffusers behind listening position. he also states that diffusers have be at-least 12" deep to be effective so regular 4" diffuser panels are in-effective.
So many options can be used, but for me option 1 has consistently sounded the best and I continue to stick with it. For others other options may sound better but what is important is that some acoustic treatment is required.
Cheers
Sid

 

[cmsajith]

Typically a HT rooms hould not have any windows. Secondly if you do have windows with glass what i understand it is better to be in the section of the room wherein reflection is desired ie the rear. Regarding reflection from glass unless a large surface area is used a small section like a standard window is not going to matter. At-least this is not audible from what I have heard. Regarding placement of diffusers/absorbers there are many schools of thought:
1. LEDE - wherein absorbers are towards the front and diffusers are to the rear.
2. What you have stated with a mix of both.
3. I read a recent paper by Dr. Toole of Harman International wherein he states that for HT's/music listening no need to treat first reflection points with absorption but place absorbers behind the speakers and place geometric diffusers behind listening position. he also states that diffusers have be at-least 12" deep to be effective so regular 4" diffuser panels are in-effective.
So many options can be used, but for me option 1 has consistently sounded the best and I continue to stick with it. For others other options may sound better but what is important is that some acoustic treatment is required.
Cheers
Sid

Using the entire wall as diffusing "can" result in null frequencies.

 

[sidvee]

Using the entire wall as diffusing "can" result in null frequencies.

I guess then it will be no different from using entire walls as absorption - which unfortunately many people i know have done for a real dead sounding room. Anyways I dont believe that a whole wall has to be treated, first reflection points and area behind main listening position has to be treated with absorbers and diffusers respectively. Also the cost will be huge as well to treat entire walls. Also room corners have to be treated.
Cheers
Sid

 

[cmsajith]

I guess then it will be no different from using entire walls as absorption - which unfortunately many people i know have done for a real dead sounding room. Anyways I dont believe that a whole wall has to be treated, first reflection points and area behind main listening position has to be treated with absorbers and diffusers respectively. Also the cost will be huge as well to treat entire walls. Also room corners have to be treated.
Cheers
Sid

No not at all. Unless there is enough distance for the sound waves to get diffused, there is no point in diffusing it as the sound will reach you even before it is diffused after it is reflected on the rear walls/diffusers (almost similar to direct reflection)

Please search for Null Frequencies and their cause and how to avoid it.

 

[nshankar]

I am not an expert on the subject, but actively following it up and trying to understand it.

What I have come across, both personally and online, are bass traps on the front corners.

I have also come across panels in the front and sides, but never seen a full front or side wall visibly treated for acoustics.

Maybe some one could educate on whether this is a science or an art.

 

[cmsajith]

Maybe some one could educate on whether this is a science or an art.

Both, but the percentage depends on the room.

 

[sidvee]

No not at all. Unless there is enough distance for the sound waves to get diffused, there is no point in diffusing it as the sound will reach you even before it is diffused after it is reflected on the rear walls/diffusers (almost similar to direct reflection)

Please search for Null Frequencies and their cause and how to avoid it.

No thanks I have done enough research on acoustics and prefer to use what I have to my satisfaction. If you can add to what I already know please do so. If not I prefer to sit this one out and see what others have to say.
Cheers,
Sid

 

[sidvee]

I am not an expert on the subject, but actively following it up and trying to understand it.

What I have come across, both personally and online, are bass traps on the front corners.

I have also come across panels in the front and sides, but never seen a full front or side wall visibly treated for acoustics.

Maybe some one could educate on whether this is a science or an art.

I firmly believe that this is a science, unfortunately there are too many confliciting views out there. One surefire way is to do some minimal treatment then measure the room frequncies from the listening position using a RS meter (corrected) or any other properly calibrated sound level meter with pink noise as a source at various frequencies (approx. 20hz to 20khz) and graph it. if you have any major nulls or peaks you have an issue. This is the only objective way to measure the acoustics of a room and all other methods are subjective.
I have done this in my room and it is fairly flat with a +/- 3 db range.
Cheers
Sid

 

[santhosh]

My first contribution to this thread - unfortunately in the form of a question.
What are the methods of preventing sound leakage from doors and windows of HT or media rooms? I have seen rubber seals (similar to ones used on car doors) that can be placed at the gaps of door and window sills in the US in places like home depot etc, but am not able find them here. Note these are for HT's that used carpenter fabricated doors and windows as opposed the better method of using pre fab doors or windows (like fennesta).

