A quick scan of some Web sites told me that the same amount of money typically would buy four 8-inchers, two 12-inchers, or one 15-incher. A few punches of a calculator told me these configurations also yielded the closest possible match in combined surface area and displacement of the different driver combinations. I then chose similarly constructed 8-, 12-, and 15-inch drivers from Dayton Audio.
To keep things simple, I stuck with sealed cabinets. Using The Loudspeaker Design Cookbook, I designed all the subs to have a Q of 0.9 — a compromise between the loud, boomy high-Q sound that mass-market consumers often prefer and the tight, highly damped low-Q sound that most audiophiles prefer. I built the cabinets from [3/4]-inch medium-density fiberboard. This left the panels in the larger cabinets freer to vibrate, so I added bracing to the 12-inchers and still more bracing to the 15. I sealed the cabinets with adhesive caulk, then stuffed them with fiberglass insulation to a density of 1 pound per cubic foot.
To power the subs, I used an ATI AT2007 amplifier rated at 200 watts (continuous) per channel. This gave the drivers all the juice they could handle. I thought about using equalization on the subs to optimize their performance, but I really wanted to hear what they could do on their own. I fleshed out the test system with my usual reference gear: three Sunfire CRM-2 front speakers and two CRM-2BIP surround speakers, driven by an AudioControl Savoy amp.
The 15-inch sub went in my “subwoofer sweet spot,” a place along the front wall of my room where I’ve found that a single sub delivers the most even sound when heard from my favorite listening chair. I then placed one 12-inch sub in each of the front corners of the room. I finished by placing 8-inch subs in the two rear corners, and also next to the 12-inch subs in the two front corners.
Many of these decisions could have gone a different way. I could have chosen thicker MDF and a fancier driver on the 15-inch sub. But how much thicker? How much fancier? I could have used weaker amplifiers on the smaller subs. But how much weaker? I’m sure many experts would have come up with different answers, but I’m not sure they’d have achieved more useful results.
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