摘要:

The auditory brainstem response (ABR) is a composite of potentials generated by neural activity stemming from several regions of the cochlea. A derivation technique is described for reducing the contributions to the ABR that arise from frequencies outside of the frequency band of interest. The technique treats averaged waveforms in an algebraic manner and uses a method of successive substitutions to obtain a derived waveform. The recorded and derived ABR waveforms were analyzed with respect to changes of latency and morphology. The behavior of the waveform components of the derived regional responses was in accord with the data of other studies in which narrow‐band responses were derived from waveforms produced by high‐pass masking of click stimuli. Frequency information was thus extracted from the ABR without the simultaneous presence of other stimuli as in masking‐based derivations. The method of successive substitutions used with brief transient stimuli of different frequencies appears to yield derived ABRs that reflect activity from different cochlear regions.

ISSN:0001-4966    

DOI:10.1121/1.390258

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A stochastic analysis for the cross‐spectral density method of measuring acoustic intensity is presented. The analysis is based on the theory of linear mean‐square estimation as applied to stochastic processes and its generality is preserved through the use of some concepts from the theory of multidimensional stochastic processes. A general theoretical expression, in terms of spatial‐correlation and cross‐spectral density functions between two closely spaced microphones, is obtained for estimating acoustic intensity. The stochastic analysis presented in this paper highlights the effects of incorporating finite difference approximations. It is also shown that how the present cross‐spectral density formula can be reduced to an exact expression for the specific case of plane‐wave sound field.

ISSN:0001-4966    

DOI:10.1121/1.390259

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Experiments were performed to investigate the potential of water‐based foams to reduce the farfield noise levels produced by demolitions activity. Measurements of the noise reductions in flat‐weighted sound exposure level (FSEL), C‐weighted sound exposure level (CSEL), and peak level were made for a variety of charge masses, foam depths, and foam densities (250:1 and 30:1 expansion ratio foams). Scaling laws were developed to relate the foam depth, foam density, and charge mass to noise reductions. These laws provide consistent results for reductions in the peak level, FSEL and CSEL up to a dimensionless foam depth of 2.5. A two part model for the mechanisms of sound level reductions by foam is suggested.

ISSN:0001-4966    

DOI:10.1121/1.390260

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

In order to examine issues related to noise monitoring in the vicinity of moderate‐sized airports, monitoring was performed for 5 months at three sites in the vicinity of the Decatur, Illinois Municipal Airport. The study issues included (1) comparison of predicted and measured day/night average sound levels (DNL), (2) comparison of individual aircraft levels with prediction, (3) temporal sampling requirements for monitoring, and (4) validation that the measured noise is aircraft noise and not other community noise. The measured DNL and the computer predictions compare quite favorably, and most individual aircraft levels compare favorably with data in the FAA computer models. In terms of temporal sampling requirements, it appears that one can use a strategy of choosing four random weeks throughout the year (one from each quarter) to achieve a +2 to −3‐dB tolerance. It was not possible to differentiate ‘‘airport’’ noise from other ‘‘community’’ noise. The results show that it may be better (and far less complex) to choose quiet sites where the airport noise predominates and measure only the total daily DNL values.

ISSN:0001-4966    

DOI:10.1121/1.390261

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

This paper describes a community attitudinal noise survey performed in the vicinity of the Decatur, Illinois Airport. Two hundred thiry‐one respondents were drawn from four distinct noise zones in populated areas near the airport. The day/night average sound levels (DNL) ranged from 44–66 dB. The area is otherwise quiet, residential with large (l/2 acre) lots. The primary analysis arrayed the percent of respondents highly annoyed versus DNL. Good agreement was found between the results of this survey and the general relation developed by Schultz from surveys worldwide, primarily in the vicinity of large commercial airports and highways. In addition, reasonable comparisons were found between respondent estimates of the number of aircraft operations and actual traffic counts. It was also found that respondents who were highly annoyed by aircraft noise were three to four times as likely to be highly annoyed by some other noise than were other respondents.

ISSN:0001-4966    

DOI:10.1121/1.390262

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The effects of some temporal factors of nonsteady noise on annoyance was investigated by means of six experiments. The factors are rising speed, fluctuation speed, fluctuation frequency, and fluctuation deviation. The results show that the ratio of annoyance and the rising speed are in linear relation in log–log coordinates and the annoyance increase with the increase of rising speed from 25 to 1000 dB/s corresponds to the increase of sound pressure level of 2.6 dB. The fluctuation speed, the fluctuation frequency, and the fluctuation deviation have little effect on annoyance provided the equivalent sound level (Leq) is constant. The validity of some rating scales of fluctuating noise is discussed on the basis of the present experimental results.

ISSN:0001-4966    

DOI:10.1121/1.390263

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A comparison was made between acoustic measurements conducted with microphones mounted in the trihedral corners of the 425‐m3NBS reverberation chamber and similar measurements using microphones located in the room interior, away from the room boundaries. Measurements of broadband and discrete‐frequency sound pressure and of reverberation time were included. It was found that for frequency bands below the 200‐Hz 1/3‐octave band, the difference in sound pressure level between the corner and interior locations was, in general, more than 9 dB. In addition, the variations in the broadband steady‐state sound pressure level and in the reverberation time were much less among the corners than among the interior locations for frequencies below 100 Hz. It is concluded that for the lower frequency bands, use of the corner locations may reduce systematic errors associated with the interference patterns and provide greater measurement precision because of the lower spatial variance.

ISSN:0001-4966    

DOI:10.1121/1.390264

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A new resonator method has been developed for measuring ultrasonic absorption in liquids in the frequency range 0.3–10 MHz. This method utilizes Raman–Nath light diffraction to detect a resonance spectrum of standing waves in a cylindrical cavity. Comparison with the spectrum obtained by conventional resonator method demonstrates that distortion of plane‐wave peaks by higher modes can be avoided with the present method. The use of a concave reflector is found to reduce a cavity loss considerably, enabling us to measure absorption down to a few hundred kHz. Results for water obtained using three types of reflectors with curvature radius 100–400 mm are shown.

ISSN:0001-4966    

DOI:10.1121/1.390265

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Ultrasonic dispersion of extensional waves in fluid‐saturated porous cylinders is studied by analyzing generalized Pochhammer equations derived using Biot’s theory. Cases with open‐pore surface and closed‐pore surface boundary conditions are considered. For both cases, the dispersion of the fast extensional wave does not differ much qualitatively from the dispersion expected for extensional waves in isotropic elastic cylinders. A slow extensional wave propagates in the case with a closed‐pore surface but not in the case with an open‐pore surface. The propagating slow wave has very weak dispersion and its speed is always lower than, but close to, the bulk slow wave speed.

ISSN:0001-4966    

DOI:10.1121/1.390266

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A spectrophotometric and a radioactive‐label technique were used to assess for acoustically induced iodine release from sodium iodide. For both techniques there was a dose‐dependent relationship between the percentage of iodine released and the ultrasound intensity (1 MHz,ISPto 30 W/cm2, continuous wave for 1 min). Iodine release decreased with increased atmospheric pressure or increased concentrations of the radical scavenger cysteamine, thus confirming that the release was related to cavitational processes.

ISSN:0001-4966    

DOI:10.1121/1.390267

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP