Abstract: A noise controlled type handset processes the output of non-directional noise detector installed outside of the handset by a first adaptive filter, delivers a control sound from a control speaker, controls the first adaptive filter so that the output of an error detector near the ear may be small, simultaneously processes the noise detection signal in a second adaptive filter, subtracts from the noise signal mixing into a bi-directional talking microphone, and controls the second adaptive filter so that the subtraction signal may be small, thereby taking back the signal of voice only by reducing noise by delivering through the speaker, and sending a transmission output at the same time.

Abstract: A cordless, wireless headset to block unwanted sound waves and/or noise from entering the ears of a user. The headset (FIG. 5) contains an electronic receiver, an audible tone/alert generator, volume control/switch and battery. The wireless headset would permit freedom of movement during sleep without danger of being entangled by cords/wires. The wireless headset would be secured to the ears and head of the user while sleeping by a Top head-strap, a Rear head-strap and Chin-strap. Referencing FIG. 1, the wireless headset will receive and interpret signals from remote sound sensor(s) and/or motion detection sensor(s). Remote sensor(s) would transmit radio signal(s) to the headset when an unwanted sound or motion is detected. The signal would be received in the wireless headset and an audible tone would be generated in the ear of the user, to alert of an important event.

Abstract: A selected electrical signal is first applied to the input of a source (30) to determine at least the impulse response (H), over a predetermined time, between the source output and the input of sensors (20). The values of the active cancellation control signal are determined in real time according to a predetermined law established in accordance with the previously determined impulse response (H), whereby the energy of the output signal from the sensors is minimised. The acoustic structure (2) is arranged so that the space (534) containing the sensors (20) and the source (30) is invariant at least during the determination of the active cancellation control signal and in the presence of a person, whereby the impulse response (H) between the output of the source (30) and the input of the sensors (20) may remain invariant.

Abstract: The system is designed for the purpose of providing a means of conducting objective assessment of the actual or "real world" attenuation which is provided by insert-type hearing protection (IHP) devices. A device is constructed to serve as the input device to any commercially available noise dosimetry instrument or sound level measuring device. A miniature microphone is mounted on, or embedded in the proximal surface of the IHP which is to be inserted in the ear or upon the ear of the user. The miniature microphone is hard wired to a miniature jack which is mounted on, or embedded in, the distal surface of the IFP device. A cable connects to the jack on the outside of the IHP device and to the input of the noise dosimetry instrument or sound level measurement device. Thereby, when the IHP device containing the above is used, the dosimetry or sound level measurement instrument conducts assessments of actual sound levels to which the hearing mechanism is exposed when IHP devices are in use.

Abstract: The invention relates to a headset (1) for a hearing protector provided with a padding part (12) having an essentially elliptical ear opening (18). The headset comprises a microphone (2), an earphone (3), and conducting wires (7) for bringing signals to the earphone (3) and from the microphone (2). According to the invention the earphone (3) is attached to a bow part (10) whose contour essentially follows the external dimensions of the hearing protector padding (12), and a mounting wing (13, 4) is connected to the bow part (10) or the earphone (3) and has a maximum dimension (A) which is smaller than the maximum dimension of the ear opening (18) and yet greater than the minimum dimension (B) of the ear opening (18), and during use the maximum dimension of the mounting wing (13, 4) is essentially horizontal.

Abstract: An active plus selective headset system for provision of active attenuation of broadband noise as well as speech filtering comprising a headset with reference microphones, residual microphones and speakers on each of a pair of open backed muffs and a controller means.

Abstract: A transducer/transmitter captures not only the acoustic signal in the voice band, as in the prior art, but also an acoustic signal that includes audio signals outside the voice band; preferably above the voice band, up to approximately 20k Hertz. A band pass filter separates the transducer signal into two components; a voice signal with overlapping noise in the range of the human voice (e.g. from about 40 Hertz to 8k Hertz) and a component that provides a no voice signal, for example a signal in a no voice band extending from above approximately 8k Hertz to about 20k Hertz.

Abstract: A method for designing a frequency periodic filter with a frequency response which has a periodic bandwidth including designing a first sampled data filter whose response corresponds to a set period and replacing each unit sampling delay by a second sampled data filter.