Good question Sid. We have some useful responses on this thread which I can get use when I get around to do it. I too have not sealed my windows, just use a double door.

The space between the two doors acts as the ideal space for a standing wave.
One has to put in wave breakers.
the ceiling of the space between the two doors should be provided with angular vees to kill the standing wave
the ceiling should be provide with sound absorbers.
the floor should be carpeted.
the distance between the two doors should be adjusted by trial and error.

Thanks Sridar. I have used this technique and it works very well as a sound-proofing technique. From your post, I learn that a wave breakers would be useful to have on one of the doors. Come to think of it, it does make sense. Noted.

I am not an expert on the subject, but actively following it up and trying to understand it.

What I have come across, both personally and online, are bass traps on the front corners.

I have also come across panels in the front and sides, but never seen a full front or side wall visibly treated for acoustics.

Maybe some one could educate on whether this is a science or an art.

Full Front wall treated to absorb is quite popular if the LEDE(Live end Dead end) technique is followed. I have followed this in my HT. As for complete side wall treatment, there are many who have done it (mostly in home theaters but not in listening rooms). But like Sid has mentioned, amplification requirements go up. Since I wanted to retain some amount of liveliness in the room (for music), I have made the bottom half of the side walls absorptive while the top half is reflective. Again, am no expert. Just what I have learnt from reading online and a bit of DIY.

I firmly believe that this is a science, unfortunately there are too many confliciting views out there. One surefire way is to do some minimal treatment then measure the room frequncies from the listening position using a RS meter (corrected) or any other properly calibrated sound level meter with pink noise as a source at various frequencies (approx. 20hz to 20khz) and graph it. if you have any major nulls or peaks you have an issue. This is the only objective way to measure the acoustics of a room and all other methods are subjective.
I have done this in my room and it is fairly flat with a +/- 3 db range.
Cheers
Sid

Very true Sid, this is a science and there is no single method for every room. Apart from the basics, I too have taken a "on a need basis" approach and now feel confident that even Sridar has mentioned that there is a bit of trial and error and experimenting.

 

[sidvee]

Very true Sid, this is a science and there is no single method for every room. Apart from the basics, I too have taken a "on a need basis" approach and now feel confident that even Sridar has mentioned that there is a bit of trial and error and experimenting.

Therein lies the key as Santhosh has so aptly put it and I concur - there is no single method of acoustic treatment that will work as an constant for every room - so definitely experiementation is needed. Even acoustic consultants custom their suggestions for each room based on listening position, speaker location etc.
Cheers
Sid

 

[jitubisht]

Full Front wall treated to absorb is quite popular if the LEDE(Live end Dead end) technique is followed. I have followed this in my HT. As for complete side wall treatment, there are many who have done it (mostly in home theaters but not in listening rooms). But like Sid has mentioned, amplification requirements go up. Since I wanted to retain some amount of liveliness in the room (for music), I have made the bottom half of the side walls absorptive while the top half is reflective. Again, am no expert. Just what I have learnt from reading online and a bit of DIY.

Santhosh,
If I am not wrong, in your HT room both the front and rear wall are anutone floor to bottom?

 

[santhosh]

Santhosh,
If I am not wrong, in your HT room both the front and rear wall are anutone floor to bottom?

Only front wall is fully absorbtive buddy. Rear is just like the side walls - half absorptive and half reflective. Diffusors will be made and added on the rear wall on the existing surface. BTW, Corner Bass Traps are also due, I don't have bass issues at the moment partly because all the corners of the room have been treated by adding high density fiberglass behind the panels. Bass hits corners of the room and it helps to use high density absorbent materials there. By corners, I mean any point where wall meets ceiling, wall meets floor and wall meets wall.

 

[santnai]

I am copying and pasting the same concern which I had asked in the earlier thread.

