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  • 1975-1979  (11)
  • 1
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    Differential sound-level meter (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Relative difference between sound-levels at two different microphone sites is measured precisely with circuit that continuously monitors gains of two acoustical channels. Difference between two pilot voltages is utilized in regulating loop to force gain of second channel to track gain of first channel.
    Keywords: MECHANICS
    Type: LAR-12106 , NASA Tech Briefs (ISSN 0145-319X); 2; 1; P. 3
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Differential sound level meter (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Small differences between relatively high sound pressure levels at two different microphone sites are measured by a device which provides electrical insertion voltages (pilot voltages) as a a means for continuously monitoring the gains of two acoustical channels. The difference between two pilot voltages is utilized to force the gain of one channel to track the other channel.
    Keywords: ACOUSTICS
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Instrumentation for measuring aircraft noise and sonic boom (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Improved instrumentation suitable for measuring aircraft noise and sonic booms is described. An electric current proportional to the sound pressure level at a condenser microphone is produced and transmitted over a cable and amplified by a zero drive amplifier. The converter consists of a local oscillator, a dual-gate field-effect transistor mixer, and a voltage regulator/impedance translator. The improvements include automatic tuning compensation against changes in static microphone capacitance and means for providing a remote electrical calibration capability.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    A high-temperature wideband pressure transducer (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Progress in the development of a pressure transducer for measurement of the pressure fluctuations in the high temperature environment of a jet exhaust is reported. A condenser microphone carrier system was adapted to meet the specifications. A theoretical analysis is presented which describes the operation of the condenser microphone in terms of geometry, materials, and other physical properties. The analysis was used as the basis for design of a prototype high temperature microphone. The feasibility of connecting the microphone to a converter over a high temperature cable operating as a half-wavelength transmission line was also examined.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-CR-145710 , PGS-TR-PH-75-16
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Instrumentation for measurement of aircraft noise and sonic boom (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A jet aircraft noise and sonic boom measuring device which converts sound pressure into electric current is described. An electric current proportional to the sound pressure level at a condenser microphone is produced and transmitted over a cable, amplified by a zero drive amplifier and recorded on magnetic tape. The converter is comprised of a local oscillator, a dual-gate field-effect transistor (FET) mixer and a voltage regulator/impedance translator. A carrier voltage that is applied to one of the gates of the FET mixer is generated by the local oscillator. The microphone signal is mixed with the carrier to produce an electrical current at the frequency of vibration of the microphone diaphragm by the FET mixer. The voltage of the local oscillator and mixer stages is regulated, the carrier at the output is eliminated, and a low output impedance at the cable terminals is provided by the voltage regulator/impedance translator.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Format: application/pdf
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  • 6
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    High-temperature microphone system (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Microphone system that measures pressure fluctuations in air or other gases is not unduly effected by temperature or rate-of-change of temperature. Easily fabricated system has proved operable at temperatures up to 430 C.
    Keywords: MECHANICS
    Type: LAR-12375 , NASA Tech Briefs (ISSN 0145-319X); 3; 3; P. 405
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Theoretical response of condenser microphones (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: 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.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Acoustical Society of America; vol. 64
    Format: text
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  • 8
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    High-temperature microphone system (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Pressure fluctuations in air or other gases in an area of elevated temperature are measured using a condenser microphone located in the area of elevated temperature and electronics for processing changes in the microphone capacitance located outside the area the area and connected to the microphone by means of 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.
    Keywords: COMMUNICATIONS AND RADAR
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    A unified acquisition system for acoustic data (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A multichannel, acoustic AM carrier system was developed for a wide variety of applications, particularly for aircraft noise and sonic boom measurements. Each data acquisition channel consists of a condenser microphone, an acoustic signal converter, and a Zero Drive amplifier, along with peripheral supporting equipment. A control network insures continuous optimal tuning of the converter and permits remote calibration of the condenser microphone. With a 12.70-mm (1/2-in.) condenser microphone, the converter/Zero Drive amplifier combination has a frequency response from 0 Hz to 20 kHz (-3 db), a dynamic range exceeding 70 db, and a minimum noise floor of 50 db ref. 20 micro Pa) in the band 22.4 Hz to 22.4 kHz. The system requires no external impedance matching networks and is insensitive to cable length, at least up to 900 m (3,000 ft). System gain varies only + or - 1 db over the temperature range 4 to 54 C (40 to 130 F). Adapters are available to accommodate 23.77-mm (1-in.) and 6.35-mm (1/4-in.) microphones and to provide 30-db attenuation. A field test to obtain the acoustical time history of a helicopter flyover proved successful.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TN-D-8327 , L-10915
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    A high-temperature wideband pressure transducer (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A condenser microphone AM carrier system, which has been developed to measure pressure fluctuations at elevated temperatures, consists of the following components: a condenser microphone designed for operation at elevated temperatures; existing carrier electronics developed under two previous research grants but adapted to meet present requirements; a 6 m cable operating as a half-wavelength transmission line between the microphone and carrier electronics; and a voltage-controlled oscillator used in a feedback loop for automatic tuning control. Both theoretical and practical aspects of the development program are considered. The three predominant effects of temperature changes are changes in the membrane-backplate gap, membrane tension, and air viscosity. The microphone is designed so that changes in gap and membrane tension tend to have compensating effects upon the microphone sensitivity.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-CR-149789 , PGSTR-PH77-48
    Format: application/pdf
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