FRIDAY MORNING, 20 MAY 2005 REGENCY E, 8:30 A.M. TO 12:00 ...

11:30
5aPAb5. Measurements of the rate of change of the power spectral
density due to nonlinearity in one-dimensional propagation. Lauren
E. Falco, Kent L. Gee, and Anthony A. Atchley Grad. Program in
Acoust., Penn State Univ., 217 Appl. Sci. Bldg., University Park, PA
16802-5018
The influence of nonlinear effects in the propagation of jet noise is
typically characterized by examining the change in the power spectral
density PSD of the noise as a function of propagation distance. The rate
of change of the PSD is an indicator of the importance of nonlinearity.
Morfey and Howell AIAA J. 19, 986–992 1981 introduced an analysis
technique that has the potential to extract this information from a measurement
at a single location. They develop an ensemble-averaged Burgers
equation that relates the rate of change of the PSD with distance to the
quantity Q p 2 p , which is the imaginary part of the cross-spectral density of
the pressure and the square of the pressure. Despite its potential applicability
to jet noise analysis, the physical significance and utility of Q p 2 p
have not been thoroughly studied. This work examines Q p 2 p for the onedimensional
propagation of plane waves in a shock tube. The use of such
a simple, controlled environment allows for a better understanding of the
significance of Q p 2 p . Work supported by the National Science Foundation,
the Office of Naval Research, and the Strategic Environmental Research
and Development Program.
11:45
5aPAb6. Nonlinear standing waves in shaped resonators driven by a
piston. Cheng Luo, Xiaoyang Huang, and Nam Trung Nguyen School
of Mech. and Production Eng., Nanyang Technolog. Univ., 50 Nanyang
Ave., Singapore 639798
The nonlinear standing waves in a shaped resonator driven by a piston
are investigated analytically and experimentally. In the study, the resonator
is an exponentially expanded horn with a piston oscillating at its large end.
The air pressure waves inside the resonator are obtained by solving a 1-D
nonlinear wave equation with the Galerkins method, taking into account
the moving boundary due to the piston. The simulation results, in terms of
the pressure waveforms, the pressure amplitudes, and the resonance frequency
shift, show that the nonlinear standing waves generated by the
piston have characteristics similar to those in the same resonator but under
entirely shaking condition. The experiment is also conducted on an exponentially
expanded resonator. The small end of the resonator is sealed and
the big end is connected to a 5-inch 40 W loudspeaker, functioned as the
driving piston. The resonance frequency shift is observed, and high amplitude
pressures, up to 0.310 5 Pa, have been detected at the small end,
which is 20 times higher than that at the big end. The experimental results
agree well with the simulated values.
FRIDAY MORNING, 20 MAY 2005
REGENCY C, 8:00 A.M. TO 12:00 NOON
Session 5aPP
Psychological and Physiological Acoustics: Auditory Perception and Psychophysics II „Poster Session…
Neal F. Viemeister, Chair
Dept. of Psychology, Univ. of Minnesota, 75 East River Rd., Minneapolis, MN 55455
Contributed Papers
All posters will be on display from 8:00 a.m. to 12:00 noon. To allow contributors an opportunity to see other posters, contributors of
odd-numbered papers will be at their posters from 8:00 a.m. to 10:00 a.m. and contributors of even-numbered papers will be at their
posters from 10:00 a.m. to 12:00 noon.
5aPP1. Sensitivity to stimulus distribution characteristics in auditory
categorization. Sarah C. Sullivan Dept. of Psych., Univ. of Texas,
Austin, TX 78712-0187, Andrew J. Lotto Boys Town Natl. Res.
Hospital, Omaha, NE 68131, Elizabeth T. Newlin, and Randy L. Diehl
Univ. of Texas, Austin, TX 78712-0187
Several experiments were performed to examine the ability of humans
to categorize sounds as a function of training distribution characteristics.
Participants were presented non-speech sounds randomly sampled from
two overlapping distributions. The sounds consisted of 25 narrow-band
noise bursts varying in center frequency from 1000–1360 Hz. Two conditions
were created by varying the ratio of stimuli in each category i.e.,
prior probabilities of each category, resulting in different ideal boundaries
maximizing accuracy. Participants were asked to categorize the sounds
as either A or B and feedback was provided. In one experiment, prior
probabilities were altered mid-session without alerting the subjects. Performance
was tracked by plotting identification functions and noting
boundary placement for each individual block. After only six blocks of
training (35 min), most subjects had established optimal or nearoptimal
boundaries. Identification function slopes were calculated and
found to be steeper than training distribution slopes; suggesting that listeners
established criterion-like boundaries as opposed to performing
probability matching. The fact that listeners adjusted their responses in
accordance to distribution changes within relatively short periods of time
demonstrates the perceptual systems effectiveness at optimizing categorization
based on distribution characteristics. Work supported by NSF and
NIDCD.
5aPP2. Hearing silent shapes: Identifying the shape of a sound
occluding surface. Ryan L. Robart and Lawrence D. Rosenblum Univ.
of California, Riverside, Riverside, CA, 92521, rosenblu@citrus.ucr.edu
While most psychoacoustics is concerned with perception of sound
sources, there is evidence that surfaces which reflect or occlude sound can
also be detected and can guide behavior e.g., M. S. Gordon and L. D.
Rosenblum, J. Acoust. Soc. Am. 107, 2851 2000. While there is also
evidence that listeners can hear the shape of sound reflecting surfaces
e.g., C. E. Rice, Science 155, 655–664 1967, it is not known whether
the shape of sound occluding surfaces can be heard. In a series of experiments,
blindfolded listeners were asked to judge the shape of surfaces of
equal area which occluded a set of loudspeakers emitting white noise.
Overall, listeners were successful at this task, with some listeners showing
near perfect performance. Follow-up experiments examined the acoustic
information supportive of this skill. The findings suggest a type of auditory
sensitivity not often considered in the psychoacoustics literature.
2596 J. Acoust. Soc. Am., Vol. 117, No. 4, Pt. 2, April 2005 149th Meeting: Acoustical Society of America 2596