摘要:

Outdoor sound communication systems for urban areas have been traditionally designed using relatively few sources of sound, located high above the buildings. Results have generally not been satisfactory because of sound attenuation in the atmosphere and diffraction by buildings. As an alternative, a block by‐block coverage system using many sound sources placed in the streets has been investigated. Extensive acoustical and meteorological field tests carried out in city streets showed that sound‐propagation conditions are generally favorable there. Typically, the mean wind and temperature gradients are small; consequently, no appreciable sound refraction effects were observed over distances of a city block or two when sound was propagated from a source 10–20 ft above the pavement. Reverberation from the building walls was not detrimental to speech intelligibility when a directive sound source was used with its axis oriented along the street. However, the intelligibility of speech received in a side street some distance away from the intersection was poor owing to excessive sound attenuation and reverberation.

ISSN:0001-4966    

DOI:10.1121/1.1909409

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The use of rating scale isosensitivity data to test a discrete, two‐state model for binary choice detection experiments is shown to be inappropriate unless new assumptions are made. It is argued that, whatever assumptions are added, rating‐scale isosensitivity curves will be different from binary‐choice isosensitivity curves. The suggestion is made that a multistate model may be more appropriate than a two‐state model for rating experiments, but the resulting isosensitivity curves appear to be too similar to those of signal‐detectability theory to make rating‐scale data useful for deciding between the theories.

ISSN:0001-4966    

DOI:10.1121/1.1909411

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1909413

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

This Letter describes a convenient technique that was used to make acoustic resistances of the order of 108Ω (mks acoustic). Each resistance was formed by compressing a short piece of copper tube onto a steel shim of known dimensions.

ISSN:0001-4966    

DOI:10.1121/1.1909417

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

In this Letter, the distance function of vector pitch detection is compared with an approximation derived by Sondhi. Using a geometric interpretation, differences between the two that may effect their pitch‐detection capabilities are made evident.

ISSN:0001-4966    

DOI:10.1121/1.1909423

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

A voice‐excited vocoder transmits a portion of the baseband signal to serve as the synthesizer excitation signal. When the input speech comes from a carbon‐button transmitter via a telephone line, the transmitted baseband must begin above 300 cps. Thus, a low pass sampling scheme for baseband digitization is inefficient. A particular bandpass sampling procedure that is applicable to a digitized VEV is described in this note. The baseband signal is sampled by two pulse trains each of frequency equal to the center frequency of the signal spectrum but displaced from each other by one‐quarter of the sampling period. To recover the signal, both sample trains are applied to a desampling filter identical to the original baseband filter, This technique makes possible the specification of a 9600 bit ser VEV for ordinary telephone speech. Testing was done on a laboratory vocoder together with a general purpose computer simulating a real‐time sampler‐quantizer, Six bit quantization of the bandpassed samples was shown necessary to produce synthetic speech that was samples was shown necessary to produce synthetic speech that was compatable in quality to that produced by the VEV in the analog mode.

ISSN:0001-4966    

DOI:10.1121/1.1909425

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The propagation of ultrasound through a classical, dilute, monatomic gas has been previously studied in terms of the Boltzmann collision equation with the collision term replaced by the relaxation model∂f∂t]coll = −(f−f̄)τwheref̄was the displaced Maxwellian distribution in the presence of the sound wave and the relaxation time τ was assumed to be independent of the instantaneous particle velocityv. This model, although yielding the correct qualitative behavior at low frequencies, did not yield the classical result for the slope of the absorption curve. Rather than taking τ to be independent ofv, it is now assumed that τ −lvwhere the mean free pathlis nowvindependent. That this new model might yield some improvement in the slope of the absorption curve at low frequencies is suggested by the fact that model yields the correct ratio of the thermal conductivity to the shear viscosity: namely, (15/4)(K/m), as opposed to the result 5 (K/m) obtained on assuming τ to be independent ofv. Some slight improvement is obtained, but the classical absorption does not result. The reason for this is briefly discussed.

ISSN:0001-4966    

DOI:10.1121/1.1909427

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

This Letter describes the design and construction of an experimental apparatus that will deform in pure shear at liquid‐helium temperatures single crystals of metals and that provides for ultrasonic measurements while the load is being applied.

ISSN:0001-4966    

DOI:10.1121/1.1909429

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Some recent measurements of the attenuation of the direct sound in concert halls have produced results that are qualitatively very similar to results obtained from measurements of the horizontal propagation of sound over open grassland. In particular, both sets of results show large attenuations in the mid‐ to low frequency region, and the actual frequency of maximum attenuation depends in both cases on the heights of the source and the receiver above the floor or ground. This Letter draws attention to the similarities between the results of the two experiments and concludes that similar processes are involved.

ISSN:0001-4966    

DOI:10.1121/1.1909431

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1909435

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP