Pi Subwoofer Project part 3

The sub got built with just enough time for the glue to dry and was immediately thrown into service for our Sound Production final.

Some things learned might be of interest to newbie box builders, like us:
Followed proper T-nut installation instructions and those suckers go-in like a dream. Ruthie and I used 2 dabs of Gorilla Glue on each T-Nut for mounting the LAB 12 driver. However, the 4 T-nuts used to mount the speaker grill used Phillips head screws, not Allen head which were used for the woofer, so we could not get enough torque to pull them all the way in. After cranking them half way we applied 2 shots with a hammer. All seems well.

We built the box in the hallway and in the tech closet at school. That meant I had to find a lumber yard which had Baltic birch ply and could do straight cuts (no table saw at school.) Nearly impossible in Manhattan. I finally found a little storefront wood guy who had a RATTY table saw; but he had a 5X5 sheet of wood, so I took the chance. His cuts were fairly consistent except for one panel which was a little small in one dimension. I only noticed it during the dry fit. Of course we went with it anyway. I have to say that is nice strong wood. It looks nice too. The panels are laid out so the edges could be seen from the top, which I like. If all the panels were the perfect size it could have been an acceptable "furniture" or home use build. I realized after seeing it together that the box is a rather nice side table.

We went glue and screw. I bought 4 big clamps because I wanted to use the no screw method, but now I know you need a nice work table, 1 million clamps and skill to do that. So, screw it.

We never had time to apply the truck liner paint I bought, so we ran it raw. We will try to finish it with paint this or next week.

Wood blocks were added to the bottom to attach casters. I did not know if they would be rattlers, but in use, they were quiet and great for a mobile sub.

As a guy with little experience with a router, I am proud to say I made the port cutout the correct size to accept a snug press-fit of the tube, flush with the front of the baffle. We ran a bead of Gorilla Glue around it on the inside to assure an air tight seal and long term stability.

We loaded the woofer in after an overnight dry and immediately put it into service. It kicked ass. It was run with another, smaller sub, both crossed low, in hopes of smoothing some room modes. (Modes make bass seem loud or not loud enough in different parts of a listening room.) Because of time constraints, I was not able to do the usual room set-up with measurements. Placement of the 3Pi near mid point of a side wail, the other sub was offset mid point along the front wall.

One other thing: We used some 1 1/4" stock ripped into a right triangle for corner bracing in the cab. I literally found this wood on the street already cut like that. My bad is that I did not calculate how much volume that took up in the cab and adjust. I am pretty sure it would be negligible, though.

I want to thank the student builders who contributed effort into this successful build, particularly Ruthie, Mitchell and Samir.  

I thought the performance during the Earpocalypse final was excellent, as heard in the overture to our program, Stravinsky's Firebird Suite (excerpted, that was the last piece of music before James Impellizeri.) Big Bass drums and tympani on that.

Here are some pics. If we get it painted, I'll post those for before/after:

After cutting the circles with a router, we
checked the LAB 12 and the port tube for fitment

Apparently I am half-way decent with a router

Back view shows the 300 watt digi plate amp.

Personally, I like the industrial look, but this
could be finished with veneer for home use
if you build one. We will try to further the
industrial look with truck bed liner
paint if there is time.

Here's the CAD drawing with dimensions

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