Showing papers on "Microphone published in 1969"

Wavenumber‐Frequency Spectra of Turbulent‐Boundary‐Layer Pressure Measured by Microphone Arrays

Abstract: Measurements of frequency spectra of smooth‐wall pressures have been made by single microphones and by a longitudinal array of four flush 0.8‐in. circular microphones connected with alternating and with common phase. The microphones were selected to suppress high wavenumbers. The measured levels set upper limits on low‐wavenumber boundary‐layer pressure. The array was designed to suppress, by its wavenumber filtering, the background acoustic duct noise at frequencies near 3 kHz. Analysis indicates that a very high phase‐speed low wavenumber pressure field dominates near this frequency. At low frequencies, single‐microphone and array spectra are dominated by the convective wavenumber component of boundary‐layer pressure and satisfactory agreement is found with theoretical predictions. [This work was supported by the Acoustics Branch of the Office of Naval Research.]

Electronic musical instrument employing mechanical resonators with regenerative effects

Abstract: A performance embellishing sound reproduction arrangement comprising an electric loudspeaker, an electric resonance device secured to the chassis of said loudspeaker in contact therewith and having a microphone and a plurality of strings tuned to selected different audiofrequencies to resonate sympathetically whenever a musical production reproduced by the loudspeaker sounds the frequencies to which the strings are tuned, and circuitry for feeding the electric signals derived from the microphone of the resonance device back to the same loudspeaker, or to a second loudspeaker located within the range of audibility of the first-mentioned loudspeaker.

Ambient noise suppressor

Abstract: Signals from a desired source, such as a person speaking, are enhanced relative to unwanted ambient sound by a speech processor that includes an array of microphones arranged at equal distances from the desired source. The unwanted sound, being ''''off-center, '''' arrives nonconcurrently at the individual microphones. The processor continuously arranges the instantaneous microphone outputs in order of their relative energy contained, and selects as its output some one of the microphone outputs that is intermediate in the instantaneous ranking.

Signal Processing for a Cocktail Party Effect

Abstract: A binaural listener has the ability to concentrate on speech from a particular location while suppressing speech from other locations (binaural cocktail party effect). Similarly, an array of microphones can be used to achieve an enhancement of intelligibility coming from a particular (on‐center) location. This paper discusses various processing schemes for the microphone outputs in order to achieve this discrimination. In particular, one nonlinear process, studied using an analog system employing subtraction, full‐wave rectification, and addition, results in reproduction of the on‐center speech without change, and in distortion and reduced level of an off‐center speech source. Because of the distortion, the suppression appears to be greater than for linear processing. In addition, this process eliminates completely any off‐center impulsive noise which is nonoverlapping at the four microphones. It has been pointed out that this process is equivalent to an instantaneous selection of the two microphone outpu...

Self-supporting headset

Abstract: A self-supporting headset is disclosed with a housing adapted to accommodate a receiver and microphone. The headset housing comfortably supports itself on the upper portion of an ear of the user. A flexible acoustic tube together with an adjustable voice tube are mounted on an upper portion of the housing forward of the user''s ear. The acoustic tube curves backwardly to provide communication between the auditory canal of the user''s ear and the receiver through a tube along the inner periphery of the housing. The voice tube provides communication between the user''s mouth and the microphone. Electrical signals are carried to and from the microphone and receiver through a pin and socket connection together with a strain relief collar device mounting a lead wire cable to the housing.

Hearing aid construction utilizing a vented transducer compartment for reducing feedback

Abstract: A hearing aid construction in which the rigid hearing aid case is divided into at least two closely spaced compartments with a microphone mounted in one compartment and a output transducer mounted in the second compartment and further comprising means for venting acoustical pressure waves within the second compartment to substantially reduce the acoustical coupling between the output transducer and the microphone positioned nearby within the rigid case.

System for producing musical tones

Abstract: Prerecorded notes of a musical instrument are stimulated to play by means of a voice-responsive system or instrumental equipment. Magnetic as well as electro-optical storage and retrieval systems are provided in conjunction with control circuit operated by a microphone or other input to convert a voice or keyboard signal, for example, into an output, as from a speaker, wherein the output is in the form of instrumental music.

Wireless microphone and adapter kit

Abstract: A wireless microphone assembly is disclosed which uses a frequency modulated transmitter having improved radiation characteristics and eliminates the need for a separate external antenna. An adapter unit is disclosed as being connectable to a conventional microphone with the adapter unit including a transmitting oscillator having its input circuit coupled with the conventional microphone output circuit via plug connectors and with the output circuit of the frequency modulated oscillator being connected via a grounding terminal to the case of the conventional microphone. The case of the conventional microphone then acts as a radiating antenna giving rise to high strength signals without the need for any protruding antenna arrangements. Mechanical construction details as well as schematic circuit diagrams are provided.

Piezoelectric pressure transducer with acceleration compensation

Abstract: Disclosed is a microphone in the form of a piezoelectric pressure transducer for detecting high intensity noise. The microphone incorporates a lightweight endpiece, preferably of beryllium metal, having a cavity for receiving an acceleration compensation weight. A preloading sleeve is attached at one end to a support while its other end is slipped over a portion of the endpiece and secured by a retaining ring. The microphone is provided with a separate compartment for housing an electric circuit receiving the output from the preloaded quartz crystals of the transducer.

Diagnostic cough-monitoring techniques

Abstract: The rate at which a human subject coughs may be determined by providing a microphone, a transmitter connected to the microphone, a receiver, a counter, and a conditioning circuit that enables the counter to advance in response to a cough sound.

Acoustic measurements in supersonic transitional boundary layers

Abstract: : Surface pressure fluctuations associated with transitional and turbulent boundary-layer flows on a sharp, slender cone at supersonic Mach numbers were experimentally investigated in a 40- by 40-in. supersonic wind tunnel using a flush-mounted 0.25-in.-diam microphone. The results at Mach numbers 3 and 4 demonstrate the feasibility of locating microphones onboard wind tunnel test models to measure overall pressure fluctuations and power spectral distributions in transitional and fully developed turbulent flows. Transition Reynolds numbers determined using a surface microphone are compared with two other established methods of detection. Selected boundary-layer pressure fluctuation characteristics (power spectral density and root-mean-square values) and transition profiles are presented. Methods of data acquisition and analysis are discussed.

Push-pull moving coil loudspeaker having electromagnetic centering means

Abstract: An electrodynamic acoustic transducer such as a loudspeaker or microphone in which the datum or center position of the diaphragm is determined by two coils. The coils are fixed to one another and to the diaphragm and cut magnetic fields. Datum currents are provided for the coils and the coils are of non-uniform density of winding and/or the magnetic fields are non-uniform. The coils and the datum currents are arranged to provide balanced forces on the coils only when the diaphragm is in the datum position.

Audio signal processor

Abstract: The output signal from a microphone is fed through a preamplifier to a variable attenuator and then to an automatic volume control (AVC) circuit. A voice operated switch is connected between the output of the microphone preamp and the attenuator and activates the latter when the output signal from the preamp falls below a predetermined minimum amplitude to introduce signal attenuation at the same rate as gain is increased in the automatic volume control circuit to thereby eliminate induced noise surges during periods of silence or low amplitude input into the microphone. The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

Body-attached switch means and holder for a microphone

Abstract: Presently disclosed is a microphone mounted on a support which is suspended from the user''s neck. An on-off switch for the microphone carries a switch actuating member terminating in proximity of the user''s head to permit head movement to close the microphone control switch.

Binaurales Hören im nichtstationären diffusen Schallfeld

Abstract: The effect of auditory reverberation suppression is demonstrated quantitively in a preliminary experiment. This proves that the rooms appear to be about 30% more reverberant during microphone transmission than when the sound is heard directly. Psychoacoustic measurement methods, based on determining the perception-threshold of the amplitude-modulation of noise signals, are used to demonstrate that the effect of auditory reverberation suppression is a consequence of the binaurality of hearing. A signal-processing model has been developed to demonstrate the mechanism of binaural reverberation suppression. This signal-processing model has been simulated by means of an electronic correlator.

Switching circuit for cancelling the direct sound transmission from the loudspeaker to the microphone in a loudspeaking telephone set

Abstract: A loudspeaking telephone set wherein a pair of gates are respectively disposed in the transmit and receive channels for the purpose of simultaneously enabling and disabling the same at a high frequency rate. A frequency control circuit adjusts this high frequency rate so that the pulses of direct sound energy from the loudspeaker arrive at the microphone just at the time that the microphone transmit channel is disabled. The undesired direct sound transmission (i.e., direct acoustic feedback) is thus cancelled out.

Some Investigations on Output Level of Microphones in Air Streams

Abstract: Investigations were made of the relation between different physical properties of a microphone in an air‐stream and the sound pressure and pressure fluctuations caused by turbulent flow. The theoretical formula for the turbulent fluctuated pressure is deduced by considering small variations of flow in a quasistationary flow tube under a low magnitude condition for percentage of turbulence. Measurements were made in a wind tunnel using condenser microphones and probe microphones of various diameters. One of the probe microphones produced an output level in good agreement with the theoretical value. Another probe microphone, which has four tiny holes located on the side wall of the tube, produced an output level 24 dB below the theoretical value. A convenient theoretical expression of the microphone output level in the airflow is obtained by assuming random incidence of the pressure fluctuation on the microphone diaphragm by an analogy with sound waves. The results obtained are in reasonable agreement with ...

Transducer apparatus and transducer amplifier system utilizing insulated gate semiconductor field effect devices

Abstract: A transducer apparatus wherein the source to drain conductance of an insulated gate semiconductor field effect device is modulated by the application of mechanical stress to the channel layer of the device. Specific transducer modifications include microphone pickups and phonopickups. The pickup may include preamplifiers in either discrete or integrated circuit form.

Microphone for digital speech transmission

Abstract: An arrangement for transforming mechanical or acoustical waves into digital electrical signals is disclosed. The arrangement includes a converter which in principle is a condenser microphone having a diaphragm which is flexible and electrically biased. Also included is a plurality of switching elements (FET''s) disposed in a stiff plate which forms a portion of the condenser microphone and arranged so that they are electrically actuated by the electric field associated with the diaphragm depending on the distance of the diaphragm from an individual switching element. Sampling circuits associated with each of the switching elements apply the outputs of the switching elements to a coding matrix and a binary output representative of the condition of the switching elements at any instant is provided. The arrangement of the switching elements along the radius of the diaphragm and the use of exclusive OR circuits in the sampling circuits are also disclosed.

Spectacle hearing aid with crossover signal routing

Abstract: A spectacle hearing aid for directing sound signals from the side of a patient''s head having a severe hearing loss to the side having normal or near normal hearing. The apparatus includes a microphone in one of the templar members of the spectacles for converting sound energy to electrical impulses and a conductor assembly adhesively bonded to the rear of the spectacle frame in a position extending transversely above the spectacle lenses. One end of the conductor assembly is connected to the microphone. The other end is connected to means for converting electrical impulses back to sound energy. In one application, the microphone is provided in one of the templar members. The ear with normal or near normal hearing is fitted with the templar member containing an amplifier. Provision is made for sound to enter the good ear in a normal manner and in addition to receive amplified sound from the other side of the head. In another application, microphones are provided on both sides of the head for receiving and amplifying sounds on both sides of the head and for transmitting the resulting amplified sound to the good ear.

First‐Order Gradient Microphone Based on the Foil‐Electret Principle: Discrimination against Air‐Borne and Solid‐Borne Noises

Abstract: Design and performance of a simple first‐order pressure‐gradient microphone based on the electrostatic principle using foil electrets are discussed. Such a microphone discriminates against air‐borne noise as well as against solid‐borne vibrations transmitted through the microphone case. For air‐borne sound originating from a spherical sound source positioned close to the microphone, the frequency response is flat within ±3 dB in the frequency range 0.1 to 3 kHz with a sensitivity of about −50 dBV/μbar in the direction of the microphone axis. In a plane sound field, the microphone exhibits the typical first‐order gradient behavior, i.e., its sensitivity rises proportional to frequency over most of the mentioned frequency range. At 0.1 and 1 kHz, the plane‐wave sensitivity is 30 and 10 dB, respectively lower than the sensitivity to sound originating from a nearby source, making this microphone a noise‐discriminating device for close‐talking applications. Rejection of solid‐borne vibrations is due to the lightness of the foil‐electret diaphragm. Compared with electrodynamic and electromagnetic transducers, the foil‐electret microphone responds 30 to 40 dB less to solid‐borne vibrations, referred to equal output for air‐borne sound.

