Index of content:
Volume 113, Issue 3, March 2003
- BIOACOUSTICS 
Theoretical calculation and experimental study on the third-order nonlinearity parameter for organic liquids and biological fluids113(2003); http://dx.doi.org/10.1121/1.1553460View Description Hide Description
In the present paper we deal with calculating and measuring the third-order nonlinearity parameter for organic liquids and biological fluids. For the organic liquids, the second-order derivative of sound speed with respect to pressure at constant entropy is discussed in terms of thermodynamic parameters, and a formula for calculating is established. Calculated results of for various organic liquids demonstrate that omitting the second-order derivative of sound speed with respect to sound pressure in an isentropic process, could overestimate the value of about 20%–30%. For measuring the finite-amplitude insert substitution technique is employed. A theoretical description of the sound pressure amplitude for the third-order harmonics is obtained using the perturbation method, in which the sound pressure amplitude of the third-order harmonics is shown approximately as a parabolic function of the propagation distance in the medium. By measuring and comparing the sound pressure amplitudes of the third-order harmonics when inserting a test sample, the reference liquid, and a comparative liquid, respectively, the value of for the sample liquid is determined with reference to known values of reference and comparative liquids. An experimental setup is developed, and the measured values of for the organic liquids agree with the predicted ones calculated by the thermodynamic methods. Furthermore, the finite-amplitude method is extended to measure the parameter for biological fluids, and the measured values of for several biological fluids are also presented.
Reverberation of rapid and slow trills: Implications for signal adaptations to long-range communication113(2003); http://dx.doi.org/10.1121/1.1539050View Description Hide Description
Many acoustic signals in animals include trills, i.e., rapid repetitions of similar elements. Elements within these trills usually are frequency modulated and are degraded by reverberation during long-range transmission. Reverberation primarily affects consecutive elements with the same frequency characteristics and thus imposes a major constraint in the evolution of design and perception of long-range signals containing trills. Here transmission of frequency-unmodulated trills with different element repetition rates was studied. Trills were generated at different frequencies to assess frequency dependence of reverberation and then broadcast under three acoustic conditions—an open field and to assess seasonal changes in transmission properties, a deciduous forest before and after foliage had emerged. Reverberation was quantified at different positions within trills. The results show strong effects of vegetation density (season), transmission distance, frequency, element repetition rate, and element position within the trill on effects of reverberation. The experiments indicate that fast trills transmit less well than slow trills and thus are less effective in long-range communication. They show in particular that selection on trills should not act only on element repetition rate within trills but also on the trill duration as effects of reverberation increased with trill duration.