摘要:

This paper presents results from an experimental investigation of the accuracy and precision of various measurement procedures for determing sound‐power output of ’’large’’ machines in the free field over a reflecting plane out of doors. The purpose of the investigation was to place error bounds on several proposed nearfield measurement procedures, chiefly through the comparison of such properties with sound power levels determined from farfield measurements. The sources used in the study included 17 portable air compressors of various types and sizes powered by internal combustion engines. The data analysis centers on the comparison of sound power levels estimated from measured sound pressure levels on two measurement surfaces, one at 7‐m radius (farfield) and a second at 1 m from the surface of the machine (nearfield). Empirical estimates of precision and accuracy are derived for each of several proposed ISO procedures for determination of sound power level. The nearfield measurements were found to produce an overestimate of the farfield power level with the magnitude of the overestimate depending on the measurement surface shape. A measurement surface shape which ’’conformed’’ to the shape of the source was found to have the smallest associated overestimate. Microphone directivity was found to lead an underestimate of sound power level.

ISSN:0001-4966    

DOI:10.1121/1.381286

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Existing methods for determining the sound absorption in rooms usually require some knowledge of the room dimensions. If sound‐pressure‐level measurements are made at various distances from a small source (such measurements herein referred to as a walk‐away test) the room sound absorption can be deduced provided the variation of sound pressure level with distance can be described by the simple equation SPL=PWL (sound power level)+10 log10(Q/4πr2+4/A′), which is commonly credited to Beranek. Unlike the reverberation time and estimated area methods (JSiαi), a walk‐away test can be used to determine the room absorption where either the room volume or wall areas and the absorption coefficients are uncertain or for rooms which are acoustically coupled to other rooms.

ISSN:0001-4966    

DOI:10.1121/1.381287

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

When usinginsitumeasurements to characterize the noise of a machine in other installations, the measurement space must meet certain qualifications, as outlined by Hübner. In cases where nearby walls and other reflective surfaces interfere, such surfaces may be given a temporary sound‐absorptive treatment. If the machine is symmetrical, measurements on an unobstructed side can be accepted as typical of both sides. Temporary barriers may be used to shield measuring microphones from the direct noise of other nearby noise sources which cannot be turned off. While some installations are hopelessly unsuitable for measurements of typical machine noise, such methods can often make an installation acceptable. Similar approaches can be applied to special‐purpose facilities used for noise measurements of machines and engines. An effective facility can be developed at minimum cost for making free‐field measurements above a reflecting plane to distances of at least 5 ft. A recently developed facility of this type in a vacant automotive collision shop was made by covering less than 50% of the hard walls and ceiling with panels of acoustic absorption. Nearly spherical speading (4–6 dB per distance doubling) was obtained out to 24 ft for frequencies above 250 Hz.

ISSN:0001-4966    

DOI:10.1121/1.381288

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Measurements of the surface acoustical intensity have been made on a large centrifugal chiller in order to determine the major noise‐radiating areas of the machine. In addition, an examination of the coherency of these major noise‐radiating areas has suggested that the total noise power can be obtained by addition of the noise power outputs of each component. The measurements were limited toA‐weighted sound‐power levels. The feasibility of the method has been checked by calculating the radiation efficiencies of the two dominant noise radiators. The values were found to be consistent with current knowledge of sound radiation from flexural waves in plates. Similar calculations based only on nearfield pressure measurements have demonstrated the very complex nature of the pressure field surrounding this type of large machineinsitu.

ISSN:0001-4966    

DOI:10.1121/1.381289

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

By using the cross‐sensor field, a beam pattern (for a one‐wave, no‐noise acoustic field) can be generated for a sparse array which is the same as for a filled array. When real‐world effects, such as noise and multiwave acoustic fields, are considered, the performance of the sparse array degrades more than the preformance of the filled array. However, by time averaging the cross‐sensor field the performance of the sparse array is noticeably improved.

ISSN:0001-4966    

DOI:10.1121/1.381290

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A model for narrow‐band surface reverberation is formulated, implemented on a general‐purpose computer, and validated. At each instant of time, the model divides the ocean surface into an annulus of incremental sectors. The time and frequency characteristics of the reverberation from each sector are modeled by passing Gaussian random noise through narrow‐band digital filters. Spherical spreading, absorption, and nonisovelocity effects are included in the model. The validation is accomplished by statistically comparing the model’s output with experimental data collected in an open‐water environment.

ISSN:0001-4966    

DOI:10.1121/1.381291

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

It is a well‐known psychophysical fact that phase changes in a three‐component signal are audible provided that the frequency separation between the components does not exceed a critical value. A possible source of these effects is the phase‐dependent level of the ’’internal components’’ caused by an interaction within the ear of acoustic frequency components and ’’combination tones’’ of the form (n+1)f1−nf2. The experiments described in this paper are intended to verify this hypothesis by both psychophysical and electrophysiological experiments. The level of the internal component as a function of phase was psychophysically estimated in a forward‐masking experiment. Besides, single cell recordings in the cochlear nucleus of the cat were performed to investigate the phase dependence. It has been possible to demonstrate the interaction between acoustic components and combination tones for both experimental approaches. It can be described as a vector addition. Subsequent psychophysical and electrophysiological experiments on the detectability limits of combination tones have shown that these limits correspond to the maximum frequency separations for the audibility of phase changes.

ISSN:0001-4966    

DOI:10.1121/1.381292

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The mechanical tuning of the basilar membrane does not appear to be sharp enough to account for frequency selectivity of primary auditory‐nerve fibers. Various ’’second filters’’ have been proposed to provide the required sharpening. We have studied the properties of one such mechanism, in which the spatial derivative of membrane displacement is taken as the excitatory signal for primary fibers, on a nonlinear computational model of the basilar membrance. Because the wavelength in response to a tone decreases as the wave travels from base to characteristic place, both the slope and curvature of membrane response are enhanced in the neighborhood of the characteristic place. Thus spatial differentiation produces sharpening resembling the difference between mechanical and neural tuning. Phase (as a function of frequency) of the spatial derivative is similar to phase of the displacement, but frequency selectivity (amplitude as a function of frequency) for frequencies below the characteristic frequency is sharpened. In addition, spatial differentiation provides the distinction between mechanical nonlinearity (related in the model to membrane velocity) and neural excitatory signal required to account for suppression of response to a tone at the characteristic frequencyf1by a second tone at a lower frequencyf2. Without this distinction, a tone at frequencyf2intense enough to suppress thef1component of response at thef1place would itself introduce a large component of response at frequencyf2.

ISSN:0001-4966    

DOI:10.1121/1.381293

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A binaural interaction model is described in which the peripheral transduction from acousticalwaveforms to firing patterns on the auditory nerves is included explicitly. Quantitative predictions are compared with available data on the binauraldetection of low‐frequency tones masked by Gaussian noise. The model describes theparametric dependence of masking‐level differences in almost all available data.

ISSN:0001-4966    

DOI:10.1121/1.381294

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Experimental studies of memory for tonal sequences have been extended to include well‐known melodies and long‐term memory. W. J. Dowling and D. S. Fujitani [J. Acoust. Soc. Am. 49, 524–531 (1971)] used real melodies in an investigation of interval (magnitude of pitch changes) and contour (direction of pitch changes). The study used the recognition paradigm, one of its advantages being that it enables subjects who have no skill in music production to carry out the tasks. However, it may be that the recognition paradigm is more useful for investigating stimulus variables rather than subject variables. The present study used a sample of professional classical musicians and a selected nonmusicians group. Both groups used an original production method to represent melodies and tonal sequences. The performance of the two groups was compared under conditions of dictation and production, using a contour task and a magnitude‐estimation task. Although the musicians were generally superior, there was little difference between musicians and nonmusicians in terms of perception of melodic contour. However, both groups performed at a much lower level when estimating interval magnitudes, suggesting that the size of pitch intervals is not normally coded in terms of magnitude. This finding is discussed in the light of Dowling and Fujitani’s interpretation; and an alternative ’’matching’’ model is proposed.

ISSN:0001-4966    

DOI:10.1121/1.381295

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP