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The oceanic dolphin genus Stenella is underrepresented in cetacean hearing data. In this study the hearing of three Stenella spp. dolphins was measured using auditory evoked potential (AEP) methods. A single male juvenile Atlantic spotted dolphin (Stenella frontalis) was rehabilitated in Key Largo, Florida, after being sighted alone and emaciated. The Atlantic spotted dolphin’s greatest sensitivity was at 40 kHz, with functional hearing up to 128 kHz. A female spinner dolphin (Stenella longirostris), housed at Mote Marine Laboratory, had peak sensitivity at 40 kHz and functional hearing up to 120 kHz, the highest frequency tested. The sensitive high frequency hearing of the spinner and Atlantic spotted dolphin is similar to that found in other oceanic odontocetes. A pantropical spotted dolphin (Stenella attenuata) was housed at Mote Marine Laboratory and hearing thresholds were determined using AEP and behavioral methods. The pantropical spotted dolphin had a peak sensitivity at 10 kHz, with a cutoff freq...

Auditory evoked potentials (AEPs) allow researchers to measure the hearing abilities of animals that would be difficult or impossible to train for behavioral measurements of hearing. The hearing abilities of live‐stranded cetaceans and wild dolphins can only be made with AEP techniques. In these situations, time with the animal is often restricted to an hour or less, and there is often little control over the acoustic environment in which the tests are performed. AEP measurements may be made while the animals are in air or in shallow pools. For cetaceans in air, sounds are typically presented with a suction cup jawphone. For cetaceans in water, sounds may be presented in a direct field (with the transducer located at some distance from the test subject) or with a jawphone. In each of these situations it is important to understand how thresholds derived from AEP measurements compare with behavioral hearing measurements. Examples of AEP measurements from wild and live‐stranded cetaceans are presented to ill...

Evoked potential measurements of two Florida manatees (Trichechus manatus latirostris) suggest that these herbivores have evolved an auditory system with high temporal resolution. The manatee modulation rate transfer function (MRTF) is maximally sensitive to a 600‐Hz amplitude modulation (AM) rate. This modulation rate is midway between the AM sensitivities of terrestrial mammals (chinchillas, gerbils, and humans) (80–150 Hz) and dolphins (1000–1200 Hz). We also demonstrate evoked potential responses to carrier frequencies up to 40 kHz. These results suggest that manatees may have reasonable underwater localization abilities despite the high speed of sound underwater, which could be important in enabling them to localize oncoming boats.

An acoustic sensor for use in a typical atmospheric condition, which contains both winds and turbulence, such as a wind and turbulence encountered on the exterior surface of a moving airborne flight vehicle includes a probe housing (10) having a streamlined shaped and a set of indentations (30, 32, 34, 36) in the exterior surface thereof extending inwardly located at a particular longitudinal location, radial airflow passages (16, 18, 20, 22) nested in respective ones of the concave indentations, the passages merging at a central manifold of the passages (26), wherein the particular longitudinal location is such as to minimize noise attributable to fluctuation in the wind in a longitudinal direction, and wherein the concave indentations have indentation depths such as to minimize noise attributable to wind transverse to the probe.

Responses of humpback whales to vessel traffic were monitored over two winter seasons during 1983–1984 in Maui, Hawaii. A variety of vessel characteristics including vessel numbers, speed, and proximity were associated with changes in whale behaviors, including swimming speed, respiration, and social behaviors. Smaller pods and pods with a calf were more affected than larger pods. A case study indicated that a calf could be sensitized by the passby of a large vessel, so that it subsequently breached in response to noise from a smaller boat engine which had not previously elicited any behavior change. These findings in conjunction with similar results from summering humpbacks in Alaska indicated disturbance of humpback whales at both ends of their range. Although substantial short‐term effects were noted, long‐term negative consequences are not apparent. Recent aerial surveys of the Hawaiian Islands indicate substantial increases in the number of humpback whales.

A circular flow tank facility has been developed which features extremely low acoustic and vibration ambient conditions. This facility is described, operating procedures associated with its use are presented, and limitations in the measurement procedures are mentioned. The flow facility has been used to measure the noise output of pressure and pressure gradient hydrophones during actual flow conditions and results of these tests are presented and discussed.

A decade ago, two of the authors presented a paper reporting on diffraction and interaural delay of a progressive wave caused by the human head [J. Acoust. Soc. Am. 36, 1993(A) (1964)]. Six live subjects were used in those experiments. The publication was delayed pending measurements on artificial heads then being planned. In this paper, two series of data obtained with the aid of the Acoustical Manikin [J. Acoust. Soc. Am. 42, 204–207 (1967)] are compared with the earlier experiments: (a) Data based on phase measurements; (b) Data obtained using a bandwidth‐limited delta pulse. All three methods provide useful information about interaural diffraction and delay, albeit the third method appears to be the most reliable.

If necessity is the mother of invention, F. V. Hunt surely was its father. Confronted with the need to play some delicate recordings of the Harvard Tercentenary in 1936, Ted invented the first phonograph pickup capable of operation with five‐gram bearing forces—a 10:1 advance in the state of the art—thereby ushering in the era of high‐fidelity sound reproduction. This was followed in rapid succession by a definitive study of tracing distortion with Pierce and Lewis, including an uncanny prediction of the feasible parameters of a long‐playing record. In 1941 and 1945 he received patents on inventions related to pickup and stylus structures, and in 1962 he again reduced the pickup bearing weights by an order of magnitude, producing successful 110th‐gram models which are yet to be commercialized. But Ted's favorite saying was that he would receive most accolades for the work done through and by his students. Two among them, Frank G. Miller (1950) and James V. White (1970), made significant contributions to t...

This paper is a survey and a progress report on present and potential instrumentation to measure loudness levels of sounds. The development of the sound‐level meter (SLM) in the 1930's, its technological and psychoacoustical evolution, and its evaluation as a measurement device are discussed. A loudness‐level monitor, designed to measure the relative loudness level of broadcast programs directly on an indicating instrument, and the development of a new set of equal‐loudness contours are described, together with a new law of loudness‐level addition for combined bands of noise which was discovered during the research. An experimental loudness level meter, devised by adapting CBS Laboratories' loudness level monitor and the potential development of an accurate and practical loudness‐level indicating device are discussed. The results of psychoacoustic evaluations of the loudness level meter versus sound‐level meter are given.

A gradient hydrophone calibrator consists of a precisely made water‐filled tank, with ports to receive the hydrophones to be calibrated and the reference pressure hydrophones, which is set into axial oscillation with suitable drivers to develop a standing wave of sound in the water. An improved calibrator is described, which, by using a very rigid tank, covers a range of 3–2500 Hz. Measurements are simplified through use of electrical feedback, which maintains a constant pressure‐gradient versus frequency function. The applications and limitations of this system to the measurement of sensitivity, frequency response, and phase response of pressure‐gradient and pressure hydrophones, and for obtaining the polar patterns of gradient hydrophones, are described.

Until recently, infrasonic phenomena have been explored mainly with pressure microphones. Gradient microphones, especially when arranged in an orthogonal bigradient array, have the capability of providing information about the direction, as well as the intensity and time of sound arrival. A low‐frequency bigradient array is described. An equivalent circuit for analyzing infrasonic gradient microphones is developed and applied to the analysis of errors that may be expected when the microphone is measured in a spherical field. A plane‐wave calibrator for infrasonic gradient microphones and windscreens, with internal dimensions of 4×4×8 ft, has been built along the principles of the laboratory calibrator for gradient hydrophones described by the present author [J. Acoust. Soc. Amer. 39, 585–586 (1966)] with the added capability for testing the acoustical symmetry of infrasonic microphones. Windscreens affect the low‐frequency response of gradient microphones and the new equivalent circuit has been applied to...

External ear replica for acoustical testing noting sensing element, ear canal and eardrum impedance

Earphone enclosures are described which embody an improved acoustical network for enhanced noise reduction and efficient performance for an earphone. The network uses two chambers, one adjacent to the ear and the other contained in a reentrant expanded portion of the enclosure. The two chambers are connected by parallel passages, one defining predominantly a resistance and the other an inertance. It is shown that this form of network is more effective than an arrangement of inertance and resistance in series. Cushions filled with nonfluid gel provide high wall impedance for improved noise attenuation and conformance with circumaural contours of the head. Values of noise attenuation are given, measured by artificial head and psychoacoustic methods. Performance of a typical earphone in the enclosure is shown.

Recent experiments in underwater directional communication necessitated the use of earphones with uniform response characteristics. Two earphones from headset P‐120‐PQC‐1 were calibrated underwater by loudness‐balance method at 50 dB above 1000‐cps threshold SPL. A 35‐dB range in response was observed in a frequency interval of 200–4000 cps, with principal resonance at 600 cps. Equalization was provided, after considering the role of the 50‐phon loudness contour, resulting in uniform response over the interval of 200–2500 cps. The experiment sheds some light on the role of aural vs bone‐conduction modes in underwater listening and suggests some approaches to improved underwater earphone and calibration methods. [Work supported, in part, by U. S. Navy Mine Defense Laboratory.]

Previously, a scheme was suggested for sensing directional perception underwater by receiving sound with two back‐to‐back cardioid pattern receptors connected to earphones via a crosscoupling network that restores normal interaural delays [J. Acoust. Soc. Am. 36, 1041 (A) (1964)]. To test this scheme, two experiments were performed. (1) Observers under water used calibrated earphones while the experimenter topside adjusted relative voltages to the crosscoupling network to simulate the bicardioid receptor array. The observers under water sensed direction with an accuracy comparable to that obtained with previous in‐the‐air experiments. (2) Two miniature hydrophone transducers were mounted 10 cm apart and were interconnected with a symmetrical phase‐shift network to produce an array with a polar pattern equivalent to two back‐to‐back cardioid transducers, over a frequency range of 200–2500 cps. With this array in variable orientation relative to an underwater projector, and with topside observers listening ...

An improved underwater earphone, insensitive to depth, has been developed. This new transducer offers good efficiency and yields speech reproduction comparable to most air acoustic earphones. The earphone design provides tympanic, rather than bone‐conduction, sensing, thereby providing directional signal information to the listener. Pairs of these devices have been used successfully in a directional communication system for underwater swimmers. Threshold levels and some man‐earphone equal‐loudness contours were obtained for this device.

The loss in acuity which occurs when ears are submerged underwater has been computed using equivalent circuit analysis for the completely filled ear canal and for the canal containing a trapped air bubble at the eardrum. Contrary to popular misconception, the bubble is, if anything, beneficial, not detrimental. This may explain the recent findings of Hollien and Brandt [J. Acoust. Soc. Amer. 46, 384–387 (1969)], who measured no significant difference in underwater thresholds with and without bubble and regarded this as evidence that the middle‐ear mechanism is not functionally operative in underwater hearing. Their contention is not supported by the present analysis. The computed differential loss between aerial and underwater tympanic transmission shows a frequency‐dependent function, which resembles Hollien's measurements, but with 10–15‐dB smaller magnitudes. Various hypotheses relating to this difference still need to be investigated; however, the predicted frequency dependence of the loss lends strength to previous observation [B. B. Bauer and E. L. Torick, J. Acoust. Soc. Amer. 39, 35–39 (1966)] that a rising pressure‐frequency response near the external auditory meatus is needed to produce a normal‐sounding underwater earphone.

An approximate analog circuit of a plane wave confronting an acoustical device of aspect radius a is shown to comprise two in‐phase voltages, respectively, having magnitudes of 2p and p and driving the device through a resistance ρc/A, and inductance 0.5 ρa/A.

A new magnetic microphone has been developed for use in hearing aids and communication and similar equipment which requires a small, light, medium-impedance microphone. The new microphone has a diameter of 1 inch and a thickness of 3/8 inch, and i t weighs 9 grams. The sensitivity is high enough to override the relatively high noise level of transistors in the frequency range most useful for voice transmission.

A calibrator has been developed for gradient hydrophones consisting essentially of a water‐filled drum driven axially by two transducer motors. To the first approximation, the sound pressure and velocity functions within the drum are those that one encounters at the pressure node and velocity loop in a standing wave.

During a previous investigation [“Researches in Loudness Measurement” IEEE Trans. Audio Electroacoust. AU‐14, 141–151 (1966)] a new law of loudness level summation was established. This law may be formulated as follows: Loudness level L of a random noise, measured in octave bands, is L = Lm+20 log Σn (pn/pnm), where Lm is the loudness level of the loudest band, pn is the sound pressure of the nth band of the noise, and pnm is the sound pressure of the nth band of the Lmth equal loudness contour. It is shown that this law, which can readily be implemented in a loudness level meter, is in reasonably close agreement with loudness levels recomputed from Stevens' equation for loudness calculation [S. S. Stevens, “Procedure for Calculating Loudness,” J. Acoust. Soc. Amer. 33, 1577–1585 (1961)].

The simplicity and convenience afforded by a single instrument has proven to be an important factor in stereophonic sound reproduction in the home. A new stereophonic projection console has been developed, based upon practical directional properties of loudspeakers. The stereophonic projection console provides satisfactory separation of left and right sounds by reflection from the room boundaries. Measured performance characteristics and subjective evaluation of the system will be presented.

The random efficiency of the second‐order Limacon transducer family, ρ = [m + (1 − m) cosθ][n + (1 − n) cosθ], is computed and minimum random efficiency of 0.125 is determined to occur when either m or n is 35 and the other is 0.

The acoustic intensity In along a unit vector n can easily be determined by using a cardioid microphone and a voltmeter. If an rms voltage e+ is generated with the microphone oriented against n, and e− with the microphone directed with n, then In = (e+2 − e−2)/(k12ρc), where k1 is the voltage sensitivity of the microphone and ρc is the specific acoustic resistance. In a plane wave reflected from a boundary (as in an impedance tube), the quantity e+2/(k12ρc) represents the intensity of the forward traveling wave and the quantity e−2/(k12ρc) that of the reflected wave. Thus the power reflection coefficient αr = (e−/e+)2.

A system including a compact array of microphones in combination with signal combining circuitry, especially suited for use with surround-sound sources, for producing two composite signals LT and RT corresponding to those required by an SQ-matrix-type quadraphonic system to establish the directional position of the sound sources. The signals produced by selected ones of the microphones are combined to produce an auxiliary signal which contains, to the extent they are present, equal proportions of signals corresponding to the signals LF, RF, LB and RB of the SQ quadraphonic system which exhibit an equal angular relationship respecting corresponding signals in a composite signal representing the sum of LT and RT. The auxiliary signal enables decoding of the directional signals in the 4-3-4 or the θ-3-4 modes.

A compatible four channel system for use in conjunction with a radio transmission system for transmitting four individual audio signals over a medium having primary and secondary information channels and first and second subsidiary information channels, the primary and secondary channels carrying information that is consistent and compatible with existing monophonic and stereophonic standards.

A PB50 test procedure especially formatted for time saving (without carrier sentence) was used in 1974/75 to measure the intelligibility quotient of Satellite Communications Modems. Tests performed within 1–2, 3–4, and 5–6 months after the start of program were repeated by the same team in 1977. Interesting learning/adjustment effects were observed. It appears that the utilization of an unfamiliar PB50 speaker/procedure test sequence may require a 24‐session‐hours learning period before stability is achieved. [This program was supported in part by the U.S. Department of Transportation.]

