My DIY Home Theater
The Subwoofer Design
The subwoofer is a standard 15-cu. ft. ported enclosure tuned to 19 Hz with two 4-inch ports. Yes, the enclosure is 2 ft x 2ft x 4ft! I used WinISD to design the enclosure. The picture shows the cabinet as the front wall was being constructed. Click the image to see it full-size. Note the 4-Ft drywall square I placed there to show the correct scale. The driver is a dual 4-ohm voice-coil Rockford-Fosgate 18-inch speaker with a free-air resonance of 22 Hz. Each voice coil is rated at 600 watts. The Xmax (voice-coil excursion) is 19 mm or 0.74 inch. A large rubber surround makes this possible. This monster can put out a 16-Hz signal that is only 3 dB down from an 80 -Hz signal. It is driven by a 2-channel amp capable of 250 RMS watts/ch or 500 watts/ch peak. It is crossed-over from the main speakers at 80 Hz. I use a Behringer sub-harmonic synthesizer in order to take maximum advantage of the capability of this sub – that’s the secret to getting a 16-Hz signal. All of these speakers radiate from the single plane of the front wall. The sub is in the left corner, and I have found that it works extremely well – it’s source can not be pinpointed – it just fills the room with awesome bass. (Actually, the whole house shakes!)
Since the theater seating is on carpet-covered concrete, there is no floor vibration to enhance the experience of low frequencies, so I secured sub-sonic vibrators to each lounge chair. These are driven by a separate 100-watt RMS subwoofer amp driven by the subharmonic synthesizer.
Suffice it to say that listening to this system is a moving experience. The sound is clean, clear, and powerful, and the low end never stops. Watching the train crash scene in Skyfall (picture in the header) with this sound system is an experience that’s hard to forget.