So I’ve started another sub project. My home theater has been without a sub ever since we moved a few years ago. I debated several ideas for the new house, everything from a small 8″ sub to a larger 12″ end table sub to a monstrous multi-15″ driver IB sub in the attic. After building up a 15″ TC Sounds sealed sub for a friend and getting a feel for some pretty hefty bass, I knew the 8″ sub project would only disappoint. Yet there just wasn’t money in the budget for a sub that size (or anything bigger), nor was there space in my room. So I decided on something in between, the Audiopulse 12″ Epic driver from TC Sounds. Parts Express is now an authorized reseller of the entire Audiopulse lineup, so I quickly snatched one up last week and finally got a chance to open it up tonight.
What’s really nice about the Audio Pulse drivers is they come with the Thiele/Small parameters of your driver tested and serialized with a data sheet right in the box. My driver came in with a slightly lower Fs (22.4 vs. 23 Hz) and much higher Vas (107L vs. 45L) and most of the other parameters were right around the published numbers. I was happy the Fs was bit lower, but the Vas threw me for a loop. The reason for the discrepancy in Vas is that numbers on PE’s web site are wrong. Those were the numbers I had originally run when determining my driver selection since it modeled really well in small ported box. I should have checked AudioPulse.com before, where the real Vas is actually 97L. Turns out this box likes a much larger vented enclosure, with good reason, the Vas is more than double what I had originally simulated. That parameter alone heavily drives enclosure volume.
Unfortunately I don’t have the luxury of just making the box bigger, since the box size was actually designed around the new entertainment center I’m building. The entertainment center has been on the to-do for nearly two years now, but I just haven’t been able to muster up the energy to design it, cut it, build it, paint it etc. That and the fact that I am not a carpenter by any means. Making speaker boxes is one thing, making furniture is something entirely different. But I had to take a stab at it, since the entertainment centers we were looking at are super expensive and none of them had the exact style we liked, or were the exact right size. That and I was set on building the sub into the entertainment center to save on space and make for a nice, integrated look.
The sub was designed to fit into the lower 1/3 of the the left bookcase on the entertainment center and allows for about a 90L enclosure with a 1.5″ baffle and plenty of bracing. After running some new numbers, it looks like I will still be able to use the 90L box, although it’s a compromised 4th order design compared against a QB3 alignment which needs 156L. So I think I am going to do a dual ported/sealed design (plug-the-port kind of design) and see what happens. A 90L sealed enclosure is slightly large resulting in a system Q of 0.63, which is a bit overdamped, but still should result is great sound, albeit somewhat less efficient and have a higher f3 (36.6 Hz) over the same volume box that’s ported (f3 ~22 Hz). Tuning frequencies from 20 to 25 Hz model well and don’t result in vents that are too long. Well, at least with only one 4″ port they aren’t too long. Port air speed is beyond the recommendation for this design, but I just don’t have the room to add more ports which take up more internal space.
Enough talk, the design details will follow shortly. For now, here’s some pics of the driver and the bookcases I have been working on, as well as the design for the sub. My complete writeup on the entertainment center will have to come at another time, but it’s coming along well so far, thought it’s worn me out and taken up two Saturdays doing so. The design I stole from my sister-in-law who is quite handy with woodworking. It’s been a pain to work on but it should be well worth the effort, not to mention the mega bucks I saved by not buying one from the store or out of a catalog.
5-23-3008 – This sub is complete! Click here for the details..