John Sayers' Design Forum

John Sayers' Recording Studio Design Forum

A World of Experience
Click Here for Information on John's Services
It is currently Thu Mar 21, 2019 4:15 am

All times are UTC + 10 hours




Post new topic Reply to topic  [ 13 posts ] 
Author Message
PostPosted: Mon Jul 06, 2009 2:02 pm 
Offline
Moderator
User avatar

Joined: Sat Dec 29, 2007 1:37 am
Posts: 727
Location: Santiago de Chile
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

_________________
http://www.javierbassino.com


Report this post
Top
 Profile  
 
PostPosted: Mon Jul 06, 2009 5:07 pm 
Offline
Senior Member
User avatar

Joined: Sat Mar 29, 2003 12:26 am
Posts: 2073
Location: Netherlands
Yes, there are tests out there. Sorry, don't have any links. Have you checked Ethan's site?


Report this post
Top
 Profile  
 
PostPosted: Wed Jul 08, 2009 6:28 am 
Offline
Senior Member
User avatar

Joined: Fri Feb 21, 2003 3:50 am
Posts: 1061
Location: New Milford, CT, USA
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:
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

_________________
The acoustic treatment experts
Buy my book


Report this post
Top
 Profile  
 
PostPosted: Wed Jul 08, 2009 11:54 am 
Offline
Site Admin
User avatar

Joined: Mon Jan 27, 2003 12:46 pm
Posts: 5369
Location: Australia
I've made it a stickey so others can access Ethan's last post - thanks mate.


Report this post
Top
 Profile  
 
PostPosted: Wed Jul 08, 2009 3:40 pm 
Offline
Moderator
User avatar

Joined: Sat Dec 29, 2007 1:37 am
Posts: 727
Location: Santiago de Chile
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

_________________
http://www.javierbassino.com


Report this post
Top
 Profile  
 
PostPosted: Thu Jul 09, 2009 1:57 am 
Offline
Confused, but not senile yet
User avatar

Joined: Thu Feb 05, 2004 1:56 pm
Posts: 2317
Location: Hanilton, Ontario, Canada
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

_________________
Good studio building is 90% design and 10% construction


Last edited by AVare on Thu Jul 09, 2009 6:09 am, edited 1 time in total.

Report this post
Top
 Profile  
 
PostPosted: Thu Jul 09, 2009 2:09 am 
Offline
Moderator
User avatar

Joined: Sat Dec 29, 2007 1:37 am
Posts: 727
Location: Santiago de Chile
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?

_________________
http://www.javierbassino.com


Report this post
Top
 Profile  
 
PostPosted: Thu Jul 23, 2009 6:47 am 
Offline

Joined: Thu Jul 07, 2005 8:59 am
Posts: 22
Location: Israel
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.


Report this post
Top
 Profile  
 
PostPosted: Thu Jul 23, 2009 7:03 am 
Offline
Site Admin
User avatar

Joined: Mon Jan 27, 2003 12:46 pm
Posts: 5369
Location: Australia
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.


Report this post
Top
 Profile  
 
PostPosted: Thu Jul 23, 2009 7:18 am 
Offline

Joined: Thu Jul 07, 2005 8:59 am
Posts: 22
Location: Israel
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.


Report this post
Top
 Profile  
 
PostPosted: Thu Jul 23, 2009 7:34 am 
Offline
Site Admin
User avatar

Joined: Mon Jan 27, 2003 12:46 pm
Posts: 5369
Location: Australia
wonderful, great info - thanks Jon.


Report this post
Top
 Profile  
 
PostPosted: Fri Jul 24, 2009 12:01 pm 
Offline

Joined: Fri Jul 24, 2009 11:49 am
Posts: 1
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


Report this post
Top
 Profile  
 
PostPosted: Sat Jan 29, 2011 8:36 am 
Offline

Joined: Tue Jan 18, 2011 6:33 am
Posts: 5
Location: Cleveland, Ohio, USA
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


Report this post
Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 13 posts ] 

All times are UTC + 10 hours


Who is online

Users browsing this forum: No registered users and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group