Acoustic treatment: is there a _too_ dense?

[GreenAsJade]

I've been reading around how to do "acoustic treatment" for our rehearsal room.

 

I've read Ethan's pages about using OC703 for panels and OC705 for bass traps.

 

I'm wondering: is there a rigid fibreglass that's _too_ dense?

 

Is there a reason not to use OC705 for all panels (not just bass traps), other than price?

 

Over here we can't get OC ... I have a CSR product instead. I was advised by the agent to buy some quite dense stuff for this purpose... I now have it sitting in the room ready for construction. But after re-reading Ethan's page I'm worried it might be the wrong stuff for the walls in general ... perhaps just good for corner bass traps.

 

The stuff I have is CSR Firbretex 350, which is 60kg/sqm. This is rather more than OC 703 (45, but not as much as OC 705 (90). The chart in Ethan's page shows that the 703 is _way_ more absorbent in the mid-high range than the more dense stuff.

 

My main goal of this whole excercise was to tame down the bright bright room I have right now (bare gyprock walls with high freq feedback all up the wazooo). Should I actually be making lower density panels (about 45kg/sqm like OC 403) for most of the walls for this purpose?

 

Thanks!

 

GaJ

[Phil O'Keefe]

I think you'll be okay with the material you mentioned.

[GreenAsJade]

cool thx. I'll break'em out of the plastic and start building then

 

(The thing that got me wondering is this: I lined the shed, between the walls, with CSR Sound Screen. This, it turns out, is 35 kg/sqm. I had a couple left over and made some acoustic panels with them. When you put your ear near these I swear you can hear them sucking the sound out of the air. It is really quiet next to them. This heavier stuff doesn't seem to have the same effect. That got me wondering....OMG, are these going to be _worse_ than the lighter panels!?)

 

GaJ

[alphajerk]

be careful deadening the rehearsal space... too dead and you will pay bigtime... its harder to play the deader the space. maintain some good RT60.

[GreenAsJade]

Thanks for this caution. Right now it is really really bright. Quite unbearable.

 

As an interim I have hung blankets all around, and though they are known to to do much, it makes it just bearable.

 

So I think I have a long way to go before it will be "too dead".

 

And the great great great thing is that doing this way (making stand-alone acoustic panels) is that if its too dead, then I can just take some out!

 

 

"Too dead"?! ... man, I long for that right now!

 

(Reeeeeeeeeeeeeeeeeeeeeeeeeeeee ARGH!! Another eardrum bust by feedback...)

 

GaJ

[alphajerk]

well, the deader you make the room, the louder you will have to play, which also means the "harder" you play, and ultimately sucks for everyone involved.

[Phil O'Keefe]

Try about 40-50% wall coverage first, and adjust it from there as needed. Don't bunch all the acoustic panels together - spread them around and leave some space between them.

 

If you space those wall panels off the wall an inch or two (with 2X2" lumber or similar), you'll increase their effectiveness at lower frequencies. That, plus the corner panels / traps, should make a significant improvement in the room.

 

Do you have carpeting down on the floor? Is it thick? Does it have pad underneath it? If it's a hard surface floor (no carpet - bare concrete, or tile or wood), you might want to put a few panels on the ceiling too.

[Ethan Winer]

 

is there a rigid fibreglass that's _too_ dense?

 

 

You already got all the right answers. I'll just add that Yes, of course it could be too dense. At some point rigid fiberglass made more and more dense would become like a solid block of glass, and obviously that won't absorb at all. The main property of interest here is called entrance impedance, which is determined by the size of the tiny fissures in the material.

 

--Ethan