I need some test information if available

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jbassino
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I need some test information if available

Post by jbassino »

Any of you guys know or have any information regarding panel absorbers?
Im wishing to have real life tests of how many frecs and how much of them lets say one 4" deep panel absorbs. (I'm not talking about coef absorption values that many website offer. if not, how much RT60 is reduced by an X amount of absorption placed and how many DBs that will change)
If none is available, I'm willing to do the tests my self including:
- Placing panels against the wall
- Spacing the panels 10cm from the wall
- Triying different density on wool used (18, 36 and 80kg/m3)
- etc

Thanks
Ro
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Re: I need some test information if available

Post by Ro »

Yes, there are tests out there. Sorry, don't have any links. Have you checked Ethan's site?
Ethan Winer
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Re: I need some test information if available

Post by Ethan Winer »

jbassino wrote:Any of you guys know or have any information regarding panel absorbers?
My company's first products were panel traps based on the design on this article, but meant to be "portable" or at least able to ship:

Build a Better Bass Trap

We had them tested at IBM's acoustics lab, and I'm glad to share the results. Unfortunately, I never saved it in electronic form, so I just dug out our old web site on the Internet Archive and here's the data for the low-bass and high-bass models (sorry about the flaky formatting):

Code: Select all

Hz. 100  125  160  200  250  315  400  500  630  800  1000 1250
LB7 1.10 0.77 0.44 0.39 0.33 0.24 0.32 0.27 0.19  -    -     -
HB7 0.46 0.48 0.78 0.68 0.69 0.50 0.35 0.31 0.23 0.25 0.23 0.20
So from this you can get a good idea of how much is absorbed and over what range.

--Ethan
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Re: I need some test information if available

Post by John Sayers »

I've made it a stickey so others can access Ethan's last post - thanks mate.
jbassino
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Re: I need some test information if available

Post by jbassino »

Thanks Ethan

But aren't they absorption coeficients rather than real life db loss or rt60 decrease?
What I'm triying to do here is to measure lets say a certain room. Add a certain amount of absorption at a certain density and see how many milliseconds they decrease the room's RT60 at each frecuency, and how many db's in frec response that represents.
The purpose of this, is that sometimes there is a big confusion between: How much RT60 changes from a bass trap, and how many db's are affected at the same time.
Yesterday, I did a test with Stuart, placing a large amount of insulation in a corner. It didnt change much the frecuency response of the room (maybe 1 or 2 db's max) but it really improved the RT60 values of those frecuencies.
So, absorption really has two ways to improve a room sound (RT60 and Frecuency - or in other words, how long each note lasts and the volume of each note), and I'm willing to try and discover how much of each of them is dependant on what type of insulation is used , plus what kind of placement is used and many more options.
If all of above has already been tested, then excuse myself. If not, I think this is a pretty insteresting subject
AVare
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Re: I need some test information if available

Post by AVare »

what you are looking for is results from reverb time equations. The effect varies with the room size, surface area and amount of absorption already in the room. It is not a strict linear relationship between number of panels and acoustic effect.

Andre
Last edited by AVare on Thu Jul 09, 2009 6:09 am, edited 1 time in total.
Good studio building is 90% design and 10% construction
jbassino
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Re: I need some test information if available

Post by jbassino »

I thought it was not linear tho.
But how can you predict such effects without actually making a bunch of acoustic treatment , placing them and the measuring your room?
There is actually a lot of questions involved regarding treatment and havent been much talked here. for instance
When making panel absorbers. does them really affect the decay of each frecuency rather than its amplitude? Or both? If so, which one has the major effect?
jonessy
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Re: I need some test information if available

Post by jonessy »

Predicting panel absorbers is tricky.

For the straightforward approach you can try my calculator which uses the transfer matrix approach.
A short description of the method can be found here.

