Acoustical Treatments Master Thread - Page 394 - AVS Forum | Home Theater Discussions And Reviews
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post #11791 of 11810 Old 03-24-2017, 12:36 AM
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Originally Posted by JMAX2016 View Post
Harrisu,
So I've really been playing around with acoustic treatment over the past two months, moving them, stacking them (for lower freq absorption), and a loooot of listening. I have a 7.2.4 setup, with a 120" AT screen. Here's what I've learned, and maybe this will help in some kind of way.

1. Only absorb the whole front wall if you have an AT screen. Otherwise, I don't like the sound. I use 1" lin, plastic membrane, 1" lin (Thanks BIG!). I love the sound of this, because less SBIR (speaker boundary effect), great speaker localization, and great bass trapping.

2. Make sure both side walls have equal amount of absorption, and at the same height and distance. In other words, symmetrical. Otherwise, I can hear the difference. My side walls are covered about 40%.

3. I like the back wall about 50% covered with absorption. I hear this difference in the dialogue.

4. I use 3" rock wool at first reflection points, and 2" almost everywhere else.

5. Ceiling clouds, I have not tried, but I want to try the at the first reflection point on ceiling.

6. With the amount of absorption I just mentioned, the amount of power you need to reach the same SPL is greater. Meaning that if you'd regularly play movies at 60% of the receiver/amp capability, you'll need to run it at 75%. But that sound will be way more clean and linear.

7. I have not used REW yet. I have the app, but no mic. I would love to measure my room. Decay times, etc. But to my ears, this is the best my room has sounded.

What do you guys think?
What size is your room?

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post #11792 of 11810 Old 03-24-2017, 07:01 AM
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What size is your room?
My room is 20x12x8.
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post #11793 of 11810 Old 03-24-2017, 08:02 AM
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Originally Posted by JMAX2016 View Post
Harrisu,
So I've really been playing around with acoustic treatment over the past two months, moving them, stacking them (for lower freq absorption), and a loooot of listening. I have a 7.2.4 setup, with a 120" AT screen. Here's what I've learned, and maybe this will help in some kind of way.

1. Only absorb the whole front wall if you have an AT screen. Otherwise, I don't like the sound. I use 1" lin, plastic membrane, 1" lin (Thanks BIG!). I love the sound of this, because less SBIR (speaker boundary effect), great speaker localization, and great bass trapping.

2. Make sure both side walls have equal amount of absorption, and at the same height and distance. In other words, symmetrical. Otherwise, I can hear the difference. My side walls are covered about 40%.

3. I like the back wall about 50% covered with absorption. I hear this difference in the dialogue.

4. I use 3" rock wool at first reflection points, and 2" almost everywhere else.

5. Ceiling clouds, I have not tried, but I want to try the at the first reflection point on ceiling.

6. With the amount of absorption I just mentioned, the amount of power you need to reach the same SPL is greater. Meaning that if you'd regularly play movies at 60% of the receiver/amp capability, you'll need to run it at 75%. But that sound will be way more clean and linear.

7. I have not used REW yet. I have the app, but no mic. I would love to measure my room. Decay times, etc. But to my ears, this is the best my room has sounded.

What do you guys think?
Thanks for sharing. My turn now
1 - Managing base decay: I have had all this done that you are doing before. I have had Lin but I just went with 1". I don't think it really matters if you have 1" then plastic and then 1". Using just 1" will absorb High frequencies just fine. I don't think making it 2" with plastic will help will Low/Mid frequencies. I use REW. In fact, I used it by placing each panel and then took reading to see what it does and then added more or removed based on what I saw. So, if you want to make sure the room decays withing 300ms, you take reading and start observing. When I took all the panels out, the dacay was going beyond 450ms. Then I added 8" 703 on front wall corneres and also in one back wall corner. Then took reading and then installed the ceiling panels (3 4" 703) and 1 4" 703 on each side side wall on 2nd reflection. Took reading and all the mid-bass (150 onward) was well within 300ms. Now if you have anything under 150 going beyond 300-400ms, you'd have to add a lot more to tame them down. In my case, I didn't. For some reason, my room does resonate at 60Hz but I think its my mic (will post question on REW thread). Other than that, my whole waterfall graph (that shows decay) is within 300 ms. So that takes care of bass.

