S87 91st Meeting: Acoustical Society of America S87

aural listening by impaired subjects. For all listening conditions for both groups of subjects, the voicing feature was perceived better than the manner feature, which in turn was perceived better than the place feature. The place feature had an advantage in the initial position, and the manner feature had an advantage in the final posi- tion for binaural and monaural listening for both groups. The voic- ing feature had a small advantage for the initial position for all con- ditions. The prolongation of the delay between the primary and de- layed signal had the greatest influence on the place errors in the initial position for both groups of subjects. [Supported by NIH NISND grant.]

11:42

MM17. Perceptual features of normally hearing and hearing impaired subjects revisited. R. M. Lawarre and J. L. Danhauer (Department of Speech Communication, Bowling Green State University, Bowling Green, OH 43403)

Perceptual strategies in rating dissimilarities among 24 prevocalic consonants paired with/a/were investigated for normally hearing and two groups of hearing impaired subjects (i.e., one with flat, and one with sloping sensorineural losses). A 57 6-item equal appear- ing interval scaling data collection method was employed. The diadic- paired stimuli were presented bilaterally at MCL. Subjects' ratings on a 1-7 scale were converted to 24 X 24 full symmetric dissimilarity matrices and submitted to INDSCAL analysis. Individual group and combined analyses were performed. Results revealed features (e.g., sibilant, sonorant, and nasal) common to all groups, as well as group- specific features showing interactions among manner, place, and voicing categories. Results were compared to earlier investigations and data showed that subjects used features in their perception of the speech stimuli, that both common and group-specific features were used, and that individual differences in subjects' weightings of features were present.

FRIDAY, 9 APRIL 1976 PRESIDENTIAL ROOM, 8' 30 A.M.

Session NN. Underwater Acoustics V: Radiation and Scattering

Ralph R. Goodman, Chairman

U.S. Naval Research Laboratory, Washington, D.C. 20375

Contributed Papers

8:30

NN1. Comparison of classical plate theory, Timoshenko-Midlin plate theory, and exact elasticity theory for calculation of transmis- sion loss through fluid-loaded plates. J. W. Young (Naval Undersea Center, San Diego, CA 92132)

Two approximate plate theories, "chssical" (CP) and Timoshenko- Midiin (TM), are commonly used in computing radiation and scatter- ing from submerged structures. These models have previously been compared with an exact elasticity theory calculation of the phase velocity of the first antisymmetric mode of an unloaded plate. On this basis, CP is limited to frequencies below 0.7 times critical for steel in water. No indication of the limitations of TM is, however, found by this calculation. A more appropriate problem for under- water applications is transmission loss through the plate. We have calculated this quantity versus frequency-thickness product and angle of incidence using both the plate models and the exact theory. This approach shows that CP agrees well up to 1.5 times critical frequency. TM correctly predicts the first and second flexural mode transmission pea•ks but fails in other ways at frequencies greater than 4.0 times critical. In particular, no effects of symmetric modes are included, and an incorrect limit is reached at grazing incidence.

8:34

NN2. Energetics of fluid loaded hull-like structures. E. F. Berkman, P. W. Smith, Jr., and E. M. Kerwin, Jr. (Bolt Beranek and Newman Inc., Cambridge, MA 02138) J

The spatial decay rate of vibratory response and of surface pres- sure for locally excited fluid-loaded ribbed plates is predicted and physically interpreted from the viewpoint of statistical energy an•ly.qj.q_ Several c_a_nopjc•l problem so!utio_n_s are comb,_'ned to yield a first order energetic model of the propagation of acoustic po wet along fluid loaded hull-like structures below critical frequency. These canonical problems are (1) damping of free flexural waves due to radiation from rib supports for periodically supported plates and,

(2) the hull grazing pressure field due to local excitation of a homo- geneous plate. Comparison is made between analytic results and limited experimental data.

8:38

NN3. Generation of sound by vortex shedding-the relevance of the Kutta condition. M. S. Howe (Engineering Department, Cambridge, England).

The generation of sound by the fluctuating lift forces on a strut or airfoil is reexamined by treating the wake vorticity as the aero- dynamic source and using the appropriate Green's function. It is shown that at low Mach numbers the intensity of the radiated sound is effectively independent of whether or not a Kutta condition is imposed at the trailing edge. It is argued that recently published theoretical results which predict a large increase in the radiated sound power when the Kurta condition is imposed, and also those which predict a channelling of an intense sound wave along the wake, are in error.

8:42

NN4. Interpretation of radiation field in terms of sub-beams. John J. McCoy (The Catholic University of America, Washington, DC 20064 and U.S. Naval Research Laboratory, Washington DC 20375)

Two frequently employed measures of a statistical radiation field, i.e., the mutual coherence function and the intensity directional spectral density, are considered as they apply to deterministic beamed signals. Mathematical formulations, in the form of differ- ential equations, that govern the propagation of these measures, had previously been presented. Here, we show that solutions of these formu!at•o•s surest an Lnterpretation of a radhtion field in terms of sub-beams. These sub-beams are the natural extensions of the ray tubes of the geometric theory. We apply the formulations to propaga- tion through a grating. Several classical results, as well as some exten- sions of these classical results, are obtained.

J. Acoust. Soc. Am., Vol. 59, Suppl. No. 1, Spring 1976

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