Abstract: A noise suppressor includes an input transducer and an output transducer adapted to be located in an ear canal. A housing is provided to support the transducers in the ear canal, and the housing provides an acoustically unobstructed passage from the entrance of the ear canal to the ear drum. The input transducer generates electrical signals in response to sound pressure waves entering the ear canal, and a portion of the electrical signal is processed to generate an inverse noise signal which is applied to the output transducer. Accordingly, the output transducer produces inverse noise pressure waves in order to reduce an undesired noise portion of the sound pressure waves reaching the ear drum. The sound pressure waves also reach the ear drum without significant alteration.

Abstract: A method and apparatus for active cancellation of vibrational noise produced by a medical instrument in the head of a patient. Vibrations from the instrument, as well as vibrations in the bone structure in the head of the patient, are sensed and processed to generate cancelling noise waves which are then fed into the inner ear through vibrators placed on the head of the patient. An equalizer shapes the magnitude and phase spectrum of the vibrational signal picked up from the drill and delivers the equalized vibrational signals to the patient. An automatic adaptive controller adjusts the equalizer using control signals consisting of vibrations from the bone structure and the drill.

Abstract: An active noise reduction headset including a headband and at least one earcup secured thereto. A microphone is mounted within the earcup for detecting and transducing acoustic pressure within the earcup to a corresponding microphone electronic signal. An electronic signal processing unit is mounted within the earcup and coupled with the microphone for generating an anti-noise signal from the microphone electronic signal. A first speaker is mounted within the earcup for receiving and acoustically reproducing an electronic anti-noise signal from the electronic signal processing unit. A second speaker is mounted within the earcup for receiving and acoustically reproducing an electronic communication signal.

Abstract: A headphone includes an acoustic pipe, a loudspeaker unit, a microphone unit and a feedback circuit. The acoustic pipe has an inner diameter substantially equal to that of an external auditory canal. The acoustic pipe has a mounting portion provided at an end thereof for being mounted on the outer ear and has an acoustically non-reflective end at the other end thereof. The loudspeaker unit is provided on one side of the acoustic pipe with a sound emitting face thereof opposed to the inside of the acoustic pipe. The microphone unit is provided on the one side of the acoustic pipe with a sound collecting face thereof opposed to the inside of the acoustic pipe. The feedback circuit feeds back an output signal of the microphone unit to an input side of the loudspeaker unit. The feedback circuit includes an equalizing section. The output signal of the microphone unit is supplied to the loudspeaker unit by way of the equalizing section.

Abstract: A method of and an apparatus for controlling noise generated in a confined space, being capable of reducing a radiating sound pressure generated from a main noise source to that of an optimal state. The method includes the steps of measuring the radiating sound pressure generated from the noise source, and generating, from an additional sound source, a radiating sound pressure having the same magnitude as the radiating sound pressure generated from the noise source while having a phase 180.degree.-shifted from that of the noise source's radiating sound pressure so that the radiating sound pressures can offset each other when they are mixed.

Abstract: An active in the ear hearing protector having an ear piece (13) and a casing (12) attachable to the ear piece, the ear piece being positionable in the ear canal of a user so as to peripherally acoustically seal the ear canal and such that the attached casing (12) is positioned externally of the ear canal. The casing (12) incorporates a microphone (14) for receiving external acoustic sound signal and a signal processing circuit (15) for receiving electrical signal from the microphone and correspondingly causing a loudspeaker (16) in the casing to generate sound signal for direction down a tube (34) extending through the ear piece to be transmitted to the ear canal. The electrical circuit (15) is arranged to limit the electrical signal delivered to drive the loudspeaker whereby to limit the sound pressure of sound signal delivered from the loudspeaker to the ear canal via the tube (34).

Abstract: The electronic stethoscope is designed to minimize the influence of the various types of noise while optimizing auscultation of the sounds of interest, and to enable a cardiologist to auscultate mechanical heart valves. It comprises a probe for sensing sounds of interest produced within a patient's body and for converting these sounds to an electric signal, and an audio amplifier and earphones for reproducing the sounds of interest in response to this electric signal.

Abstract: An ear defender having one or more microphones (1) for detecting the sound level in the proximity of the wearer's ear, one or more speakers (4) for generating a noise reduction signal within the earshell, and a digital feedback controller (W) for generating a feedback signal derived from the output of the microphones and for applying said feedback signal to the speaker inputs, and estimation means (F') for providing an estimation of the earshell transfer function and subtracting from the input to the feedback controller a signal representing the estimated electroacoustic transfer function of the system. The operation of the digital feedback controller may be controllable by the output of a computational circuit (C) operable on the difference between the microphone output and the feedback controller input modified by a model (F") of the electroacoustic transfer function.

Abstract: An adaptive multi-channel active acoustic attenuation system is provided for attenuating complex acoustic waves. The system includes a plurality of input sensor nodes and a plurality of error sensor nodes. Each node includes a central processing unit and a network interface. A medium physically interconnects each of the network interfaces to a communication module of a controller by means of a control bus or the like. A control network is provided for controlling communication between a communication module of a controller and each of the network interfaces to control the flow of data along the medium.

Abstract: A method and apparatus for active cancellation of vibrational noise produced by a medical instrument in the head of a patient. Vibrations from the instrument, as well as vibrations in the bone structure in the head of the patient, are sensed and processed to generate cancelling noise waves which are then fed into the inner ear through headphones or through vibrators placed on the head of the patient. An equalizer shapes the magnitude and phase spectrum of the vibrational signal picked up from the drill and delivers the equalized signal to the patient. An automatic adaptive controller adjusts the equalizer using control signals consisting of vibrations from the bone structure and the drill.

Abstract: An ear device protects a user from damaging sound levels while permitting the user to hear and understand conversation in a noisy environment. The device includes an enclosure system for at least partially isolating the user's ear drums from ambient sounds, at least on directional microphone, an adaptive band pass filter and a speaker. The adaptive band pass filter further includes adaptive high pass and adaptive low pass filters which adaptively and independently control the range of the pass band depending upon the characteristics of the noise in the user's environment. A speaker transmits the processed signal to the user. The adaptive filter also includes a detector connected to receive the processed signal which controls the gain of the system to prevent overcompression of the audio signal. The adaptive filter further includes an adaptive compression circuit utilizing multiple time constants to control the response time of the adaptive filter under various conditions.

Abstract: A reception volume limiting circuit includes a detecting section, an A/D conversion section, a control section, and a speech data calculating section. The detecting section performs detection/rectification and smoothing of a receiver driving AC signal and outputs a DC signal corresponding to the level of the receiver driving AC signal. The A/D conversion section converts the DC signal into a digital signal. The control section calculates a time average value by averaging the digital signal every predetermined time interval, adds the currently stored attenuation amount to the time average value, and compares the time average value with a predetermined threshold value representing a critical sound pressure for protection of listener's hearing.

Abstract: A noise cancellation module is combined with a telephone handset or article of headwear to cancel a selected frequency or range of frequencies so as to enable a user to better use the handset and function with the headwear in place.

Abstract: An improved audio system designed to maintain a desired sound at the ear of a listener by using an equalization filter (2). The equalization filter (2) is continuously adjusted in response to the signal (9) from a sensor (8) which monitors the sound close to the listener's ear. The audio system can be combined with an active noise control system (3) to reduce interference from external noise.

Abstract: A headphone assembly for an active noise cancellation system has a rigid moulded plastics shell having a rigid baffle dividing the shell interior into a front volume and a closed rear volume, both of which may be filled with an acoustic foam. The baffle has a central opening in which is mounted a headphone transducer, and a seal cushion is disposed around the mouth of the shell, to effect an air-tight seal against the user's head. The headphone transducer has two effective sound radiating surfaces of different sizes, and may be constructed as a form of orthodynamic drive unit. In the latter case, the orthodynamic drive unit diaphragm may have two separate coils of different radial extents.

Abstract: A frequency selective hearing protection device and method utilizes adaptive filtering to hinder transmission of frequency components in ambient sound above a preselected threshold level. Sound frequency components which are not above the threshold level, such as normal speech, are allowed to pass. Electrical analog signals produced by a transducer are converted to a stream of digital input signals. The digital input signals are applied to a digital filter such as an FIR filter implementing a time domain difference equation. As a result, digital output signals are produced which are reconverted to analog output signals and applied to an actuator to produce audible sound. To adjust the frequency response of the invention to suppress gain at frequency components above the threshold, windows of input and output data signals are first assembled. Respective frequency domain transforms such as fast Fourier transforms provide spectrums representative of frequency component amplitudes.

Abstract: Telephone headsets used by operators and airline pilot headsets are subject to substantial amounts of interfering ambient noise which detract from the intelligibility of incoming speech. Noise reduction circuitry does not altogether eliminate the interfering sound. A headset speaker and error microphone housing are disclosed which enable a greater amount of unwanted noise elimination. The speaker and microphone are configured closely with respect to each other and also to the user's ear. They are acoustically isolated in their own chamber. The microphone is located approximately on the speaker axis and protrudes substantially into the user's ear; and also is disposed close to the speaker cone surface. Additional acoustical tuning features include venting ports in the housing, and acoustic damping padding at the microphone entrance and on either side of the speaker. These expedients enhance the ability of the noise-cancelling circuitry to effectively reduce the undesired noise heard by the user.

Abstract: An earphone for use in an active noise reduction system includes a shell accommodating a microphone closely adjacent to a driver shaped and sized to fit in the concha of an ear.

Abstract: An audio frequency compressing system for amplifying an input signal to produce a power output signal while removing high-level signals which could harm a listener. Gain control in the feedback path of an amplifier includes both a gain controller circuit for supplying a constant feedback impedance and a plurality of resistors which can be coupled to the gain controller circuit to increase or decrease the feedback impedance. Coupling of the resistors to the gain controller circuit is controlled by a feedback control circuit having both an automatic gain control circuit and a continuous high-level protection circuit.

Abstract: Detection of higher order mode transverse modal energy is suppressed for an acoustic wave propagating longitudinally through a duct. First and second microphones are placed in respective first and second nodal planes of the second higher order mode, and the outputs of the microphones are summed. For the first higher order mode, the output of the first microphone is equal in amplitude and opposite in phase to the output of the second microphone, and the resultant sum is zero. For the second higher order mode, the output of each of the first and second microphones is zero, and the resultant sum is zero.

Abstract: An earphone device includes an acoustic tube having an inner diameter substantially identical to that of the external auditory canal has an ear mounting portion at one end and an acoustic non-reflecting portion at the outer end. An earphone unit and an internal microphone unit are mounted on the periphery of the acoustic tube adjacent each other and communicate with the interior of the acoustic tube with their respective vibration plates facing inwardly of the tube. The phase of the signal representing the external noise in the acoustic tube picked up by the internal microphone unit is reversed and combined with the audio signal fed to the earphone unit.

Abstract: The Active Sound Absorber of the invention is based on an electroacoustical transceiver defined as a bilateral electroacoustical transducer acting as both a diaphragm actuator and motion sensor, and an associated mutual inductance discriminator, in a electroacoustical positive feedback system. Selected embodiment of such a system is an unvented hearing aid where the Active Sound Absorber combats the occlusion effect.

Abstract: Disclosed is a headset apparatus for use in an intercommunications system, the headset suppressing both noise in the vicinity of a transducer delivering sound to an operator's ear and in outgoing speech from the operator.

Abstract: An earpiece has a structural configuration effective to removably interlock its outer surface contiguously to the outer ear auricle of the earpiece wearer. A microphone substantially exclusively receives, from the air of the external auditory canal, outbound voice sounds caused by the reverse modulation of the tympanic membrane when the earpiece wearer speaks. An outbound audio circuit is electrically connected to the microphone which converts the outbound voice sounds to electrical voice signals. The outbound audio circuit amplifies the outbound electrical voice signals to a preselected fixed level output gain and removes noise from the voice signals.

Abstract: A headset for acoustic reproduction of an electronic signal which electronic signal is representative of the summation of a desired audio signal and an anti-noise signal. The headset includes a headband, an earcup mounted to the headband, a driver mounted within the earcup which receives and acoustically reproduces the electronic signal, a directional microphone which detects and transduces the acoustical pressure within the earcup cavity, means for generating the anti-noise signal from the microphone signal, and a positioning member for mounting the microphone to the earcup in a position so that the microphone is acoustically coupled to the driver. The microphone is oriented so that its vented or open face is pointing towards the driver. If the driver is provided with an inner dome portion and an outer annulus portion the microphone is positioned by its attachment to a grille plate extending across the driver, the microphone being mounted to the grille plate on a side opposite the driver.

Abstract: An active acoustic attenuation system specifies the error signal (44) to correspondingly specify the output acoustic wave. In the preferred embodiment, the error signal (44) is specified by summing (210) the error signal (44) with a desired signal (204) to provide a specified error signal (206) to the error input (202) of the adaptive filter model (40) such that the model (40) outputs the correction signal (46) to the output transducer (14) to introduce the canceling acoustic wave which specifies the output acoustic wave such that a desired signal is present in the output acoustic wave.

