Soffit Bass Trap and HVAC

[Vanhoecke]

I'm thinking about creating a soffit that will double (in part) as a bass trap, but I want to make sure I understand the construction. The room is approx. 19'x13' with 9' ceilings. The soffit will be about 10"-12" deep and will extend 2' from the side walls (19' demension) and 4' from the front and rear walls. The soffit will house recessed lights and an HVAC duct for the HT. Is it as simple as installing 4"-6" of OC 703 along the bottom of the soffit frame and covering it with GOM? Obvisously I will need to cut out openings for the lights and HVAC grills. (How much clearence should I leave around the lights?)

The front soffit covers an I-beam and the HVAC duct leading upstairs -- I was not planning on installing any OC 703 in this soffit. The front soffit is actually part of the ceiling, which is hung on RSIC-1 hangers with double 5/8" rock and GG.

Regarding the HVAC, I'm planning on tapping into the main supply plenum off the furance with some 6" flex duct, running this through a damper then a silencerhttp://rewci.com/6siforroduld.html (picture attached) before it enters the HT wall (below the ceiling at soffit level). Once inside the HT the 6" flex duct will tee and two seperate 6" flex ducts will delver air through two 6" grills. Hopefully this will reduce the noise from the air rushing over the grill. Should the connection in the wall be hard pipe (i.e., a short piece of 6" round sheet metal wrapped with MLV and chalked with GG in the wall?


Any thoughts?

 

[Scott R. Foster]

Acoustically what you seek is as simple as you suggest. A run of 4 to 6" thick upholstered mineral fiber along the room's ceiling / wall corners will make for a nice broadband absorptive treatment.

I would however be concerned about the recessed light fixtures and all the heat they can put off - that you took that factor into account and kept the install fire safe.

remember - safety fast!

 

[Vanhoecke]

Thanks Scott. Does it matter what type of fiberglass material is used (e.g., backed, unbacked, etc.)?

Also does anyone have any recommendations for recessed lights that I can put in the bass trap/soffit that don't generate excessive heat, or alternatively does anyone know what the safe set back distance is for insulation near a recessed fixture?

 

[Scott R. Foster]

Just plain old naked semi-rigid fiberglass [3lbs. pcf] or rockwool [go a little denser about 5 lbs pcf, or +/- 60 kg/m3] panels will do just fine. Keep em at least 4" thick and they'll work great.

Good Luck!

 

[majorloser]

Just plain old naked semi-rigid fiberglass [3lbs. pcf] or rockwool [go a little denser about 5 lbs pcf, or +/- 60 kg/m3] panels will do just fine. Keep em at least 4" thick and they'll work great.

Good Luck!

YUCK, rockwool. Makes me itchy just thinking about that stuff. Used to work in a cryogenics plant were we had loose rockwool in the towers.

The stuff is very dense and works great for insulation.

 

[Scott R. Foster]

YUCK, rockwool. Makes me itchy just thinking about that stuff. Used to work in a cryogenics plant were we had loose rockwool in the towers.

The stuff is very dense and works great for insulation.

Works just as well as fiberglass as an acoustic absorber too. Both fiberglass and rockwool come in a wide bariety of densities.. though if you match acoustic properties between the two materials the rockwool equivilent will be somewhat denser.

For portable panels it makes a difference IMO - fiberglass being as acoustically effective, yet lighter is a nice touch. For a built-in - or hang and forget solutions I can't see where it really matters.

Also rockwool is flakier and so you're probably more likely to get it down the back of your shirt when working overhead - so I guess that makes fiberglass easier to work with in this application - but for either I suggest a disposable paper suit and hat [like painters use]. That way you keep it off yourself pretty well and then toss the residue away instead of running it through your washing machine. [gloves and googles aint a bad idea either]