摘要:

The results of a search and critical evaluation of the literature pertinent to both the use and the characterization of the performance of antivibration mountings for the control of noise and vibration are described. First to be discussed are the static and dynamic properties of rubberlike materials that are suited for use in antivibration mountings. This is followed by analyses of the simple (one‐stage) mounting system and its subsequent, impaired performance when second‐order resonances occur either in the isolator (wave effects) or in the structure of the mounted item itself (nonrigid supporting feet). A discussion is then given of the performance of the compound or two‐stage mounting system which possesses superior isolation properties for high frequencies. Next, the four‐pole parameter technique of analysis is described and applied, in general terms, to the characterization of the performance of an antivibration mounting with wave effects for the cases where either the supporting foundation or mounted item are nonrigid. The methods adopted for the direct measurement of antivibration‐mounting performance are described, followed by an explanation of how this same experimental determination of transmissibility can also be made using an indirect measurement technique based upon four‐pole parameter analysis considerations.

ISSN:0001-4966    

DOI:10.1121/1.383546

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

This paper describes a precision ac null‐detecting arrangement that has a resolution of better than 0.001 dB for reciprocity calibration of condenser microphones. Systematic errors are analyzed in depth. The uncertainty of the absolute open‐circuit sensitivity is predicted to be less than 0.005 dB, which is approximately an order of magnitude improvement over conventional calibration arrangements. With international standardization, a comparison accuracy of a few thousandths of a decibel can be achieved.

ISSN:0001-4966    

DOI:10.1121/1.383547

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The authors describe a low‐cost ultrasonic amplifier suitable for animal studies. The amplifier delivers 100 V to a solid‐dielectric loudspeaker at 100 kHz, with a 2 V peak‐to‐peak drive. It uses a quasicomplementary, symmetry transistor output stage with short circuit protection. The authors also discuss the problem of identifying crossover distortion while driving a capacitive load.

ISSN:0001-4966    

DOI:10.1121/1.383548

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The growth rate of roots is reduced by exposure to ultrasound at 10 W/cm2for 1 min. The reduction is somewhat greater at 1 MHz than at 5 MHz. A hydrostatic pressure of 30 atm reduced, but did not eliminate, the effect of ultrasound on growth. The frequency and pressure dependence taken together with earlier observations support the postulate that a cavitationlike mechanism is at least partly responsible for the action of ultrasound on the growth of these developing plant tissues.

ISSN:0001-4966    

DOI:10.1121/1.383549

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A single, focused, ultrasound beam of 3.5 W total acoustic output for 2 s at 3.3 MHz was used to create a series of overlapping lesions to sever the corpus callosum of the rat on the midline. A theoretical and experimental determination of the ultrasound field is described and histological evidence of the lesions is provided. Good correlation occurred between the theoretical and experimental results only for the intensity contour lines examined. The experimentally derived focal intensity of 162 W cm−2(at 25 °C) was 24% of the intensity predicted from theoretical calculations. A difference of 2 mm was found for the axial position of maximal intensity, thermocouple plotting showing the focal region to be nearer the transducer than expected from the theory. Histological results indicated that, under certain conditions, from a single dose of ultrasound two lesions could be obtained corresponding to both the theoretically and experimentally derived locations. At lower intensities it was possible to ulitize the upper location to sever the corpus callosum, the lower intensity site then being subthreshold for the rat brain. The trackless localized damage caused by ultrasound makes this method of obtaining split‐brain rats suitable for behavioral and biochemical studies, where any nonspecific damage may have undesirable effects.

ISSN:0001-4966    

DOI:10.1121/1.383550

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

In normal woodwind tone production the nonlinear flow control properties of the reed transfer energy among the harmonics of the spectrum, and the favored playing frequency is one for which the air column input impedance is high at several harmonics. Above the middle of the second register, woodwinds have only one participating impedance peak; yet these notes can be played even without the use of a register hole, despite competing possibilities of low register intermode cooperation. Such notes are possible because enhancement of the reed’s transconductanceAnear its own resonance frequency can offset the small input impedanceZof the air column so that (ZA−1) ≳0, providing an additional means for energy production above cutoff. Spectral levels as a function of blowing pressure, air column impedance, and reed characteristics are derived. Experiments on the clarinet show that the player can adjust the reed resonance frequency from about 2 to 3 kHz. When the reed frequency is adjusted to match a harmonic component of the tone, the amplitude of that component is increased, and the oscillation is heard as being stabilized in loudness, pitch, and tone color.

ISSN:0001-4966    

DOI:10.1121/1.383448

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

There are indications in the literature on speech perception that differences in rise and decay times of the amplitude envelope are relevant physical correlates in phonemic contrasts. Yet, little is known about the perception of rise and decay times as such. In the present study we have attempted to establish JND’s for both rise and decay times of 1000‐Hz sine waves as well as white noise bursts by means of an adjustment method. The rise and decay of stimulus amplitude were synthesized to be linear functions of time. Results show that the JND for a change in rise/decay time is generally about 25% of the duration of the rise/decay time. This Weber fraction is a minimum at rise/decay times of about 80 ms and increases significantly for rise/decay times below 20 ms. Of the four signal conditions (rise versus decay, sine wave versus noise), discriminations of decay time in noise bursts were performed with the greatest accuracy (at moderate rise/decay times), while changes in onset time of sine waves were discriminated best at very short rise times (where energy splatter may have contributed an additional cue).

ISSN:0001-4966    

DOI:10.1121/1.383551

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The purpose of this study was to quantify the effect of timing errors on the intelligibility of deaf children’s speech. Deviant timing patterns were corrected in the recorded speech samples of six deaf children using digital speech processing techniques. The speech waveform was modified to correct timing errors only, leaving all other aspects of the speech unchanged. The following six‐stage approximation procedure was used to correct the deviant timing patterns: (1) original, unaltered utterances, (2) correction of pauses only, (3) correction of relative timing, (4) correction of absolute syllable duration, (5) correction of relative timing and pauses, and (6) correction of absolute syllable duration and pauses. Measures of speech intelligibility were obtained for the original and the computer‐modified utterances. On the average, the highest intelligibility score was obtained when relative timing errors only were corrected. The correction of this type of error improved the intelligibility of both stressed and unstressed words within a phrase. Improvements in word intelligibility, which occurred when relative timing was corrected, appeared to be closely related to the number of phonemic errors present within a word. The second highest intelligibility score was obtained for the original, unaltered sentences. On the average, the intelligibility scores obtained for the other four forms of timing modification were poorer than those obtained for the original sentences. Thus, the data show that intelligibility improved, on the average, when only one type of error, relative timing, was corrected.

ISSN:0001-4966    

DOI:10.1121/1.383552

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A recent study [Olive and Spickenagel, J. Acoust. Soc. Am. 59, 993–996 (1976)] has shown that area parameters derived from linear prediction analysis can be linearly interpolated between dyad boundaries with very little distortion in the resultant synthesized speech. The success of area parameter interpolation raises a question: can other acoustic parameters, such as the power spectrum of the speech waveform, be similarly interpolated? The spectrum is of special interest because speech can be synthesized in real time from spectral parameters on a programmable digital filter. To study this question a speech analysis–synthesis system using spectral parameters (samples of power spectra at different frequencies) was simulated. These parameters were determined from the speech signal at every dyad boundary, and interpolated for intermediate values. Dyad boundaries (representing the limits of transition regions between phonemes) were determined manually. Informal listening tests comparing synthetic speech with and without linear interpolation showed slight degradation in the interpolated speech. This degradation is significantly reduced by using an additional point within the dyad boundaries for interpolation.

ISSN:0001-4966    

DOI:10.1121/1.383553

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

For 140 male subjects (20 per decade between the ages 20 and 89) and 72 female subjects (20 per decade between 60 and 89, and 12 for the age interval 90–96), the monaural speech‐reception threshold (SRT) for sentences was investigated in quiet and at four noise levels (22.5, 37.5, 52.5, and 67.5 dBAnoise with long‐term average speech spectra). The median SRT as well as the quartiles are given as a function of age. The data are described in terms of a model published earlier [ J. Acoust. Soc. Am. 63, 533–549 (1978)]. According to this model every hearing loss for speech (SHL) is interpreted as the sum of a loss classA(attenuation), characterized by a reduction of the levels of both speech signal and noise, and a loss classD(distortion), comparable with a decrease in signal‐to‐noise ratio. Both SHLA+D(hearing loss in quiet) and SHLD(hearing loss at high noise levels) increase progressively above the age of 50 (reaching typical values of 30 and 6 dB, respectively, at age 85). The spread of SHLDas a function of SHLA+Dfor the individual ears is so large (σ=2.7 dB) that subjects with the same hearing loss for speech in quiet may differ considerably in their ability to understand speech in noise. The data confirm that the hearing handicap of many elderly subjects manifests itself primarily in a noisy environment. Acceptable noise levels in rooms used by the aged must be 5 to 10 dB lower than those for normal‐hearing subjects.

ISSN:0001-4966    

DOI:10.1121/1.383554

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP