Yamaha YST-SW011 - Manual (Page 9)

5
Advanced Yamaha Active Servo Technology
The theory behind Yamaha Active Servo Technol-
ogy is based on two factors: the Helmholtz resona-
tor and negative-impedance drive. Active Servo
Processing speakers reproduce the bass frequen-
cies 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 Helmholtz resonance theory, be
output from this opening as waves of great ampli-
tude if the size of the opening and the volume of
the cabinet are in 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 in
the cabinet.
This problem is resolved by a 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, the system utilizes a special nega-
tive-impedance output-drive amplifier that sub-
tracts the output impedance of the amplifier.
By employing negative-impedance drive circuits,
the amplifier is able to generate precise, low-ampli-
tude, 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-imped-
ance output drive amplifier and a speaker cabinet
featuring a Helmholtz resonator, reproduce an
extremely wide range of frequencies with out-
standing sound quality and low distortion.
The features described above combine to create the
fundamental structure of conventional Yamaha
Active Servo Technology.
Our new Active Servo Technology — Advanced
Yamaha Active Servo Technology — adopts
Advanced Negative Impedance Converter (ANIC)
circuits, which allow the conventional negative
impedance converter to dynamically vary to select
an optimum value for speaker impedance variation.
With these new ANIC circuits, Advanced Yamaha
Active Servo Technology provides a more stable
performance and improved sound pressure com-
pared to conventional Yamaha Active Servo Tech-
nology, resulting in more natural and dynamic bass
reproduction.
High-amplitude
bass sound
Cabinet
Port
Air woofer
(Helmholtz resonator)
Advanced Negative
impedance Converter
Active Servo
Processing
Amplifier
Signals of low amplitude
Signals
YST-SW011,030_UB.book Page 5 Wednesday, December 15, 2004 5:56 PM