However there are other things that should be taken into consideration, such as mounting conditions (i.e. how the membrane is attached to the construction), which may have a great effect on the results.
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Re: I need some test information if available

Post by John Sayers »

Hi jonessy - thankyou for your link to your calculator. I notice you differentiate between the sir-backed and absorber-backed membrane. In a studio we built back in the 70s we used 2' x 2' panels with absorber-backed membrane but I've never seen ant reference to that design until now. :)

At a studio build I once observed a method of measuring the frequency using a contact mike attached to the panel and viewed on a RTA (real time analyser) - the panel was then excited by a sine wave sweep via a speaker - the resonant frequency clearly stood out and could be adjusted by tightening or losening the screws holding the panel.
jonessy
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Re: I need some test information if available

Post by jonessy »

Nice practical way to deal with this... :)

There are actually some significant differences between an air-backed or an absorber-backed membrane. Generally speaking:

1. An air-backed construction will demonstrate less absorption at its resonant frequency because energy losses are only from the motion of the panel itself. Adding an absorber behind the panel increases losses, so the overall absorption will rise.

2. An absorber-backed construction will normally have a wider Q.

3. An absorber-backed construction will demonstrate a lower resonant frequency, due to different compressibility of air in the cavity.

:)
Jon.
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Re: I need some test information if available

Post by John Sayers »

wonderful, great info - thanks Jon.
lung0801
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Re: I need some test information if available

Post by lung0801 »

The easiest way to predict the improvement of RT is hiring an acoustic consulting firm, they have modeling software, such as EASE, ODEON, CATT, to predict the room's RT before and after providing acoustic panels.

Cheers
Calvin
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Re: I need some test information if available

Post by Tubamark »

jbassino wrote:Any of you guys know or have any information regarding panel absorbers?
Im wishing to have real life tests of how many frecs and how much of them lets say one 4" deep panel absorbs. (I'm not talking about coef absorption values that many website offer. if not, how much RT60 is reduced by an X amount of absorption placed and how many DBs that will change)
If none is available, I'm willing to do the tests my self including:
- Placing panels against the wall
- Spacing the panels 10cm from the wall
- Triying different density on wool used (18, 36 and 80kg/m3)
- etc

Thanks
Pardon me for waking an aging thread . . .

The old rule of thumb that you are seeking [every doubling of absorption results in 3dB reduction] certainly is appealing. Unfortunately, it's only valid for diffuse, large, low-absorption spaces - the spaces in which the Sabine equation works very well. Since few rooms DIY'ers deal with meet these criteria, it's pretty hard to equate # panels to decibels.

However, if you've managed (by the various other calculation methods out there) to get a reasonable estimate of the reverb change in question, you can estimate the dB reduction by the simple inverse-square rule. Essentially: for every halving of RT60, you will see approx -3dB.

Caveats/factors to consider:
--DB Reduction assumes measurement at a location greater than the critical distance.
--Critical distance varies with RT
--"Reverberation" in the classic sense is not possible in rooms that are small, or oddly proportioned, or highly damped --The soundfield is never fully diffuse, and decay levels/rates are not constant throughout the space.

The latter point is why it's so tricky to predict the decay/reverberation of typical studio builds in the first place.

--- Mark
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Re: I need some test information if available

Post by Stephaned12 »

jbassino wrote:Thanks Ethan

But aren't they absorption coeficients rather than real life db loss or rt60 decrease?
What I'm triying to do here is to measure lets say a certain room. Add a certain amount of absorption at a certain density and see how many milliseconds they decrease the room's RT60 at each frecuency, and how many db's in frec response that represents.
The purpose of this, is that sometimes there is a big confusion between: How much RT60 changes from a bass trap, and how many db's are affected at the same time.
Yesterday, I did a test with Stuart, placing a large amount of insulation in a corner. It didnt change much the frecuency response of the room (maybe 1 or 2 db's max) but it really improved the RT60 values of those frecuencies.
So, absorption really has two ways to improve a room sound sticker personnalisé Cagnes sur mer (RT60 and Frecuency - or in other words, how long each note lasts and the volume of each note), and I'm willing to try and discover how much of each of them is dependant on what type of insulation is used , plus what kind of placement is used and many more options.
If all of above has already been tested, then excuse myself. If not, I think this is a pretty insteresting subject
Me in any case, I opted for a soundproof room to test an amp and I must admit that it looks good.
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