AudioControl Half Octave Equalizer/Analyzer Richter Scale Series Three. Excellent condition, works well. Comes from an audiophile home! AudioControl Richter Scale Series III Half Octave Equalizer Electronic Crossover w/ original microphone The Richter Scale is a bass management system designed to have your subwoofer breaking new ground. A 24dB/octave, Linkwitz-Riley alignment will precisely match the crossover frequency of your subwoofer. A six band equalizer controls the critical bass region of 22.5 Hz to 125 Hz in one-half octave steps. A built-in lab-grade analyzer and warble tone generator enable precise measurement and calibration. The Subsonic filter prevents damage to your subwoofer by preventing inaudible tones from reaching the speaker. With the Richter Scale in your system, youll hear much cleaner and tighter bass. 6 bands of one-half octave bass equalization 24 dB per octave independent programmable electronic crossover Warble Tone Test Signal Generator Lighted dB meter Special rumble-reduction circuit 18 dB per octave fixed subsonic filter @ 20 Hz The Analyzer uses a variable warble tone oscillator and analog meter for precise optimization