Ship's warning system

Abstract: A SHIP''S WARNING SYSTEM FOR DETECTING VESSELS APPROACHING IN THE FORWARD SECTOR BY ANALYZING SOUNDS RECEIVED BY A PLURALITY OF FORWARD-LOOKING MICROPHONES. SOUNDS ARRIVING FROM ASTERN ARE DETECTED BY AN AUXILIARY MICROPHONE. THE SIGNALS FROM THE VARIOUS MICROPHONES ARE SEQUENTIALLY SAMPLED AND AMPLIFIED IN AN AUTOMATIC GAIN CONTROLLED AMPLIFIER IN WHICH THE GAIN IS LIMITED BY THE AMPLITUDE OF THE LARGEST RECEIVED SIGNAL. RELATIVELY INTENSE SOUNDS FROM THE FORWARD SECTOR ARE AMPLIFIED AND ACTUATE AN ALARM. RELATIVELY INTENSE SOUNDS FROM ASTERN AFFECT THE AUXILIARY MICROPHONE MOST STRONGLY AND REDUCE THE GAIN OF THE AMPLIFIER SO THAT THE CORRESPONDING SIGNALS FROM THE FORWARD-LOOKING MICROPHONES CANNOT ACTUATE THE ALARM.

Transmit only acoustic coupler

Abstract: A transmit only acoustic coupler for semipermanent attachment to the microphone cover of a telephone handset, permitting selective transmission of live voice or recorded voice and/or tone encoded data, includes a hearing aid type of dynamic speaker with no back venting, and a valve arrangement adjustable between open and pneumatically sealed positions.

Use of Probe Microphones to Measure Sound Pressures in the Ear

Abstract: The usual techniques employed when probe microphones are used to measure sound pressures at the eardrum are shown to give results with a best accuracy of ±10 dB in the frequency range 10 kHz–30 kHz. Both the size of the ear cavity and the position of the probe within it affect the output from the microphone.

Radio transceiver with variable audio amplification

Abstract: A radio transmitter, especially for vehicular two-way communication, has a fixed unit including an amplifier system and a detachable handset containing a microphone which can be rendered operative by pushing a press-to-talk button. A second, independent switch is operable to turn on the microphone with an increased gain of the amplifier system to enable message transmission without removal of the landset from its hook.

Dynamic Moving Coil Microphone.

Abstract: 1,173,623 Moving coil microphone ELEKTROAKUSZTIKAI GYAR 14 Feb, 1967 [14 Feb, 1966], No 7109/67 Heading H4J In a moving coil microphone in which the moving coil 4, Fig 1, is mounted between the resilient brim and a dome 1 of a diaphragm, and wherein the chambers adjoining the resilient brim are acoustically coupled through a passage, the acoustic impedance Z of the passage which may comprise a number of radial recesses 7 in the annular diaphragm seat 6 is at most as great as the net acoustic impedance Zb acting directly on the dome, this being that due to chamber 9 as modified by chamber 18 and its acoustic filling 14 and that due to the inlet apertures 20 and chamber 3 It is secondly stipulated that the acoustic impedance Zb should not exceed twice that of the annular air gaps between the moving coil and the yoke 10, and the moving coil and the core 11 In a modification in which the coil is mounted on a cylindrical carrier, the carrier is extended to make the length of the gap at least 3l/2, where " l " is the length of the coil The carrier may be integral with the rim or the dome Electrical networks corresponding to the arrangements are described with reference to Figs 2, 4 and 5 (not shown)

Mechanism and method for measuring sound absorption

Abstract: An electromagnetic tone generator transmits a tone burst comprising sound waves of known wavelength and intensity into one end of a tube, the other end of which tube is fitted against the surface of a material which reflects the sound waves back along the interior of the tube with a reduction in intensity proportional to their loss of acoustical energy. A microphone is exposed interiorly of the tube at a known distance from each end of the tube. Electronic time delay and gate circuitry feed into a monitoring circuit the electrical oscillations from the microphone produced by a selected series of clear sound waves of the original and the reflected sound bursts for a comparison of amplitudes.

Hand microphone for sound recording and reproducing instruments with ac switching

Abstract: A hand microphone for use with sound recording and reproducing instruments and including a control portion from which various control functions can be initiated in the instrument, one of which control functions involves switching an alternating voltage circuit, the unit for switching such circuit including a transistor having its collector-emitter path connected in series in such alternating voltage circuit and a mechanically stationary electronic switch connected to the base of the transistor for applying thereto, when the electronic switch is closed, a bias voltage which causes the transistor collector-emitter path to conduct current in both directions.

Underwater microphone testing device

Abstract: This invention pertains to an apparatus and method of objectively testing microphones mounted in diving masks as an integral part thereof. The apparatus comprises an especially made manikin, a pressurized chamber, a source of recorded audio test signals, and an indicator device.