"In my case I treated all my walls with Anutone Synth, Anutone acoustic board and third layer with fabric from top to bottom. I haven't done any acoustic treatment for the ceiling. My ceiling is Gypsum board POP and Mr. Praveen from Anutone told me ceiling does not require any treatment and If I have to treat ceiling then I need to demolish my existing ceiling and I was not in favor of it.
As I understand the above material will act as sound absorber but with my little knowledge on acoustic treatment for dedicated HT room there should be mix of reflection and absorption, now my worry is whether my room has become a dead room? How will I test whether all the frequency is travelling to the listener ear without getting absorbed in between? If it is happening then Do I need to go for a diffuser or reflection board on top of absorption board? "

Sid - My Cieling height is 9 Feet. By going through the thread I feel that my HT room is dead probably I need to go for some reflection material on top of absorption.

Regards,

Santosh

 

[sidvee]

I am copying and pasting the same concern which I had asked in the earlier thread.

My ceiling is Gypsum board POP and Mr. Praveen from Anutone told me ceiling does not require any treatment and If I have to treat ceiling then I need to demolish my existing ceiling and I was not in favor of it.
As I understand the above material will act as sound absorber but with my little knowledge on acoustic treatment for dedicated HT room there should be mix of reflection and absorption, now my worry is whether my room has become a dead room? How will I test whether all the frequency is travelling to the listener ear without getting absorbed in between? If it is happening then Do I need to go for a diffuser or reflection board on top of absorption board? "

Sid - My Cieling height is 9 Feet. By going through the thread I feel that my HT room is dead probably I need to go for some reflection material on top of absorption.

Regards,

Santosh

Santosh - As I understand when you have a ceiling height of 9' then really the ceiling does not need any treatment as it does not contribute too much. If you had a lower ceiling height say 7' or lower then it is important to treat the ceiling. This is what quite a few people with acoustics background told me. Another easy way to treat a ceiling is to use drop ceiling with ceiling tiles below your exisiting ceiling so there is no need to demolish. Of-course it is extra cost and in your case I am not sure if it will really help.
Now concerning your second query if you read my earlier post I have described a method to measure and graph your room. If you do this and have a fairly flat (+- 3 db) line of all frequencies then you are fine meaning all frequencies are reaching your listening position.
Finally regarding dead sounding rooms - this is hard to define and quantify as it is subjective but one way to determine this is if you have to turn up the volume very loud to make dailogue or lyrics intelligible even with a decently powered amp (say 100-120 watts) then potentially you may have a dead sounding room. two ways to remedy this - get a more powerful amp. or take out some of the absorbers from the walls where there are no reflection points (ie 1 or 2nd reflection points).
Again I am no professional but hope this helps (and no flames please - just trying to help).
Cheers,
Sid

 

[santhosh]

"In my case I treated all my walls with Anutone Synth, Anutone acoustic board and third layer with fabric from top to bottom. I haven't done any acoustic treatment for the ceiling. My ceiling is Gypsum board POP and Mr. Praveen from Anutone told me ceiling does not require any treatment and If I have to treat ceiling then I need to demolish my existing ceiling and I was not in favor of it.

Santosh, since the walls are already done, let us not do anything now. But don't worry about it too much. Since your ceiling is reflective, add a thick carpet between your front speakers and your listening\watching position. If you are unhappy with the sound, you can always hang some acoustic panels from your current false ceiling.

As I understand the above material will act as sound absorber but with my little knowledge on acoustic treatment for dedicated HT room there should be mix of reflection and absorption, now my worry is whether my room has become a dead room? How will I test whether all the frequency is travelling to the listener ear without getting absorbed in between? If it is happening then Do I need to go for a diffuser or reflection board on top of absorption board? "

Sid - My Cieling height is 9 Feet. By going through the thread I feel that my HT room is dead probably I need to go for some reflection material on top of absorption.

I would suggest same approach as for your ceiling. Start using your room and address issues on a symptomatic approach. Making parts of your room reflective is very easy - add some wooden panels on portions of your room will make it partially reflective.

Don't worry about hearing all frequencies, you will hear everything as long as there is nothing (absorbent\diffusive\reflective) between you and the speaker emitting the sound. What you don't want to hear is the first reflections (nothing to worry, you are covered there on three sides and your roof is anyway high). What you may miss is having some reflections to give you that tad bit of liveliness to the music (IMO not required for movies).

Just chill and enjoy your HT

 

[cmsajith]

I was a little bit busy and I couldnt followup this thread.

