Yamaha AV-90PY Owner's Manual download pdf (Page 6)

The theory of the 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 small 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.

Thus it is this problem that is resolved through the

employment of a design in which the amplifier functions to

supply the signals. If the electrical resistance of the voice coil

is 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 (28 Hz – 20 kHz) with amazing

sound quality and less distortion.

The features described above, then, are combined to be the

fundamental structure of the Active Servo Technology.

YAMAHA ACTIVE SERVO TECHNOLOGY

Air woofer

(Helmholtz resonator)

Negative-impedance

output drive

High-amplitude

bass sound

Active Servo

Processing Amplifier

Signals

Port

Cabinet

Signals of low amplitude

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Yamaha AV-90PY Owner's Manual Page 6

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