Active Servo Technology - Yamaha NS-P400 Owner's Manual

ACTIVE SERVO TECHNOLOGY

The theory of Active Servo Technology is 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 output
from this opening as waves of great amplitude if the
design is such that 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.
High-
amplitude
bass
sound
REMOVING THE FRONT GRILLE (for NS-M40 and SW-P40 only)
The front grille is fastened to the enclosure at four points,
and can be removed if desired. To remove the grille, first
hold the bottom of the grille and unfasten the lower part of
the grille by pulling it gently, and then hold both sides of the
grille and slowly pull straight away from the speaker. To
reattach, line up the four pegs on the inside surface of the
grille with the four corresponding holes on the speaker and
push gently.
Cabinet
Port
Negative-impedance
output drive
Active
Servo
Processing
Amplifier
Signals of low amplitude
Thus it is this problem that is resolved through the
employment of a design in which the amplifier functions to
supply 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, and,
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, and 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 Active Servo Technology.
Air woofer
(Helmholtz resonator)
Signals
Note
When the grille is removed, take care not to touch the
speaker unit with your hands or to exert excessive force with
tools.
15