Transmission Of Acoustic Signals Research Articles

Combination earmold and receiver adapter

First Page

Loudness matching in the sound field of a room

Two loudspeakers are placed several meters apart in an acoustically good lecture room (V = 987 m3, Trev≃1 s). The signal is fed alternately to the speakers via a soft switch and individual 40 dB (0.1 dB least count) attenuators. The burst durations are each 1 s. The observer sets the level of speaker A, and the subject is instructed to adjust the level speaker B to a matching loudness. He is free to move around in the room while carrying out the match. Preliminary results indicate that about 65% of the time subjects match loudness to better than 2 dB. About 40% of the time subjects match loudness to better than 1 dB. Since there is a ± 5.6 dB rms Rayleigh‐distributed spread in the point‐to‐point transmission of acoustical signals in a room, the listener's performance implies accumulation of the equivalent of some half‐dozen statistically independent samples of the sound field for each matching sequence. [Work supported by NSF.]

Transmission of a pulsed acoustic signal at a two-fluid interface

The transmission of an acoustic pulse with a plane front at a two-fluid interface is considered. An exact solution is obtained and several properties are derived. Numerical examples are given, showing patterns of the transmitted signal for different pulse shapes and incident angles. It appears that penetration at angles above the critical incidence (according to Snell’s Law) is indeed possible, depending on how the incident pulse is shaped. This happens at the cost of a self-demodulation of the signal.

Quantitative Analysis of Prairie Grouse Vocalizations

The structure of homologous vocalizations of Greater PrairieChickens (Tympanuchus cupido) and Sharp-tailed Grouse (T. [Pedioecetes] phasianellus) was studied during four mating seasons in northwestern Minnesota. In this region males of the two species form display grounds in similar areas and occasionally occur together in mixed grounds where they hold mutually exclusive territories. Hybrids constitute approximately 3% of the combined populations. This study tested the hypothesis that the structures of homologous vocalizations varied predictably with function to assist in reproductive isolation. Aggressive calls were more similar between the species than courtship calls. The dichotomous nature of the birds' vocal systems could promote heterospecific spacing and inhibit mating. The calls of two hybrid males varied in complex ways from those of either parental species. Although prairies are poor environments for transmission of acoustical signals, both species of grouse depend heavily on vocalizations in their communication. Sound transmission is enhanced in these species by low frequencies, use ofsound windows, and crepuscular displaying. Greater Prairie-Chickens (Tympanuchus cupido) and Sharp-tailed Grouse (T. phasianellus; A.O.U. 1982) are sympatric through a narrow zone in the midwestern and north central United States. In this zone hybridization typically occurs at a rate of 1-3% of the parental populations (Johnsgard and Wood 1968, Sparling 1980) although it has been recorded as high as 25% of the combined populations (Lumsden 1970). Ecological isolating mechanisms based on habitat preferences are weak, for males of both species frequently use the same areas for display grounds (Ammann 1957). Similarly, post-mating mechanisms are of little significance because hybrid females are fertile, their fecundity comparable to that in intraspecific matings (McEwen et al. 1969, Sparling 1980). Male hybrids however, may be unsuccessful in attracting mates. Several studies (e.g., Hamerstrom and Hamerstrom 1960, Lumsden 1965, Hjorth 1970, Johnsgard 1973) have suggested that displays may be very important in maintaining species integrity. Descriptions of visual displays, for example, indicate that courtship displays are very different between species while forms of agonistic behavior are similar. Through the use of playback experiments, I (Sparling 198 lb) showed that vocalizations are also important for maintaining species integrity because both Greater Prairie-Chicken and Sharp-tailed Grouse males responded to some of the other species' aggressive calls. The primary purpose of this paper is to further explain the role of vocalizations as isolating mechanisms between Greater PrairieChickens (GPC) and Sharp-tailed Grouse (STG). I test the hypothesis that structural differences among homologous calls vary predictably with function. An underlying premise of this hypothesis is that homologous epigamic vocalizations are more different between species than agonistic vocalizations. This relationship between epigamic and agonistic vocalizations could result if this dichotomy decreased transfer of information between potential heterospecific mates while promoting spacing between aggressive individuals. A second objective of this study is to examine relationships between the structure of calls and their functions. GPC and STG inhabit open grasslands where sound attenuation is especially high (Morton 1975, Marten and Marler 1977, Wiley and Richards 1978). Yet many of the vocalizations given by these birds, particularly the prairie-chicken boom, are noted for their long traveling distances. This acoustical property is probably related to the structure of the signals and to the way in which they are emitted.

Wellbore instrument hanger

A sub for use in an acoustic telemetry system provides a sound path of low impedance to facilitate the transmission of acoustic signals through a string of pipe positioned in a wellbore. The sub section of pipe includes a tubular receiving member positioned in the bore of a pipe section and spaced from the interior walls thereof. Ports and flow channels are also provided to permit the passage of well fluids through the pipe section when an acoustic instrument is positioned in the tubular receiving member. A lateral shoulder is formed in the interior wall of the receiving member and is arranged to matingly receive a flat portion on the instrument. The abutment of the flat portion of the instrument and the shoulder provides a positive sound path for transmission of longitudinal sound waves from the instrument to the receiver member. The receiver member in turn is connected to the pipe section by longitudinal portions essentially concentric with the axis of the pipe section so as to provide a direct low impedance sound path for the efficient direct transmission of longitudinal sound waves.

