Low Profile Bass Traps Built Into The Walls?

[Introspector]

I have an idea that I've been wanting to bounce of the minds of Audioholics for a while now. A co worker of mine is getting ready finish his large basement to include a home theater and also a music rehearsal room. I have an idea for his design but I want to get your feedback on it first.

Here is the goal: to achieve substantial bass traps while maintaining as normal household looking a space as possible.

Here's the idea: Frame the concrete basement with 2x4 or 2x6 studs as usual. Pack the space between the studs with rigid or low density fiberglass insulation. Drywall the ceiling and walls as usual EXCEPT, leave a one or two foot band open around the perimeter of the ceiling and tops of the walls. Cover this opening with acoustic fabric.

The Theory: This configuration would combine the concepts of corner bass traps and coupled spaces with the familiar and functional drywall ceilings and walls we all know and love. Obviously the insulated studs could be covered in fabric in their entirety with wooden slats added to improve mid and high frequency reflections. But this is a very 70's studio look and not something that looks normal in a contemporary home. However, a one foot band of fabric that matches the wall paint, circling the perimeter of the ceiling and walls is a lot more subtle. It also then provides functional walls upon which pictures and such can be hung and drywall ceilings into which recessed lighting can be installed.

The Question: Would such a design result in the bass trap effect that we all desire? Would low frequency energy collecting in the upper corners of the room be drawn down into the walls and above the ceiling where it would be absorbed by the fiberglass insulation?

Please offer your affirmations and your critcisms. Like I said, I have an upcoming opportunity to incorporate this idea into a co worker's design. But if I convince him to do it and it doesn't work.... oh boy...

 

[bpape]

From an absorbtion standpoint it will work fine. The problem is that you completely blow the isolation value of a drywall ceiling by leaving that area uncovered - especially where bass builds up the most.

My suggestion would be to build and drywall the room and then construct a soffit around the perimeter that is just framing, absorbtion, and cloth. Basically the same look and performance but you don't lose the isolation.

Bryan

 

[gullfo]

i second the soffit approach

 

[Phil Taylor]

A modification suggestion for the total trap/soffit would be to do as Bryan says -- but for the majority of the lengths and widths of the soffits - finish the underside with drywall so recessed lighting cans can be inserted. You could still leave the corners and sides open, covered with acoustical cloth and packed with insulation but have the added advantage of somewhere solid to mount accent lighting cans.

 

[Introspector]

Thanks for the thoughtful feedback...

Thanks for getting me thinking about isolation. The ceiling of the space is currently 12" or 18" engineered trusses filled with insulation. This provides substantial isolation already but we will be talking about significant pressure levels from the rehearsal room. The outer walls of the space are the concrete foundation of the house, so isolation is not an issue there. A compromise would be to fully seal the ceiling with drywall and maybe even an extra layer of MDF and viscoelastic adhesive at all the seams, but then apply the wall bass trap concept in the outer walls along the foundation.

I will need to meet with my co worker regarding the aesthetic impact of soffits, which I recognize are an excellent acoustic element. If he is open to the use of soffits, then I could tie the outer wall volume into the soffits for a combined effect.

As long as there is framing going on, I already plan on incorporating vertical corner bass traps everywhere possible.

Thanks for the positive feedback. If soffits will not be an option due to aesthetic or build complexity concerns, then I'm thinking that applying my concept just to the outer walls will provide the opportunity for low profile bass traps.

 

[bpape]

If you tie the soffit into the wall cavity, you're still losing the isolation. Concrete outside the stud or not, the sound will go right through the lack of drywall and flank around your isolation up through the space between the stud wall and the concrete and straight up to the space above.

Think of the aquarium analogy. If there's a hole, doesn't matter where or how big, you're going to get wet.

Bryan