I designed this subwoofer (Photo 1) for flexible use in high-quality audio systems. In particular, I use it in my own system in combination with the S24. The subwoofer uses two Peerless XXLS-P830845 12-inch long-stroke woofers. Each woofer is mounted in a separate closed box. The woofers are mounted opposite to each other to cancel the vibrational forces acting on the enclosure.
Each woofer is driven by a dedicated power amplifier. An active DSP with adjustable low-pass filters is used match the subwoofer to the main loudspeakers. In addition, the DSP provides a Linkwitz pole-zero equalisation, which is tuned yield a flat acoustic frequency response down to a -3 dB point of 21 Hz. The quality factor was set to Q = 0.65, which results in a very well-controlled impulse response.