A system including a compact array of special purpose microphones and an encoder, especially suited for use with surround-sound sources, for producing two composite output signals equivalent to those required by the "SQ" quadraphonic system to establish the directional position of the sources. The output signals from the system can be used directly to record an "SQ"-matrixed tape, or they can be applied to a disc cutter to produce an "SQ" record, or they can be broadcast for reception by FM receivers equipped with an "SQ" decoder, resulting in the generation of outputs in the quadraphonic "SQ" listening system which reproduce the directional characteristic of the original sound sources. Thus, the system performs the function of a conventional multimicrophone and encoder system for "SQ" recording or broadcasting.

The two‐microphone technique has been used to obtain data from which values of acoustic impedance have been calculated for perforated‐sheet linings. The magnitude and argument of the impedance values have been plotted as a function of frequency, wave amplitude, and duct Mach number for five different lining geometries. These results are compared to theoretical values of lining impedance obtained from a set of equations based on past work [E.J. Rice and C.E. Feiler, NASA TN D‐6178 (1971); E.J. Rice, AIAA Paper 73–995 (1973); W.A. Bell, B.R. Daniel, and B.T. Zinn, AIAA Paper 74–61 (1974); A.S. Hersh and T. Rogers, AIAA Paper 75–495 (1975)]. Although the agreement between experiment and theory is good in general, it is not good in detail because the complicated flow field near the orifices is not fully understood nor completely modeled by the theory. Suggestions for possible improvements to the impedance model are discussed.

In an earlier study [J. Acoust. Soc. Am. 54, 334 (1973)] we reported that the subjective quality of music appeared to be unaffected by processing signals through all‐pass phase‐shift networks as used in the SQ quadraphonic matrix encoding system. These conclusions were based on the results of a same/different experiment in which the listeners appeared to be operating at a chance level for a two‐alternative forced‐choice paradigm. They responded with an equal likelihood (50%) of same and different regardless of the nature of the stimulus pairs. Additional experiments have been performed with speech samples using several lists of Harvard PB Sentences. In a same/different experiment, the listeners overwhelmingly judged “same” regardless of conditions. However, in an A‐B‐X experiment, the listeners favored the “B” choice, the one nearest the time to the unknown. Foil conditions of high‐pass filtering, low‐pass filtering, and peak‐clipping were included to verify the performance of the listeners. Correct responses to these conditions were provided except at near discrimination thresholds. One may therefore conclude that such all‐pass networks have no audible effect on subjective quality. In addition, whe presented with a difficult A‐B‐X discrimination task, a significant response bias results from a preference to the stimulus closest in time to the unknown.

With conventional earphone listening, accurate simulation of the direction of sound arrival is impossible because the sound field is not fixed in space but rotates with the head. A system for overcoming this limitation has been developed. Signals are transmitted by electromagnetic or underwater radiation to two directional receptors attached to the listener's head. The receptors are connected to the earphones through a Ster-Bin network. This network divides each of the signals from the receptors into two parts. One part is fed into its corresponding earphone; the other is delayed with respect to the first by the time interval required for sound to travel normally between the two ears, and is fed into the opposite earphone. In addition, both parts are modified at high frequencies to simulate the diffraction effects attributable to the head. The varying relative signal strengths from the directional receptors, as a function of the direction of signal arrival, modified by the Ster-Bin network, provide the listener with orientation capability. Further apparatus improvement and applications to aerospace and underwater swimmers' communications devices are envisioned.

A pressure‐gradient hydrophone exhibiting uniform response and precise polar pattern has been developed based on the moving‐coil principle. The coil, under mass control, closely matches the impedance of the medium contributing to high sensitivity. Equivalent‐circuit analysis demonstrates how to select the electrical‐termination resistance for any desired degree of damping and for proper phase‐shift control. Theoretical performance is compared with measurements using a CBS Laboratories gradient hydrophone calibrator, and in free field. [Work supported by U. S. Naval Air Development Center, Johnsville, Pennsylvania, under subcontract from Sanders Associates, Nashua, New Hampshire.]

