Manifold Design

[darrellh44]

Hi,

I'm planning a 4-driver manifold IB to be installed in the attic over my HT room. The ceiling has 16" joist spacing, but I would like make the box opening approx 20"-22" square. Is there a problem with have a joist running thru the center of the opening (see diagram - the manifold would sit on top of the green members).



Also has anyone lined the inside of the manifold with 1" 705 fiberboard? It seems like this would isolate an manifold resonances from the room. Is this worth doing?

Thanks,
Darrell

[ThomasW]

darrellh44 said:

Is there a problem with have a joist running thru the center of the opening (see diagram - the manifold would sit on top of the green members).

Nope not a problem

Also has anyone lined the inside of the manifold with 1" 705 fiberboard? It seems like this would isolate an manifold resonances from the room. Is this worth doing?

We're trying to create bass not absorb it. In addition only added mass types of damping will damp cabinet resonances

[darrellh44]

Hi Thomas,

I see your point about creating bass and not absorbing it, but I wasn't trying to keep the manifold itself from resonating, but just trying to keep the resonances from reaching the listening area.

Instead of fiberboard, how about lining the inside with 1/2" sheetrock with green glue between layers?

Thanks,
Darrell

[inm8]

darrellh44 said:

...I wasn't trying to keep the manifold itself from resonating, but just trying to keep the resonances from reaching the listening area.
Instead of fiberboard, how about lining the inside with 1/2" sheetrock with green glue between layers?

If you position the drivers so they are set-up as opposing pairs (ie: one driver on each vertical face of a square manifold) then you won't have any problems with mechanical vibration, because the forces will cancel (as per Newton 3).

At high spls vibration will be induced by the pressure wave, but that has nothing to do with the IB being coupled to your house. Regardless of the source, an object will always resonate at it's resonant frequency.