摘要:

Electric responses evoked by transient acoustic stimuli were recorded by gross electrodes from the periphery and cortex of the cat. The responses to clicks and to the rapid onset of bursts of noise or tones are characterized by a sharpN1peak in the peripheral response and by a broader cortical response. When the rise time of the onset of bursts of noise (or tones) is lengthened, or when a burst of sudden onset is presented in a noise background, it is possible to obtain cortical responses under conditions for which theN1component of the peripheral response is undetectable. These results and associated findings are interpreted by considering the degree of synchronization of the discharge and the wave forms of the activity of units that contribute to responses recorded by gross electrodes. A simple statistical interpretation is presented.

ISSN:0001-4966    

DOI:10.1121/1.1909497

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The reverberation chamber technique was used to determine the sound spectra and acoustic power radiated by air jets over a range of subsonic velocities. Different air jets were used with round and square velocity profiles; nozzles of circular cross section, and nozzles with saw‐tooth and corrugated ends were also used. Of these nozzles only the latter type gave a significant (9 db) reduction in sound power output for a given exit‐pressure ratio. A study was made of the limitations of the reverberation chamber technique caused by the absorption in the chamber. When this absorption became considerable, the measurement of sound pressure level in a circle around the sound source revealed a directional pattern, and the assumption of uniform energy distribution in the chamber became invalid. This situation was noticeable at frequencies above 5 kc in the National Bureau of Standards chamber, owing to air absorption.

ISSN:0001-4966    

DOI:10.1121/1.1909499

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Experiments using synthetic speech show that third‐formant transitions are cues for the perception of /b,d,g/. Detailed results are presented for a variety of third‐formant transitions paired with each of a number of second‐formant transitions in initial position before the vowels, /i/ and /æ/.The results obtained with various third‐formant transitions depend in part on the steady‐state level of the third formant, implying the existence of third‐formant loci analogous to those previously found for the first and second formants. The data of the present experiment are not sufficient to permit a specification of these loci.The effects of third‐formant cues are independent of the two‐formant patterns to which they are added. When a third‐formant cue enhances the perception of a particular phoneme, it typically does not do so equally at the expense of the other response alternatives.

ISSN:0001-4966    

DOI:10.1121/1.1909501

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Speech intelligibility was examined at high noise levels for a range of speech and noise spectra. Over a wide range of conditions, deterioration of speech intelligibility was observed with a constant speech‐to‐noise (S/N) ratio at high noise levels. Little change in intelligibility was observed for over‐all speech levels to 130 db in the absence of background noise. Control tests ruled out distortion within the equipment as the factor associated with the loss of speech intelligibility.

ISSN:0001-4966    

DOI:10.1121/1.1909503

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The utilization of a particular form of stereophonic information was studied with respect to the intelligibility of a single speech source heard in the presence of a voice babble of other speakers. The reception of monosyllabic words, presented against a babble of 1, 2, 4, or 7 talkers, was compared under two listening conditions: (1) In thestereophoniclistening condition, one set of background talkers was presented to one earphone, another set of background talkers was presented to the other earphone, and the test words were presented binaurally, in phase; (2) In thecontrollistening condition, only a single set of background talkers, and the test words, were presented to a single ear. The stereophonic advantage, for 50% word intelligibility, ranged from 12 db with 1 background voice per channel to 5.5 db with 7 background voices per channel.

ISSN:0001-4966    

DOI:10.1121/1.1909505

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Ultrasonic absorption and velocity in acetic acid and triethylamine were measured up to pressures of 3280 kg/cm2. The results show that the relaxation frequency in each liquid is independent of pressure to within experimental accuracy (±5%). The pressure data confirm the assumption of Heasall and Lamb that the loss in triethylamine is a rotational isomeric effect. The results in acetic acid are in agreement with the predictions of the monomer‐dimer theory.Comparison with previous results in carbon disulfide and glycerol shows that, depending upon the mechanism, increasing the pressure can cause the relaxation frequency in a liquid either to increase, decrease or remain constant. It appears that the pressure dependence of the relaxation frequency can be useful in distinguishing the type of relaxation present.

ISSN:0001-4966    

DOI:10.1121/1.1909507

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The echo returned by a body is known to be frequency dependent if the incident sound has wavelengths greater than or comparable with the over‐all dimensions of the body. Unfortunately, a theoretical investigation into such a dependence involves lengthy computation since exact mathematical solutions are required. In this paper the results are presented of calculations which determine the echoes from the end‐on aspect of a rigid prolate spheroid of fineness ratio 5/3 and from the beam‐on aspect of an infinite circular cylinder, the incident sound consisting of plane monochromatic waves. These are compared with similar known results for a sphere. It is shown for these particular examples that the frequency dependence of the echo varies significantly with the shape of the body which returns the echo. It is suggested that bats use such properties in determining the form of their surroundings.

ISSN:0001-4966    

DOI:10.1121/1.1909509

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A new approximate expression is proposed for the frequency of the point of minimum velocity in a cylindrical shell which is more accurate for higher values of the order numberm(displacements ∼cosmθ). This and earlier approximations are compared with results of precise calculations. The transition between approximations is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1909511

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Standing‐wave measurements are discussed which show that the bottom of a fresh‐water lake near Washington, D. C. behaves acoustically as a pressure‐release surface between 50 and 500 cps. A correlation technique is presented which makes it possible to distinguish between the part of an acoustic signal which arrives by a direct path and the part which experiences a bottom reflection. Results of a study of the acoustic behavior of the lake bottom by this method confirm the conclusions reached from the standing‐wave measurements for frequencies up to 1600 cps. Correlation and transient measurements of the acoustic velocity in the bottom sediment are presented which indicate that the pressure‐release characteristics result from an acoustic velocity in the bottom of less than one‐tenth that of water. This low velocity is attributed to the presence of gas resulting from decaying organic matter in the bottom. The gas greatly increases the bulk compressibility of the bottom sediment and hence lowers the sound velocity.

ISSN:0001-4966    

DOI:10.1121/1.1909513

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A pulsing technique for measuring the blocked impedance of an electroacoustic underwater sound transducer is described. The method permits measuring the blocked impedance under free‐field acoustic loading conditions without resorting to clamping the transducer or to the usual interpolation method. Both theory and measurements are discussed. A means of readily identifying the natural resonance frequency from either an impedance or an admittance plot is also presented.

ISSN:0001-4966    

DOI:10.1121/1.1909515

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP