This is the view into the mouth of the manifold. I had originally planned to build it to accomodate eight 15" drivers but decided to reduce it to four. These pictures were taken before I cut it down to 4 drivers.

The manifold is built of two layers of 3/4" MDF laminated as an inner box and outer box. I built the inner box first then build the outer box to fit precisely.

This is a close-up of the edge detail, I couldn't resist... had to apply at least some finishing touches.

Here is the complete manifold (built for eight drivers) ready for the holes to be cut. I'll be cutting it down to a four driver manifold next.

I'll be cutting the manifold down right at the ruler on the edge closest to the driver.

Here it is cut down to size, I'm beginning to route the recesses which will receive the subwoofer drivers.

All the driver recesses and cutouts complete.

And the top plug fitted in place. I opted to insert the plug inside the box rather than just slap a top over the piece, this is more structurally significant.

This shows how I'll be mounting the manifold in the ceiling between the joists. These supports are made of 3/4" birch ply. This is cabinet grade plywood with no voids. It is extremely strong and very rigid. I'll be attaching them to the joits with pocket holes and high sheer strength screws. Once the supports were installed I was able to jump up and down on each one without any flex. I weigh about 165 pounds. The manifold should just slide down between them and I'll screw them together with plates.

I primed, textured, then painted the inside of the manifold to resemble our ceiling. I'm considering leaving the manifold open, kind of like a skylight. I have a hunch it may be less obtrusive done this way, if not I'll just add a cloth grill or similar.

Here are the temporary plugs that will be in place while I test only two drivers. You can see the hardware I'll be using to mount the drivers. These conduit clamps were suggested by the guys over at The Cult of the Infinitely Baffled form and are very strong. This makes it easy to mount the drivers while in the attic.