摘要:

A fixed amplitude sinusoid that was frequency modulated by a sawtooth or triangle wave was used to mask a 20‐msec pure‐tone signal. The linear portions of the modulating waveforms were 150 msec in duration and swept the masker frequency between 1.5 and 0.75 kHz. A frequency contour of the masking was obtained when the temporal position of the signal was fixed relative to the sawtooth or triangle and the signal frequency was varied. A temporal contour of the masking was measured when the signal frequency was fixed and the temporal position of the signal was varied. Temporal and frequency selectivity indicated by differences of 30–40 dB of masking were observed in both kinds of contours. A linear model consisting of a bandpass filter followed by a power integrator provided a fair approximation to principal features of the masking contours when the bandwidth of the filter was 100–200 Hz and the time constant of the integrator was 10 msec. Similar resonant systems are found in spectrum channel vocoders and in instruments that produce speech spectrograms. The model tends to underestimate the masking at the higher frequencies and does not exhibit the type of deep, narrow‐band notches that are found in frequency contours of the masking.

ISSN:0001-4966    

DOI:10.1121/1.1914345

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The sound‐pressure transformation of the pinna and the ear canal of the guinea pig has been measured in the frequency range 1–15 kHz. Below 1 kHz, the outer ear does not cause any significant modification in sound pressure. Between 3 and 10 kHz, the pinna provides a boost in pressure which can specifically be attributed to resonance in the concha. This boost, however, is dependent on the location of the sound source with respect to the pinna. The largest amplification is obtained when the speaker is pointed directly into the entrance of the ear canal. The acoustic behavior of the ear canal of the guinea pig is similiar to that of a rigid circular cylinder, open at both ends, about 9 mm long and 2.5 mm in diameter. The pressure transformation between the eardrum and the entrance to the ear canal is strongly dependent on the loading effect of the middle ear. Thus, experimentally induced changes in the impedance of the middle ear, and natural changes due to disease alter the sound transmission across the eardrum of this animal. In normal animals, the eardrum pressure is roughly 5 dB higher than the free‐field pressure in the frequency range 1–10 kHz. This boost is attributed partly to the effects of the body and partly to the sound‐pressure transformation by the outer ear.

ISSN:0001-4966    

DOI:10.1121/1.1914346

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

In certain types of musical performances systematic deviations from the frequencies of the equally tempered scale have been observed. In such scales the octave interval exceeds a 2:1 frequency ratio slightly. Experiments were carried out in which musically trained subjects matched the upper octave of a reference tone with a subsequent variable tone. Both signals were complex tones. The results show that (1) generally the physical size of the perceptually pure musical octave, briefly the physical musical octave (PMO), exceeds a 2:1 frequency ratio also when complex tones are used, and (2) the PMO is intensity dependent. This intensity dependence can be explained as a consequence of a pitch‐intensity dependence in complex tones. A stretched scale derived from the experimentally established average PMO at different frequencies shows striking similarities with the stretched scales observed in musical performances.

ISSN:0001-4966    

DOI:10.1121/1.1914347

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1914348

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A short review is given of the acoustics of the reverberation chamber. Earlier work by Sabine, Bolt, and Cook is discussed, and the effects of moving the position of the source, the receiver, and a reflecting vane are considered. The statistical properties of reverberant sound fields without time‐varying elements are reviewed, and the space‐variances obtained by averaging at discrete points and along a continuous traverse are compared. The case of the reverberant sound field produced by a band of noise is then taken up, and finally some areas needing further study are mentioned. These include the accurate measurement of the power output of a pure‐tone source, and the theory and practice of moving reflectors.

ISSN:0001-4966    

DOI:10.1121/1.1914349

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

In practice, many sources of sound such as motors, pumps, fans, blowers, and transformers radiate sound having discrete frequency components. The reverberation room is a particularly convenient environment in which to determine the sound power produced by such sources provided that the measurement uncertainty can be reduced to an acceptable value. If the measurement uncertainty lies within standardized limits, the room is said to “qualify” for measurements on sources of discrete‐frequency sound. The causes of the various uncertainties in the determination of sound power have been considered. It is shown that, in effect, the discrete‐frequency room qualification procedure allows the measurement uncertainty to be estimated for a monopole‐type sound source. The problems involved with discrete‐frequency and swept‐frequency qualification procedures are discussed, and experimental qualification data for several rooms with and without vanes and other accessories are presented. Methods of generating the frequencies necessary for the room qualification procedure are examined. From both theoretical and experimental studies it can be concluded that a major factor affecting the qualification of the reverberation room is the uncertainty in the measurement of the mean‐square sound pressure throughout the room. This factor can be minimized by increasing the number of independent samples that one uses to estimate the mean‐square pressure in the room, either by using a sufficiently long continuous microphone traverse or by using multiple microphones. At low frequencies (say, below 500 Hz in a 280‐m3reverberation room) the variability of the sound‐power output with source position (change in radiation impedance) is also a major source of the uncertainty of the sound‐power estimate if the sampling of the sound field has been accomplished adequately.

ISSN:0001-4966    

DOI:10.1121/1.1914350

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The measurement of sound‐power injection into a reverberant room is subject to statistical uncertainties owing to large fluctutations of sound‐pressure level with variations in source frequency and source and/or receiver position. Especially for low‐frequency pure‐tone sources, point‐source theory indicates a requirement of many microphone and source positions if radiated power is to be accurately measured. An investigation has been conducted to determine the effect of finite source size on the power statistics in a reverberant room for pure‐tone excitation. Theoretical results indicate that the standard deviation of low‐frequency pure‐tone finite sources is always less than that predicted by point‐source theory and measurably less when the source dimension approaches one‐half of an acoustic wavelength. A supporting experimental study was conducted utilizing an 8‐in. loudspeaker and a 30‐in. loudspeaker at eleven source positions. The resulting standard deviation of sound‐power output of the smaller speaker with source position is an excellent agreement with both the derived finite‐source theory and existing point‐source theory if the theoretical data is adjusted to account for experimental incomplete spatial averaging. However, the standard deviation of the sound‐power output of the larger speaker with source position is considerably lower than point‐source theory indicates, but in good agreement with the derived finite‐source theory.

ISSN:0001-4966    

DOI:10.1121/1.1914351

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Approximately 150 sound‐power‐level tests have been conducted of unitary and room air‐conditioning equipment at Kodaras Acoustical Laboratories (KAL). This paper submits a complete description of the reverberation rooms used in conducting the tests as well as information regarding the temperature‐ and humidity‐control systems, room noise levels with and without the control systems operating, and the measurement instrumentation used at KAL. In addition, problems encountered in selecting microphone locations, loading the test specimens, dealing with pure tones and other every day practical problems and their solutions are discussed. Future changes that will be made to this facility as a result of our experience will be presented.

ISSN:0001-4966    

DOI:10.1121/1.1914352

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Two kinds of documents prescribe standards for noise measurements on machines and stationary equipment in the field. Fundamental methods of measurement are described in standards prepared by American National Standards Committee S1 for which the Acoustical Society of America serves as the Secretariat and by Technical Committee 43 of the International Organization for Standardization (ISO). Test codes applicable to specific types of equipment are prepared in the United States by engineering societies and trade associations. These two classes of documents should be mutually supportive and interdependent, but such is not always the case. The requirements of existing standards on noise measurementsin situare summarized, the shortcomings of these documents are described and the needs for new standards are reviewed.

ISSN:0001-4966    

DOI:10.1121/1.1914353

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Even under free‐field conditions there are three types of errors in the measurement of machine noise: (1) the nearfield error, (2) the error caused by suing a limited number of measuring points, and (3) the error in measuring sound pressure at each point. The magnitude of these errors is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1914354

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP