Butterfield Audio: Subwoofer

This subwoofer was designed specifically to give me low, tight bass without annoying my neighbors. This was achieved by using two ten inch subwoofers on opposite sides of a sturdy cabinet, in a bipole configuration. The Peerless XLS 10" woofers were chosen for their low resonant frequency, and being over damped. Mass was added to each woofer to lower the resonant frequency further, and increase the Q. Since the point was NOT to annoy the neighbors, a loss in efficiency was readily acceptable. Here is a graph of the measured impedance response with 222 grams added to each woofer. Here are the T/S parameters obtained from my measurements with the added mass:

Parameter Re Fs Vas Qms Qes Qts
Value 3.9 ohms 12.66 hz 3.22 ft^3 4.21 .348 .322

A quick simulation of the subwoofers in a 4.6 cubic foot box shows a response close to the desired response, with Fc of 20 hz, and a Qtc of 0.5.

Impressions:
Well, I haven't received a complaint from the neighbors (yet). I have felt the floor for vibrations while the subwoofer is playing and they do exist, but they are small. Especially compared to any down-firing subwoofer of any size. The bass is very articulate, playing dance beats and double bass equally well. Movie explosions are wonderful, however the usual impact of vibration is somewhat diminished, forcing you to listen more to the rumble instead of feeling it. (Thank goodness.) Surprisingly, efficiency still is not a problem. I have the volume on my Parts Express class A/B amp set in the middle, and I have the subwoofer output on my outlaw receiver/amplifier turned to negative 7 dB. This is quite surprising to me since my main speakers are also very efficient. I suppose it has a lot to do with the corner loading on the sub.