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Discussion Starter · #1 ·
I am treating a small mixing room and need to cover the ceiling to conceal air ducts and plenums primarily for aesthetic reasons, but also to prevent the soft-side ducts from acting like high-Q traps - the 1/4 wave narrow-band suck-outs I measured were exact 4x multiples of the duct diameters of 18", 12", & 8" ducts. the 6" ducts did not produce much of a suck-out effect due to my belief that the 4x wave frequency does not effectively penetrate the outer duct covering and thus is reflected. But that is beside the point I am writing about here.

The room is non-rectangular (roughly 8'x14'x13'x15') - two parallel walls, two non-parallel walls, and has certain irregular ceiling features as well. About 80% of the ceiling is 120" high parallel to the slab floor. Two walls are double isolated 2x4 frame 1/2" drywall on one side and 5/8" MDF with carpet on the other; the other walls are thick exterior with drywall, 2x6 frame, and cement board siding. I measured a response rise at 107 Hz, assumed as the 1/4 wave of the floor to ceiling resonance.

My goal is increased bass absorption, to allow me to better hear the octave below my Mackie HR824-II nearfields (25-50 Hz) at an appropriate level so my mixes will translate properly and with pitch definition and timbre as well if possible.

I have purchased Armstrong (5/8" thin) 2'x4' tiles. These are very lightweight fiberglass (not the heavy fiberboard kind), somewhat soft and flexible, with the thinnest of plastic membrane-like coatings on the finished side, yellow fiberglass on the other side. I expect them to act like a plastic membrane over thin 703-type material though I have not performed any tests.

I will be suspending them 21" below the 120" ceiling, with a portion at an angle - about 2/3 of the ceiling will end up parallel to the floor.

I plan to fill the entire space above the tiles with un-faced fiberglass, in an attempt to leave a minimum of unfilled space while effectively surrounding all existing duct-work. I expect the lowest bass to penetrate the tiles and be damped just as if I was building "super-chunk" type broadband absorbers, and my room should retain some HF life due to reflections off the thin plastic tile finish. I am also planning to build a super-chunk style absorber in the acute angle corner.

Does anyone have any experience with this lightweight, flexible ceiling tile material? I have not yet started laying in the fiberglass above the ceiling tiles, which will be a lot of work that I will not do if it won't help. I am using the philosophy "more bass treatment is always better in a small room."

I am using an extremely low-capable (19 Hz claimed) 100 lb. purpose-built monitor/mixing room subwoofer (Mackie HR series). This is not a sound reinforcement sub, nor is it an LFE-centric theater sub. So I will have plenty of bass to absorb!
 

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Ethan Winer's site says that you can lay fluffy fiberglass panels on top of the drop ceiling grid and get effective bass trapping. That would a lot cheaper I think. I bought mineral wool batting at Menard's. 3"x24"x48. 5 sheets for $40.
 

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Discussion Starter · #3 ·
Thanks. I plan to do just that, and have in fact already purchased the fluffy fiberglass insulation material.

My question was can I lay this stuff on top of the tiles, or does it have to lay on the grid without any tiles? Perhaps that is what you mean by "on top of the grid..."

The tiles in this case are only decorative, I am not counting on any absorption from them directly, I just want to confirm that they are transparent to bass frequencies below about 110 Hz so the fluffy stuff above them can do its work.
 
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