NBS Special Publication, Ausgaben 300-308U.S. Government Printing Office, 1972 |
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absolute pressure absorption accelerometer accuracy acoustic acoustic impedance ambient anemometer angle applied atmospheric audiometer autocollimator average barometer Bureau of Standards cistern có có có coefficient computed constant correction coupler curve cylinder decibels deflection value density determined dewpoint diameter difference earphone effect electrical equation error flow fluid free-field frequency given gravity heat hygrometer impedance indicated instrument Key words laboratory liquid load manometer measured meniscus ment mercury column mercury surface meter method micrometer microphone mixing ratio mounting National Bureau nozzles obtained percent pickup piston gage precision procedure proving ring psychrometer range reading reference relative humidity saturated saturation vapor pressure scale shown in figure sound pressure level standard deviation test chamber thermocouple threshold tion tube U-tube uncertainty vacuum valve vapor pressure velocity vibration viscosity voltage volume water vapor weight wet-bulb temperature zero
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Seite 71 - T. specimen is determined by measuring the change in the decay rate of sound in a reverberation room when the test specimen is brought into it. The test signal is turned on long enough for the sound pressure level in the reverberation room to reach a steady state. When the signal is turned off, the sound pressure level will decrease and the rate of decay, d, may be determined from measurements of the average time, T, for the sound pressure level to decay through a certain range. The absorption, A,...
Seite 71 - ... Nonlinear Decays — Do not use decays that deviate substantially from a straight line over the measuring range when graphed on a logarithmic scale. By "substantially" it is meant that the uncertainties do not overlap when the decay times are measured for the two halves of the decay as outlined in 5.5.3. Make periodic checks of linearity, for curved or broken line decays indicate conditions that should be avoided. The conditions may often include a sound field that becomes less and less diffuse...
Seite 35 - NOTE 1 — The values stated in US customary units are to be regarded as the standard. The metric equivalents of US customary units may be approximate.
Seite 89 - When source room levels and receiving room levels are to be measured with the same instruments perform sensitivity checks before beginning the measurements in each room and at intervals during the test, to assure drift of not more than 0.5 dB.
Seite 9 - Available for a nominal charge from the American Standards Association, 70 East 45th Street New York 17, New York and the Compressed Gas Association, Inc., 500 Fifth Avenue, New York 36, New York.
Seite 78 - Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions" and Classification E 413 for "Determination of Sound Transmission Class.
Seite 71 - This Tentative Recommended Practice has been approved by the sponsoring committee and accepted by the Society in accordance with established procedures, for use pending adoption as standard.
Seite 40 - ... spaced at least one-half wavelength apart (3). For the purposes of this test method it is sufficient to ensure that microphone positions are separated by at least 1 m (3.3 ft). Do not use microphone arrangements that are obviously symmetrical, such as all in the same vertical or horizontal plane. 8.1.5 Averaging Time — For each sampling position, the averaging time shall be sufficient to yield an accurate estimate of the time-average level. In general, longer averaging times will be necessary...
Seite 71 - Diffraction effects5 usually cause the area of a specimen to be effectively greater than its geometrical area, thereby increasing the measured coefficient. When the coefficients are large the measured values may exceed unity. Since the effects of diffraction are less when the area is greater, laboratories are urged to use a specimen size of at least 6.69 m2 (72 ft2). 4.4 A coefficient measured by this test method should be used with caution, for, not only are the areas encountered in practical usage...