Yamaha soavo-900sw User Manual

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In 1988, Yamaha brought to the speaker systems utilizing 
YST (Yamaha Active Servo Technology) to give powerful, 
high quality bass reproduction. This technology uses a 
direct connection between the amplifier and speaker, 
allowing accurate signal transmission and precise speaker 
control.
As this technology uses speaker units controlled by the 
negative impedance drive of the amplifier and resonance 
generated between the cabinet capacity volume and port, it 
creates more resonant energy (the “air woofer” concept) 
than the standard bass reflex method. This allows for bass 
reproduction from much smaller cabinets than was 
previously possible. 
Yamaha’s newly developed Advanced YST II adds many 
refinements to Yamaha Active Servo Technology, 
allowing better control of the forces driving the amplifier 
and speaker. From the amplifier’s point of view, the 
speaker impedance changes depending on the sound 
frequency. Yamaha developed a new circuit design 
combining negative-impedance and constant-current 
drives, which provides a more stable performance and 
clear bass reproduction without any murkiness.
Advanced Yamaha Active Servo Technology II
High-amplitude 
bass sound
Port
Cabinet
Advanced impedance Converter
Active 
Servo 
Processing 
Amplifier
Signals of low amplitude
Air woofer 
(Helmholtz resonator)
Signals