Measurements of Acoustic Properties of Hard-Pack Snow

AbstractThree experiments were conducted to assess acoustic properties of hard-pack snow. One test involved transmission of acoustic signals in the frequency range 100-20 000 Hz through natural snow-pack in order to measure signal loss of a point acoustic source. At all frequencies the relatively high-energy input signal decays rapidly by energy dissipation, with nominal diffusion occurring at large distances from the source. Signal persistence is greatest in the frequency range 100-200 Hz, In a second test, acoustic bursts in snow columns under deformation were recorded. Spectrum analysis in the frequency range 500-14000 Hz reveals dominance of signal amplitudes at frequencies between 1 000 and 10 000 Hz. This dominance is attributed to the strong attenuation properties of snow and suggests the use of waveguide or collector techniques to monitor natural acoustic emissions in snow-pack. In a third test several waveguide geometries and materials were evaluated for their acoustic signal interception and transmission characteristics. In general, metallic waveguides show the least attenuation of the configurations tested.

Measurements of Acoustic Properties of Hard-Pack Snow

Abstract Three experiments were conducted to assess acoustic properties of hard-pack snow. One test involved transmission of acoustic signals in the frequency range 100-20 000 Hz through natural snow-pack in order to measure signal loss of a point acoustic source. At all frequencies the relatively high-energy input signal decays rapidly by energy dissipation, with nominal diffusion occurring at large distances from the source. Signal persistence is greatest in the frequency range 100-200 Hz, In a second test, acoustic bursts in snow columns under deformation were recorded. Spectrum analysis in the frequency range 500-14000 Hz reveals dominance of signal amplitudes at frequencies between 1 000 and 10 000 Hz. This dominance is attributed to the strong attenuation properties of snow and suggests the use of waveguide or collector techniques to monitor natural acoustic emissions in snow-pack. In a third test several waveguide geometries and materials were evaluated for their acoustic signal interception and transmission characteristics. In general, metallic waveguides show the least attenuation of the configurations tested.

On the Theory of Multi-channel Transmission of Acoustic Signals

On the Theory of Multi-channel Transmission of Acoustic Signals

Use of arrays for acoustic transmission in a noisy ocean

The ocean can be regarded as a horizontally stratified waveguide for the transmission of acoustical signals. The use of transducer arrays in the ocean presents special problems that are not present in an infinite homogeneous medium. For example, the signal at the receiver is the sum of many arrivals and each arrival is dispersive. In the normal mode formalism, the solution for a single frequency source can be expressed as the product of spectrum functions. Each spectral component is the horizontal component of wave number κ. The responses of waveguide transmission function, transmitting arrays, and receiving array can be expressed as functions of κ. Because of the horizontal stratification, horizontal and vertical arrays have quite different properties and are considered separately. The horizontal array is much less critical in design and operates more as it would in homogeneous space. The vertical array operates as a mode filter and is extremely sensitive to the depth and phase adjustment of the transducers. The signal output of the receiving array filter is the product of source, transmission, and receiver functions of κ. The maximum signal‐to‐noise ratio is obtained when the receiver array amplitude and phase response are the complex conjugate of the signal field at the receiver divided by the noise power. The condition is analogous to the matched filter condition of electrical circuit theory. The effect of fluctuations of the stratification of the ocean on sound transmission is included in an approximate treatment. The radiation in a mode is assumed to be trapped, and the radiation scattered by inhomogeneities can be ignored. The average signal transmission was found to depend on the correlation functions and distribution functions of the irregularities. The maximum signal‐to‐noise ratio is obtained when all modes or arrivals can be added coherently; i.e., no phase fluctuations exist. The performance of the arrays decreases as the phase fluctuation increases. Upper and lower limits of the signal‐to‐noise ratio are given for small and large phase fluctuations. The degree of coherence of the modes has been related to the reproducibility of the signal transmission between a single source and a single receiver.

Design and Calibration of Wide-Range Acoustic Transducers

Wide-range (5 cps-250 kcps) electrostatic transducers have been designed for the transmission and reception of acoustic signals through air. These transducers include both the solid dielectric-type transducer constructed from metalized plastic films, and conventional air dielectric condenser microphones of unusually high sensitivity. Techniques for designing an optimum transducer for various applications are discussed on the basis of signal-to-noise ratio. sensitivity, directivity, frequency response, and the complementing electronic equipment. Various methods for the calibration of these transducers over the frequency range from 5 cps to 250 kcps are discussed.

Acoustic Lloyd Mirror Effect in Deep Ocean Water

Measurement of acoustic signal transmission between source and receiver suspended from surface ships on the deep ocean is described. The four sources suspended at a chosen depth (maximum 225 ft) beneath the sending ship were keyed in sequence by 0.5-sec cw pulses. The pulses were received by a hydrophone suspended at chosen depths (maximum 400 ft) beneath the receiving ship. Sources and hydrophones are nondirectional. Signal strengths are presented graphically; one figure for each day of operation. Each figure contains four charts; one for each of the four signal frequencies used. Bathythermograph data are presented. The data are discussed in the light of the Lloyd mirror effect. Correlation with sea state is suggested.