# panel absorbers 1/2" thick?



## Guest (Oct 24, 2007)

Hi,

I have broadband absortion in a room of 11X13X8. 
I've made 3 panel absorbers to absorb between 270 Hz to 310 hz, with these 3 panels the trough or "dip" in the frequency response was improved by around 5 db.
Trough before 3 panels added can be seen at image gallery under Richard Daigle; http://www.hometheatershack.com/photopost/data/500/spot1.jpg 
The 3 panels seems to have improved the sound when recording with guitar.
I have peaks in different places of the room at around 390 to 450, see same image as mentioned above for example.

Should I make panel absorbers to absorb between 400 to 440 hz? they would be around 1/2" thick (for example; 1/8" plywood over 1/2" mdf frame=420hz) 

OR 

Should I make MORE panels to absorb between 270 Hz to 310 hz?

If I make 1/2" panels should I put 1/4" insulation inside cavity or not?

How can I measure the resonant frequency of the panels, can I use any kind of contact mike? Is there any way I can measure it with a microphone? 

Finally when doing impulse response with a 5" speaker rather than 7" speaker (7" Subwoofer with 2 small speakers), the trough or "dip" looks much better, around 10 db difference when compared with subwoofer.

What is the reason for this?

Am I correct in assuming that I should use 7" Subwoofer for doing an impulse response?

Thank you for your help, 
Richard :scratch:


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## Ethan Winer (Jul 21, 2006)

Richard Daigle said:


> Should I make panel absorbers to absorb between 400 to 440 hz? they would be around 1/2" thick (for example; 1/8" plywood over 1/2" mdf frame=420hz)


A room that size benefits most from broadband absorption, not tuned.



> Am I correct in assuming that I should use 7" Subwoofer for doing an impulse response?


If you're measuring your room, you should use the same speakers you use when listening.

--Ethan


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## Guest (Oct 28, 2007)

Hi,

I have 4" rigid insulation (4 and 6 psf) in the ceiling with an air space of 8", if I added another 2", I'd have an air space of 6".

Would this help improve the trough between 270 and 310 hz?

OR if I added another 4" in the ceiling instead of 2", I'd have an air space of 4", would this improve the trough even more?

Is there a point where adding more ridgid insulation in the ceiling doesn't help?


Have a good day,
Richard


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## Ethan Winer (Jul 21, 2006)

Richard,

Adding more absorbers to cover more surface area helps more than beefing up a fewer number of absorbers. So the better solution is more panels. Here's a test I did comparing six absorbers 6 inches thick to 12 thinner panels (3 inches thick):

www.ethanwiner.com/density.html

(The main purpose of the tests was to compare density, but I also compared the number of panels too.)

--Ethan


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## Guest (Oct 30, 2007)

Thank you for your reply.

When I add more rigid insulation on the walls, the sound when recording the guitar begins to sounds dull, this is why I was considering adding more insulation in the ceiling.
The dull sound may be a result of the lack of reverb (RT60 is too low)
I have two spots left where I can put panel absorbers; but whenever I put panel absorbers there the sound becomes dull.

I was thinking of trying a panel absorber of 210 hz or 265 hz (closer to trough) but I'm not sure if it will work, what do you think? 

Here is a list of everything in my studio:

Ceiling: 3 panel absorbers at 90 hz 
2 panel absorbers at 80 Hz 
4" of rigid insulation in ceiling with with 8" air space ( panel absorbers are behind 4" rigid insulation)

Walls: 

front 2'X6'X4" (rigid insulation)
front 1 panel absorbers at 110 Hz
front 1 panel absorbers at 280 Hz

RHS 2'X6'X4" (rigid insulation)
RHS 1 panel absorbers at 90 Hz
RHS 1 panel absorbers at 315 Hz
RHS Helmholtz slat (260-310 Hz) 

LHS 1 panel absorbers at 150 Hz
LHS 1 panel absorbers at 135 Hz
LHS 1 panel absorbers at 187 Hz

Back 1 panel absorbers at 295 Hz

Corners: 

rigid insulation from floor to ceiling (shaped like triangles 20 pieces per corner, each piece is 4" thick, triangle size is 34" X 24" X 24") 
3 panel absorbers at 90 hz 
3 panel absorbers at 80 Hz

Note: All panel absorbers are 2' X 6'
10 of those panel absorbers are portable, I found that being able to move them around improved the sound.
I also have 4 small circular helmholtz of 160 hz which has improved the sound a little, maybe because they act as diffusers more than anything else.

Thanks again for your input, 

Richard


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## tweeksound (Jul 31, 2007)

When it comes to absorptive panels, it's less about tuning the panels to have effect on a very small range of frequencies and more about having a consistent effect on a very wide range of frequencies.
Especially in a recording studio of any type.

If you're using panels that have a high absorptive coefficient at 400 Hz, they will very likely have an equal or higher coefficient all the way up the scale.
(Unless they have a paper or foil face which will reflect higher frequencies but not lower ones.)
The thicker your panels, and the further from the wall they get, the lower the frequencies they will control.

That's where the balance comes in. If you have a carpet, 1" foam, 1" panels, and a bunch of thin treatments like that, it's only going to control the reflections of the higher frequencies and have no effect on lower freq's. That's why you're getting a "Dull" sound. If you add more 1" panels, dull will turn to boomy, and boxy and muffled.

