1431 A
Variable Q Active Filter
31 Band '/3 Octave Equalizer

KEY FEATURES
• Variable Q filter set
• 31 bands of boost and cut
• Select between 6 dB or 12 dB
of boost and cut

KEY SYSTEM SPECIFICATIONS
Center Frequencies: 20, 25, 32, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400, 500, 630, 800, 1 k, 1.25k, 1.6k, 2k, 2.5k, 3.15k, 4k, 5k, 6.3k, 8k, 10k, 12.5k, 16k, 20k Hz

Maximum Boost/Cut: 12 dB

Low-Cut Filter
Corner Frequency: 43 Hz

Frequency Response
at Unity Gain:
(High-Pass Filter Disengaged) 20 Hz - 20 kHz, ± I dB

Total Harmonic Distortion
at Unity Gain:
(20 Hz - 20 kHz, 0 dBu Output) < 0.01%

Noise at Unity Gain: < -85 dBu, 20 Hz - 20 kHz

Maximum Input Level
at Unity Gain: + 20 dBu (7.75 Vrms)

Maximum Output Level: + 20 dBu (7.75 Vrms)

DESCRIPTION

The Altec Lansing 1431A is a boost and cut '/3 octave graphic equalizer whose primary use is for tuning the overall frequency response of a sound reinforcement system, both to increase gain-before feedback and to compensate for the deficiencies in the acoustic environment and the sound system.

The active Q variable filter set utilized in the 1431A allows effective equalization with few problematic side effects. As Figure 1 illustrates, the filter characteristics vary with the amount of boost or cut used. At low control settings, the filter Q is very wide. As the control is boosted or cut, the filter Qnarrows so that there is minimum interaction between adjacent frequency bands. The filter response is designed to affect a'/:,-octave range.
Each of the 31 'V;3-octave filters provide 12 dB of boost or cut at ISO frequencies 20 Hz through 20,000 Hz. The faders have a positive detent in the center, flat-response position. The gain control also has a center detent at unity gain.
A low-cut filter switch, with a 43 Hz corner frequency and 18 dB per octave slope, is located on the front panel. A range select switch allows selection of either 6 dB or 12 dB of boost or cut.