Showing papers on "Microphone published in 1971"

Head‐Related Two‐Channel Stereophony with Loudspeaker Reproduction

Abstract: Reproducing stereophonic signal pairs with two loudspeakers on the front left and right of a listener yields acoustical crosstalk resulting from sound diffraction at the head. Stereophonic phantom sound sources are therefore heard only between the two loudspeakers. However, signal pairs can be constructed from the original signals generating extremely lateral phantom sources. A filter for this purpose is constructed using concentrated elements (“90° filter”). The complex frequency response of the 90° filter is determined in a listening experiment with narrow‐band noise. Two 90° filters are combined for a two‐channel reproduction system. Signals received by a dummy head with a microphone in each ear are fed to the inputs of the 90° filters. This transmission system was tested for its directional fidelity with many test persons. Localization is nearly ideal for the entire horizontal plane including front‐back discrimination and is partly correct even for the median plane.

Dipole antenna arrangement for radio with separate speaker-microphone assembly

Abstract: A speaker microphone assembly, used with a portable radio unit containing receiving and transmitting equipment for receiving and transmitting radio signals, includes a housing with a helical antenna element mounted to the top wall to form one element of a dipole antenna. A coaxial cable having inner and outer conductors is connected from the portable unit equipment to the speaker microphone housing. The center conductor is connected to the helical antenna and the outer conductor is terminated in the housing at a first point which is ground potential. A second outer conductor surrounds and is insulated from the first outer conductor, and is connected to the first outer conductor at the first point. The second outer conductor extends for a predetermined length along the first outer conductor to form the other element of the dipole antenna.

Multimicrophone loudspeaking telephone system

Abstract: A modified speakerphone conference system with a plurality of microphones employs a comparator in combination with logic circuitry that selects the microphone with the greatest output and connects it to the speakerphone input while simultaneously disconnecting the others. In the absence of other inputs, a microphone that has control retains control despite pauses. Control can be seized, however, by any microphone with an overriding signal. Switching and the transmission of background noise are both minimized.

Tissue conduction microphone utilized to activate a voice operated switch

Abstract: A voice-activated transmit switch (VOX) for high noise environment voice communication systems which employ a speech microphone, a transmitter and a receiver. A separate tissue-conduction microphone is employed to generate a signal which activates a transmitter enabling and receiver disabling circuit. The tissue-conduction microphone is positioned in contact with the user's neck tissue in the vicinity of the larynx. A bandpass filter eliminates the unwanted signal from the tissue-conduction microphone output and passes the desired speech signals to an amplifier. The amplifier output actuates a Schmitt trigger which in turn operates a transmitter enable-receiver disable switching circuit. Delay means are provided so that the transmitter does not turn off during brief intersyllabic pauses.

Noise exposure computer and method

Abstract: A portable, fully automatic instrument for at any given time determining precisely a person''s cumulative noise exposure as a percentage of permissible noise exposure is disclosed. The instrument includes a microphone for sensing sound levels, a sound level measuring circuit, an A weighting circuit, a rectifying circuit, a variable-gain ratio amplifier, a noise threshold level circuit for removing from consideration the noise levels below a predetermined threshold level, a converter output circuit, and a readout device for indicating the cumulative percentage of allowable noise exposure that has been experienced. The instrument converts incident sound level pressures in excess of the predetermined threshold level for the time periods of occurrence of the various sound levels into a representation indicative of a cumulative percentage of permissible noise exposure. A method for sensing sound levels above a predetermined threshold, providing a continuous summation of the sound levels for their respective time periods of occurrence, and conversion of the resultant summation to a cumulative percentage of permissible noise exposure is also disclosed.

Percussive musical instrument with transducer for actuating an electronic tone generator

Abstract: A microphone is positioned adjacent a playing member capable of being struck with drum sticks, foot-operated beaters, or the like. The electric output of the microphone, in response to such striking, is rectified and added to the electric potential supplied to an electronic audio tone generator, to activate the latter and produce a desired tone. The generated tone is amplified and fed to an audio speaker, headphone, recording instrument, or other audio output device.

Equalizer utilizing a comb of spectral frequencies as the test signal

Abstract: A system and method is described for electronically equalizing the composite transfer function of a loud speaker system and room which receives the sound generated by the speaker system. A test signal source is broadcast into a room through the normal loud speaker amplifier system. A substantially flat microphone and preamplifier is used to detect the system and feed the detected audio signal through a bank of audio filters substantially covering the low, middle, and high range audio spectrum from approximately 30 cycles to 20 kilohertz (KHZ) by using approximately three narrow band peaking filters per octave. The power in the bandwidth of each filter is detected and measured against a known reference and the individual gain of each of the filters is adjusted to obtain a substantially flat acoustic response. The normal conventional input sound source, be it a tuner or tape deck, is then fed through the adjusted bank of narrow band filters directly into the audio sound system for broadcast into the room in the conventional manner.

Experimental Investigation for Detection of Sound-Pressure Level by a Microphone in an Airstream

Abstract: Investigations were made to find a physical concept for evaluating the pressure level of sound that exists in an airflow by means of a wind screen or probe microphone. In order to provide a sound pressure in the airflow, sound of a known pressure level, which is assumed to be of higher level than the aerodynamically generated noise, was radiated into a duct from an external sound source. The output level of the microphone was measured for various differences between the sound‐pressure level produced by the external sound source and the pressure fluctuation level of turbulence in the airflow. Results obtained agree with the superposed level of output by sound pressure and output produced by pressure fluctuation of turbulence. A new concept for characterizing microphone response to wind‐flow fluctuation is presented. This characteristic is defined by the difference between the magnitude of the pressure fluctuation of turbulence and the output level of the microphone produced by the turbulence‐fluctuated pre...

Group communication apparatus

Abstract: First and second conference tables are provided at separated locations. Each table carried a plurality of outward facing microphones alternating peripherally of the table with a plurality of inward facing loudspeakers. Participants sit only in front of the microphones and each participant is represented at the remote table by the correspondingly situated loudspeaker. A transmitter control means at each table senses a selected microphone in use and passes a control signal characteristic of that microphone over a communications link. A receiver control means at each table selects, upon receipt of the control signal, the appropriate loudspeaker corresponding to the selected microphone and feeds to that loudspeaker an audio signal from the selected microphone over a telecommunications link. A microphone may be selected on the basis of a push button switch or on the basis of audio signal level or both. Visual indicators at each microphone and loudspeaker indicate when they are in use.

Voice switched microphone control system

Abstract: Voice activated control apparatus selectively connects one of a plurality of microphones to an audio line and inhibits all other microphones from capturing the line while the initial connection is maintained. Each microphone is connected to an associated speech detector and relay. In response to voice signals from a microphone, the associated speech detector activates a relay which connects the microphone to the line and generates a signal which inhibits the other relays. Other users cannot interrupt the present speaker because their relays remain inhibited as long as the speaker continues. The same circuitry can accommodate any number of microphones.

Speech in deep-submergence atmospheres.

Abstract: Among the factors that could affect the intelligibility of helium speech at deep submergence are an upward shift of formant frequencies in accordance with the velocity of sound, a disproportionate shift of first formant frequencies as a result of increased pressure, attenuation of high frequencies of the voice just when they become essential, deterioration of microphone response with depth, change of the diver's hearing above 3 kHz with depth, occupational deafness above 3 kHz, and acoustic reaction of a mask cavity as opposed to the larger space of a habitat or diving bell. Of these, the first and the last two are the most important. The key to the problem is a microphone of satisfactory design. In conjunction with such a microphone, a helium translator can be made to restore intelligibility even when the listener has a severe high‐frequency hearing loss.

Silent emergency alarm system for schools and the like

Abstract: In a school each classroom (or other area) is instrumented with a hidden microphone and receiver tuned to a non-audible frequency. The receivers'' outputs are connected to a central display unit in the school''s administrative office. Each instructor is provided with a small concealable transmitter which, when hand activated by the instructor upon the occurrence of any emergency, generates a non-audible signal at the receiver''s tuned frequency.

Performance of Individual Hearing Aids Utilizing Microphone and Induction Coil Input.

Abstract: Physical measurements of gain, maximum power output, frequency response, and harmonic distortion were made on each of two body-type hearing aids on both the microphone and induction coil settings. ...

Earphone receiver attenuation measurement technique

Abstract: A system for measuring the effectiveness of the sound attenuating function of an earphone sound attenuation cover by employing the earphone transducer as a microphone and measuring the noise level with the ear cover in place on the user''s ear and with the cover removed, the difference in decibels being interpreted as the acoustic attenuation provided by the ear cover.

Inertial reaction transducers

Abstract: An acoustic transducer having good speech intelligibility with inherent significant suppression of ambient noise. Incorporates inertial mass reaction in efficient, compact and lightweight arrangement. In one form includes a predetermined weight or block suspended by a vibratory diaphragm and linked to the electromechanical or motor section, to impart a specific upper resonant frequency. In another, the weight is mounted directly upon the armature. Effective over a relatively wide speech band. Has a single resonant frequency that is readily controlled and manufactured. Provides inherent roll-off beyond this frequency to extend response, yet substantially reduce noise. Applications include: contact head microphone; in-mask microphone; in-ear receiver.

Free-Field Correction for Laboratory Standard Microphones Mounted on a Semiinfinite Rod

Abstract: A theoretical study has been made on the free‐field correction of laboratory standard microphones mounted on a semiinfinite rod. In the analysis, we have discussed the diffraction phenomena of plane sound waves by the actual microphone system, taking into consideration the effect of a recess as well as the interaction between microphone diaphragm and medium. A new method of solving wave equations met with these boundary conditions, called the infinite‐matrix method, is presented in this paper. Our whole problem is divided into three parts. The first is concerned with the external free field, which can be solved rigorously by Wiener‐Hopf technique; the others refer to the solution of the sound field inside a recess and, finally, to motions of a diaphragm. After putting these solutions into the form of matrix equations with unknown variables, we obtain a system of simultaneous matrix equations by connecting solutions with each other. Numerical results are given for the free‐field correction of the Western Electric Company type 640AA microphone. Comparison with the experiment, made at the National Bureau of Standards, indicates that sufficient agreement is obtained.

Electromagnetic telephone date coupler

Abstract: A data coupler for coupling a data terminal to a telephone network without direct conductive connection. Data signals are electromagnetically coupled to the earpiece speaker of a telephone handset from an induction coil integrally molded in a sound muffling cup in which the earpiece of the handset is engaged. Automatic gain control is provided by a negative feedback loop having a microphone pickup mounted in the cup.

Directional microphone for head mounted midget hearing aids

Abstract: A miniature microphone for a head-mounted midget hearing aid wherein the diaphragm divides the microphone housing into two separate chambers, the housing having a forward portion with a sound admitting aperture therein which is substantially non-restrictive to passage of sound waves therethrough so that the sound waves may freely enter one of the chambers within the housing; the microphone housing also having a wall portion at the rear of the microphone, said wall portion having a plurality of minute apertures therethrough and defining a transmission time delaying acoustic resistance admitting sound pressure variations into the other chamber of the housing

An Ear‐Like Coupler for Calibration of Earphones

Abstract: A coupler for earphone calibration has been developed that mimics the acoustic properties of the outer ear and has a simple geometry. It consists of an outer portion corresponding to the auricle, a canal corresponding to the ear canal, and an acoustic network reproducing the acoustic impedance at the eardurm. The sound pressure is measured at the eardrum location by means of a 14‐in. condenser microphone. According to comparative measurements, the acoustic impedance at the end of the coupler canal follows the average eardrum impedance with satisfactory accuracy within the frequency limits of 100 and 7000 Hz. The coupler also produces essentially the same pressure transformation between the microphone, midcanal, canal entrance, outer rim, and 1 cm outside the outer rim as the pressure transformation in an average ear between corresponding points. The coupler may be used for supraaural earphones as well as for insert and circumaural earphones. It can be manufactured according to rigorous specifications.

Quiet turn-on circuit for carbon microphones

Abstract: A preamplifier for a carbon microphone is provided at its input with a field effect transistor biased to a non-conductive state. When the microphone switch is turned on to connect the microphone to the amplifier the source of the bias is substantially cut off but an RC delay circuit is provided to maintain the bias momentarily to keep the amplifier inoperative until the rush of current through the microphone subsides so that the usual ''''click'''' sound is not heard when the microphone is turned on.

Sound activated controller

Abstract: According to one preferred embodiment, a controller in accordance with the invention includes a microphone, threshold circuit and high gain amplifier arrangement for selectively converting sound energy into digital signals which after filtering are used to energize a control circuit that provides an enabling signal, of a controlled time duration, to a switching device.

Ambipolar microphone unit

Abstract: A microphone unit for incorporation in a telephone headset or the like including a low signal output transducer, and a polarity independent current control amplifier circuit for amplifying the transducer signals and having a pair of substantially identical parallel oppositely connected main current control devices, such as transistors, each having their load terminals arranged for controlling current flowing in a normal forward direction which is opposite to that of the other so that there will always be one fully conductive and one partially conductive or nonconductive path across the microphone unit terminals independently of the polarity of the D.C. current to be modulated by the microphone unit. Drive circuit means energized by the voltage on the telephone lines applied to the microphone unit terminals are provided to receive the transducer signals and amplify the same before being applied to the control terminals of the current control devices regardless of the polarity of the energizing voltage.

Microphone having coupled acoustic circuits

Abstract: A microphone having a response characteristic in a set frequency range and a reinforced response at the upper limit of this range and comprising a housing containing an electroacoustic transducer with at least one diaphragm for producing output signals as a function of the sound striking the diaphragm and a substantially cylindrical acoustic resonance chamber coupled to the diaphragm. The opening to the acoustic resonance chamber forms the main sound inlet opening, and at least one group of subsidiary sound inlet openings are formed in the chamber walls.

Acoustical filtration method and apparatus for obtaining instrumental tones

Abstract: Electrical signals containing a large number of high-frequency components from a tone generator are amplified and converted by a small loudspeaker into audible-tones, which are led through an acoustical horn disposed in an enclosure, said accoustical horn having a multiplex-resonance characteristic to a microphone at the throat of the horn thereby to be converted again into electrical signals, which are amplified and finally converted by a second loudspeaker into audible tones.

Hydrosonic diving communication amplifier system

Abstract: Intelligible audio communications between a diver and a surface boat, or from the occupant of a recompression chamber to the outside, are ensured by interposing an electronic system between a microphone and a speaker to block major portions of gas-flow noise generated as the gas is transferred. A preamplifier stage is electrically connected to the microphone, and a preamplifier filter defines the passband of composite signals composed of gasflow noise and audio communications. An attenuation stage receives the composite signals and further excludes signals lying outside the composite signals'' passband, and notches out high intensity gas-flow noise concentrated at a particular noise frequency predetermined by spectral analysis of the composite signal. Necessarily, a portion of the audio communications, centered about the noise frequency, is also blocked; however, the remainder is sufficient to enable reconstruction of intelligible speed at an interconnected speaker.

Method and apparatus for the indirect measurement of blood pressure

Abstract: A method and apparatus for automatically detecting the blood pressure of a person by auscultation in which a standard blood pressure cuff is connected to a pressure transducer for providing a pressure signal and a microphone is used for providing an electrical signal from the Korotkoff sounds detected. The Korotkoff sound electrical signal is amplified and passed through a bandpass filter which has a flat response between approximately 50 and 160 Hz and a sharp cutoff below 50 Hz. The resultant signal is then summed with the pressure signal to provide an output which indicates the pressures at which the five phases associated with the Korotkoff sounds occur.

Speech Communication in Diving Masks. I. Acoustics of Microphones and Mask Cavities

Abstract: The acoustic properties of representative diving‐mask cavities were measured, using a high‐impedance sound source. Curves of impedance presented to the lips and of microphone transmission, relative to those of free space, were obtained. Both nonabsorbent cavities and cavities with standing‐wave absorption adaptable to a marine environment were investigated.

Instrument for purifying sounds through sympathetic vibration

Abstract: A very carefully tuned stringed instrument is provided with a range preferably approximating that of a piano. The strings are disposed in the path of ambient sound waves, such as music, and function to purify or eliminate those components of the sound which are not attuned to one or more of the instrument strings. A microphone may be utilized to pick up the purified sound and, in one embodiment, a portion of the apparatus constituting the purifier is disposed on one side of a soundproof wall such that the microphones which pick up the purified sound are not subjected to the sound source. In a variant embodiment, a chromatic set of tuning forks may be utilized in conjunction with the strings to assist both in tuning the instrument and in carrying out the purification process. An instrument in which a complete set of tuning forks or other tuned elements are used in place of or in combination with strings is also contemplated, the inventive concept being the purifying nature of the closely tuned vibratory elements responding sympathetically to the ambient sound.