I couldn't resist posting one more photo of Bruce Thigpen's fan-driven infrasonic subwoofer, this time showing the drive-unit in operation. Loaded with an infinite baffle—it is in the next room—it fires into a foam-lined sub-chamber, which low-pass filters the residual fan noise, leaving just the awesome infrasonics to pressurize the room next door. Because the fan is providing the main motive power, just 30W of audio signal was required to create an spl of 115dB at 8Hz!