The subwoofer is, in many ways, the centerpiece of the system. It is a 6th order Class II Chebyshev alignment, built into a 40 cubic foot triangular area in an attic space above the bar. Its design came about when my father in law heard my subwoofers at home and decided he wanted the same sound, but didn't want any - repeat, any - boxes in the room if possible. So, I commandeered the attic space and had the architect put power and line wiring up into the space, as well as leaving an opening into the listening room for the driver.

  The driver is a 15" Cerwin-Vega LE15-D dual voice coil driver, chosen both for its parametric match to the design requirements and also for its extremely high efficiency. With a 32 x 40 foot room with 23 foot cathederal ceilings to fill with sound, every watt counts. It is wired single-coil, presenting a 4 ohm load, while still providing reasonable efficiency (91.5 dB/W/m). Thiele/Small parameters for single-coil operation are as follows:

  Cabinet alignment is Thiele's alignment 25, with the following parameters:

Translating this into speaker parameters for the above driver:

This requires a monster box, but allows the sub to play flat (measured!) down to 12 Hz, from a 30 Hz fs driver.

  The amplifier chosen was an Adcom GFA-535, a seemingly puny 65 WPC amp. However, consider: in bridged mode, this amplifier is capable of delivering 260 watts into a 4 ohm load, which matches the driver power handling nicely. There is also about 3 dB of headroom. All it requires is a fan to keep it cool, which I found out after about the first ten minutes of listening.

CONSTRUCTION

  The box was "lined" if you will with standard 5/8" sheetrock, taped shut all around the perimeter. Light fixtures, outlets, etc. were sealed up with expanding foam goop to provide airtightness. A frame was constructed by the builder to cover the 18" x 24" opening into the listening room.

  The driver is mounted on a piece of 1" MDF cut to fit into the opening. The opening was lined with a door-jamb like collection of wood to make mounting and dismounting the speaker easy. Vents are two 3" diameter PVC pipes, each of which is approximately 4" long.

  The amplifier/fan combo is mounted directly in the enclosure, with a remote on-off switch controlling power. A surplus 12 VDC power supply is plugged into a switched outlet on the receiver; when the power is turned on, a capacitor/transistor/SCR timing circuit is activated that delays turn on for a few seconds. A large relay is triggered to provide power to the amp. When the receiver is turned off, the sub amp is immediately turned off. There is almost zero turn on/off thump with this setup; the relay "clack" is louder than any noise made by the driver.