Showing papers on "Microphone published in 1975"

Parametric array in air

Abstract: An experimental investigation of the parametric array in air was conducted using a circular piston transducer which produced spherically spreading, collinear, primary beams at frequencies of 18.6 and 23.6 kHz. Since source levels were not strong (about 110 dB re 0.0002 μbar at 1 ft), the 5−kHz difference frequency signal generated by the parametric array was relatively weak. Because of space limitations, all measurements were made in the nearfield of the array. Spurious difference frequency signals resulting from intermodulation distortion in the receiving system were suppressed by judicious choice of electronic components and by the addition of an acoustical filter in front of the microphone. The classic properties of the parametric array were observed. The 5−kHz beam was narrow, and no minor lobes were evident. The propagation curve first increased with increasing range, reached a broad maximum, and then gradually decreased. Theoretical predictions were based on a perturbation solution of Burgers’ equat...

Coincident microphone simulation covering three dimensional space and yielding various directional outputs

Abstract: A microphone assembly for simulating a plurality of coincident microphones has at least four microphone units mutually disposed at the integration points of an integration rule for the surface of a sphere. In one embodiment, four such microphone units are disposed on respective faces of a regular tetrahedron.

The Design of Precisely Coincident Microphone Arrays for Stereo and Surround Sound

Abstract: So-called “coincident” microphone arrays are often used for recording stereo or surround sound. Experience has shown that two of the main causes of poor image localisation and of spurious secondary images are: (i) the usual capsule spacing of 3 to 10 cm, and (ii) poor polar diagrams and polar phase responses in the treble. These defects also cause a significant degradation in the tonal quality if a stereo or surround sound recording is mixed down to mono or matrixed either to modify the recording’s stereo effect or for 2-channel quadraphonic encoding. Because there are practical limits on the smallness of low-noise directional microphone capsules, it has not hitherto been possible to design precisely coincident microphone arrays. Such precise coincidence (ideally to better than 5 mm) is necessary whenever signals are to be mixed or matrixed, in order to avoid high-frequency cancellation effects. We describe the use of a tetrahedral array of capsules with electronic spacing compensation to ensure effective coincidence of all outputs. Let the polar diagram of an individual capsule in an array (with respect to the capsule’s notional centre) be f (x,y,z), where (x,y,z) are the direction cosines of the direction from which a sound arrives, with the x-axis forward, y to the left side, and z upward, and with x2 + y2 + z2 = 1. It is not widely realised that in absolute physical terms, there is no such thing as the “position” of a capsule. If a capsule has its notional centre at the coordinates (u,v,w), then its polar diagram relative to the origin of coordinates at angular frequency ω is

A directional microphone array for acoustic studies of wind tunnel models

Abstract: An end-fire microphone array that utilizes a digital time delay system has been designed and evaluated for measuring noise in wind tunnels. The directional response of both a four- and eight-element linear array of microphones has enabled substantial rejection of background noise and reverberations in the NASA Ames 40- by 80-foot wind tunnel. In addition, it is estimated that four- and eight-element arrays reject 6 and 9 dB, respectively, of microphone wind noise, as compared with a conventional omnidirectional microphone with nose cone. Array response to two types of jet engine models in the wind tunnel is presented. Comparisons of array response to loudspeakers in the wind tunnel and in free field are made.

Inertial microphone system

Abstract: An inertial-reaction microphone transducer mounting supported on the wearer's head away from the mouth for transmitting speech to the exclusion of ambient. A compliant, radial array of elastomer supporting material presses the transducer gently to the head. The transducer and supporting array may be mounted in a cup covering one ear, or it may be mounted in a capsule having an acoustical labyrinth frequency-selective vent for the neutralization of noise.

Boardroom sound reinforcement system

Abstract: A sound reinforcement system for a meeting room provides improved effective communication between several individuals located at a distance from one another within a room, as around a large conference table in a corporate boardroom, by positioning a pair of speakers driven out of phase with one another at each individual location and positioning a microphone within the acoustical cancellation zone of the corresponding speaker pair. Acoustical gain is further improved by feeding the signal from each microphone to all speaker pairs except the one to which it corresponds and/or by making the level of a signal arising from a speaker pair proportional to its distance from the microphone that picked up that signal.

Microphone for the transmission of body sounds

Abstract: A microphone for the transmission and conversion of low frequency body sound signals, characteristic of blood pressure conditions, the microphone featuring a Seignette salt crystal wafer as a transducing element, a foamed body as a transmitting element, a vibrating mass on the microphone membrane, and a deflection-limiting safety plate. The membrane carries a contact-focusing touch plate, and the entire housing is enveloped in a sound insulating rubber jacket.

Resilient microphone mounting

Abstract: A microphone holder essentially comprises a microphone supporting cylinder for mounting a microphone therein, an attaching cylinder located outside the supporting cylinder, and a stepped connecting cylinder for connecting the supporting and attaching cylinders together, all of which are integrally formed of a resilient material to support the microphone in suspension, thereby isolating it against oscillations which may be imparted thereto.

Noise rejecting electronic sphygmomanometer and methods for measuring blood pressure

Abstract: A noise rejecting electronic sphygmomanometer comprises a conventional cuff-type sphygmomanometer having an inflatable bladder and pressure monitoring manometer connected thereto. A first microphone, having a sound pickup directed inwardly to be toward a patient's arm when the cuff is installed thereabout, is provided for picking up Korotkoff sounds as the cuff is deflated and blood flow in a patient's arm resumes. To avoid spurious indications caused by background sounds, a second microphone, having a pickup directed to pickup background noises, is also provided within the cuff. The outputs of both microphones are fed into electronic discrimination circuitry.

Combination microphone, speaker, and control unit for a radio transceiver

Abstract: A combination microphone, loudspeaker, and control unit is disclosed which is adapted to be coupled by a multiconductor cable to a radio transceiver which is capable of transmitting and receiving a plurality of radio signals at preselected frequencies. A multi-conductor cable is secured to a housing for the unit and is adapted to electrically connect the unit to a radio transceiver. A multi-position switch is mounted in the housing and connected to the cable, with the switch being operable to select individually the preselected frequencies. An electromechanical transducer is mounted in the housing and connected to the cable and operable to convert audible sound wave signals into corresponding audio frequency electrical signals and audio frequency electrical signals into corresponding audible sound wave signals. A transmit/receive switch is mounted on the housing and coupled to the cable and the transducer for selectively enabling the transducer to convert audible sound wave signals into corresponding audio frequency electrical signals and audio frequency electrical signals into corresponding audible sound wave signals. A volume control is mounted on the housing and coupled to the cable and the transducer for varying the amplitude of the audio frequency electrical signals applied to the transducer.

Reversible anti-noise microphone

Abstract: This microphone has two opposed faces. The sound to be picked up may be directed toward either one of the two opposed faces with equivalent electrical output from the microphone in either case. Since background noise impinges equally on both of the two opposed faces, its effect on the microphone diaphragm is self-canceling, and causes substantially zero output from the transducer.

Determination of masking-level differences in a reverberant environment

Abstract: A masking‐level difference paradigm was used to measure release from masking in a reverberant environment. Microphones were placed in the ears of a mannequin which was situated in a reverberant chamber. A single white‐noise source was fed into loudspeaker also situated in the chamber with the loudspeaker facing one corner of the chamber to minimize the direct sound reaching the mannequin. The output of each microphone served as the masker, while the signal (250‐Hz pulsed tone or speech) was electrically inserted at the subject's earphones. For the diotic case, the output of one of the microphones was fed to both ears of the subject. For both signals, the MLD was found to be approximately 3 dB. Results will be discussed in terms of a decorrelating effect produced by longterm reverberation.

Singing suppressor device

Abstract: Singing suppressor device for preventing singing or self-oscillation caused by acoustic feedback arising in an audio-frequency signal transmitting electroacoustic chain comprising a sound sensing device (microphone), an amplifier and a sound generator. The invention relies on the variation in the temporal order of the delay time of an electrical delay unit, on an analog and/or digital principle, inserted into the electroacoustic chain. The variation of the delay time is performed by a control generator which, with the aid of an appropriate circuit (e.g. a modulator or an auxiliary generator) continuously changes the delay time as a function of time. This ensures that singing arises only at a considerably higher sound pressure level, because owing to the varying delay time appropriate amplitude, frequency and phase conditions to induce feedback are met for a short time or moment only.

Photo acoustic cell

Abstract: Three embodiments of an improved photo acoustic cell for use in analyzing solid and quasi-solid samples are disclosed. Each cell includes a sample holding chamber having one wall or portion of one wall thereof made from a light transparent material. The sample holding chamber in each embodiment is connected to a microphone by a thin tube which renders the cell, which includes the chamber tube and microphone, an acoustical resonant structure at a frequency within the response characteristics of the microphone. In one embodiment, means are disclosed for pressuring the inside of the cell as well as equalizing the pressure on the outside of the tube. In a second embodiment, the sample to be analyzed forms a portion of the cavity walls and means are provided for reducing the pressure in the cavity to hold the sample securely to the remaining structure for defining the cavity. In this embodiment a fiber optic element brings the light into the chamber. In the third embodiment the cell is mounted relative to a support structure so that different portions of the sample can be brought into relationship with can advantageously be employed to analyze plates, paper or the like which result from chromatographic techniques.

Stereophonic recording and playback apparatus

Abstract: Apparatus for making stereophonic recordings using multiple microphones, and playing back the recordings through multiple speakers, wherein each of the microphones is mounted with a corresponding speaker in a single enclosure. For convenience, the microphones and speakers may be connected by flexible leads to a separate record-playback unit, and, since each microphone is permanently located immediately adjacent a corresponding speaker, the apparatus is capable of accurately reproducing the recorded sounds in their apparent locations by providing the same stereophonic separation for recording as for playback.

Communications headset with rotatable and tiltable electrical connector

Abstract: This headset includes a single earphone and a boom mounted microphone. The headset is mounted on a yoke adapted to fit over a wearer's head with the transducers on either side of the wearer's head. The earphone transducer is in a housing spaced from the wearer's ear and coupled thereto through a flexible tube and an earpiece. A reversible microphone is mounted at the end of a curved conduit whose opposite end is supported on the housing by an electrical connector including an articulated plug assembly which permits rotation and tilting of the conduit with respect to the housing while maintaining electrical connections between the microphone and circuit elements within the housing. The conduit is curved to bring one side or the other of the microphone adjacent to the wearer's mouth when the headset is in place, and the curved conduit is properly positioned by appropriate rotation and tilting of the articulated assembly. The rotation and tilting accommodates shifting of the headset from one side to the other of the wearer's head, while maintaining the microphone in position adjacent one corner of the wearer's mouth.

Apparatus for interfacing between telephone and wireless communication systems

Abstract: An apparatus for interfacing between a telephone instrument and a wireless communication system is disclosed Subsystems of the apparatus include: telephone answering; telephone handset acoustic coupling (called "audio transducer"); transceiver acoustic coupling (called "audio mixing"), and a voice-loop circuit which isolates incoming and outgoing communication signals Features of the invention include the use of the second (transceiver) acoustic coupling subsystem which allows, among other functions, any microphone (supplied with the transceiver) to be acoustic impedance-matched to the apparatus

Evaluation of the intensity method of sound power determination

Abstract: If the sound power of a source is obtained by forming the surface integral of the normal component of the sound intensity vector, the shape of the surface of measurement is unimportant and projection error only occurs as a result of nonideal polar response of the composite microphone. Furthermore, the sound power of the source may be determined selectively in the presence of background noise originating outside the closed surface. If a sufficient number of points of measurement are taken, the error depends mainly on the signal−to−noise ratio at each point and on the accuracy of the measuring system.Subject Classification: 50.25, 50.85.

Moving magnet contact acoustic transducer

Abstract: A dynamic acoustic transducer device of small, compact, highly efficient design, wherein a vibratable diaphragm is supported in an open side of a casing, a pair of permanent magnets being secured to the diaphragm for vibrational movement therewith, the magnets extending into the casing and being respectively surrounded by an electric coil winding which is isolated against vibrations of the diaphragm, the coils being connectable with a signal circuit. When the dynamic transducer comprises a microphone, the device is susceptible of mounting in an operating position by adhesively securing the outer surface of the diaphragm to a vibratable surface of a musical instrument, or other vibratable medium so that the relative movements between the magnets and coils in response to the sensed vibrations will function to produce a modulated output signal capable of being amplified and coupled to a loudspeaker. When the transducer is embodied in a device for the generation of sound waves, for example, in a loudspeaker system, a modulated electric signal is utilized to energize the coils and by interaction with the magnets to drive the diaphragm.

Infrared laser detector employing a pressure controlled differential optoacoustic detector

Abstract: An infrared laser absorption spectrometer is disclosed wherein a pair of detector cells are disposed serially along the laser beam path. The laser beam is modulated to produce a modulation of the absorption by the sample materials in the two cells. Modulated absorption by the samples produces an acoustic wave in each cell which is detected by a suitable microphone and subtracted so as to produce a difference signal corresponding to the difference in infrared absorption between the two cells so that undesired background effects common to both cells are cancelled. A pressure controller, which is responsive to the pressure difference between the sample pressure in the two cells at a frequency substantially below the beam modulation frequency is employed for controlling the pressure differential. In one embodiment the pressure controller includes a compliant membrane partitioning the two cells so that the membrane may move so as to equalize the pressures. In a second embodiment, deflection of the diaphragm of a differential microphone coupled into both cells is employed to derive an output utilized to control either the flow through the cells and/or the volume of the respective cells to control the pressure difference between the cells.

Compensated speaker-microphone

Abstract: A microphone which consists of a speaker having a base resonant frequency, a suppression circuit for reducing the frequency response of the speaker at the base resonant frequency, and a high pass filter for reducing the base frequency response of the speaker is disclosed. The speaker creates electrical signals in response to sound waves received and the suppression apparatus reduces the relative magnitude of the electrical signals having frequencies substantially equal to the base resonant frequency of the speaker. The high pass filter reduces the magnitude of all electrical signals having frequencies below a predetermined frequency, and thus a desired microphone frequency response is obtained. A communications system which uses a receiver to drive a speaker in one mode of operation and uses the speaker as a microphone followed by a compensation network and a transmitter in another mode of operation is also disclosed. The compensation network consists of a base resonant suppressor apparatus for attenuating the peak response of the speaker at the resonant frequency, and a high pass filter to reduce objectionable low frequency responses of the speaker.

Line level microphone with built in limiter

Abstract: A line level microphone. The microphone includes an amplifier and a peak limiter variably shunting the input of the amplifier to substantially avoid distortion or clipping of the microphone output signal.

Stereo microphone apparatus

Abstract: A stereo microphone apparatus is provided which includes a pair of microphone units carried on a headband at opposite ends thereof. The apparatus further includes a pair of windscreens for covering the microphone units, respectively, each of which being capable of housing a human or dummy pinna.

Telephone mouthpiece keyboard

Abstract: Apparatus and method for providing tone operating capability to a dial telephone is disclosed. The standard mouthpiece together with the original microphone of the dial telephone are removed. The present invention provides a replacement mouthpiece attached to the telephone in place of the standard mouthpiece. The replacement mouthpiece includes a relatively small microphone electrically coupled to the transmitter connections in the telephone and having a sound receiving element. A plurality of keyboard elements are located in the replacement mouthpiece generally around the sound receiving element of the microphone. The keyboard elements correspond to respective telephone operating digits and symbols and are adapted to be actuated by the user of the telephone.The replacement mouthpiece includes means for generating an output signal responsive to the actuated keyboard elements to operate the telephone. The generating means is electrically coupled to the transmitter connections when the replacement mouthpiece is attached to the telephone so that both the output of the microphone and the generated output signal are transmitted through the transmitter connections.

Noise-cancelling microphone using a piezoelectric plastics transducing element

Abstract: A noise-cancelling communication microphone using a piezoelectric plastic as the transducer element has been developed. The bimorph structure adopted in conjunction with an impedance matching preamplifier circuit and suitable acoustic design provides an adequate, stable output at low impedance, with an acceptable frequency response. The susceptibility of the microphone to electromagnetic fields is low.

Microphone coupler for hearing aid having inverted conical end configuration

Abstract: A microphone coupler or artificial ear for coupling a microphone and a hearing aid to test the operational characteristics of a hearing aid includes a cavity having a predetermined volume, an opening extending from one end of the coupler to the cavity and is in communication therewith for receiving microphone means therein. The other end of the coupler has an inverted conical configuration in in which an ear mold of a hearing aid is to be disposed, and a hole extends between the inverted conical end and the artificial ear cavity. A non-hardening moldable material is positioned within the inverted conical end around the ear mold which mechanically holds the ear mold in position and provides acoustical sealing during testing of the hearing aid.

Method and apparatus for receiving sound intended for stereophonic reproduction

Abstract: A method for receiving sound intended for stereophonic reproduction and an apparatus for applying this method. The sound is received by means of two or more microphone pairs of the dummy head type. The microphone pairs are coupled so that signals collected by microphones located on similar sides of the dummy heads are essentially additively combined. The resultant signals can be further processed in a known per se manner and can be used for recording or immediate retransmission. The number of microphone pairs is at least two and depends on the reception conditions. The distance between the microphone pairs is likewise dictated by the reception conditions. The apparatus comprises at least two microphone pairs of the dummy head type and means for essentially additively combining the signals from microphones located on similar sides of the dummy heads.