摘要:

The reverberant response of hard‐walled rooms to recycled excitation (“retroreverberation”) is analyzed by means of an electrical analogy theory. Solutions are found in the form of chains, a new link being added each time the excitation is recycled. The solutions describe the time dependence in both the onset and decay phases of the retroreverberation process. The solution is extended mathematically to the frequency domain, in which the method finds its most suitable expression. The physical applicability of the mathematical model has been established by experiments in a reverberation chamber. The experimentally observed temporal behavior of the sound field in the chamber has been predicted by use of the theoretical formula, and the time and frequency constants of the formula have been evaluated and interpreted. The work has provided justification of the initial ideas previously reported [see M. Novoa Nava, “Retroreverberation,” J. Acoust. Sec. Am.53, 798(L) (1973)] and the basis for a quantitative method for measuring the time constants involved.

ISSN:0001-4966    

DOI:10.1121/1.1903475

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Feasibility of performing transmission loss and diffraction measurements using correlation techniques has been demonstrated in an earlier work. In the present paper, these methods are extended from a simplified anechoic environment to a more complicated reverberant environment. The reverberant environment is considered to be the worst condition under which measurements can be made, and thus a true test of the method. Various difficulties are encountered in translation of this method to a reverberant environment and these difficulties are discussed and their solutions indicated. Results suggest that the correlation technique will be a viable measurement method.

ISSN:0001-4966    

DOI:10.1121/1.1903476

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Apodization, a process in which the energy in a diffraction pattern is redistributed among the main lobes and the side lobes, has proved its usefulness in optical imaging systems and in linear sonar arrays. It can also make the numerical reconstruction of holograms more adaptable to varying requirements. To demonstrate, the hologram of a rectangular slot is first reconstructed numerically in the conventional manner. It is then reconstructed after apodizing the diffraction pattern contained in the hologram. One type of apodization led to a reconstructed image that accentuated the discontinuity at the edge of the slot. Another type gave an image with a concentration of energy at the center of the object, thus minimizing interference from nearby objects. It is expected that the method can be extended to other objects by expressing them as summations of rectangular slots.

ISSN:0001-4966    

DOI:10.1121/1.1903477

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

We have investigated the dependence of several anatomical parameters of the guinea‐pig middle ear on body weight, and thus on age. In particular, the volumes of the tympanic and epitympanic cavities are found to increase with age, with the tympanic cavity growing somewhat more slowly. The mass of the incus appears to be independent of body weight. These results are important for establishing the values of parameters used in mathematical models of the middle ear. They are also relevant to theoretical considerations of the significance of middle‐ear resonances.

ISSN:0001-4966    

DOI:10.1121/1.1903478

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Data from first‐order auditory fibers are modeled as a simple renewal process. The interarrival times of neural spikes are treated as a geometric process at multiples of the period of the input signal modified by some temporal jitter, characterized as a frequency‐dependent random variable with a standard deviation proportional to a small fraction of the period of the waveform. Two classes of models are considered: a timing model in which psychophysical decisions are based on the time taken to obtain a predetermined number of counts on many parallel channels, and a counting model in which psychophysical decisions are based on the number of neural events that occur within some fixed time on many parallel channels. For both models it is assumed that the geometric parameter is monotonically a power function of signal intensity, that the threshold criterion of activity in a channel is independent of frequency, and that the number of channels is independent of both signal intensity and frequency. Predictions concerning the discrimination of change in frequency and intensity of a sinusoid are derived. Existing data, both for intensity and frequency, are sufficiently consistent to reject the timing model (which one would expect from other considerations), but they are not sufficiently consistent to provide either a strong test of the counting model or sharp estimates of the parameters of the model.

ISSN:0001-4966    

DOI:10.1121/1.1903479

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Excerpts from sustained vowels as well as pure‐tone bursts were used as input signals to the guinea pig's auditory nervous system. Single unit responses to these signals were recorded from the cochlear nucleus. The results indicated that a neuron's response pattern to a particular vowel was determined by the ratio of the vowel's spectral energy that fell within the excitatory and inhibitory areas of the neuron. Addition of energy in a neuron's inhibitory region resulted in major modifications in the response of the neuron to both vowels and sinusoidal inputs. Generally, the addition of inhibitory energy resulted in a “temporal sharpening” of the response pattern.

ISSN:0001-4966    

DOI:10.1121/1.1903480

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Listeners monitored a rapid series of tone bursts to detect intensity increments in a 1000‐Hz tone presented in continuous white noise. The data were analyzed using TSD statistics and suggest that performance was close to that observed in more conventional paradigms. Possible violations of TSD assumptions are discussed and it is concluded that TSD may be used to analyze the performance of people listening to rapid trains of tone bursts as well as when discrete trials are used.

ISSN:0001-4966    

DOI:10.1121/1.1903481

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

An analysis is made of data from a number of field investigations concerning the influence of steady‐state broad‐band noise on the hearing of workers, exposed to it continuously for eight hours a day. The results relate to exposure times ranging from 10 to 40 years and to noise with noise‐rating numbers for 500 to 2000 Hz (NR) ranging from 75 to 98 or sound levels from 80 to 103 dBA. Noise‐induced shifts of the median hearing levels as well as shifts indicated at the 90th, 75th, 25th, and 10th percentiles, were determined for seven frequencies between 500 and 8000 Hz as a function of exposure years and sound level. The variability in hearing levels associated with noise exposure was shown to be constant after ten exposure years and an increasing function of sound level at each frequency except 4000 Hz. At this frequency, the variance in hearing levels decreased with increasing sound level. The limit of permissible noise exposure, defined as the maximal level which did not cause measurable noise‐induced shift in hearing levels of workers exposed to it irrespective of exposure years, was shown to be NR 75 or 80 dBA. An acknowledgment is made of the need for hearing‐conservation measures given exposure conditions which exceed 80 dBA.

ISSN:0001-4966    

DOI:10.1121/1.1903482

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Weber's law holds over at least an 80‐dB range for intensity discrimination of 200‐msec bursts of noise. Weber's law holds over a comparable range when information regarding intensive differences is effectively restricted to a limited frequency region by the addition of a relatively intense band‐reject noise. In particular, no failure of Weber's law is observed at intensities for which the discharge rates of fibers innervating the frequency region of the stopband are presumably saturated. These results do not support the generally accepted notion that a spread of excitation along the cochlear partition with increasing intensity is necessary for the auditory system to maintain its large dynamic range.

ISSN:0001-4966    

DOI:10.1121/1.1903483

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Persons suffering from perceptive deafness commonly find it difficult to understand amplified speech, and their understanding of speech is easily destroyed by competing speech or noise. One source of perceptive distortion is recruitment, which exaggerates loudness differences among the acoustical elements of speech. A transposition of these distorted loudness relationships from the deaf‐subject span of hearing to the normal span is illustrated graphically, and achieved in practice with an electronic processor. A recording of processed speech, simulating for normal listeners the loudness relationships perceived by deaf subjects with recruitment, accompanies this paper. Recruitment‐compensation processing for hearing aids is also simulated. The recruitment simulation is validated by an experiment with four unilaterally deaf subjects, who compared processed speech in the normal ear with unprocessed speech in the impaired ear. The simulation suggests that (1) recruitment is a sufficient cause for loss of intelligibility in the deaf, whether or not there are other causes; (2) compensation for this recruitment is a necessary, although possibly insufficient, condition for restoring that intelligibility; (3) the benefit of using both compression and post‐compression equalization in a hearing aid designed to compensate recruitment is likely to be considerably greater than the arithmetic sum of the separate, limited benefits of each process; and (4) the combined processing, by restoring redundant speech‐recognition cues to the subjects's perception, can increase the resistance of intelligibility to acoustical interference.

ISSN:0001-4966    

DOI:10.1121/1.1903484

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP