Yamaha NS-P400 Owner's Manual

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Contents

15EnglishACTIVE SERVO TECHNOLOGYThe theory of Active Servo Technology is based upon twomajor factors, the Helmholtz resonator and negative-impedance drive. Active Servo Processing speakersreproduce the bass frequencies through an “air woofer”,which is a port or opening in the speaker’s cabinet. Thisopening 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 outputfrom this opening as waves of great amplitude if thedesign is such that the size of the opening and the volumeof the cabinet are in the correct proportion to satisfy acertain ratio.In order to accomplish this, moreover, the amplitudeswithin the cabinet must be both precise and of sufficientpower 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 theemployment of a design in which the amplifier functions tosupply special signals. If the electrical resistance of the voicecoil could be reduced to zero, the movement of the speakerunit would become linear with respect to signal voltage, and,to accomplish this, a special negative-impedance output-driveamplifier for subtracting output impedance of the amplifier isused.By employing negative-impedance drive circuits, the amplifieris able to generate precise, low-amplitude low-frequencywaves with superior damping characteristics, and thesewaves are then radiated from the cabinet opening as high-amplitude signals. The system can, therefore, by employingthe negative-impedance output drive amplifier and a speakercabinet with the Helmholtz resonator, reproduce an extremelywide range of frequencies with amazing sound quality andless distortion.The features described above, then, are combined to be thefundamental structure of the Active Servo Technology.The front grille is fastened to the enclosure at four points,and can be removed if desired. To remove the grille, firsthold the bottom of the grille and unfasten the lower part ofthe grille by pulling it gently, and then hold both sides of thegrille and slowly pull straight away from the speaker. Toreattach, line up the four pegs on the inside surface of thegrille with the four corresponding holes on the speaker andpush gently.NoteWhen the grille is removed, take care not to touch thespeaker unit with your hands or to exert excessive force withtools.REMOVING THE FRONT GRILLE (for NS-M40 and SW-P40 only)Signals of low amplitudeAir woofer(Helmholtz resonator)Negative-impedanceoutput driveHigh-amplitudebasssoundSignalsActiveServoProcessingAmplifierCabinetPort

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