Cylindrical bass traps - Do they work?

[brandondrury]

I was doing a little online research and found this:

http://ic.net/~jtgale/diy2.htm

I'm skeptical. Should I be?

Brandon

[Ethan Winer]

Brandon,

> I'm skeptical. Should I be? <

You should always be skeptical about everything.

The simple answer is that fiberglass is a great absorber, and when enough of it is placed in the room corners it absorbs well to a fairly low frequency. There's nothing magical about a round shape, which has pros and cons. The pro is the round shape has a favorable "angle of incidence" to sound waves approaching from all directions. The con is the same round shape, because there's a less favorable angle when most of the waves are coming from one direction.

I have no doubt that a bass trap made from three feet of 10" pipe insulation works, though it would work a lot better if it were larger. What bothers me about those plans, and Jon Risch's similar plans elsewhere, is the author's misguided notion that fiberglass needs to be sealed with end caps. You can't seal a porous material like fiberglass!

--Ethan

[brandondrury]

I see. So with that logic, simply cramming a bunch of fiberglass into a corner will basically do the same thing. Is this correct?

I know I've scene pictures where one studio simply cut 703 into triangles with one 90 degree angle. These were stacked in the corner. It seams like the stacking would be more effective simply because it would be more dense. Is this a correct assumption?

Brandon

[barefoot]

Yes, filling the corner gives the most effective absorption, but it's not necessarily the most cost effective method. For example, two layers of 703 mounted diagonally across the corner would probably yield very similar absorption numbers, but require maybe half the material. But I bet it's no trivial task to find the design that optimizes the price to performance ratio, and it's most likely very situationally dependent. In any case, I doubt that tube traps are anywhere close to being the most efficient use of valuable studio space.

Thomas

PS - notice the concentrated use of words like "probably", "maybe" and "likely" in this post?

[Ethan Winer]

Brandon,

> So with that logic, simply cramming a bunch of fiberglass into a corner will basically do the same thing. Is this correct? <

Yes, and one of the points I make in my Acoustics FAQ is that fiberglass batts, still in the plastic wrapper and put in the room corners, does a great job. That's the ultimate "ghetto" bass trap.

--Ethan

[ChrisWiggles]

fiberglass batts, still in the plastic wrapper and put in the room corners, does a great job. That's the ultimate "ghetto" bass trap.

I have one of those. I'm too lazy to get around to unpacking and making floor to ceiling corner traps with nice covering fabric.

[mtl777]

Doesn't the plastic interfere with absorption? It's not porous, right? What happens to the absorption coefficients then?

Mitch

[Ethan Winer]

Mitch,

> Doesn't the plastic interfere with absorption? <

Not at bass frequencies!

--Ethan

[Consul]

If thin plastic affected bass frequencies, this business of bass traps would be a hell of a lot easier than it is.