# Ceiling mounted bass trap material questions



## BrianSexton (Jan 12, 2012)

I've been trying to come up with a plan for ceiling/wall corner mounted bass traps, being that the vertical corners of my living room are unavailable.
To clarify, they would be mounted horizontally at the ceiling/wall intersection.
I'd like to use a locally available "Safing" insulation (4pcf mineral wool, 4"thick, 24x48") but I'd need to build a frame so it doesn't sag. 
What I'm thinking is it may be cheaper in the long run to just get a stiffer material to work with.
Are the OC 703/705 stiff enough to not require extensive bracing?
I'm also wondering which would be easier to build, a 45degree, triangle trap, or a soffit style. I think a 45 would be more acceptable to the Girlfriend.

Also, what is the best way to find the most effective placements for treatments? Something similar to the subwoofer crawl, (and putting the treatment where the offending peaks are loudest/longest)?

I've done multiple searches on the subject already, but haven't really found what I'm looking for.
Thanks in advance!


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## SAC (Dec 3, 2009)

Build a frame just as one would do for a vertical corner trap. Use cheap plastic orchard bird netting for support of the fill and use the 'cheap' OC pink fluffy stuff commonly available for attic insulation as fill. 

I would also face them with a minimum of 6mil plastic sheeting so as to act as a selective LF trap that will reflect the energy above ~600 Hz back into the space so as not to overly deaden the room. The combination of stretched plastic and bird netting should be more than sufficient to prevent undue sagging or distention from the fill.

Use reasonable precautions handling the Fiberglass fill as to minimize irritation, and maximally fluff it up to fill the space. And cover with a face frame mounted stretched non-flammable fabric material


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## BrianSexton (Jan 12, 2012)

Thanks for the tips!
A brief room description:
This is not a dedicated home theater (my pockets aren't deep enough at the moment to pursue that).
It is our living room, which has lots of glass (great view of a wetlands/lake) with a brick fireplace.
The room is very reflective, and in fact has quite an echo (REW waterfall shows a long resonance time around 1k)
So, that is also on the agenda.
The main resonance issue is at around 36hz, I know any "reasonable" (sizewise) treatment is going to be limited in effect, but I think something would be better than nothing, right?
I am also pondering a resonator, but want to try broadband first, because it should knock the echo down, if nothing else...


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## SAC (Dec 3, 2009)

Use the waterfall for Modal issues below ~250 Hz. Here you employ bass traps that are selective for LF and faced with 6mil or greater plastic in order to reflect (reject) the specular energy above about 600 Hz.

Optimal porous Bass trap construction has been suggested above.

Above the modal range where specular energy dominates, the ETC response is used to analyze the specular behavior. Based upon the ETC, you will identify high gain indirect 'reflections', and resolve their individual paths and points of boundary incidence, and then treat these incidence points with broadband absorption or diffusion, depending upon the arrival time and the response desired.

For broad band absorbent panels suitable for addressing specular reflections, the best material density characteristics are either ~3lb/ft^3 Fiberglas or 4 lb/ft^3 mineral wool.

The minimum configuration that should be considered for a broadband panel is 4" thick with a 4" boundary gap. (Any thinner and the effective low frequency extension suffers.)


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## BrianSexton (Jan 12, 2012)

Ok, I don't see ETC response listed in REW, or does it not have that?

Does the plastic over the corner bass trap help the low frequency absorption, or just reflect back the highs?

For a corner mounted ceiling trap, WAF dictates that the face be 24 inches or less, leaving not a very deep trap, is pink fluffy still the prefered media?


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## BrianSexton (Jan 12, 2012)

Behind the trap is an interior wall, 2x4 frame...would it be worth my while to remove the drywall behind the trap?


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