Ceiling tiles using rigid fiberglass


So I'm in the process of finishing a basement to include a dedicated audio space, which will be 35' x 23' x 8'6". Walls framed and electrical mostly done. I am trying to determine the most effective method of creating an acoustically absorbent ceiling while maintaining a nice look.

I have looked into 'acoustical' ceiling tiles but the data is obviously not promising. The idea that I favor right now is to buy the rigid fiberglass, cut it into 2' x 2' squares, wrap them in an acoustically transparent cloth, exact type TBD, and drop them into a standard grid. In effect, I'd be creating my own ceiling tiles, the benefit being that they'd actually be of acoustic benefit, instead of the off-the-shelf tiles which don't work all that well.

The main questions I have are:

(1) Is this a reasonable approach? Has anyone here tried this?
(2) If so, what to do with the gap between the rigid fiberglass and the main level floor (joists are 2x10s)? Is it best to use 1" rigid and stuff the rest with fluffy, 2" and stuff, 4" and stuff, or will they yield similar acoustic results? If I use 4", will stuffing the gap even make a difference? I think the 1" rigid plus fluffy is the least expensive option, but performance is more important that cost here.

I'm also very open to ceiling tiles which are acoustically transparent enough to let the incident waves penetrate to fluffy fiberglass underneath. This would be a very attractive option, as it may yield great performance with less effort (I'm doing all the construction work myself, so anything that saves time is welcomed!).

Apologies if this has been posted elsewhere, but I searched for quite a while.....

Thoughts?
cathode

Showing 1 response by ngjockey

Currently open joists?

Here's an unusual method, and I admit I've never tried it on a ceiling. Insulate as usual between the joists but be careful that the insulation stays above the bottom of the joists. Another vote for "Safe and Sound", being far cheaper than rigid fiberglass and far better than soft fiberglass. With 1"X 2" make a lattice of 4' squares under the joists and screw 1/4" hardboard to that but only to/through the lattice. Doesn't have to be precisely 4' squares. Take advantage of the joist spacing and cut the panels accordingly. Use lots of screws, like every 2 or 3". You don't want rattle. The gaps can be puttied up, sanded and painted. Saying hardboard over drywall because I wouldn't want to see drywall fall down but drywall is more fire resistant. Full 4'X8' could sag but that doesn't mean you can't screw down the center of 4X8 sheets. Actually, maybe go 4'X2' lattice although that does reduce effectiveness.

The more rigid and thick the membrane, the larger area (lattice) it needs to vibrate but that also means that it can "absorb" lower frequency. Drywall can be used as a membrane but not over a small area when mounted rigidly. There are flexible mounting tricks but nothing I would advise for a ceiling.

To ensure nothing falls down on the membrane and potentially rattles or impairs vibration, any kind of mesh/screen/open fabric barrier can be stapled to the joists before the lattice. Plastic wouldn't breathe and paper not much better.

Essentially the entire ceiling becomes a membrane trap that would be effective for mid to upper bass while not sucking out high frequency. It's a narrow band trap while soft traps are wide band. The membrane works by converting movement to heat but more effective with a acoustically damped chamber, which would be the joist space. The depth of the joists helps too. Some say the ideal chamber should be airtight but, on this scale, be practical.

http://www.realtraps.com/modecalc.htm

The link above might help predict your room behavior.