Headphones have a small cavity between the diaphragm and the ear canal with a microphone in the cavity closely adjacent to the diaphragm providing a feedback signal that is combined with the input electrical signal to be reproduced by the headphones to provide a combined signal that is power amplified for driving the diaphragm.
The invention relates to a method and to apparatus for attenuating externally originating noise reaching the eardrum while still enabling communication via an electro-acoustic path. Apparatus according to the invention comprises passive attenuation means disposed about each ear and delimiting a cavity (10). In addition it includes active attenuation means comprising a loudspeaker (6) placed inside the cavity (10) and a microphone (8) placed in the external ear duct or at the inlet thereto, said loudspeaker and microphone being interconnected by a constant gain amplifier (11) and an active analog filter (12) of the polynomial type, with the passive components thereof being designed to provide a given transfer function. One application lies in the construction of protective headsets fitted with incorporated loudspeakers enabling electro-acoustic communication.
The present invention is concerned with a receiver device for converting electrical signal from a headphone, a telephone receiver or the like into acoustic signals. More particularly, it relates to a noise reducing receiver device in which acoustic signals in the vicinity of an electro-acoustic transducer element are converted by a microphone into electrical signals and negatively fed back to an amplifier circuit which is adapted for amplifying input electrical signals and supplying the amplified signals to the electro-acoustic transducer element. In the noise reducing receiver device, the input electrical signals are amplified by the amplifier circuit and converted by the electro-acoustic transducer element into output acoustic signals. A microphone is arranged in the vicinity of the electro-acoustic transducer element and adapted for converting the output acoustic signals and external noise into electrical signals, which are negatively fed back to the amplifier circuit via a feedback circuit. The output acoustic signals may be heard at a desired noise reduction level by adjusting the transfer function H of the electro-acoustic transducer element, the transfer function A of the amplifier circuit, the transfer function M of the microphone and the transfer function .beta. of the feedback circuit within a range determined by .vertline.AHM.beta..vertline.>>1.
In order to overcome problems in an active noise reduction system of sound buffets at low frequency and signal enhancement caused by imperfect transfer functions of a noise cancelling sound generator and a microphone, one or more high pass filters for reducing low frequency signals are provided in a feedback loop between the sound generator and microphone. A low pass filter is provided for extending the bandwidth of the system but which does not introduce unduly large phase shifts.
A headset with a light incorporated within is disclosed. A representative embodiment of the invention may be construed as an aviation-style headset that includes a first earcup and a second earcup each comprising active noise reduction (ANR) circuitry, a headband interconnecting the first earcup and the second earcup, and a boom microphone coupled to one of the first and second earcups. The headset also includes a rotating housing coupled to at least one of the earcups. A first light-emitting diode (LED) is mounted in the rotating housing. The rotating housing is rotated to point light from the LED in a desired direction. The headset also includes a switch mounted to one of the earcups for controlling the LED. The ANR circuitry is electrically coupled to at least the first LED to deliver power to the LED. Other systems and devices are also disclosed.
An acoustic detector that includes active noise cancellation is presented. An acoustic detector converts sound waves, which include sound waves of interest as well as noise, to an electronic signal. An operator listens for a characteristic sound, for example the sound characteristic of fluid leaking from a pipe, as she varies the position of the transducer. At least one other acoustic detector is positioned in order to monitor noise. The electronic signal from the noise monitoring acoustic detector and the electronic signal from the acoustic detector are combined in a processor in order to cancel the noise. In some embodiments, the operator may adjust a cancellation band so that some frequencies are not cancelled. For example, the operator may adjust the cancellation band so that a co-worker's voice may be heard.
