Yamaha 900SW - Manual (Page 21)

17
En
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