I decided to call my infinite baffle sub The Badwater Bass'n. For those that don't know, Badwater Basin is the lowest point in North America at 282 ft below sea level. I'm hoping to go 256 Hz below C level! (middle C is at 261 Hz but can vary from 256-280 Hz depending on scale). Since the sub system will be composed of two manifolds that are located in the crawl space under the living room they will also be below "see" level.
I am using eight (8) Acoustic Elegance IB15 drivers. They were purchased a little over year ago and were the last available with copper shorting rings. These were handmade by John Janowitz. The drivers are 8 ohms each and will be connected in 4 channels of 2 drivers for a 4 ohm load per channel. I have two Face Audio F1200-TS amplifiers powering the IB System.
I purchased two cast iron grills from Van Dykes. They were on sale for half price. I have been looking for grills for about a year now. I thought about getting the cast iron grill inserts for gas grills and even found some the right size. However,a couple weeks ago I found the ones below and decided to get them since I like the look.
On May 17 I cut the plywood for the manifolds. I bought 3/4" 11 ply birch veneer/poplar layers from Menards. It is almost the same as some baltic birch I used for another project and stiffer than Arauco plywood. I am only going to use one layer of wood and I was able to cut both manifolds from 1 piece of plywood. I cut it the same day I made another subwoofer. The pile on the left is for the IB system and the pile on the right is for the 12" dual opposed sub I made.
I cut all the pieces using my circular saw, a straight edge, and some clamps. I then cut the openings with a Jasper jig and my Bosch plunge cut router. I then glued the edges with PL Premium and clamped and nailed them together. I used some 12" strips of plywood to strengthen the joints by installing them vertically along the joints at each corner. I finished making the boxes on Memorial Day (May 28).
I removed the carpet and refinished the wood floors back in January. The joists run lengthwise in the room so I was afraid I wasn't going to get the manifolds symetrical. However, after more measuring they were going to be the same. I started the opening on Memorial day. I used my Rotozip for 3 cuts on the first hole and the router for the last cut. Because I have wood floors I was able to use one of the boards as my reference point. I then drilled a hole up from the bottom (I was in the crawl space) by the stud for the first corner of my opening. My opening is is 14 3/4" x 18 1/2". This size was dictated by the cast iron grates I purchased.
For the second hole I used the router for all cuts. I used a Freud spiral upcut bit and cut 1/4" at a time out of the 3/4" thick wood floor. For both holes I screwed the cast iron grate to the floor (with the screw in the scrap portion) and used it as a guide for the router or Rotozip. It worked great. However, I realized as I was cutting that it would have been even easier to make a guide using a scrap piece of plywood and screw it to the scrap part of the floor and then route around the whole piece of plywood.
Since my manifold is large than my boxes I had to reduce the ends of the manifold a little. My boxes are 17 1/4" wide and the manifold opening is 18 1/2". I bought some scrap 2x6" boards at Menards for a total of $5 and cut two for each end of the manifold. I slid them up between the joists and screwed them in. I made sure the inner boards had exactly 15 3/4" of space between them so they would line up with the inside of the manifold.
I have super chunk bass traps in the front of the room that go from floor to ceiling. You can see the bass trap in this picture.
I screwed the grate to the scrap portion of the floor. I then ran the router along one side with using a spiral upcut bit. I did about 3 cuts before going through the floor.
The hole is now cut and the grate is in place. I had to remove the bottom foot of my bass traps to allow space for the router to make the cut. The bass trap will actually cover one corner of the grate.
I cut some scrap 2x8's and made double ends for the manifold. My manifold opening is bigger than the actual manifold so I made the inner end line up exactly with the inside of the manifold.
I installed the manifolds last Wednesday. I slid the manifold under the crawl space near the opening. The drivers were handed down to me through the opening and I installed them in the manifold. Due to clearance issues, two of the drivers face in and two face out. I installed the in facing drivers first from the inside of the manifold and then the out facing drivers from the outside of the manifold. I just used #8 Spax screws for installation. I like them because I don't need to drill a pilot hole and they hold great in plywood. I used 1 1/4" screws with the points sticking out on the other side so that the full width of the screw is in the plywood.
After installing all drivers, I had my brother jack up the manifold to the joists while I pulled up from the top. I then fastened steel straps to four corners between the manifolds and the ends. I also put a strip of gasket material between the manifold and joists/ends to seal it up.
I had drilled a small hole in the bottom of the manifold and I used it to run a pair of wires through. I will move the amps to the basement, but for now I put them in the living room and ran the wires up through the grate. This will allow me to easily change the gain while setting things up.
I finished the build on Thursday evening and then went camping for the next three days. However, I did get a change to listen Thursday evening. It is absolutely incredible! The sound quality beats anything I have ever heard and the headroom seems infinite. It has the slam of ported subs and the extension of sealed. The bass is so clearly defined, articulate, and musical. My wife listened and she even commented on how good it sounded.
Edited by desertdome - 6/6/12 at 1:45pm