Abstract: A device for performing electroacoustic functions including noise cancellation, communication interface, and headphone functions. The device includes a composite transducer which is connected to a control unit. The composite transducer, which is adapted for use with the human ear, includes: at least one input transducer for converting acoustic waves into electrical signals, and an output transducer facing the ear for converting electrical signals into acoustic waves. The transducers are oriented to be substantially coplanar to each other. The control unit includes circuitry for driving the output transducer based on electrical signals from the input transducer(s) with an amplitude and phase to perform the noise cancellation, sound filtering, communication interface, and headphone functions. The composite transducer includes a multiple baffle acoustic diffuser which performs frequency filtering, allows sound origin selection, and lengthens the paths of selected sounds entering the composite transducer.

Abstract: This invention is concerned with a device for reducing the external noise reaching the ear in extremely noisy places such as in the vehicle or construction sites. According to the present invention, the external noise in picked up by a microphone provided in the vicinity of an electro-acoustic transducer element, such as a headphone unit, provided in the vicinity of the wearer's ear, and the noise signal converted in this manner into electrical signals is produced as the acoustic signal by the electro-acoustic transducer element. The transfer characteristics and controlled in such a manner that the produced noise signal prove to be an acoustic signal which is of the same frequency spectrum and opposite in phase with respect to the external noise reaching the wearer's acoustic meatus from outside to reduce the external noise reaching the acoustic meatus.

Abstract: A device for performing electroacoustic functions including noise cancellation, communication interface, and headphone functions. The device includes a composite transducer which is connected to a control unit. The composite transducer, which is adapted for use with the human ear, includes at least three transducers, oriented to be substantially coplanar to each other: two oppositely oriented input transducers for converting acoustic waves into electrical signals, and at least one output transducer oriented facing the ear for converting electrical signals into acoustic waves. The control unit includes circuitry for driving the output transducer based on electrical signals from the input transducers with an amplitude and phase to perform the noise cancellation, sound filtering, communication interface, and headphone functions.

Abstract: In a talk/listen headset, essentially comprising two ear protection capsules (1, 2) connected to one another via a headband (3), two microphones (6, 7) are located in one of these along a vertical (9) which runs, projected on the head of the wearer, through the middle of the temporal bone and extends up to the mandibular angle. While the upper microphone (6) acts in the area of the end of the zygomatic arch, the lower microphone (7) is located in the area of the articular process of the ascending ramus of the jaw. Both microphones (6, 7) react to solid-borne sound and are piezoelectric resonators with a mass-forming body, an impedance converter and a filter/equalizer, the microphones being connected to one another in terms of voltage in order to absorb or compensate the local tone amplitudes to the bottom and to the top caused by the reproduction. This has the effect that this indirect reproduction of the voice is optimised in terms of tone and timbre.

Abstract: A device for performing electroacoustic functions including noise cancellation, hearing aid, communication interface, headset, feed for recording device, and headphone functions. The device includes composite transducers connected to a control unit. The composite transducers can be mounted on a headband and are configured to include input transducers for converting acoustic waves into electrical signals for processing by a control unit, and output transducers for converting the processed electrical signals to processed sound waves. The control unit includes an inverter/amplifier and a mixer/output amplifier for inverting the electrical input and controlling the gain for either adjusting the gain to maximize a noise cancellation function or increasing the gain beyond the minimum level heard by the ear to a desired level for a hearing aid function.

Abstract: 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.

Abstract: An audio compression system wherein the compression theshold may be adjusted to a calibrated level. The audio compression system is utilizable in a receiver system whereinan audio input signal received by the receiver system via a communications channel is applied to conditioning circuitry. The conditioning circuitry, in turn, provides a conditioned input signal to an acoustic transducer element for generating a corresponding audio output signal. The audio compression system compares the conditioned input signal and an initial threshold signal to provide a comparator output signal corresponding to the difference between the conditoned input signal and the initial threshold signal. The comparator output signal is provided as a control input to the conditioning circuitry. If the conditioned input signal exceeds the initial threshold signal for a preselected period of time, then the initial threshold signal is switched to a second threshold signal.

Abstract: Microphones sample the sound output from the speakers of a sound amplification system. The resulting time domain analog signals undergo a Fast Fourier Transform which yields frequency domain signals representative of the intensities of the frequency bands which compose the sound. The intensities or levels of each band are compared to stored permissible level limits for each frequency band. Attenuators respond to signals indicative of band levels being exceeded by respectively attenuating the frequency bands to which they are tuned so the speaker output does not contain frequencies which exceed permissible limits. The time weighted permissible averages for each frequency are also integrated to provide for production of signals representative of the cumulative sound dosage.

Abstract: A device for performing electroacoustic functions including noise cancellation, hearing aid, communication interface, headset, feed for recording device, and headphone functions. The device includes composite transducers connected to a control unit. The composite transducers can be mounted on a headband and are configured to include input transducers for converting acoustic waves into electrical signals for processing by a control unit, and output transducers for converting the processed electrical signals to processed sound waves. The control unit includes an inverter/amplifier and a mixer/output amplifier for inverting the electrical input and controlling the gain for either adjusting the gain to maximize a noise cancellation function or increasing the gain beyond the minimum level heard by the ear to a desired level for a hearing aid function.

Abstract: Improvement in active noise reduction based on a negative feedback electro-acoustical system which consists of an Electronic Earplug seated in the concha fossa combining active and passive noise reduction in the quiet zone at the ear, a bilateral transducer circuit which drives a speaker as an acoustical velocity source, a shunt feedback control filter network which improves stability and increases noise reduction, and a combined input noise-filter/feedback system. A typical application is in a noisy environment for hearing protection and for improved communication capability, e.g., in vehicular communication, telephone, intercom, hearing aids, and stethoscopes.

Abstract: A sound cancellation system wherein a pair of sensors and actuators are positioned immediately adjacent an associated ear of an inhabitant of an enclosure so as to provide a cancellation zone immediately adjacent an associated ear without interfering with adjacent zones. A controller receives a synchronization signal so as to cancel a selected noise associated with a synchronization signal. The sensors and actuators are mounted to a seat which is to be occupied by an inhabitant of the enclosure.

Abstract: A combination ear protector and communications headset particularly adapted to the rugged, lightweight, convenience needs of aircraft ground crew members that are required to work in a hazardous noise environment. The headset includes two earplug-type transducers that function as a combination ultrasensitive microphone and speaker which are automatically inserted into the user's ears when the invention is disposed for use, thereby sealing the interior of the ear from ambient noise. In the ear protection mode of use, the headset is quickly and easily convertible to communications usage.

Abstract: The effectiveness of electronic earmuffs is improved by incorporating a mechanism which causes the middle ear muscles to contract before an intense sound is generated. This contraction is achieved by incorporating a wireless receiver into the earmuff. Immediately prior to the generation of the intense sound, the wireless receiver receives a signal which causes it to generate a loud, non-damaging sound in a loudspeaker in the earmuff. The received signal is generated by a radio frequency transmitter that is activated immediately prior to the activation of the mechanism producing the intense sound. The non-damaging loud sound from the loudspeaker causes the middle ear muscles to contract (this is a natural reflex of the ear). The intense sound is received outside the earmuff before the reflex contraction of the middle ear muscles has been relaxed.

Abstract: 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.

Abstract: A protective earmuff which transmits normal sound levels and clips higher amplitude sound levels by causing an amplifier to go into saturation when the input signal is greater than a preset amount. The sound is received by a microphone, amplified and transmitted to the ear of the user by a speaker. The output of volume level is controllable independently of the clipping level. Also disclosed is a circuit allowing user control of both the clipping level and the volume level independently.

Abstract: A voice signal compression system wherein the compression threshold may be adjusted to a calibrated level. The system includes a variable gain amplifier for amplifying a voice input signal based on the application of a variable control voltage. A driver increases the power gain of the amplified input signal to provide a power-boosted output signal. In addition to applying the power-boosted output signal to an acoustic output transducer, the power-boosted output is also applied both to a peak detecting comparator and to a threshold reset timer. The comparator produces a digital output that triggers an attack/decay timing generator which produces the control voltage for the variable gain amplifier. The comparator initially is set to a high threshold state by the threshold reset timer. As the levels and peaks of the input signal increase, the comparator begins to trigger digital pulses to the attack/decay timer.