You need to have bass traps to create the balance of high freq' control and low freq' control.
You can make these bass traps by using 2,3, and 4+ inch rigid fiberglass in the corners where the low freq's collect.

Get some low freq' control in there and the dullness will turn back into balanced.
And don't cover every inch of the room either way. That will be unnatural and sound dull again.

The point is to get your room as under control as you can without losing the naturalness of natural reverb.
This allows your speakers to do what they do best. If your speakers and amp have a flat response from 10 Hz - 25,000 kHz, the only thing to get in the way of that response is your room.
That's why they test speakers and microphones in an anechoic chamber which is just an extremely dead space.

Here's a great place to find out the coefficients of most acoustic materials.

http://www.bobgolds.com/AbsorptionCoefficients.htm


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## Guest (Nov 2, 2007)

Thank you for your reply

I have a hard wood floor and for all 4 corners I use rigid insulation, I think the method I used is called "super chuncks", but I'm not sure, front of triangle or super chuncks (rigid insulation) is 34" wide and 2 other sides 24", triangles 4" thick reach from floor to ceiling 1" airspace behind triangles.
And behind rigid insulation (super chuncks) is 1 panel absorber of 90 hz and 1 panel absorber of 80 hz
One of the corners doesn't have panel of 80 and 90 hz behind super chuncks but the other 3 corners do.
On the front wall I used 2'X6'X4" (rigid insulation)
and on one of the side walls I used 2'X6'X4" (rigid insulation)
I also build many other panels absorbers as listed in 10/30/07

Note: All panels absorbers are 2' X 6' (80, 90 hz and others)

The sound that I have now is not bad, but I'm wondering if I can make it better.
I find that my "f note" from smallest string (when I put a capo on first fret) sounds a little "weak" or dull.
I was thinking of making a panel absorber at either 205 hz or 260 hz, not sure yet!
If I'm understanding correctly 205 might be a better option, than 260 hz because I already have 3 panels of 280, 295, and 315 hz
Do you think adding another 2" in the ceiling would help trough between 270 and 310?
There is also a peak that occurs soon after, see http://www.hometheatershack.com/photopost/data/500/spot1.jpg

Have a good day,
Richard


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## Josuah (Apr 26, 2006)

I'm going to be a little blunt now, but I don't think you're getting what people are saying. You really should be trying to build absorbers that are full-range, and well spread throughout the surfaces of your room. One problem you'll have if you absorb only specific frequencies is the other frequencies will still bounce around. So some things will be "boomy, echo, and smear" while others won't. That won't sound good. A room that is "dead" for everything except the subwoofer is a common result, and that's going to be horrible.

If you absorb everything, then what you hear will be the sound coming from the speakers/instruments, instead of the sound coming from the reflective surfaces. Maybe you're a little worried about things sounding too dead, but that's not a reason to absorb only some frequencies and not others.


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## Ethan Winer (Jul 21, 2006)

Josuah said:


> Maybe you're a little worried about things sounding too dead, but that's not a reason to absorb only some frequencies and not others.


This is an excellent point. I often see people express fear that using thick panels versus thin will absorb too much and make their room too dead sounding. But it doesn't work that way. Overall liveness and deadness is dictated by total surface area. Increasing the thickness simply extends the absorption to lower frequencies, which is always welcome. There is some additional surface area with thicker panels, due to the larger edges. But that's a side effect which can be easily calculated and factored in to a total treatment solution.

I'll also take this opportunity to editorialize a bit about the fear of making a room too dead. :nerd:

In my opinion, small room ambience is always bad ambience and should be avoided. The classic debate is whether the listening room should contribute to the overall sound of playback. I say it should not. Maybe a rich person with a really large room can get away with more liveness, because all of the room surfaces are far enough away to reduce the problems caused by nearby refections. But for the rest of us with normal size rooms, absorbing (or diffusing) those reflections is the better choice.

I understand that preference is a factor - some people claim to prefer a room with more liveness. My response is that a well treated room can be an acquired taste, and once you've lived with a truly neutral sounding, albeit deader, room for a few weeks or months, you will learn to appreciate the lack of coloration. The problem trying to convince most folks of this position is the _vast majority_ have never heard a properly treated room. :hissyfit:

--Ethan


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## Guest (Nov 5, 2007)

This is a quote from Rod Gervais (I think he’s a professional) at musicplayer.com forums, a question in which he answered for me (Richard Daigle)

“First you want to tame the room in general - this means broadband attenuation (as Glenn mentioned above) - treat the room corners with 4" straddling the corners (super-chuncks even better, deal with first reflections on your walls and ceiling - after all of that - if you test and find a hot spot - deal with it.”

Notice that he didn’t say “only do broadband absorption because the room is small”.
He also wanted me to deal with “a hot spot” if I found one. This is why I built the 3 panel absorbers in the frequency area of the trough. 

Professionals don’t always agree on how to treat a room!
You (Ethan) even said, “I understand that preference is a factor - some people claim to prefer a room with more liveness”

Whether we agree or not, it is important that we respect one another’s opinions.

Thanks for your reply, it gives me more to think about!
I might do only broadband attenuation and then compare it with more panels in the trough to see which one sounds better.
Also I might add more rigid insulation to see if I acquire a taste for it or not.

Have a good day,
Richard


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