摘要:

For measurement situations involving sound fields that are not well specified, uncertainties associated with the choice of diffraction correction to be used for a typeL(“one‐inch” nominal diameter) microphone can exceed errors in its calibration by one to two orders of magnitude. One benefit from use of smaller microphones is reduction of these uncertainties. Facilities at the National Bureau of Standards have recently been developed for free‐field and pressure calibration of “half‐inch” nominal diameter laboratory microphones by reciprocity. Both facilities use a grounded shield configuration and insert voltage techniques to determine the open‐circuit sensitivity of a microphone. User‐interactive computer programs provide on‐line computations, display, and storage of calibration results. Adaptors are used to perform pressure calibrations in ANSI S1.10‐1966, (RI971) couplers from 50 to 20 000 Hz; use of other couplers could extend this range. Free‐field calibrations for normal incidence are performed from 2000 to 20 000 Hz; this range can also be extended. These methods are used to determine the differences between pressure and free‐field calibrations for various types of microphones, as well as the influence of protective grids of microphones on their free‐field calibration.

ISSN:0001-4966    

DOI:10.1121/1.2017418

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Rome Air Development Center, Hanscom AFB, MA 01731 A transform diffraction theory for either parabolically anisotropic or isotropic media has been formulated under the usual Fresnel region approximations. In rectangular coordinates this approach results in a double inverse spatial Fourier transform integral over the limits of a finite aperture [T. L. Szabo, J. Acoust. Soc. Am.63, 28–34 (1978)]. For circularly symmetric aperture functions, the integral is a Hankel transform. Both forms have been used to obtain analytic expressions for the near and far fields of tapered sources. More difficult cases have been treated by superposition and FFT routines. Calculations will be presented for the fields of focussing and defective transducers.

ISSN:0001-4966    

DOI:10.1121/1.2017429

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Interior noise in an automobile vehicle is known to have an important influence on product acceptability and is therefore an important automobile design consideration. Lightweight unibody construction and other automobile weight‐saving efforts have been known to result in increased interior noise, particularly noise in the low‐frequency range (20‐200 Hz). Vehicle testing has indicated strong correlation between panel motion (i.e., vibrating roof, windows, floor, etc.) and this measured noise, and it has been suggested that the noise may be modulated by the passenger compartment cavity resonance. This paper reviews the application of the finite element method for analyzing the acoustics of the passenger compartment and for computing panel‐excited interior noise. By modeling the complete structural‐acoustic dynamic system, which is comprised of the interior acoustic resonances as well as the vibration modes of the structural enclosure, this analytic method can be used to identify the influence of individual panels on the interior sound pressure field. The capabilities of the method are illustrated by applications to the production automobile, and experimental verifications of the various techniques are presented to illustrate the accuracy of the method.

ISSN:0001-4966    

DOI:10.1121/1.2017433

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Airborne electro‐optical packages are now being considered with increasingly demanding performance requirements. Aircraft linear and angular vibration disturbances thus require more effective isolation and control procedures. Computer aided design of passive vibration isolator locations for two isolators located at arbitrary points along a simply supported beam has been conducted by using a Fibonacci search to minimize the sum of the angular vibration responses at the beam ends [P. W. Whaley and J. Pearson, Shock and Vibration Symposium, 17–19 October 1978].That work is currently being extended to the multiple isolator case, and also to the distributed isolator case. In addition, the distributed optimum control using modern control theory was examined for the simply supported beam and a closed form solution was calculated [W. P. Whaley, ASME Paper No. 78‐WA/DSC‐39, presented to the 99th ASME Winter Annual Meeting, San Francisco, CA, 10–15 December 1978]. The subject of this paper is future efforts being directed towards a unified vibration control theory utilizing both passive and active isolation and control techniques. The optimization theory, relying heavily on modern control theory, should be utilized to design the optimum vibration isolation configuration given a particular airborne electro‐optical system. [This work was conducted while the author was assigned to the Air Force Flight Dynamics Laboratory.]

ISSN:0001-4966    

DOI:10.1121/1.2017437

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The transient response is predicted for an elastic cylindrical shell impinged upon by a plane acoustic wave in a fluid. The approach is numerical and in particular applies theUSA‐STAGScode which combines the finite element method for the structural analysis and the doubly asymptotic approximation (DAA) for the fluid‐structure interaction. Several causes are analyzed, and the computations are compared to an exact solution [H. Huang, J. Appl. Mech.37, 1091–1106 (1970)]. The agreement is very close, a fact which, in the situation considered, strongly supports the applicability ofUSA‐STAGSto fluid‐structure interaction problems, and more generally validates the DAA methodology.

ISSN:0001-4966    

DOI:10.1121/1.2017439

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Removal of the silent closure interval from /spa/ or /sta/ typically results in the perception of /sa/. To determine whether this phenomenon is an instance of phonetic (as distinct from auditory) perception, we used the method of duplex perception. This has the advantage that a single stimulus pattern yields speech and nonspeech percepts simultaneously [D. Isenberg and A. M. Liberman, J. Acoust. Soc. Am.64, S20(A) (1978)]. Applying this method to the synthetic syllables /spa/ and /sta/, we separated the F2‐F3transitions (which alone distinguished the syllables} from the base (the pattern common to the two syllables). When the base is presented in isolation it sounds like (s‐a/ or /as/ depending on whether or not a silent interval is present. The transitions alone sound like nonspeech chirps. When the base and the transitions are presented dichotically, listeners simultaneously hear a syllable and a nonspeech chirp. In the ear which receives the base, they hear /spa/ or /sta/ when a silent interval is present, contingent on the transition in the other ear; when the silent interval is absent, /sa/ is heard with either transition. In contrast, the nonspeech chirps, heard in the ear which receives the transitions, do not change with the presence or absence of the silent interval. Given that the speech changes while the chirp does not, the effect of silence in cueing the stops can hardly be interpreted as an instance of auditory interaction: it can more plausibly be seen as a result of distinctively phonetic processes. [Work supported by NINCDS and NICHD.]

ISSN:0001-4966    

DOI:10.1121/1.2017446

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

At an earlier meeting, we presented results of a study of the effects on phonetic identification of orthogonal variation in a temporal cue and a spectral cue that are the common acoustic products of a single phonetically significant act. Within limits, contrasting phonetic identifications could be obtained by varying either one, and the presence of an extra amount of one could compensate for the absence of the other (thus a trading relation was established). We suggested ways of pairing the cues in syllables for discrimination judgements to test whether the implied perceptual equivalence was genuine. This paper reports the results of such a test. The appropriate pairs did prove hard to discriminate. We propose that the equivalence thus demonstrated is due to a perceptual system specialized to take account of the common origin of the two cues. [Work supported by NICHD.]

ISSN:0001-4966    

DOI:10.1121/1.2017452

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The onset of the first auditive startle response to frequency modulated linear ramps was studied. Upward and downward ramps, (0.5–0.75, 1–2, and 2–4 kHz) served as stimuli for 50 rabbits from eight litters with five replications. Animals were tested from age 6–l0 days. At 6 days there were no behavioral responses to sound. At day 7 only responses to the 0.5–0.75 kHz ramp was observed. On day 8 responses to 0.5–0.75 and 1–2 kHz were observed. At age 9 days responses to all stimuli were noted and replicated at age 10 days. For all litters, the downward ramps evoked a greater response than upward ramps; in fact downward ramps were equivalent to a response level 1 day earlier than upward ramps for all frequency areas. Although the low frequencies were the first to evoke behavioral responses, the basal portion of the cochlea is the first to mature. The position that the basal turn mediates early low‐frequency responses (Rubel, 1978) will be discussed along with neonatal rabbit processing of frequency specific calls.

ISSN:0001-4966    

DOI:10.1121/1.2017459

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Low‐frequency sensitive fibers from the amphibian papilla of anurans (Bufo americanusandRana pipiens) respond to combination tones of the form f2–f1in the same way as do mammalian cochlear nerve fibers, even though the structure of the receptor organs is quite different in the two classes. In anurans the shapes of the combination tone and pure tone tuning curves are similar, suggesting that the amphibian papilla fibers are responding to energy generated at the difference frequency. Furthermore, the response of a fiber to a tone pair, whose frequencies are harmonically related and whose fundamental is near the fiber's best excitatory frequency, can be almost totally eliminated by the addition of energy at the fundamental provided it is of appropriate intensity and relative phase. Systematically varying the phase of the fundamental produces a sharp minimum in firing rate with a maximum occurring about 180° later. These results suggest that a basilar membrane is not necessary for propagation of energy at the difference frequency; it can be transmitted by the inner ear fluids and the tectorial membrane. [Supported by NIH Grant NS‐09244.]

ISSN:0001-4966    

DOI:10.1121/1.2017463

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Post‐stimulus‐time histograms (PSTs) were obtained for responses to tone and wide‐band‐noise bursts with stimulus rise times (RTs) between 0–25 ms. For the longer RTs, the PSTs built up to a peak and then decayed, and the results resembled those reported by Rigdenet al.[J. Acoust. Soc. Am.63, S77(A) (1978)]. At low‐sound intensities the time delay to the peak approached the stimulus RT, and the delay decreased as intensity increased. In some units, during certain time intervals, firing rate was a nonmonotonic function of sound intensity even though overall firing tale increased monotonically. These shape changes and nonmonotonicities were not present for the shortest RTs, suggesting that they do not reflect a time‐dependent nonlinearity and may result from an interaction between the long stimulus RT and a monotonically increasing nonlinearity followed by adaptation. Adding a suppressing tone above CF produced PST shape changes and rate changes similar to those caused by decreasing the sound intensity, further suggesting that intensity‐dependent nonlinearities are located peripherally to the site of adaptation.

ISSN:0001-4966    

DOI:10.1121/1.2017467

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP