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In 1988, Yamaha brought to the marketplace speaker systems utilizing YST (Yamaha Active Servo Technology) to give
powerful, high quality bass reproduction. This technique 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 speaker cabinet
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.
Today’s bass reflex speakers use a Helmholtz resonator to improve their
bass reproduction.
However when reproducing bass that is in the frequency region of this
Helmholtz resonator, air moves violently in and out through the port
between the interior and exterior of the speaker, sometimes producing
noise due to the turbulent air flow at the end of the port.
The port and the cabinet resonate at a frequency that is determined by their
dimensions and shape. On the other hand, turbulence in the air flow at the
end of the port contains a broad range of frequency components that are not
present in the input signal. This noise occurs because the broad range of
frequency components includes components that match the resonant
frequencies of the port and cabinet, causing strong resonance.
The Twisted Flare Port developed by Yamaha changes the
way in which the port widens toward its end, and also adds
a “twist” to suppress airflow turbulence at each end of the
port and thus prevent noise from occurring.
This eliminates the “muddy sound” and “wind noise” that
until now have been characteristic of bass reflex speakers,
allowing bass to be reproduced clearly.
ADVANCED YAMAHA ACTIVE SERVO TECHNOLOGY II
TWISTED FLARE PORT
High-amplitude
bass sound
Port
Cabinet
Advanced impedance
Converter
Active
Servo
Processing
Amplifier
Signals of low amplitude
Air woofer
(Helmholtz resonator)
Signals
Conventional Port
Air turbulence on both ends of the port creates noise
Air turbulence is
produced.
Turbulence is
diffused, air flow
becomes smooth.
Twisted Flare Port
