Primary vibrations from a repetitive source of such vibrations are nulled in a location by specially generated secondary vibrations fed to the location from an actruator. The actuator is driven by a waveform generator which is synchronized to the source by a synchronizing signal on the line which is derived otherwise than from the source. In FIG. 2, the synchronizing signal is derived from the output of a residual vibration sensor via a filter or a phase-locked loop (FIG. 3 and 4).

Improved method of an apparatus for cancelling vibrations from a source of repetitive vibrations

Active noise control systems such as for regulating flame noise including a detector transducer responsive to optical radiation from a turbulent flame source, means for phase changing and amplifying signals generated by said transducer, and means for expressing the phase changed amplified signal as an acoustic emission from an output transducer, eg a loudspeaker, located in the region of the flame source.

Active control of flame noise

The machine tool (1) has a frame with a horizontal axle (3) carrying two rotating worktables (4a,b) which move past a tool head. A microphone (20) is mounted on the tool head and is connected to a nearby loudspeaker (22), via a phase shifter (21). This changes the phase of the signals picked up by the microphone by approximately 180 degrees to interfere with and nullify the noise generated by the tool.

Machine tool with active noise reduction

The processing system involves a first sound emitter e.g. motor and/or vacuum pump (1) generating sound waves (AP1) with a given sound and amplitude and a second sound emitter e.g. a loudspeaker (2,3) generating sound waves (AP2) with a second phase in opposition to the first and an amplitude which is tuned to the amplitude of the sound waves provided by the first device, to cancel the sound from the first emitter. The semiconductor elements are contained within a processing chamber (P) and the sound wave generating devices are contained within a common sound-insulation chamber (4) linked to the processing chamber. The loudspeaker has a sensor e.g. a microphone (S) with an amplifier (3), used to detect the sound from the first emitter.

Device and method for treating semiconductor elements

The invention discloses a coupling feedforward active noise control system for suppressing noises in a distribution room. Three of four walls of the distribution room are wall bodies and one wall is a heat-radiation iron gate. Besides, a transformer is installed in the distribution room. The control system comprises a noise monitoring device for collecting a noise signal of the transformer, a noise suppression device for outputting a signal for suppressing transformer noise signal, and a control host connected with the noise monitoring device and the noise suppression device. The noise suppression device and the control host are arranged at one side of the heat-radiation iron gate. The noise suppression device being a mobile device is arranged between the heat-radiation iron gate and the transformer. The control system can be installed simply and conveniently; and no special requirement on the noise source equipment and the operating field is needed. Moreover, compared with noise reduction measures like sound insulation wall installation, the provided control system enables the cost to be lowered.

Coupling feedforward active noise control system

1,199,925. Noise reduction. MIDLAND TRANSFORMER CO. Ltd. 22 Nov., 1967 [8 Sept., 1966], No. 40157/66. Heading H4J. In reducing noise emitted by a source, sound waves are picked up adjacent the source, a signal is generated from the sound waves, and sound waves are reproduced adjacent the source at approximately the same amplitude and frequency as the emitted sound waves and approximately 180 degrees out of phase with the emitted sound waves. The apparatus comprises, adjacent a source 10 (Fig. 1), a microphone 11 and moving coil loud-speaker 15 coupled by an amplifier 13. Phase change occurs in the amplifier 13 or by making appropriate loud-speaker connections. Alternatively, adjacent a source 16 (Fig. 2) are a microphone 17 and " Stentorphone " device 19 coupled by an amplifier 18 in which phase change occurs. In the device 19 pulsating blasts of compressed air from a source 20 are released into a horn by a valve 22 vibrated by electromagnetic means (not shown) in sympathy with the signal to be reproduced. Reduction of noise caused by a mechanical saw or by aircraft at an airport may be effected.

Hinksman Ernest Alan

Papers

Improvements in or relating to Noise Reduction