Abstract: In a hearing device, such as a circumaural earmuff cup or a circumaural earphone cup, either of which comprises an earpad assembly in contact with the external ear, through which sound is conducted to the external ear for the purpose of providing at the eardrum a sound pressure having a prescribed ratio with respect to the sound pressure at a source, the invention comprising a predetermined sound leakage path through said earpad assembly, to reduce the variable in said ratio, that is customarily encountered caused by the variations in the shape of the external ear from one user to another and by variations in position and force of contact of the earpad resting against the pinna.

Abstract: 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.

Abstract: A combination ear protector and communications headset particularly adapted to the rugged, lightweight, convenience needs of aircraft ground crew members. The headset includes a noise cancelling microphone mounted directly on the headband where disposition either before the user's mouth or in an out-of-the-way on-top-of-the-head position is possible. In the ear protection only mode of use, the headset is disclosed to be optimally clean and unencumbered, but is quickly and easily convertable to communications usage.

Abstract: A signal compression system includes a plurality of channels. A plurality of these channels include a bandpass filter (for filtering out all but a portion of an input signal), an intensity detector (for deriving a spectrally weighted estimate of the intensity of a broader spectral portion of the input signal than the bandpass filtered spectral portion), and a divider (for compressing the bandpass filtered spectral portion using a variable gain having a preselected functional relationship to the spectrally weighted intensity estimate). The signal compression system preserves cross-channel information.

Abstract: A hearing protective device consisting of a headset having opposite earmuff and/or earplug assemblies resiliently connected by a headband assembly including a normally open power switch closed when the headband assembly is put on the user's head. The switch controls the energizing of the electrical circuitry of the device. Each earmuff and/or earplug assembly has an outwardly-facing microphone and an inwardly-facing sound reproducer, connected to circuitry defining respective stereo channels, each channel including preamplifier circuitry and a respective power amplifier drivingly connected to one of the sound reproducers. The circuitry also includes a hyper AGC circuit which receives and sums signals from the amplifier chain and derives attenuation signals therefrom which are fed back to the amplifier circuitry and which reduces the gain of this circuitry when the input sound exceeds a certain level.

Abstract: Apparatus for improving the audibility of incident sound (4) to a person (3) operating in an environment where there is a substantial background noise field (2) coming from a source (1) of repetitive noise, comprises an adaptable waveform generator (7), a first electro-acoustic transducer (10) receiving a synthesized cancelling waveform from the generator (7) and generating a cancelling noise to at least partly null the background noise, a second electro-acoustic transducer (11) to sense the partially nulled background noise, and adaptor (13) to modify the output of the generator (7) on the basis of the electrical output signal from the second transducer to minimize the nulled background noise, and sensor (5) to feed a triggering signal (6) derived from the source to the waveform generator. The electro-acoustic transducers (10, 11) can be mounted in headset (8) holding the transducers adjacent to an ear of said person without substantially impeding the arrival of said incident sound (4) to said ear.

Abstract: A protection circuit for limiting the sound pressure level provided by transducer loads, such as headphones, in which there is provided interconnections between the input to the transducer load and the transducer load such that when loudness exceeds a predetermined limit, the connection to the transducer load is opened and the circuit turns off the audio signal to the transducer load and optionally illuminates an LED. After a predetermined time interval, the circuit automatically resets; however, if the sound pressure level has not been reduced below the predetermined limit, the circuit again immediately turns off the audio signal to the transducer load and this is continued until such time as the sound pressure level is reduced below the predetermined limit.

Abstract: A sound detecting device for amplifying distant or weak sounds, including a novel loud sound suppressing circuit for temporarily shunting the amplifier input signal to ground whenever the amplifier output signal exceeds a predetermined amplitude. The microphone, amplifier, and sound suppressing circuit are mounted in a wand shaped much like a flashlight. The wand can be attached to headphones.