2 : Room Reflection. So after installing bass traps (or Mid-bass traps I should call), I moved my target to room reflection. At this point, I already have 1" lin on front wall and 50% back wall covered with 2" 703 and corner bass traps and panels on top and side wall. Checked the Impulse response. From top of my head, it should be below -20. When I checked, I hardly had any spike going above -20. Now, there has been discussion where some say to have Lin on front wall and some say that you are damping the room too much if your front wall is completely covered. So, it was time to find out. I took the whole 1" Lin off. Then put 1 2" 703 behind C starting from its tweeter height going up. Then took reading and guess what !!! I didn't see any noticeable change in reflection. So Lin really wasn't taming that much for me for early reflection and I think it was damping my room.

Now all that is purely based on what REW is showing me. Listening is obviously the final answer to all the changes which I'll be doing over the weekend. As of now, I have 3 corners covered with 8" 703 with front ones from top to bottom and back only up to ear level (since I don't want it to absorb L/R reflection). Then I have only 1 2" 703 panel on each side wall parallel to each other and 3 4" panels on ceiling (1 for L, 1 for R and 1 for C). Then I have 1 4" 703 behind C on front wall starting from tweeter to all the way up. All this has gotten the low frequency under control within 300ms and also the reflection.

BTW, I do have AT screen but its not weave. Its a Perf screen with 1.3 gain (amazing . With screen on, I do loose 8db on high frequency which Dirac (room correction system) fixes for me. I guess the point I'm driving to is that Lin on front wall might not be necessary and its definitely not for helping out with mid bass. With a setup above 5.1, we do have speakers firing towards the front wall and it might help absorb them. But I don't want to just put it there and go with it. Instead, I want to first listen to my room and if I find that its too reflective, only then I'll add more absorption. This will ensure that I'm not over absorbing. My speakers are 106dB sensitive so I can easily over damp my room and crank up the volume and they won't give up on me.

Last edited by harrisu; 03-24-2017 at 08:21 AM.
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post #11794 of 11810 Old 03-24-2017, 07:48 PM
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Originally Posted by harrisu View Post
Thanks for sharing. My turn now
1 - Managing base decay: I have had all this done that you are doing before. I have had Lin but I just went with 1". I don't think it really matters if you have 1" then plastic and then 1". Using just 1" will absorb High frequencies just fine. I don't think making it 2" with plastic will help will Low/Mid frequencies. I use REW. In fact, I used it by placing each panel and then took reading to see what it does and then added more or removed based on what I saw. So, if you want to make sure the room decays withing 300ms, you take reading and start observing. When I took all the panels out, the dacay was going beyond 450ms. Then I added 8" 703 on front wall corneres and also in one back wall corner. Then took reading and then installed the ceiling panels (3 4" 703) and 1 4" 703 on each side side wall on 2nd reflection. Took reading and all the mid-bass (150 onward) was well within 300ms. Now if you have anything under 150 going beyond 300-400ms, you'd have to add a lot more to tame them down. In my case, I didn't. For some reason, my room does resonate at 60Hz but I think its my mic (will post question on REW thread). Other than that, my whole waterfall graph (that shows decay) is within 300 ms. So that takes care of bass.

2 : Room Reflection. So after installing bass traps (or Mid-bass traps I should call), I moved my target to room reflection. At this point, I already have 1" lin on front wall and 50% back wall covered with 2" 703 and corner bass traps and panels on top and side wall. Checked the Impulse response. From top of my head, it should be below -20. When I checked, I hardly had any spike going above -20. Now, there has been discussion where some say to have Lin on front wall and some say that you are damping the room too much if your front wall is completely covered. So, it was time to find out. I took the whole 1" Lin off. Then put 1 2" 703 behind C starting from its tweeter height going up. Then took reading and guess what !!! I didn't see any noticeable change in reflection. So Lin really wasn't taming that much for me for early reflection and I think it was damping my room.

Now all that is purely based on what REW is showing me. Listening is obviously the final answer to all the changes which I'll be doing over the weekend. As of now, I have 3 corners covered with 8" 703 with front ones from top to bottom and back only up to ear level (since I don't want it to absorb L/R reflection). Then I have only 1 2" 703 panel on each side wall parallel to each other and 3 4" panels on ceiling (1 for L, 1 for R and 1 for C). Then I have 1 4" 703 behind C on front wall starting from tweeter to all the way up. All this has gotten the low frequency under control within 300ms and also the reflection.

BTW, I do have AT screen but its not weave. Its a Perf screen with 1.3 gain (amazing . With screen on, I do loose 8db on high frequency which Dirac (room correction system) fixes for me. I guess the point I'm driving to is that Lin on front wall might not be necessary and its definitely not for helping out with mid bass. With a setup above 5.1, we do have speakers firing towards the front wall and it might help absorb them. But I don't want to just put it there and go with it. Instead, I want to first listen to my room and if I find that its too reflective, only then I'll add more absorption. This will ensure that I'm not over absorbing. My speakers are 106dB sensitive so I can easily over damp my room and crank up the volume and they won't give up on me.
Interesting... Especially the part where you said it measured the same taking the Lin out... Let us know how the listening goes!
What are you using for a mic for REW? And don't you need a sound board to hook the mic and on the other end your computer into?

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post #11795 of 11810 Old 03-24-2017, 09:25 PM
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Question

I just inherited 10 panels of Armstrong Ceilings Shasta White Textured 15/16-in Drop Acoustic Panel Ceiling Tiles (Common: 48-in x 24-in)

... ideas on useful or interesting things to do with them?

I have 2" OC703 I'm starting to make wall (maybe ceiling) panels with. Currently two 2" panels (2.5" frames) hang on side-wall first reflection (just in front of the row of seating) - on diagram, black with red border

I'm also thinking I'll put in a ceiling cloud : on diagram, has yellow border

Most of the ceiling is 9' and all speakers are hug at about 7.5' ... Atmos ceiling speakers (A) are at 9'
There is very little space behind the main speakers behind the AT screen - thought maybe using the Armstrong panels there - will they make a difference being only 1" thick?

interested in your thoughts on where treatments should go and what to do with the 1" Armstrong panels.

thx!

thx
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post #11796 of 11810 Old 03-25-2017, 03:20 AM
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Quote:
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What are you using for a mic for REW? And don't you need a sound board to hook the mic and on the other end your computer into?
Most people use the MiniDSP UMIK-1 microphone that only requires a spare USB port on the computer. They are calibrated at factory so fairly accurate once you load in the calibration file in REW.

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post #11797 of 11810 Old 03-25-2017, 06:31 AM
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Hi: I'd like to get some feedback concerning corner traps. I recently soundproofed my entire room. This involved tearing out the drop ceiling and installing double drywall, GG, safnsound, isolation clips and hat channel. However, this increased my ceiling height, so the ceiling is now about a foot taller than previously. My existing GIK corner bass traps are now too short to cover the increase in height. Is it worth investing in 4 one foot corner traps to correct this, or is it not worth addressing in your opinion?


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post #11798 of 11810 Old 03-25-2017, 06:53 AM
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Hi: I'd like to get some feedback concerning corner traps. I recently soundproofed my entire room. This involved tearing out the drop ceiling and installing double drywall, GG, safnsound, isolation clips and hat channel. However, this increased my ceiling height, so the ceiling is now about a foot taller than previously. My existing GIK corner bass traps are now too short to cover the increase in height. Is it worth investing in 4 one foot corner traps to correct this, or is it not worth addressing in your opinion?


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they do the most good where all three corners meet. you could have a gap in the middle between the two you have stacked.
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post #11799 of 11810 Old 03-25-2017, 08:38 AM
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they do the most good where all three corners meet. you could have a gap in the middle between the two you have stacked.


Thanks, but I don't think I understand the second part of your comment. Do you mean if I added a small one, there would be a gap between them and it would be better to order new ones at the correct height?


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post #11800 of 11810 Old 03-25-2017, 09:12 AM
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Quote:
Originally Posted by healthnut View Post
Thanks, but I don't think I understand the second part of your comment. Do you mean if I added a small one, there would be a gap between them and it would be better to order new ones at the correct height?


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We assume that you currently have two corner traps stacked on top of each other, if you lift the top one so it is against the ceiling you will get the most benefit without adding more traps.

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post #11801 of 11810 Old 03-25-2017, 11:20 AM
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We assume that you currently have two corner traps stacked on top of each other, if you lift the top one so it is against the ceiling you will get the most benefit without adding more traps.


Thanks for the reply. I have one trap on each corner, but they're all too short to reach the ceiling, by about a foot. Looks like I need to add smaller ones to reach into the ceiling.


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post #11802 of 11810 Old 03-25-2017, 11:28 AM
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Thanks for the reply. I have one trap on each corner, but they're all too short to reach the ceiling, by about a foot. Looks like I need to add smaller ones to reach into the ceiling.


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Cool, I didn't know the GIK corner traps were available in 8ft tall units, I thought they were around 4ft each.

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post #11803 of 11810 Old 03-25-2017, 12:08 PM
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Cool, I didn't know the GIK corner traps were available in 8ft tall units, I thought they were around 4ft each.
GIK bass traps are stackable and support 50 lbs weight. Didn't know they had 8 foot version, always known them to have 4 feet pieces. Many bass traps to choose from including the alpha series if you want traps with some diffusion. I don't have corner traps, just the 244 bass traps behind my rear wall and they do improve decay times in my room.

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post #11804 of 11810 Old 03-25-2017, 02:46 PM
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I have 2 4 footers bass traps stacked in each rear corner. Front wall I have a 4 foot and custom sized bass trap sitting on my sub. They did a great job helping to even out the bass and lower the decay time.
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post #11805 of 11810 Old 03-26-2017, 05:54 PM
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Quote:
Originally Posted by Mashie Saldana View Post
Most people use the MiniDSP UMIK-1 microphone that only requires a spare USB port on the computer. They are calibrated at factory so fairly accurate once you load in the calibration file in REW.
Thanks Mashie. I'm going to look into getting one! Looks like Parts Express has it for $85. Their website has it for $75. I'm not sure if that includes shipping too or not.

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I just inherited 10 panels of Armstrong Ceilings Shasta White Textured 15/16-in Drop Acoustic Panel Ceiling Tiles (Common: 48-in x 24-in)

... ideas on useful or interesting things to do with them?

I have 2" OC703 I'm starting to make wall (maybe ceiling) panels with. Currently two 2" panels (2.5" frames) hang on side-wall first reflection (just in front of the row of seating) - on diagram, black with red border

I'm also thinking I'll put in a ceiling cloud : on diagram, has yellow border

Most of the ceiling is 9' and all speakers are hug at about 7.5' ... Atmos ceiling speakers (A) are at 9'
There is very little space behind the main speakers behind the AT screen - thought maybe using the Armstrong panels there - will they make a difference being only 1" thick?

interested in your thoughts on where treatments should go and what to do with the 1" Armstrong panels.

thx!

thx
No help?

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post #11807 of 11810 Old 03-26-2017, 11:16 PM
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Using Owens Corning 703 2" panels, I'm putting 4" thick panels in 1X6 pine frames behind Open Baffle Rythmik subs and 2" panels in 1X4 pine frames behind Maggie 3.6 speakers. I'm covering the frames and panels with Magnepan speaker cloth to match the speakers. I would like to seal the fiberglass surfaces so it does not migrate into the room. I'm thinking of mixing some powdered wall paper glue and brushing that on the fiberglass. I don't think it would turn the panels into reflective surfaces. Another possible solution would be to spray a light coat of 3M spray adhesive on all surfaces.
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post #11808 of 11810 Old 03-27-2017, 08:02 PM
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My 24 OC703 panels arrived. Took them down to the theater and opened them up. When I got back from being out of town, this is how I found them on the porch.



Nobody warned me that the panels would smell like decaying salmon on the side of the road once the packages were opened up. A quick google search informed me this was common and the smell should go away in a couple days to a couple of weeks. I can still smell a hint of it on the panels, but I think it is mostly aired out now.

I have the bulk of the framing done behind the speakers to insert 9 of the panels. I used standard 2X4's with 2X2's placed above and below them to hold the panels 1.5" off the back wall for an air gap. They fit perfectly flush and I'll be placing a 100% black polyester fabric over the panels after they are installed.



