ISSN:0001-4966    

DOI:10.1121/1.1906717

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.2143408

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

Recordings have been made of the sounds made by the various fish which inhabit the Narragansett Bay area. Of more than 25 species studied, only six produced significant amounts of noise. These were the red‐winged and common sea robin, the toadfish, the long‐horned sculpin, the puffer, and the burrfish. The signals from the recordings were later fed into a harmonic analyzer whose output meter was replaced by an Esterline Angus recording milliammeter. Readings were taken at intervals of 25 c/sec. throughout the entire audible frequency spectrum. Each selected portion of noise was replayed into the analyzer for the measurement at each frequency. The microphones were calibrated so that approximate intensities could be measured. The spectral distribution of the sound is reported for each of the noise‐making species. A second type of noise, not previously reported, has been observed in the case of the toad fish.

ISSN:0001-4966    

DOI:10.1121/1.1917271

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

For a circular plane piston of radiusa, producing an ultrasonic beam of propagation constantk(or 2π/λ), theoretical expressions are derived for special values of the velocity potential at high frequencies. These apply forka⩾ 100 at distanceszfrom the source governed by (z/a)3⩾ka. The velocity potential averaged over a measurement circle equal to the piston is found, and also the potential at the rim of such a circle. The first quantity agrees well with results computed otherwise by Huntington, Emslie, and Hughes. Some remarks on wave front shapes are added. One conclusion is that the assumption of a collimated plane‐wave beam near such a source is not universally very good, although it has some approximate relevance.

ISSN:0001-4966    

DOI:10.1121/1.1917273

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

The effect of viscosity on a second‐order acoustic field has been studied when the time independent relation between the excess pressure and the excess density is replaced by a relaxational one. The method used is similar to that of Eckart except that some terms explicitly neglected by him are included. The introduction of relaxation indicates that steady flow caused by higher order terms is not only caused by the viscosities but is affected by the relaxational relation between the pressure and density. The calculations also indicate that quartz wind measurements are not equivalent to absorption measurements because the temperature variations of the viscosity coefficients enter into the flow problem. If these calculations are correct they suggest interesting problems on classical liquids and give a method to distinguish between relaxational and viscous effects. The introduction of relaxation also explains simply Liebermann's measurements on ethyl formate.

ISSN:0001-4966    

DOI:10.1121/1.1917280

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

As a part of an investigation of the properties of the Riverbank reverberation chamber, comparisons were made between reverberation coefficients and statistical coefficients calculated from impedance‐tube data for 2‐ and 4‐in. Fiberglas board and for resonator‐type panels. One of the objectives of the tests was an investigation of materials for use as possible standards for comparison of reverberation chambers. Tests on resonator panels were suggested by Ingård and Bolt who have found that the impedance could be calculated and was independent of the angle of incidence when the air‐space backing was divided into small cells. Construction details are given for the resonator panels, which consisted of perforated hard‐board mounted with air‐space backing and covered with cloth to obtain a resistance at resonance somewhat greater than ρc. One panel with a 2‐in. air space was designed for resonance at about 700 c/sec. and the other with a 9‐in. air space, for resonance at about 140 c/sec. A panel for about 350 c/sec. was also obtained by using the 2‐in. air space with the facing for the low frequency panel. For Fiberglas, fairly good agreement was found, except near 500 c/sec. where the reverberation coefficient exceeded the statistical coefficient. For the resonator absorbers, however, the reverberation coefficient was considerably greater than the statistical coefficient between 300 and 700 c/sec. and was less at frequencies between 100 and 250 c/sec. The reasons for this difference between the two types of absorbers is being investigated.

ISSN:0001-4966    

DOI:10.1121/1.1917282

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

As part of the study being made in the Sound Laboratory of methods for standardizing hearing diagnostic equipment, measurements have been made comparing the sound pressures developed by earphones in several couplers, used at various laboratories in the calibration of earphones, with the sound pressures developed at the entrance to the ear canal when the earphones are placed over the ear itself. The couplers used in the comparison are the NBS Coupler No. 9A, the “Type I” coupler of the American Standards Association Standard for Coupler Calibration of Earphones, and a British coupler developed at the National Physical Laboratory. Necessarily, only a small number of human subjects could be employed. However, these data are being used primarily for orientation with respect to the design of a new coupler which will present to the earphone a better replica of the acoustical load afforded by the ear.

ISSN:0001-4966    

DOI:10.1121/1.1917292

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

In the theories of pitch perception now widely supported, pitch is regarded as a unitary attribute of auditory experience. There is good evidence, however, that there are actually two pitch‐like attributes, and it is reasonable to suppose that the duplexity of pitch is a reflection of duplexity in the auditory process. The first step in the process is analysis in frequency, performed by the cochlea, which distributes stimulus components of various frequencies to spatially separated channels. The second step, according to the scheme postulated here, is autocorrelational analysis, performed by the neural part of the auditory system, of the signal in each frequency channel. The basic operations of autocorrelational analysis are delay, multiplication, and integration. The nervous system is nicely set up to perform these operations. A chain of neurons makes an excellent delay line. The spatial aspect of synaptic summation provides something very close to multiplication. And the temporal aspect of synaptic summation is essentially running integration. The duplex theory suggests, therefore, that neural circuits following the autocorrelation model supplement the cochlear frequency analysis. The postulated neural autocorrelator of course does not compute autocorrelation functions of the acoustic stimulus: it operates upon afferent neural signals. Because the markedly non‐linear process of neural excitation intervenes between the stimulus and the autocorrelation, the latter gives rise in certain instances to pitches that are not readily explained if the relatively linear cochlear analysis is considered to be the only one. “The case of the missing fundamental” and Schouten's residue effect, for example, are readily accounted for by the duplex theory. In addition, the theory provides a rational basis for the octave relation and for the consonance of other simple harmonic relations.

ISSN:0001-4966    

DOI:10.1121/1.1917296

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

The speculations concerning the intensity‐pitch relationship or illusion as well as divergent findings stimulated a variation of the usual experimental approach to the intensity‐pitch phenomenon. Two subjects were presented with test tones either gradually increased from zero intensity to comparison level or increased to maximum intensity and then decreased to comparison level. Immediately upon presentation of the test tone the subject was presented with a comparison tone and asked to vary its frequency to match the final pitch of the test tone. Three or more attempts were made and a median value accepted. Thus, half the test tones wereincreasedin intensity to the comparison level and half were carried on to maximum intensity and thendecreasedto the comparison level. Five frequency levels were employed, 100, 300, 1200, 2800, and 4000 c/sec. Comparison levels for test tones varied by 5‐db steps from just above threshold to the threshold of feeling. The results of this pilot study partially confirm earlier studies; variations up to 150 cents(112 semitones)particularly on the lower tones, lower tones depressed and higher tones raised in pitch with an increase in intensity (some exceptions in the lower tones), marked individual differences and rather poor consistency in pitch judgments. Pitch judgments were almost impossible at maximum intensity levels and judgments made on tones with intensitydecreasingfrom maximum to comparison level are in contrast to those made on the same intensity level when intensity wasincreasedfrom zero. These findings indicate the pattern of pitch response is markedly irregular, The dissimilarity of the pitch curve of ascending and descending intensities might indicate some physical compensation and attenuation of the ear mechanism itself or perhaps a non‐linear spread of stimulation in the cochlea together with some form of “after‐image” or slow recovery, or perhaps some similar phenomenon at the cortical level.

ISSN:0001-4966    

DOI:10.1121/1.1917299

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

A photographic method using mechanical scanning for displaying the space patterns of sound and microwaves is described. A probe pickup scans the sound or microwave field and the amplified probe output controls the brilliance of a small lamp affixed to the probe. A camera set at time exposure records the light intensity variations of the lamp as it moves across the scanned field, forming a pattern on the film of the amplitude distribution. Phase fronts can be delineated by adding a constant amplitude signal to the probe output. Photographs are included which show: sound and microwave patterns of lenses, diffraction at a straight edge and disk, refraction by a prism, diffusion of sound by a divergent lens, and radiation from loudspeakers. Also, by transposition of source and receiver, directional patterns of transducers acting as microphones are obtained which (by reciprocity) appear identical with their radiation patterns. This provides a means for examining the directional characteristics of non‐reversible transducers such as a carbon microphone. A calibration method is described which allows the relative value of the field intensities to be determined.

ISSN:0001-4966    

DOI:10.1121/1.1917306

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP