I have read your bass trap how-To and found the design quite interesting.

At first I thought the way you did them was kind of ghetto, but after some time, by comparison, I am really liking the idea. With 20-30 or so 4" panels to make in total, it will certainly be faster and cheaper than what I had planning (ie. to frame my panels with pine and then stain and varnish).

On that note, I have a few questions:

1) Have you noticed the bolts as a visible component under the muslin? Also, because the bolts/washers compress the mineral fibre at their points of contact, have you noticed the depressions they create as visible?

2) Have the bolts migrated or the panels deformed at all as a result of the hanging pressure? Is the plywood holding?

3) I read in the guide above that you adhered cross-slats for the mid/high absorbers by Super 77 to the mineral fibre. What was this for, and did using Super 77 work all by itself?

4) Are there any suggestions you could make about improving the design, now that you have had that time to get used to it?


Thanks,
Mike

Cheap, easy and effective was what I was after... so yeah, there was a hint of ghetto in there. I also wanted something easy to mount/remove and store if the girlfriend decided at some point they were just too hideous (or I wanted to liven the room a bit).


The bolts are invisible under the muslin. They create enough pressure to just counter sink themselves enough to be flush with the FRK. Additioanly, if you wrap the fabric nice and tight, it will simply be taught over the dimple.


They are holding up really surprisingly well. The shear strenth is not great, but the compressive strenth is very good and by using the 2 panels it acts like ply wood in a way. No sagging to speak of and the opposite pull of the plywood and the mineral wool create a turn buckle of sorts pulling in opposite directions keeping things taught.

Yup, Super 77 all by itself. The wood strips served a few purposes. First, they giv a bit of air space behind the panels to add to their absorbption. (Ethan mentions a 1/4" space behind panels in his Acoustics FAQ.) Also, i give you a surface to attach the dry wall screws to. Again, you don't want to swing on these things, but the downward force when hanging is distributed much like a picture frame. It is no less secure than a full length mirror or large picture on the wall.

Not really. The only thing I have really changed is I have cut the chains in some places to make mounting a bit easier. Otherwise, I am quite pleased and a bit surprised at how well they are holding up. I might, maybe, add a washer on the back to give a bit more of a belt and suspenders approach to attaching the chain. But if you use the 8pcf mineral wool, you'll be amazed at how strong that stuff is.