DIY Panel Bass Traps: what to use for the limp-mass membrane??

[LexFactory]

Hi all,

so I've been working on solutions for bass trapping and early reflection damping in my new mix room. I've spent quite a bit of time reading the excellent resources online from Ethan Winer and Glenn K. at GIK Acoustics, as well as some others.

Unfortunately, we're a small studio and need to get this new room off the ground quickly and on a tight budget. I'd love some RealTraps MiniTraps, and I'd also be very happy with some GIK Acoustics 244 panels, but I'm in L.A. and shipping costs for both are just huge (would it kill you guys to get a local Los Angeles retail presence?? ;-) )

So after quite a bit of song-and-dance trying to track down some decent rigid fiberglass in the L.A. area (which is no easy task, I must say!), I found Insulation Wholesalers in Pomona, CA with great prices on OC703-equivalent 2" panels from CertainTeed and also some Roxul rock wool 4" panels. I placed and order for quite a few of the 703's and also for six of the rock wool panels. The rock wool panels will be the bass traps, and the 703's will be the early reflection absorbtion.

Anyway, to the point! It seems like the main factor differentiating DIY bass traps from RealTraps and GIK panels is the "limp mass membrane." I understand that it's intentionally vague (gotta protect trade secrets!), and believe me, if I could afford RealTraps right now or even the shipping on GIK panels to L.A., I would! But since I have to make these myself, what's the skinny on the limp mass membrane? What does it consist of? Where is it placed on the panel? Where can I get said material myself? What exactly are its effects on the efficacy of standard rigid fiberglass? Is it a worthwhile added expense?

Basically, HELP MEEEEEEE! ;-)

Also, I'd love suggestions on what to do about framing (making sure a maximum amount of side surface area is exposed, whether to use wood or metal, etc).

I'd also love some suggestions on what kind of fabric to use for covering and where to get it.

Thanks for any help!

[tINY]

http://www.soundsuckers.com/barriers.htm#barriers

http://www.soundcontrolroom.com/prod...ndBarriers.htm

http://www.acousticalsolutions.com/p...nd_barrier.asp

http://www.auralex.com/sound_isolati..._sheetblok.asp



Look here - One of these web sites has an 818 area code....




-tINY

[kurt]

I’m interested in this question too. tiny’s links are all about stopping sound from travel thru the walls. Does the same material apply when the goal is bass trapping and early reflection damping?

[mbrebes]

Most of the time, a limp-mass membrane is used to stop transmission of sound through walls. In bass trap construction, usually you will have a membrane that consists of a sheet of plywood. In this Ethan Winer article, he explains using 1/4" and 1/8" plywood as the membrane for low(80-150Hz) and high(150-300Hz) frequency bass traps, respectively. Here's the link:
http://www.ethanwiner.com/basstrap.html

[Glenn Kuras]

Hey guy

>(would it kill you guys to get a local Los Angeles retail presence?? ;-) )<

It still has to be shipped out there and stored. I have tried to work the numbers but really the savings is not all that great. With shipping out to LA the GIK 242 is about $65.00, the GIK 244 is about $83.00 and the tri trap is $140.00, as it stands now coming from us. Not so bad when you think about it.

For a limp membrane you want to use FRK on the front of the panel. You may be able to find it local but if not check out http://sensiblesoundsolutions.com/in...38ab767a336f69
Great guy and great service from them.
As far as building, just frame it up and drill some holes in the sides to let sound in.

Hope that helps and if you don't want to deal with messy fiberglass, just give me a call.

Glenn

[Ethan Winer]

Alexey,

> I'm in L.A. and shipping costs for both are just huge <

For the cost of one of those AKG microphones listed on your web site you could buy at least a few traps including the shipping. Ya gotta get your priorities straight!

> It seems like the main factor differentiating DIY bass traps from RealTraps and GIK panels is the "limp mass membrane." <

I can't speak for Glenn's traps, and the way we do it is proprietary. Buying rigid fiberglass with an FRK facing is not a bad choice. It's not the same as the material we use, and it doesn't have all the same advantages. (It's not a "limp mass" either.) But it works well, especially if you don't want to pay much.

--Ethan

[Glenn Kuras]

We do not use the FRK either, but have seen some great results from it..

Glenn

[Brad McGowan]

Having made more than enough of my share of traps in all different shapes and sizes, I personally would rather just call up Glenn and spend the extra money on his stuff that I know works while I actually spend my time making music. I feel the same way about cables these days too. No more soldering 8-channel snakes for me.

If someone really has their heart set on figuring out what makes the GIK and Real Traps products work the way they do, why not spend the money on one or two and reverse engineer them. If you do that, however, you had best keep the secret to yourself or else you might have a couple pissed off guys having lawyers send you letters.

Brad

[LexFactory]

Thanks everyone for the responses!

As I understand it, the FRK facing exists for the purpose of reflecting higher frequencies back into the room, so as to not deaden it too drastically. Is this accurate? If so, why does it have a positive effect on the low end absorption?

And Ethan, you're certainly right that I could get a few bass traps for the cost of one AKG C414, but my budget doesn't currently allow for it. Also, my room needs a LOT of treatment.

I just got back from Insulation Wholesalers with my order, and I only spent $248 total. I got the following for that money:

- Eighteen 2" thick panels of OC703-equivalent rigid fiberglass from CertainTeedPro (2' x 4')
- Six 4" thick panels of Roxul Safe semi-rigid mineral wool (2' x 4')

Right now it just makes more sense financially for me to go this route. And in the future, if/when the budget increases to allow for purchasing professionally constructed bass trapping, I'm sure I can sell my DIY panels to another small studio here in L.A. and probably even turn a small profit. Just gotta make 'em look nice :-)

Anyway, thanks again everyone for the responses. They've been great!

So if I did want to add some sort of material for the membrane, what specifically would anyone suggest? Also, where does it go on the panel? On the side facing the wall, or the side facing the room?

[LexFactory]

Whoops, ignore my question about what to use for the membrane, Glenn answered it and I skimmed passed it accidentally.

[tINY]

The limp mass works, generally, by turning mechanical motion (sound energy) into heat. The surface moves, absorbing the sound energy, and then the limp mass damps it out into heat. Without the limp mass, a 1/4 sheet of hardboard will re-transmit the energy back into the room.

Did you see the vinyl sheet and plywood laminate? Making a sealed box full of fiberglass insulation with that laminate on the side facing the room should work pretty well.

Ethan used to have an article on his site about membrane traps......



-tINY