WM8 "BASSIS" Bass Equalizer

Adaptable to all acoustic-suspension speakers.
Adjustable bass boost and damping.
23 dB Maximum boost.
Balanced inputs/outputs available.
20 Hz subsonic filter.

The BASSIS is a specialized parametric equalizer with two purposes: (1) to correct the irregular bass response of many acoustic-suspension loudspeakers; (2) to extend the bass response as much as two octaves lower. The damping (Q) of the new bass cutoff can be adjusted according to the listening room acoustics and the user's tastes. In consequence, any speaker can be corrected to obtain deep yet well controlled bass, providing music with a greater sense of impact and "openness".

graphCurve A is an example of the bass response of a typical "boomy" speaker, with bass falling off below 60 Hz. By adjusting the BASSIS, its own frequency response (curve B) may be made the inverse of the speakers curve, down to 15 Hz. The combination of the equalizer and speaker is shown in curve C, with a smooth response and a -3dB point at 15 Hz. Note that it is generally not possible to perform this sort of correction with a conventional graphic equalizer, due to the spacing of the frequency bands of the sliders.
The BASSIS can also reduce the "boominess" of poorly-tuned vented loudspeakers; or the vent can be plugged for use with the full range of equalizer options.
The BASSIS employs a 4 amplifier bi-quadratic filter, with additional op-amps to allow independent adjustment of the various parameters, and to ensure system compatibility. The circuit contains high-speed op-amps, film capacitors and metal film resistors. Four rotary controls are provided for each channel, to match the cutoff frequency and damping of any acoustic-suspension speaker and to set the bass boost and net damping. A 20Hz high-pass filter (subsonic filter)  can be switched in from the front panel to eliminate unwanted subsonics.

Frequency response: 2Hz to 100 KHz, + 0.2 dB/ -3 dB
Harmonic distortion: less than 0.01% (at 1 KHz)
Signal to noise ratio: better than 110dB
Input impedance: 100K
Output load capability: 100 Ohm min
Output impedance: 10 Ohm typ
Maximum input voltage: 25 V peak-peak (8.8 V RMS)
Maximum output voltage: 25 V peak-peak (8.8 V RMS)
Power supply requirement:120 VAC, 60Hz, 10W
Dimensions: 17"W X 10"D X 3.5"H
Construction: All metal cabinet, black with white legend

Bass boost range: 0-24 dB (0-46 dB)
Net Q range: .25 to 1.0
Speaker resonance range: 30 Hz to 130 Hz
Speaker Q range: -4dB to +6 dB at Xover frequ.
20 Hz Cut: on/off
Bypass: on/off
Power switch: on/off
Input, output: RCA phono and XLR balanced
Line power fuse: 1 Amp
Power: IEC connector for line cord

WM8-AA Bassis equalizer 24 dB max boost, potentiometer for all controls
WM8-MONO-AA Bassis equalizer 24 dB max boost, mono version of above
WM8-23-AA Bassis equalizer 23 dB max boost, stepped attenuators for all controls
WM8-23-MONO-AA Bassis equalizer 23 dB max boost, mono version of above

The Fs and Boost controls have 24 step attenuators; the Qb and Qs controls have 12 step attenuators.