摘要:

The upper limits for the reverberation time andQfactor of acoustic reverberation chambers with perfectly rigid walls with a smooth surface are determined. The reflection factor for a rigid wall of arbitrary thermal conductivity is determined from a consideration of the viscosity and heat conductivity‐boundary layer. The cases of isothermal and adiabatic boundary conditions are discussed. At very low frequencies the boundary absorption and at very high frequencies the volume absorption are the important factors in determining the losses. The analogous problem of the electric reverberation chamber is compared with the acoustic case. For some conditions the electric and acoustic equations are identical in form, if the electric skin depth is replaced by the thickness of the acoustic viscosity boundary layer. At comparable wavelengths and room sizes the electricQfactors are approximately factor of 50 higher than the acoustic upper limiting values.

ISSN:0001-4966    

DOI:10.1121/1.1908598

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The masking of one click by another was studied as a function of the time interval between the pulses. Two‐alternative forced‐choice procedures were employed to measure thresholds before and after the masking click. Both forward and backward masking were found; the forward effect was more pronounced and longer lasting. Backward masking studied in this way extends beyond what can be explained by peripheral intensity‐latency conversions.

ISSN:0001-4966    

DOI:10.1121/1.1908600

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Results from previous experiments have suggested the notion that the neural information for the lateralization of brief sounds comes largely from the basal turn of the cochlea. An examination of that notion which uses stimuli at the two ears of different frequency content shows that the relation is not so simple. When stimulus clicks to the two ears are identical, then approximate simultaneity places a unitary click‐image in the center of the head; and when the stimulus click to one ear differs only moderately in frequency content from the click to the other, then a single click‐image is still heard but the stimulus click of high‐frequency content must be delivered later than the low‐frequency click in order to place the image in the center of the head. If the frequency difference is great, however, a unitary click‐image is no longer heard. Instead, the sound breaks up into two images, one of high and one of low pitch, which may be independently brought to the median plane of the head by appropriate adjustment of the interaural temporal relation of the dichotic stimuli. Current auditory theory about localization and pitch neither predicts nor accounts for the presence of two such images.

ISSN:0001-4966    

DOI:10.1121/1.1908602

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

This report describes manometric apparatus developed for registering the involuntary displacements of the human tympanic membrane during the reflex contraction of the middle‐ear muscles. Recent tests with the new method have been uniformly successful in 14 inexperienced subjects, as contrasted with only 20 out of 57 previously. The reflex reactions have also been recorded from subjects who had been judged nonreactors in previous tests. Extensive repetitions of tests on one subject have yielded a close quantitative relation between stimulus and response‐index magnitudes. In this set of experiments the stimulus was a click‐free tone of 500 cps, graded in steps of 1 db. The threshold sound pressure level was about 111 db, and response magnitude rose in sigmoid fashion with progressively stronger stimuli.

ISSN:0001-4966    

DOI:10.1121/1.1908604

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The changes in “threshold” and maximum responses for cochlear microphonic potentials and whole‐nerve action potentials were measured following acoustic trauma with 500‐cps tones. The cochlear‐microphonic responses were measured locally in the first turn of the cochlea for 500‐, 2000‐, and 8000‐cps test tones and locally in the third turn for a 500 cps test tone. The whole‐nerve action potentials were measured in response to 500‐ and 5000‐cps tone pips. Injury to the organ of Corti in the first and third turns was rated after examination of histological sections of the temporal bones. The physiological measurements, the injury ratings, and the sound pressures and durations of the traumatic exposures were examined together for correlations and analyzed for common factors. The results served primarily to confirm previous conclusions. For durations of exposure from 5 to 80 min, equal total acoustic energy in the exposure produced equal changes in the electrophysiological responses. The ratings of anatomical injury in the cochlea departed significantly from this relation and tended to depend more strongly on sound pressure than on duration of exposure. The “threshold” shifts for CM responses from the first turn were the same for the three test frequencies, but loss of maximum potential was significantly different for the three test frequencies. The factor analysis grouped the whole‐nerve AP responses to 500‐cps tone pips with the CM responses from the first turn instead of with the CM responses from the third turn.

ISSN:0001-4966    

DOI:10.1121/1.1908606

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The speaker's numerical estimation of his own vocal level, theautophonic response, was found to grow as the 1.1 power of the actual sound pressure produced. When listeners judged the loudness of another speaker's vocalization (the phoneme [a]), the exponent was 0.7. The disparity between these exponents suggests that the speaker does not rely solely upon his perception of loudness in judging his own relative vocal level. The minor role played by loudness in the autophonic judgment is further demonstrated by the fact that the form and exponent of the subjective scale for autophonic responses remain relatively invariant under wide changes in auditory feedback.The power laws governing the autophonic response (exponent 1.1) and loudness (exponent 0.6) were used to predict successfully the outcome of cross‐modality comparisons in which subjects tried to match their vocal level to sounds of various intensities presented either by loudspeaker or by earphone. The slope of the matching function, relating the criterion SPL to the vocal SPL in log‐log coordinates, is given by the ratio of the two exponents.Unless the speaker tries deliberately to hold a constant level, the amount of sidetone gain with which the voice is fed back to the ears alters the voice level. The degree to which the speaker lowers his voice when the sidetone is increased is also predicted by the exponents governing the autophonic scale and the loudness scale.

ISSN:0001-4966    

DOI:10.1121/1.1908608

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The fine‐structure acoustic‐impedance curve of the ear obtained from normal humansin vivois used to develop a network model of the middle ear. First a model representing the middle ear during stapedius muscle contraction is constructed, representing the middle ear with the stapes blocked. A further development adds a circuit corresponding to the input impedance of the cochlea as seen from the stapes. To decrease the influence of the eardrum itself, the eardrum was coated with collodion. Good agreement is found between the input impedance measured at the ear and calculated from the model over the range investigated, from 200 to 1800 cps. The effect of the collodion coating is investigated and the earlier model is modified to fit the input impedance of the uncoated ear. The agreement is not so good as in the case of coated drum. The reason is suggested to lie in the complicated motion of the uncoated eardrum, which could not be represented by the simple circuit of the model.

ISSN:0001-4966    

DOI:10.1121/1.1908610

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The frequency response characteristics of condenser microphones at low ambient pressures are of interest when such microphones are used to make measurements on high‐altitude rockets and capsules. Pressure response curves at a number of ambient pressures in the range 106d/cm2(atmospheric pressure at sea level) to 1.7×104d/cm2(atmospheric pressure at 90 000 ft alt) have been obtained for two commonly used condenser microphones (Western Electric 640AA, Bruel and Kjaer type 4111). Features of the response curves are discussed from a qualitative point of view.

ISSN:0001-4966    

DOI:10.1121/1.1908612

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A study of vowel sounds by means of a spectral analysis keyed synchronously to the voice pitch has been carried out. Spectra are obtained by Fourier analysis of individual pitch periods which were established by visual inspection of oscillogram. A digital computer served as the analyzer. The spectra are represented by a pattern of zeros and poles obtained by a process of successive approximation, again carried out by computer. The contributions from vocal tract and glottal source can be uniquely separated and examined. These results show that vowel sounds can be represented by a sequence of poles arising from the vocal tract and a sequence of zeros character the izglottal excitation. The frequencies of the vocal tract poles agreed with previous measurements, but the damping factors were not entirely consistent with earlier estimates. The zeros showed approximately uniform frequency spacing, particularly at high frequencies. A theoretical development indicated that this characteristic was to be expected from the known structure of the glottal excitation. The zero pattern was used to estimate the ratio of open‐to‐closed time for the glottis during voicing.

ISSN:0001-4966    

DOI:10.1121/1.1908614

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A theoretical study is made of attenuation of ultrasound in cylindrical and rectangular waveguides. The systems treated consist of a piston source radiating into a bounded, inviscid fluid and a receiver of the same size as the source. Expressions for receiver output are derived, and acoustic loss as a function of path length is computed for various source and waveguide configurations. Boundary conditions corresponding to both perfectly rigid and perfectly free walls are considered. The waveguide approach is extended to the limiting case of radiation into an unbounded medium, and results are given for both square and circular systems. In the latter case the curve of loss versus path length agrees well with that previously obtained using more conventional diffraction theory.

ISSN:0001-4966    

DOI:10.1121/1.1908616

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP