The ATP-Series of attenuators allows the output level of a network of 25V or 70V speakers to be controlled from a wall-mounted volume control without affecting overall amplifier volume settings.A bypass function overrides the volume control knob setting when activated by 9V to 30V DC.Applying 9V to 30V DC between pins labeled D+ and D- bypasses the volume control function and provides full volume audio to the speakers.The ATP-Series attenuators feature etched faceplate markings.