Sid, From your posts I feel that you have assumed that I am telling to cover all the 4 walls with acoustic materials. No I am not, even I was telling almost same as you were telling except the rear walls to have fully covered with diffusers. I am not an expert in this and I had written based on the knowledge gained through interactions with some of the Sound \ Acoustic engineers esp. some of the designers from GIK Acoustics.

What I understood and what I feel is that for an HT room (not a listening room) the entire front wall, side walls, ceiling, floor and back walls has to be treated for mid and high freqs except the side walls' end. The diffusers in the back wall will be useful if we have enough distance b/n the listener and the diffuser (atleast 6-8ft) else its always better having a dead back wall since the wall is very near to the listener (but in this case the entire side walls and ceiling will not be treated fully). For Low freqs all the 4 corners with bass traps (top to bottom chunk traps are more effective) and the 4 top corners with 3pointed traps and the middle portion of the side walls' top.

Only in recording studios specifically for music will have entire walls with diffusers as the scenario is different. I have seen (pics) several recording studios with full of diffusers front/side/back.
Sample pic of a well known recording studio: http://gallery.avsforum.com/data/509/screenshot_0124.jpg. (Is this pure science or art, no idea)
Another listening room : http://img268.imageshack.us/img268/1228/palroom3.jpg
For listening rooms we need to have specific (can be DIY also, but based on some of the proven designs like QRD) kind of diffusers at strategic positions esp at the front centre and the side walls and back walls along with the basstraps. The above pic of the listening room will give you an idea. But using diffusers entirely is very tricky and complicated. Here the diffusers will act as sound breakers as well as reflectors.

For both HT and music, he suggested to have front walls, back walls with absorbers (dead back wall if it is near to the listening position) and treat the first\second reflection points on all surfaces along with the bass trap.

In most of the cases with 4 bass traps and side walls first and second reflection points will do the trick to a great extend. Then based on the room response for peaks and nulls, do specific treatment. But this will be a compromise for "purists" compared to dedicated HT rooms and listening rooms and when the cost is considered we have to take the decision which one to go for.

Following picture shows a sample setup from GIK Acoustics: http://www.gikacoustics.com/images/room_layout_662.gif. Please note the distance from the listener to the back wall and the locations of the diffusers.

 

[Asterix]

Hi all

Interesting thread .... will keep following as I too believe that each room is unique in its sonic signature and the approach to accoustic treatment will have to be thru experimental trials.

@Santhosh/SId

Should the first reflection points be treated with absorbtive material or diffusive material?

How effective is a decorative shelf/wall hanger (jute) as a diffuser, particularly for high frequencies?

Cheers

 

[cmsajith]

@Santnai, the 1st and 2nd reflection point treatments should not be covered or removed as they are critical for horizontal soundstage. Overdoing of this points will not have any effect in the room response as there will not be any low frequencies trapped in that area. If it is an overdone room, Try removing the panels \ covering with thick plastic sheet to reflect the mid and high or hanging pictures with glass front above the 1st and 2nd reflection points on the side walls. If you need more liveleness, try covering the "Y" portion of the back wall if the back wall is represented as X Y X X Y X. Once you find the desired effect, use diffusers on those area.

Another suggestion would be not to make any closed false ceilings as they can act as resonance chambers.

 

[cmsajith]

Hi all

Interesting thread .... will keep following as I too believe that each room is unique in its sonic signature and the approach to accoustic treatment will have to be thru experimental trials.

@Santhosh/SId

Should the first reflection points be treated with absorbtive material or diffusive material?

How effective is a decorative shelf/wall hanger (jute) as a diffuser, particularly for high frequencies?

Cheers

Using diffusers is a really tricky business and complicated since the diffusion direction is very important. Trial and error method using diffusers will be an endless story. An easy method is to make it as absorbers. Moreover a diffuser should have enough depth to diffuse the sound waves properly. If you have a shelf on the side walls, then my suggestion would be to make a 2" depth niche on the shutter (leaving the frame of the shutter) and use it to fill the absorbing material as it can function both as a shutter and an absorber, some times you can tweak\experiment by keeping the shutters half closed to make it as a partial absorber and a diffuser(provided you have done acoustics inside the cabinet) something like this : http://mcabsorbers.co.uk/mc_listening_room_plan_1.png