For 150mm width of panel absorber I need 150 mm rockwool?

hugo_inside · Post by **hugo_inside** » Thu Apr 14, 2005 9:37 am

I'm thinking of made some panel absorbers for my rehearsal rooms. But I dont understand if panels are 150mm width:

1.- how much rockwool I need for it?

2.-If using 40 mm of rockwool it's enough, where should I attach it? close to wall, close to the air or in the middle?

knightfly · Post by **knightfly** » Thu Apr 14, 2005 9:56 pm

40mm will help quite a bit; place it at the front of the absorber, so you have an AIR gap behind the rockwool. This lowers the frequency where the rockwool stops working very well. So 40mm rockwool, 110mm air space, wall. This will work best for that thickness of rockwool... Steve

hugo_inside · Post by **hugo_inside** » Thu Apr 14, 2005 10:13 pm

thanks for answering Steve...

And if I do many panels 150, 100, 50 mm wide with 40 mm of rockwool...

a) this could be better? or is the same absortion.

1.) 40 mm rockwool , 110 mm air , wall
2.) 40 mm rockwool, 60 mm air, wall
3.) 40 mm rockwool, 10 mm air, wall

b) Should I put a thicker rockwool???

knightfly · Post by **knightfly** » Sat Apr 16, 2005 8:38 pm

Hugo, thicker is usually better but the only way to be SURE is to actually MEASURE and LISTEN to the room, and put whatever absorption thickness and area that's necessary to balance the reverb time... Steve

hugo_inside · Post by **hugo_inside** » Sun Apr 17, 2005 8:57 pm

Thanks Steve ,

1.- There a link of "how to measure a room"?

2.- With panel absorber this rule works: "the more the better"?

3.- The important thing in panels is " to give an air space between the absorber and the wall"??

knightfly · Post by **knightfly** » Tue Apr 19, 2005 10:25 am

1.- There a link of "how to measure a room"?

http://www.etfacoustic.com/

Check out their "demo room" pages for a lot of good info.

2.- With panel absorber this rule works: "the more the better"?

No, the rule that works is "the right amount" - this takes some study and listening/testing.

3.- The important thing in panels is " to give an air space between the absorber and the wall"??

This depends on what you mean by "panel" - this word is used to describe too many different things and concepts, so ends up meaning nothing.

In acoustics, the actual meaning of "panel absorber" is taken to mean a lightweight panel, sealed in front of a box made of heavy materials, with either rigid fiberglass or mineral wool absorbent fastened BEHIND the light panel, just far enough away from the light panel (usually plywood, sometimes fiberboard) so that the panel can vibrate without being damped by the absorbent.

This works by the panel responding to bass pressure which flexes the panel; some energy is converted to heat by this flexing. When converted to heat, the sound is no longer a "sound", so it's absorbed. Then, the vibrating panel tries to move the air within this box back and forth through the absorbent; when this happens, MORE sound is converted to heat because of the restrictions of the absorbent material, so MORE bass is "trapped".

The center frequency of the panel absorber is controlled by the mass of the front panel and the depth of total air gap BEHIND the panel, and assumes that all OTHER sides of the "box" are infinite mass (very heavy) - the sharpness of the PEAK in absorption is controlled by damping of the panel and air space; thicker absorbent will broaden the response so it's more smooth. At NO TIME should the panel be allowed to contact the absorbent, or it will lose efficiency from the damping effect of touching the insulation.

Just using insulation batts with covers of cloth is an entirely different thing; these need to be AWAY from walls for best performance, the further from the wall the lower the effective frequency range of absorption. Theoretical PEAK absorption takes place at 1/4 wavelength from whatever solid wall is BEHIND the absorber - this would be about 5 FEET for a frequency of 60 hZ.

For more, try this link -

http://forum.studiotips.com/viewforum.php?f=8

And this one (be sure to read ALL the sections in BOTH these links)

http://www.saecollege.de/reference_mate ... stics2.htm

I know you are stressed out about finishing your project, but I also know you won't be happy if you rush things and spend money you don't HAVE to spend; for this reason, PLEASE slow down a bit and STUDY this area before you "jump in" - I don't recommend doing ANYTHING to a room until you HEAR it, because theory and reality don't often agree in acoustics... Steve