Poly's and absorption

Post and discuss acoustic topics, Studio design, construction, and soundproofing here

Poly's and absorption

Postby drnelson » Thu Oct 17, 2013 6:44 am

I have a few projects with very bad flutter echoes. I tend to lean to to poly's in large rooms to break up the flutter and I can get some mid to LF absorption out of them as well, which is often needed in the large rooms. They are cost effective and fairly easy for a wood shop to construct . I do not want to reduce the reverb time of these rooms any more then they are now. I have one room that already has too much absorption were hardwood poly's tend to absorb. I'm thinking maybe two layers of skins on the poly's might help, and then would green glue help or make it worse?

Dan
drnelson
Site Admin
 
Posts: 147
Joined: Sat Jan 31, 2004 12:18 am

Re: Poly's and absorption

Postby bert stoltenborg » Thu Oct 17, 2013 12:43 pm

Hardwood poly's and absorption?
Every kind of diffusion absorbs a bit, but I cannot imagine that hardwood is absorbing more than other materials in the same shape.
If you view life with the knowledge that there are no problems, only opportunities, you are a marketing manager.......this is my personal philosophy
bert stoltenborg
 
Posts: 4555
Joined: Sun Apr 18, 2004 11:03 am
Location: Achterhood, Netherlands

Re: Poly's and absorption

Postby drnelson » Fri Oct 18, 2013 3:41 am

The absorption caused by the resonating panel. I think if leave them unfilled I will minimize the low frequency absorption of the vibrating panel, if I am reading chapter 5.7 of Mankovsky's text correctly.
drnelson
Site Admin
 
Posts: 147
Joined: Sat Jan 31, 2004 12:18 am

Re: Poly's and absorption

Postby bert stoltenborg » Fri Oct 18, 2013 10:12 am

Filling them should lower the Q and making the absorption more broadband.
Making these sheets heavier should lower the resonance frequency.
Adding GG will also lower Q of the resonating panels, but I am not sure this is significant.

I would like to see if these resonators really contribute in any significant way to the reverberance of the room.
If they do, I would guess filling them is a way of taming them.

When I did a little investigation on plate resonators and especially 1/4 lambda resonators you could see in a waterfall when undampened they did add narrow band sound to the sound field.
When a little wool was added they didn't do anything at all. A friend of mine coincidentally performed the same measurements and reported the same results.
And I recall Eric telling the same story.
If you view life with the knowledge that there are no problems, only opportunities, you are a marketing manager.......this is my personal philosophy
bert stoltenborg
 
Posts: 4555
Joined: Sun Apr 18, 2004 11:03 am
Location: Achterhood, Netherlands

Re: Poly's and absorption

Postby Scott R. Foster » Fri Oct 18, 2013 11:17 am

When used in verb chambers where no absorptive properties are desired Poly's are made so that the panel is high mass... I recall there is an AES spec for reverb chamber design that giver a figure for how massive Poly's used in such venues should be - though I doubt that level of acoustic inertness need be considered for general use.

What type and thickness are the panels you are bending that you find overly resonate?
SRF
Scott R. Foster
 
Posts: 3854
Joined: Mon Feb 02, 2004 12:41 pm
Location: Jacksonville, FL USA


Return to Discussion

Who is online

Users browsing this forum: No registered users and 1 guest