Manifold size vs. opening size

[robertr]

This forum is very useful and interesting. The FAQ section states that an IB manifold should be as small as possible. However, it also states that the opening should ideally be the same size as the summed area of the drivers. Since these goals conflict, which is the more important?

[ThomasW]

Unless there's a typo somewhere there's no mention of making manifolds as small as possible. The FAQ does says a IB manifold should be as short as possible.

[robertr]

Sorry, when I said "small" I meant short. Keeping it short limits the opening size, yes? Would two separate short manifolds (for, say, an 8 driver IB) be preferable to one longer manifold?

[ThomasW]

robertr said:

Sorry, when I said "small" I meant short. Keeping it short limits the opening size, yes?

This is as short as a manifold could be for holding 18" drivers, and the opening is pretty big.

Would two separate short manifolds (for, say, an 8 driver IB) be preferable to one longer manifold?

The idea is to avoid having a deep manifold. So in an optimal situation two short manifolds would be better than one really deep one. Since phase issues begin to develop when the drivers are stacked one behind the other.

[robertr]

Thanks Tom. Would putting two short manifolds together (so that they share a common wall) work?

[ThomasW]

I can't visualize what you're talking about.

[robertr]

Something like this:

       D      D      D     D
    -----------------------------
    :             :             :
    :             :             :
    :             :             :
    :             :             :
    :             :             :
    -----------------------------
       D      D      D     D

[ThomasW]

Where's the opening?

[robertr]

It's a top view. The opening is "behind" the monitor screen.

[ThomasW]

robertr said:

It's a top view.

That tells me little about where the sound exists that drawing.

[twisterz]

Hello Thomas

I think Robert is thinking of 2 of these next to each other


What about one manifold with the other 4 woofers on the ends & back. A 2'X4' manifold would have an opening big enough for 8 18" woofers.

[robertr]

You got it, Twisterz.

[chrisbee]

Being horribly pedantic.

A 3 x 3 opposed 18" driver manifold with one driver on each end:

3 x 18" = 54" + (4 x 2" for spacing) = 62" minimum length.

1 x 18 + 4" (spacing) = 22" minimum width.