Yamaha YST-SW305 - Manual (Page 16)

12
ADVANCED YAMAHA ACTIVE SERVO TECHNOLOGY
The theory of Yamaha Active Servo Technology has been
based upon two major factors, the Helmholtz resonator and
negative-impedance drive. Active Servo Processing
speakers reproduce the bass frequencies through an “air
woofer”, which is a port or opening in the speaker’s cabinet.
This opening is used instead of, and performs the functions
of, a woofer in a conventionally designed speaker system.
Thus, signals of low amplitude within the cabinet can,
according to the Helmholtz resonance theory, be outputted
from this opening as waves of great amplitude if the size of
the opening and the volume of the cabinet are in the correct
proportion to satisfy a certain ratio.
In order to accomplish this, moreover, the amplitudes within
the cabinet must be both precise and of sufficient power
because these amplitudes must overcome the “load”
presented by the air that exists within the cabinet.
Thus it is this problem that is resolved through the
employment of a new design in which the amplifier supplies
special signals. If the electrical resistance of the voice coil
could be reduced to zero, the movement of the speaker unit
would become linear with respect to signal voltage. To
accomplish this, a special negative-impedance output-drive
amplifier for subtracting output impedance of the amplifier is
used.
By employing negative-impedance drive circuits, the
amplifier is able to generate precise, low-amplitude, low-
frequency waves with superior damping characteristics.
These waves are then radiated from the cabinet opening as
high-amplitude signals. The system can, therefore, by
employing the negative-impedance output drive amplifier
and a speaker cabinet with the Helmholtz resonator,
reproduce an extremely wide range of frequencies with
amazing sound quality and less distortion.
The features described above, then, are combined to be the
fundamental structure of the conventional Yamaha Active
Servo Technology.
Our new Active Servo Technology — Advanced Yamaha
Active Servo Technology — adopted Advanced Negative
Impedance Converter (ANIC) circuits, which allows the
conventional negative impedance converter to dynamically
vary in order to select an optimum value for speaker
impedance variation. With this new ANIC circuits, Advanced
Yamaha Active Servo Technology can provide more stable
performance and improved sound pressure compared with
the conventional Yamaha Active Servo Technology, resulting
in more natural and dynamic bass reproduction.
High-amplitude
bass sound
Cabinet
Port
Air woofer
(Helmholtz resonator)
Active Servo
Processing
Amplifier
Signals
Signals of low amplitude
Advanced Negative-
impedance Converter