Showing papers on "Microphone published in 1972"

Bone conduction microphone assembly

Abstract: A bone conduction microphone assembly with a transducer mounted in a transducer mount supported from a surrounding support member by spring means which yieldably urges the transducer mount against the user''s head with predetermined pressure.

Orally operated electronic musical instrument

Abstract: Means forming an air channel is connected between the output of a loudspeaker and the input of a microphone. The output of the microphone is amplified by means of an amplifier, the output of the amplifier being fed to the speaker, an acoustical feedback path thus being formed between the speaker and the microphone. A mouthpiece is connected in this acoustical path such that an operator can determine the frequency of the feedback signal by adjusting the size of his oral cavity, thus forming musical tones.

Guitar,radio,microphone combination with self-contained energy source and amplifier

Abstract: A musical instrument which has a guitar, radio and microphone connected to a source of electrical energy and to a single amplifier. The main body of the guitar is hollow having a battery pack and radio mounted therein. A microphone is mounted to the main body of the guitar and is connected to the battery pack and to the amplifier of the radio. Means are mounted to the main body beneath the guitar strings for producing audio electrical signals in proportion to the sounds generated by the strings. The means are connected to the radio amplifier. Switches are mounted to the main body and are connected to the radio, microphone and means for allowing the musician to selectively connect the microphone, guitar and radio together for producing a combined sound through the radio speaker or alternatively for operating only the microphone or the microphone and guitar.

Apparatus for web tension measurement

Abstract: Tension in a web of paper is measured by exciting transverse vibrations in the web, by means of a moving coil loudspeaker, sensing the vibrations by means of a microphone, and applying part of the output of an amplifier; connected between the microphone and the loudspeaker, via a frequency-to-voltage converter, to a meter which is adapted to give a reading indicative of the web tension. The apparatus may be used as a portable device or fitted to a machine to control the braking torque applied to a reel of paper by comparing the signal from the converter with a reference signal, and using the resultant signal to control the applied braking torque.

Capacitance Microphone Dynamic Membrane Deflections

Abstract: In order to describe the operation of capacitance microphones accurately, it is necessary to have solutions for both the static and dynamic deflections of the moving electrode The authors have previously presented numerical solution approaches to the static deflections caused by the electrical biasing of the microphone The present paper describes an application of finite difference methods to the differential equations describing the dynamic membrane motion due to the acoustic excitation The solutions include the effects of the static deflections and the motion of the thin air film between the microphone's electrodes The numerical results are compared with published results for simplified stationary electrode geometries and with experimental data on more complicated geometries at different tension levels The predicted mode shapes and resonant frequencies change greatly depending upon the magnitudes of the membrane tensions and the back chamber volume

Hearing aid with valved dual ports

Abstract: A hearing aid casing having a plurality of sound conducting passages, preferably a forwardly directed passage and a rearwardly directed passage, each communicating through a "mixer" valve to a microphone interiorly of said casing; the valve may be operated to close either passage leaving the other open or to reduce the effective cross-sectional input of one passage while leaving the other open. The valve may support a sound filter in the sound path to the microphone; the passages may each be provided with filter plugs.

Microphone-speaker device

Abstract: A hand-held tape recording device comprising, within a casing, a reversible electro-acoustic transducer serving as both a microphone and a speaker which performs the functions of converting sound waves into electrical signals and electrical signals into sound waves, tape recording means connected to the transducer, and a concave elliptic sound reflector having first and second foci and juxtaposed to the reversible electro-acoustic transducer for directing sound waves to and from the transducer. The reflector has plural radial splits to facilitate variation in curvature thereof, and the device further includes means carried by the casing for moving the center of the reflector in a direction aligned with the axis of the reflector to vary the curvature of the reflector.

The Precision of Reverberant Sound‐Power Measurements

Abstract: Determination of sound power in a reverberation room is subject to a random error whose size can be estimated and controlled by the knowledgeable laboratory manager. Under ideal measurement conditions the random error can be expressed as a product of three factors: a frequency‐averaging factor governed by spectrum shape and room reverberation time, a spatial‐averaging factor determined by the number and separation of fixed microphones or the path shape and size for a traversing microphone, and a rotating‐diffuser factor depending on the size and shape of the rotating diffuser in relation to room size and reverberation time. Continuing progress in this field is teaching us to incorporate nonideal measurement conditions into our error estimates. In particular, we report progress in understanding the effects on random error due to (1) finite averaging time, (2) presence of a direct field component, and (3) insufficient modal overlap at low frequency.

Hands-free emergency telephone system

Abstract: An all weather emergency-reporting telephone call box employing a hands-free communication system is provided. The call box uses a speaker and microphone coupled through electronic circuits which provide hands-free operation for voice reception and transmission. The housing is formed of heavy material in a configuration selected to minimize the opportunity for vandalism. Direct communications access to the emergency station can be gained by opening a door which operates a micro-switch and prepares the system for hands-free operation.

Electronic stethoscope system

Abstract: A method and apparatus for the detection of heart sounds and fidelity reproduction for diagnostic purposes including a pick-up or sensing device which has an annular projection forming a pickup head with a cone-shaped interior and also has a dynamic microphone. The pick-up head has a lip configuration such that a frequency range of between 20 and 1000 cps can be detected with adequate intensity. A dynamic microphone operates a class ''''A'''' amplifier to provide amplification without signal distortion. Multiple distribution of detected sound is contemporaneously and simultaneously available to listeners, and at the same time the sound can be recorded on tape. Sound analysis with respect to frequency content and amplitude is made as well as comparison to predetermined heart malfunctions for clinical diagnosis.

Calibration of Condenser Microphones under Increased Atmospheric Pressures

Abstract: The sensitivity and frequency response characteristics of type‐L standard laboratory microphones were measured with an electrostatic actuator at surface and at 12 different levels to 31 atm absolute (ATA) in a hyperbaric chamber. The microphones were measured in compressed air and a helium‐air environment, with and without the capillary pin. In addition, one microphone remained at a depth of 31 ATA for 24 h to measure its stability under pressure. Results indicated a loss in sensitivity in compressed air and helium‐air as a function of pressure. In a compressed‐air environment a resonant peak occurred at 4000 Hz, which shifted to 8000 Hz in the helium‐air environment. The microphones showed extremely close agreement between compression and decompression, between different pressurizations, and between different microphones. Also, there was no change in sensitivity over a 24‐h period of pressurization at 31 ATA. Calibration data at several pressures are given.

Hearing aid with directional microphone system

Abstract: A hearing aid is depicted which has a highly directional microphone system comprising means defining a front-to-back acoustic conduit through the hearing aid and a microphone assembly supported in acoustic isolation within the conduit in such a way as to define a sound passageway around the microphone assembly. The microphone assembly includes an acoustically sensitive diaphragm and associated electro-mechanical transduction means. A housing for the microphone assembly has a front orifice communicating exclusively with one side of the diaphragm which presents a predetermined acoustic impedance to sound waves of predetermined audible frequencies propagating in the passageway. The housing for the microphone assembly also has a rear orifice which communicates exclusively with the opposite side of the diaphragm. The rear orifice is effectively spaced from the front orifice by a predetermined acoustic path length which is such that sound waves, at least those in low and middle ranges of audible frequencies reaching opposite sides of the diaphragm through the front and rear orifices in the microphone housing establish a pressure gradient across the diaphragm. The rear orifice has a predetermined acoustic impedance greater than the acoustic impedance of the front orifice and of such magnitude as to produce a substantially cardioid directional characteristic for the hearing aid.

Aircraft ground traffic control system

Abstract: Mounted on each airplane is a small waterproof loudspeaker that transmits a coded high frequency acoustic signal while the airplane is on the ground. A plurality of microphones are located along the runways, taxiing strips, ramps, and gate positions. The acoustic signals will propagate a limited distance so that only a near-by microphone will be activated thereby, thus making it very simple to continuously monitor the positions of airplanes on the ground. Each microphone is separately connected to a recognition circuit which in turn activates a corresponding display indicator. The indicators are arranged on a display panel in the form of a map of the airfield.

Apparatus and method for the measurement of acoustic absorption and impedance

Abstract: Apparatus and method for measuring the acoustical impedance and/or the absorption coefficient of materials of the class which exhibit nonlinear behavior at high sound intensities. A high-intensity biasing noise having a broadband spectrum and a low intensity pure sinusoidal tracer tone are introduced in combination into a standard impedance tube or standing-wave apparatus. The standing-wave pattern in the tube is measured by a pressure microphone probe movable along the axis of the tube. The tracer tone is retrieved by highly selective filtering and used to provide a measurement signal which corresponds to the response of the material. By sampling the standing wave pattern in the tube, the entire spectrum of the broadband noise response may be obtained.

Electrets in Miniature Microphones

Abstract: The electret capacitive microphone element is ideally suited for miniature applications. The simplicity of its structure leads to a straightforward design even in very small devices. Since the electret foil is the only moving element, and the foil‐back electrode spacing the only critical dimension, the electret cartridge is simple in design and extremely rugged. Careful design of the cartridge and associated preamplifier is required to minimize the microphone's self noise. The principal aspects of a miniature electret microphone design are discussed, including the cartridge and the preamplifier, and two examples of small omnidirectional microphones are given.

Acoustic feedback stabilization system particularly suited for hearing aids

Abstract: Linearity is increased and distortion reduced in a miniature acoustic amplifying system by providing an acoustically communicating passage between the microphone and speaker diaphragms to define a negative acoustic feedback loop for the amplifying system. The negative acoustic feedback is feasible because of the miniature arrangement itself of the microphone and speaker wherein the distance of the acoustic passage can be made a small fraction of the wave length of the highest frequency in a given frequency range to be amplified. An adjustment is provided for changing the acoustic coupling between the microphone and speaker diaphragms to thereby adjust the negative feedback loop. This adjustment can also serve as a volume control and the entire system is highly suitable for use in hearing aids wherein miniature microphones and speakers are utilized in close physical proximity.

Personal sound monitor

Abstract: A personal sound monitor wherein the sound is detected by a microphone and converted to a related electrical signal. The level of the signal is used to gate one of the plurality of levels in a scanning digital counter, the levels corresponding to various predetermined sound levels. The scanning counter controls the gating of various frequencies to an accumulating counter so that the total count is proportional to the integrated sound level to which the individual has been exposed.

Remote banking intercom system

Abstract: An intercom system for remote banking which facilitates communication between a teller terminal and a remotely located customer terminal. A two-way speaker is provided at the customer''s location and a separate microphone and a speaker are provided at the teller''s location. An amplifier in the communication path linking the two stations is connected such that normally its input is responsive to the customer two-way speaker with its output feeding the teller speaker, permitting the customer to talk to the teller. When the teller speaks into the microphone, and assuming his volume level exceeds a predetermined first level, the amplifier automatically switches to connect the teller microphone to the amplifier input and the customer two-way speaker to the amplifier output, permitting the teller to talk to the customer. When the level of the teller microphone signal falls below a second predetermined level which is less than the first level to permit the teller''s voice to drop without losing control of the direction of communication, the intercom system will switch to again permit the customer to talk to the teller. The system is additionally provided with a muting signal which disconnects the teller speaker whenever the ambient noise level at the customer''s location is high due to mechanical movement of a drawer or pneumatic carrier at the customer''s location.

Shock insensitive transducer

Abstract: A microphone with a transducer having a vibratal diaphragm at one end defining one of the walls of a diaphragm chamber and a shock mount diaphragm at the other end defining one of the walls of a cavity, the diaphragm chamber and cavity being acoustically interconnected, and the transducer being mounted on the microphone casing for translation along the axis normal to the diaphragm, the shock mount diaphragm being connected to the microphone casing, whereby a shock or vibration impressed upon the microphone casing with a component normal to the diaphragm changes the size of the cavity to produce a pressure which is transmitted to the diaphragm cavity to oppose inertial deflection of the diaphragm responsive to the shock or vibration.

Switching apparatus for single button hand microphone

Abstract: A microphone switching apparatus for operating a recorder. The apparatus is incorporated into a hand microphone housing having a speaker, a microphone element, and an opening through which a control button for the apparatus extends. The apparatus is generally made up of a multi-region magnet movable along a path relative to a number of reed switches. Switching positions lie along the path which is defined by a slot in the apparatus frame corresponding to the opening in the housing. The control button is connected to a bolt which in turn is connected to the magnet. Movement of the button to the various switching positions will result in a combination of the reed switches being picked and dropped by the magnet. The picking and dropping of the reed switches will provide operating signals to the recorder. Also, maintaining the control button at two of the switching positions requires operator control in that if the operator releases the button, it will spring back to a previous position. Springs indirectly acting against the magnet cause the button to spring back to the previous position. As to the remaining positions, springs also indirectly act against the magnet, but latching means will maintain the button in place in the absence of operator control.

Method and apparatus for measuring the timing of quartz crystal timepieces

Abstract: For measuring the timing of quartz crystal timepieces there is provided a microphone pickup which is adapted to pick up vibrations from the casing of the timepiece and to convert these mechanical vibrations into an electronic or electrical signal which is amplified and fed to a crystal filter, the filtered signal then being further amplified and supplied to a counter. This enables the vibrations generated within the casing by a quartz crystal to be measured and the accuracy of the timepiece to be checked.

Vibrational Relaxation Times of Methane and Oxygen at Increased Pressure

Abstract: A study of the effect of microphone design on sound absorption and velocity measurements has been carried out for pressures ranging from 1 to 18 atm. Results of this research show clearly that losses may be introduced by the microphone itself and that this problem becomes more severe with increasing pressure. A microphone has been developed which completely eliminates such effects at lower pressures and greatly reduces them at higher pressures. Measurements in CH4 gave a pressure dependence of the effective specific‐heat ratio in good agreement with theory. Extrapolation to zero pressure gave a result in good agreement with that obtained by using the vibrational specific heat calculated from the Planck‐Einstein formula. Relaxation times τv were determined as a function of pressure p0 and lead to the averaged value p0τv = 1.565±0.013 (μsec⋅atm). This is in good agreement with recent results using the spectrophone method (1.60 μsec⋅atm) and in significant disagreement with results obtained from fluorescence...

Foil-Electret Transducer Arrays for Real-Time Acoustical Holography

Abstract: The foil-electret microphone principle can be employed to construct two-dimensional transducer arrays in a relatively simple fashion. Two different designs of these arrays are described which contain N2 microphones arranged in a N×N square matrix. The first design incorporates a backplate consisting of N×N elements and a foil electret. The array elements can be interrogated in parallel or in series. For series operation N2 switches are required. The second design utilizes a backplate and an electret foil each with N strips of metalization arranged in an overlapping fashion. This array cannot be sampled in parallel; however, for serial sampling only 2N switches are necessary. Both designs can also be used with external biasing. Tests on l6×16 element arrays of these designs indicate usable frequency ranges of at least 70–250 kHz in air and 0.3–2 MHz in water. At 100 kHz in air, the sensitivity of elements is found to be uniform to within ±2.5 dB and, for the first design, the total interelement crosstalk is about -35 cLB. Acoustic shadows of a few objects recorded at 40 frames/ second by the l6×16 array in air are displayed. Larger foil-electret arrays (e.g. 200×200 element) promise to be inexpensive and rugged tools for acoustical holography.

Color Presentation of Breath Sounds

Abstract: A simple ‘color-organ’-loudspeader assembly was connected to a microphone inserted in the mouthpiece of a whole body volume-displacement plethysmograph to record panting breath sound frequencies as co

Ipsi-Lateral No-Mould Fitting of Hearing Aids

Abstract: Measurements of the frequency response curves of the combined sound pressure in the ear canal—natural sound and amplified sound—with a no-mould fitted hearing aid are reported. Two sets of measurements were made: the first one shows the typical frequency response shape in ear canals grouped after their size—wide, normal and narrow —and the second one how the shape of the response curve can be affected by changing different parameters in the sound path from hearing aid microphone to sound tube opening. The frequency response curve in a no-mould fitting very often needs to be changed to match the specific audiogram and ear canal size of the patient. The influence from the different parameters on the frequency response curves are reported, but not all parameters have the same degree of modifying effect,—even some modification methods are recommende not to be used in the fitting work. The best means to modify the frequency response curve is a change of the I. D. (inner diameter) of the sound tube. This findin...

Speech Intelligibility in Naval Aircraft Radios

Abstract: : A study was made to determine how speech intelligibility in naval aircraft radio communications is affected by cockpit noise, by the microphone, helmet, and microphone used by the pilot, and by the vocabulary employed. Using six standard word lists, speech-intelligibility tests were administered to 20 Navy enlisted men for 38 hours of listening. Cockpit noise in which the lists were recorded was both in-flight and simulated. The talker and the speech- processing equipment are largely responsible for the quality of the transmissions. Cockpit noise, microphone, and man-worn gear have negligibly degrading effect upon intelligibility of the aircraft radio communications. Speech-processing is recommended to achieve improved intelligibility. Recommendations are made for choosing optimum intelligibility tests for assessing military speech communication systems and for revising the Brevity Code words.

Attenuation equalizing acoustic coupler

Abstract: An acoustic coupler with equalized attenuation over the entire voice range. The coupler contains a microphone and has a sound muffling cup for snugly receiving the speaker end of a telephone handset. A plurality of series connected, independently, mechanically tenable, op-amp filters connect the microphone to a signal receiving circuit. The filters are tuned to selected center frequencies to equalize the frequency response between the input of the telephone speaker and the input of the signal receiving circuit.

Telephone systems with reduced acoustic feedback

Abstract: Feedback in an electro-acoustic transducer unit for connection into a two-way communication system is reduced or eliminated by acoustic means dependent on relative positioning of loudspeaker and one or more microphones, or electrically, by cancellation of signals due to unwanted sound components derived from a pair of microphones The operation of the microphone and loudspeaker can be alternated at an ultrasonic frequency or a single transducer can be used as microphone and loudspeaker alternately at such a frequency A transducer having a pair of speech coils in pushpull formation is described, as well as a laminated structure for use in the housing of the apparatus

Movable magnet loudspeaker

Abstract: A transducer device such as a loudspeaker or microphone has the electrical coil stationary with respect to the acoustic diaphragm. The diaphragm is actuated by a movable permanent magnet which interacts with the field of the stationary electrical coil. The preferred permanent magnet is one having a high torque-to-weight ratio with respect to an external field. The cobalt-rare earth magnets are examples of such permanent magnets.