[TRADERXFAN]

I was considering building my own treatments and have read quite a bit now. It seems that a big contributing factor in the effectiveness for the panel is a "limp mass membrane" both Realtraps and Acoustic Sciences Corporation use a limp mass membrane in their panels to boost the attenuation at lower frequencies.

Looking for something to use in my build plan I was able to find 2 limp mass products that might work

"audio seal sound barrier"
http://www.acousticalsolutions.com/products/blocking/sound_barrier.asp

and auralex sheetblok available at different retail sites.
http://www.auralex.com/sound_isolation_sheetblok/sound_isolation_sheetblok.asp

both of them list a 1#/sq foot dense vinyl.

So my question to all of you DIY'ers or Pro's out there... how well would you guess that adding a layer of one of these to one side work on an panel (2'x4'x4") of 8# mineral wool for dealing with the lower frequencies?
Any better suggestions for a material "limp mass membrane"???

Thanks.

[rajacat]

http://www.soundproofing.org/infopages/flooring.htm

Better prices...I believe.

Raj

[Scott F.]

If you want something nearly as effective and far less expensive, try either 60 or 90 mil elastomeric roofing (commonly known as rolled rubber roofing material). You should be able to call your local roofing contractor and pick up his 'cut off''s' or leftovers from projects for next to nothing.

It works really well. I used it to soundproof our offices at work (metal studs, insulation, 60 mil rubber roofing, 1/2" drywall). If you close my office door, I can crank the heck out of my stereo and you can barely hear it outside (I've got door gaskets and a floor sweep in the door).

[bpape]

OK - timeout - think there's some confusion here.  The rolled roofing works OK for isolation.  However, to use as a limp membrane in front of a treatment to tune it as a more broadband absorber, I'd stick with the MLV, or a thinner membrane depending on the tuning you want and how broadband you want.

Bryan

[Scott F.]

I misread the post thinking it was about soundproofing a room to be built.  My bad 

In the immortal words of Rosanne, Rosanna Dana.......Never mind.

[bpape]

ROTFL!  Yeah, easy enough to do.

Bryan

[TRADERXFAN]

Thanks for the info Bryan!

I was hoping for some feedback on whether or not applying this 1#  vinyl material to one side of a 4inch min wool (8#) would be GOOD thing to help absorb bass in a hanging panel trap configuration… doesn’t seem like anyone cares to comment directly on the effectiveness?   Anyone please?

Also on the realtraps site, they mentioned something about mineral fiber tends to sag and lump (evidently more than fiberglass)… is this true?

What is the lifespan of rigid fiberglass and mineral fiber of same density? I was under the impression that they were essentially identical.


Also, I wanted to run this idea passed you guys for an alternative to the limp mass panel above. - I was thinking of making my own bass trap corner "crates":

Take 4 sections of 2'x4' - 4 inch 8# min wool stacked face to face,
Then cut the width to 16”.
The result 16” wide by 16” deep by 4’ high “blocks”
Put them in a wood frame “crate” (constructed of thin sliced MDF strips to form the edges. Mdf because of the rigidity and its very straight) and wrap with fabric
I would put these in my room corners, stacked 2 high, which for me runs floor to ceiling.

(The excess 8” from each 2 groups of panels cut, placed in the "crate" side by side would be used to make a 3rd “block” 16" wide)
I found the sheets of the material described above locally for about $11/panel with tax.
So 8 panels would make 3 blocks, at a price of about $31/block for the insulation. Then I have to figure out the additional cost of MDF, glue, screws, and fabric.

I  think this would be a good bass trap, and at a good price/performance ratio.  Does this seem like a sound design?

Since I have a dedicated room, I am also able to put these blocks around some of the floor/wall corners around the room, and would be easily removable.

If too much high/mid is getting absorbed, I would go back and face some of them…


Thanks guys!

[bpape]

If you want to make a real membrane absorber, then you'll need to have it over a sealed cavity.  There is no need to use 4" 8lb mineral wool in that configuration.  Up to say 4" deep, 1" of OC703 spaced 1/2" behind the 1lb vinyl will provide excellent results - again, being farily narrow.  The membrane must be free to vibrate and the air cavity behind must be static to act as a spring.

Your 16x16 absorbers will work very well and be much more broadband.  If you want to kill their absorbtion a bit in the upper mids and highs, just bond some FSK to the flat face.  This will also provide a bit of a hump in absorbtion which will be centered based on the density and flexibility of the material behind it. 

Mineral wool can sag over time but should last you quite a while if mounted properly.

Bryan

[TRADERXFAN]

Thanks again Bryan... I think the blocks are the way I am going to go.

Any advice on how to mount them properly? I thought simply pressing them into the crate, against each other face-to-face, would be fine and they would stand up on their own? Is there more to it than that?