If there are any comments or suggestions on the direction I'm headed with this, it would be greatly appreciated.
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post #11809 of 11810 Old Today, 08:42 AM
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When Soundproofing is acoustic treatment

I don't hear this discussed on the forums much, and in fact, when I brought it up with Ted from the Sound Proofing company he commented he is a sound proofing guy and not an acoustics guy. The common technique we use of creating decoupled damped walls is actually an acoustic treatment approach as well. The theory as to why is very rational and sound, but I've hardly ever heard mention of it. I know that Nyal Mellor of Acoustic Frontiers talks about this, as does Dr. Earl Geddes, and Dr. Peter D'Antonio. Why isn't this discussed more here? I think its a pretty important concept.


When using tuned bass traps we typically target problem frequencies, but with the walls of our theater we could not easily do that. I suppose with a BEM analysis of the wall structure itself we might be able to first predict the problem areas and then predict the tuned frequency of the walls, but I suspect hitting those tuned frequencies would be really hard. None the less, the Low Q of the resonant frequency of the walls is probably sufficient to provide fairly broad LF damping.


This also makes me think that intentionally varying the walls depths, insulation density, rigidity, etc. might also help create a broader set of frequencies that we have optimal damping for. When I talked with Dr. Geddes about this he said that while the concept is known to be true, it hasn't been studied extensively. Mostly because its really hard to test this in a lab in a meaningful way. As a result it is not possible to know or even guess the amount of LF damping available using this technique. He mentioned that his own dissertation noted that it doesn't really matter if you have one or two wall pairs treated, the effect was the same. His point was that you don't need symmetric bass damping in a room, the room doesn't care, the bass will be damped just the same (that is, if one wall has twice the damping of two individual walls, it will damp the bass in the room the same as if you did two walls with half the damping. Obviously more damping means more damping).


In my theater I had a few fortuitous changes to my theater design that has created 4 walls and a ceiling that are all decoupled CLD walls with different cavity depths, insulation levels, and rigidity. I plan to do some testing of the room using my accelerometer on the wall surfaces at various locations to see if I can pinpoint a resonant frequency and Q for either the whole wall or section of the wall. I have a feeling the wall doesn't always act as one structure at all frequencies and will show more than one resonance. I suspect as frequencies become lower the wall/room boundaries begin to act as more and more of one structure, but I'm not sure my test would show that. I would have loved to test the room's LF damping caused by the construction but that is not possible. Even if I tested the room before the theater was built it would not have shown anything meaningful, since the room's boundaries and volume and changed drastically.


If anyone has any other ideas of how to test this, that would be great. One thing I'm really curious about is where the damping effect stops and additional bass trapping becomes necessary. My assumption is that this only works at fairly low frequencies, but where does it stop? 30hz? 60hz? 100hz? Those all make a big difference. The amount of velocity absorption or additional tuned absorbers needed are drastically different for each of those scenarios. What if it actually is effective right on up to 200-300hz? Then you could get away with modest 4" or 6" velocity absorbers in some key locations and not need to waste much space with true bass trapping.
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post #11810 of 11810 Old Today, 04:40 PM
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Acoustic recommendations

Hello, I have a separate thread but thought I'd try here as well.

So I have a soon to be spare room in my home that I'll be transforming into a theater room. The layout is interesting, kinda square I guess with vaulted ceilings. Angles from 8ft up to 12ft. There's also a cove in the room with 3 large windows that take up alot of wall on the right side. Cant do panels there so thinking heavy curtains. Attached is a diagram of my plans. I kinda slapped it together but the important info is there.

Red triangles represent potential corner traps using roxul safe n sound wall to ceiling. I also may build a 12" x 16" soffit trap in the cove ceiling since I'll have plenty of roxul material laying around. I also currently have 7 2'x4' & 7 2'x2' of 2" owens 703 panels that's framed and wrapped already for use. Room has heavy thick carpet already. Installing a 7.2 system in there.


From hours of researching I'm thinking of using kraft paper or FRK on all bass traps and using my 2" 703 panels at first reflection areas?

Should I treat the ceiling at all or leave it as is?

Any thoughts on this layout and plan would be appreciated. Thanks
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Last edited by HTaddiction; Today at 04:47 PM.
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