Showing papers on "Microphone published in 1978"

Cross‐spectral method of measuring acoustic intensity without error caused by instrument phase mismatch

Abstract: The theory of a new method of measuring acoustic intensity is presented. The method uses measurements of the cross spectrum of the pressures at two closely spaced microphones. To eliminate the measurement error due to instrument phase mismatch, a circuit switching procedure is used. The method is applicable to any acoustic field subject to the condition that the product of the wave number and the microphone spacing remains small. The method has been verified by laboratory experiment.

Sonotubometry. An acoustical method for objective measurement of auditory tubal opening.

Abstract: The sound conduction method for measurement of the Eustachian tube opening has been studied and modifications made in the test procedure to increase its easy performance and reliability. By holding the sound source near to the nostril, mounting the microphone into a circumaural ear defender and by feeding the output of the microphone through a filter with a very narrow bandwidth (3.16 Hz) many of the pitfalls of the sound conduction technique described earlier could be removed. Recording of the transfer function between the nasal tip and external auditory meatus and recording of the spectrum of swallowing sound revealed that the useful frequency range for the measurements was upwards from 5-6 kHz. By using the three frequencies 6, 7 and 8 kHz the method showed tubal opening in 90 or 95% of normal ears depending on whether the minimum amplitude accepted was ≥5 or 1-4 dB, respectively.

Theoretical response of condenser microphones

Abstract: Modifications to prior theory yield expressions for the frequency response and equivalent lumped elements of a condenser microphone in terms of its fundamental geometrical and material properties. Results of the analysis show excellent agreement with experimental data taken on B&K pressure microphone types 4134 and 4146.

Hearing aid with digital processing for: correlation of signals from plural microphones, dynamic range control, or filtering using an erasable memory

Abstract: In an illustrated embodiment a behind-the-ear hearing aid includes a microphone, an amplifier-low pass filter circuit, an analog to digital converter, a digital integrated circuit arithmetic and logic unit for implementing a n-th order transfer function in the Z domain, a digital to analog converter and an output transducer, for producing the desired sound response. A memory multiplexer is provided for loading of the multiplier coefficients necessary to adapt the transfer function circuit to essentially any class of hearing deficiency into an erasable programmable read only memory (EPROM). The structure is such that the coefficient memory may be loaded after the standard universal hearing aid has been completely assembled, and indeed the hearing aid may be reprogrammed as needed after a period of use, essentially without disassembly.

Microphone shock mount and assembly

Abstract: A shock and vibration isolating mount for a microphone and the assembly of such a mount with a microphone in which the mount has a lower frame mounted on the post of a stand by a swivel. The lower frame is semicylindrical, and it is hinged at one edge to an upper frame also semicylindrical. The upper and lower frames each carry a pair of closed bands of elastomer material under tension, one pair of bands extending transversely around the lower frame in spaced relation and the other pair of bands extending transversely around the upper frame in spaced relation. The microphone is disposed between the upper and lower frames and between the first pair of bands and the second pair of bands, and the frames are provided with a latch mechanism at their edges opposite the hinge to prevent the frames from opening from a closed position to an open position except when the microphone is to be removed from the mount. The mass of the microphone and the compliance of the bands forms a mechanical moving system with a resonance below the frequency range of the microphone.

Noise monitoring apparatus

Abstract: An apparatus for monitoring the noise which impinges a human ear and for generating a signal representing the noise level accumulated over a period of time. Typically, the apparatus can be located in a hearing protector worn by a worker in a noisy environment. A microphone generates a signal having a magnitude representing the detected noise level of the ear which signal is processed by an absolute value circuit and a root mean square circuit to generate a signal having a magnitude proportional to the logarithm of the detected noise level. This logarithmic signal is converted by a voltage to frequency converter and a counter accumulates a count total proportional to the noise level over a period of time. The apparatus includes visual and aural alarms to indicate a maximum allowed noise level and dosage. The apparatus can also be inserted into a storage unit for reading the data, calibrating the noise monitor circuitry and recharging the batteries in the apparatus.

Apparatus for wireless transmission of a teaching program in a classroom

Abstract: Apparatus for wireless transmission of a teaching program in a classroom comprises a transmitting unit comprising a casing which houses one or more tape recorders with operating elements, a microphone and a plurality of infrared transmitters. A removable cover which can be hung on the wall has additional infrared transmitters connected by a cable to the transmitting unit. Each student has a head set with an infrared receiver, earphones and a microphone. The transmitting unit is remotely controlled by a portable ultrasonic transmitter. When not in use, the headsets are placed in a cabinet where the batteries of the headset are charged by means of induction coils on the head sets being magnetically coupled with induction coils in the cabinet to which high frequency current is supplied. The students may also have cassette recorders which, when not in use, are placed in charging chambers where power is transmitted from primary windings in the chambers to secondary windings in the cassette recorders to charge the batteries of the recorders.

Audio-visual headphones

Abstract: A pair of headphones has a right speaker for the right ear and a left speaker for the left ear of the user. The speakers are electrically connected to each other and to a sound input source whereby the speakers reproduce sound from the sound input source. A pair of goggles is coupled to the headphones and covers the eyes of the user. A plurality of lamps are provided in the goggles, visible to the user. A microphone is electrically connected in circuit with a source of electrical energy and the lamps whereby sound reproduced by the speakers is picked up by the microphone, converted into electrical energy which varies in intensity with variations in the sound, and varies the energization of the lamps to provide a light pattern which varies in accordance with variations in the sound.

Priority mixer control

Abstract: A priority mixer control for a multi-microphone audio system comprises a threshold signal generator that develops a scanning D.C. threshold signal starting at a maximum level for a time T1 and then decreasing in amplitude as a function of time. Each microphone channel is provided with a control channel including a comparator that compares the microphone signal, as an A.C. signal, with the threshold signal, and that switches the microphone channel to "on" condition when the microphone signal exceeds the threshold; all of the control channels are coupled to a threshold signal restoration means that drives the threshold signal back to its maximum level each time an audio channel is switched "on". An audio channel that has been switched "on" remains "on" for a time T2 substantially longer than the time T1. The number of channels currently in "on" condition is continuously monitored and the output gain is reduced whenever two or more channels are in "on" condition.

Telephone earphone amplifier

Abstract: This telephone earphone amplifier is turned on automatically when the telephone handset is taken off-hook. To this end, the dc bias provided to the microphone from the telephone line is used to turn on a semiconductor switch that connects dc power to the amplifier. The amplifier itself is connected to amplify the incoming audio, so as to provide greater volume e.g., to aid persons of impaired hearing.

Electrodynamic transducer with longitudinally moving magnet

Abstract: According to the invention, the electrodynamic transducer comprises a coil with a pair of sections wound in opposite directions. Placed inside the coil is a magnet capable of moving in a longitudinal direction. The unlike poles of the magnet are located in different sections of the coil. The magnet is mechanically coupled to an actuator. The stereophonic and monophonic pickup heads and the electrodynamic microphone are built around said electrodynamic transducer.

Localization of sound producing animals using arrival time differences of their signals at an array of microphones

Abstract: This method provides a reliable means to determine distance between vocalizing individuals and their locations through a prolonged period of time without disturbance to the communication process by the presence of an observer. The accuracy of this method was tested by varying the arrival time differences on the microphone grid for known locations in a random fashion. This test shows that a vocalizing animal within an area of 4 ha surrounding the microphone array can be localized with an accuracy of ±1 m. The accuracy decreases with the distance from the central area and as a function of the geometry of the array. The location of an individual can be determined based on 5 vocalizations given in sequence.

Mechanically biased semiconductor strain sensitive microphone

Abstract: A piezo-electric transducer element is disclosed which is formed by selected etchings from boron doped silicon. The transducer includes a diaphragm and a spring lever adapted to bias the transducer element into a state of strain so that a vibration of the diaphragm is transmitted to the transducer element. The transducer element is particularly suitable for use in a telephone microphone.

Sound intensity meter

Abstract: Acoustic intensity is measured by a pair of closely spaced microphones aligned in a given direction. One microphone is connected directly to an integrator the output of which is connected to a multiplier while the other microphone is connected directly to the multiplier. The multiplier output is proportional to the imaginary part of the cross-spectrum of the two microphone signals which when time averaged represents the absolute value of the sound intensity in the given direction if the microphone systems are properly phased matched.

Mobile CB transceiver

Abstract: A mobile citizens band radio transceiver having the circuitry partitioned so as to permit the chassis housing the receiver circuitry, transmitter circuitry and frequency synthesizer circuitry to be installed in a remote location in a motor vehicle such as behind the dashboard, under the seat or in the trunk thereof, or the like, so as to reduce the possibility of theft and/or the likelihood that the chassis could cause injury to the occupants of the vehicle in the event of an accident or sudden stop by efficiently housing all of the control circuitry in a combination microphone and control unit adapted to be held in the hand of the operator of the vehicle and operated by the same hand which is holding the combination unit. By having all of the controls located in the microphone, a jack plug arrangement or the like can be utilized so that the microphone can be easily removed when the operator is not in the vehicle so that no sign of the presence of the CB radio will be visible to a potential thief. The partitioning of the circuitry between the controls in the microphone and the frequency synthesizer located on the remote chassis is enabled by the use of a memory in the control circuit for storing data words corresponding to the various CB radio frequency channels to be selected, manually-operable channel selection circuitry for addressing a given word in the memory and circuitry for serially transmitting the data word indicative of the selected channel to the remotely located frequency synthesizer thereby significantly reducing the size and number of electrical connections therebetween. The remotely located frequency synthesizer serially receives the stored control word and uses one or more portions thereof to preset counters in the frequency synthesizer circuitry so as to operate a phase-locked loop at precisely the given channel selected by the operator.

Acoustical properties of the National Bureau of Standards anechoic chamber

Abstract: The acoustical properties of the large anechoic chamber at the National Bureau of Standards were investigated by two methods over the frequency range 40–63 000 Hz. In the first method described, deviations of mean‐square sound pressure from an assumed inverse square law were measured as a sound source and microphone were moved apart. Over most of the frequency range, the deviations were found from a least‐squares curve‐fitting procedure by means of digital‐computer processing of the data. The effective acoustic centers of the sources were obtained as a by‐product of the procedure. In the second method, the source and microphone were kept at a fixed separation as they were moved together across the chamber, and deviations from the mean value of the sound pressure level were estimated from recordings. The significances of the two methods are discussed with a view towards their application.

Pivoted plural microphone assembly

Abstract: A novel microphone assembly including three microphones which are rotatably or pivotably supported relative to each other and relative to a supporting handle housing structure wherein the left and right microphones rotate the same amount relative to a center axis of the microphone structure and wherein the center microphone can be extended different lengths and directed in different directions so as to vary the mixing ratio relative to the other microphones and including a ganged variable resistor to which the center microphone is connected so as to automatically control the mixing ratio between the signal from the center microphone with the two outer left and right microphones. The microphone assembly can be folded into a compact package and the microphone has superior localization characteristics for reproduction of sound.

Electrostatic microphone with damping to improve omnidirectionality, flatten frequency response, reduce wind noise

Abstract: An electret microphone in which the condenser unit of the microphone is contained within a cylindrical shell open at one end and mounted coaxially on a larger cylindrical casing at the other, the region surrounding the shell and extending to the casing having a mass of closed cellular plastic foam therein, and the open end of the casing being covered by a layer of open cellular foam plastic, the mass of closed cellular foam plastic and layer of open cellular foam plastic being contained within a wire grill.

Microphone support with simultaneous adjustment of plural degrees of freedom

Abstract: A microphone (11) is secured to one end of a unidirectionally flexible tape (12) which is removably storable in a housing (10) after passage through a tracking mechanism (13). That mechanism is part of a further mechanism (26, 37, 41) for holding an exiting portion of the tape in the angular orientation assumed by the tape at the end of a removal operation.

Method and apparatus for measuring characteristics of a loudspeaker

Abstract: A loudspeaker and a microphone are arranged in a normal room, the loudspeaker being supplied with an impulse signal. A direct response sound from the loudspeaker and reflected sounds from wall surfaces in three directions of the normal room are converted into a response signal by the microphone. The response signal is A/D-converted, and then Fourier-transformed. The Fourier-transformed response signal is converted into a response signal with an absolute value, and then into a logarithmic response signal. The logarithmic response signal is filtered to eliminate signal components corresponding to the reflected sound. The filtered logarithmic response signal is A/D-converted, and supplied to a recorder.

Hearing aid with signals modulated onto radio waves - may include optical radiation for transmission from microphone unit to loudspeaker unit

Abstract: The hearing aid has its microphone located in a transmitter and its loudspeaker (which fits into the user's ear) located in a receiver. The transmitter and receiver are spacially separate and connected via free space. The free-space link between transmitter and receiver may be via high frequency radio waves or via light, esp. IR. Both the transmitter and receiver contain their own dc supplies such as batteries. The receiver contains a device to limit power consumption during the breaks in transmission. Alternatively, the receiver may have no dc supply of its own; in this case the transmitter transmits at a high power.

Automatically supervised alarm system

Abstract: An alarm system including an alarm which is actuated when a sensor such as a microphone detects an emergency condition. In one embodiment the output of the microphone is fed through a filter circuit tuned to frequencies characteristic of breaking glass. In conventional systems failure of the microphone may remain undetected but in the system of the present invention an alarm is instituted when the sensor detects any emergency signals and when the sensor fails to detect a reference signal. The reference signal is produced at regular intervals but the alarm instituting means includes a delay and is operable to switch off the reference signal within the delay period to avoid false alarms.

High-temperature microphone system

Abstract: Apparatus for measuring pressure fluctuations in air or other gases in an area of elevated temperature. A condenser microphone is located in the area of elevated temperature and electronics for processing changes in the microphone capacitance is located outside the area and connected to the microphone by means of a high-temperature cable assembly. The microphone includes apparatus for decreasing the undesirable change in microphone sensitivity at high temperatures. The high-temperature cable assembly operates as a half-wavelength transmission line in an AM carrier system and maintains a large temperature gradient between the two ends of the cable assembly. The processing electronics utilizes a voltage controlled oscillator for automatic tuning thereby increasing the sensitivity of the measuring apparatus.

Telephone terminal with loudspeaker output - has two microphones whose outputs are subtracted to eliminate background noise

Abstract: The telephone terminal consists of a loudspeaker (12) and two microphones (10, 11) equidistant from it. The outputs of the microphones are subtracted from one another to eliminate sounds from the loudspeaker (feedback) and background noise in the room. The user speaks into one of the microphones so that after subtracting the microphone outputs only the signal representing his voice is passed on. The two microphones are connected via amplifiers to a differential amplifier (24) whose output passes to a line transformer (28).

Electronic timepiece with electroacoustic transducer

Abstract: The invention relates to an electronic timepiece provided with an electroacoustic transducer for transmitting acoustic signals to indicate a time of alarm, and also for receiving information in the form of acoustic signals to control different functions of the timepiece. Coded acoustic information is delivered to the transducer, for example, by a special apparatus intended for that purpose, and serve to control different functions of the timepiece through a watch and transducer control logic network. The logic network is interconnected with the frequency divider chain, a display control circuit, and a transducer. The logic network includes a selector which connects the transducer either to the output of an alarm logic circuit for delivering alarm signals to the transducer at the time of alarm, or to a transducer detector for transmitting the electrical signals delivered by the transducer acting as a microphone to a watch logic circuit. The watch logic circuit, in turn, controls the alarm logic circuit, the frequency divider chain, and the display control circuit of the timepiece.

Studies on the spatial variation of decaying sound fields

Abstract: The spatial variation of the reverberation time was measured in the NBS reverberation room in the 1/3‐octave bands from 80 to 10 000 Hz to determine the following: (1) the effects on the precision of the spatially averaged reverberation time due to (i) vane speed and vane orientation, (ii) loudspeaker location, and (iii) the area and location of an absorbing panel and its absorption coefficient; (2) the selection of the parameters in (1) above such that the measurement uncertainty of the reverberation time is minimized; and (3) the overall measurement uncertainty for this optimum configuration as a function of the number of microphone locations and the number of decay curves recorded at each microphone location. For an 11‐m2 panel with relatively little low frequency absorption and with the vanes oriented at 22.5° from the vertical and rotating at 7.5 rpm, an analysis of variance indicated that the total uncertainty of the measured average reverberation time (one standard deviation from the mean) was less...

Sound operated control device

Abstract: Two microphones, with at least one being directional and sensitive to different sound, are utilized in conjuction with a comparator circuit and a switching circuit to control electrically energized equipment such as alarm systems, machinery, safety devices and the like. The comparator circuit rectifies the output from each of the microphone amplifiers into either a positive or negative voltage, respectively. The switching circuit is set to pass current only when the voltage from the selected directional microphone exceeds the other microphone voltage by a predetermined value.

Loudspeaker call system

Abstract: PURPOSE:To realize the detection of the transmission signal featuring a high S/N regardless of the noise within car and thus to ensure a high-quality mutual loudspeaker call by using the bone conduction transmitter microphone and the faint field transmitter CONSTITUTION:When the driver speaks, the vibrations according to the contents of the utterance are transmitted via the bone conduction to the bone conduction transmitter microphone 5 which is pressed by the frame of the glasses, thus obtaining the telephone signal output according to the vibrations This signal output is modulated by faint field transmitter 6 and then discharged into the car via antenna 7 incorporated into the glasses frame The modulated output is then received through antenna 8 and transmitted by transmission signal radio receiver 9 to mobile transmitter/ receiver 10 directly or via demodulation to be transmitted to base station 12 through antenna 11 While the electric waves arrived station 12 are demodulated via antenna 11 and transmitter/ receiver 10 and then amplified 13 to be discharged through speaker 14 in the form of the voice In this case, the sensitivity of microphone 5 is very low to the air vibrations, and accordingly the acoustic combination can be ignored even though the sound volume of speaker 14 may be increased