A number of years ago Wiener [J. Acoust. Soc. Am. 19, 143–146 (1947)] published a paper on head diffraction; however, his data were limited to 6000 cps and did not include interaural delays. The present set of measurement extends to 10 000 cps, includes interaural delays, and covers a larger number of angles of incidence than explored by Wiener. The results can be applied to the design of high‐quality earphones and to development of directional perception apparatus.

In the equivalent circuit analysis of acoustical structures, invariably the question arises on how to represent distributed‐constant members with lumped‐parameter electrical components, to a given degree of accuracy. For a tube (or spring), a T‐type configuration, with the arms consisting of inductors each equivalent to 12 the total inertance and the center leg, a capacitor equivalent to the total acoustical capacitance predicts the 14‐wavelength resonance frequency within a 10% error. For shorter wavelengths, an equivalent circuit of equal quality is obtained by treating the tube as n equal segments where n is the number of 14‐wavelengths of the highest frequency of interest approximating the length of the tube. When n is doubled, the error is reduced to within about 3%.

An improved understanding of some stereophonic phenomena may be obtained by use of acoustical pressure phasors to portray sound pressure at the ears of the observer. With the help of phasors it is possible to expand and modify certain conclusions of previous observers, and to validate some previously unpublished observations; stereophonic “law of sines” is derived. The existence and location of “out‐of‐bounds” stereo‐phonic image is analyzed and verified. The “allowed maximum out‐of‐phase ratio” is derived, together with the observation that this maximum is exceeded by certain microphone arrays. The motion and elevation of the center image in stereophonic reproduction is observed and explained.

A miniature pressure‐gradient microphone exhibits improved noise discrimination and extended crossover frequency. Ability of a cosine pressure‐gradient microphone to discriminate against the pickup of unwanted noise is known to be limited by the acoustical pathlength between the two sound entrance points in front and back of the diaphragm. Noise discrimination is further limited by unwanted phase shifts occurring in the acoustical treatment surrounding the diaphragm. A miniature, efficient magnetic transducer actuated by a slender drive pin connected to a pressure‐gradient diaphragm permits a reduction of diaphragm size with corresponding decrease of front‐to‐back distance. Added symmetrical acoustical networks avoid differential phase shifts. Further enhancement of noise discrimination stems from a mechanically balanced system that diminishes sensitivity to mechanical vibration. Prototypes exhibit noise discrimination of 40 dB at 200 cps and a crossover frequency above 5 kc/sec. [This work was supported ...

The use of the conventional analog for diaphragms in equivalent circuits often causes serious difficulties. The action of a diaphragm is shown to be analogous to that of a system of ideal transformers, each corresponding to an area of the diaphragm. The ancillary concept of “acoustical ground” analogy is introduced to facilitate synthesis of equivalent electrical circuits. The analysis includes equivalent circuit representations of a piston diaphragm, multiple diaphragms, diaphragms with subdivided sides, and articulated diaphragms, etc., together with examples. Simultaneous use of the transformer analogy of diaphragms and the transformer analogy of transducer couplings is treated in the Appendix.

Heretofore unexplored psychoacoustic phenomena having special bearing on matrix quadraphony have been studied using centrally located observers facing a small end of a simulated rectangular living room with loudspeakers in the corners. It was observed that (1) monotonic all‐pass phase‐shift networks (“psi‐networks”) do not perceptibly affect sound quality; (2) signals applied to the two front loudspeakers through differential quadrature filters appear to spread out and to shift towards the loudspeaker carrying the leading signal (“quadrature shift”); (3) directional cues attributable to signals from the front loudspeakers are relatively uninfluenced by lesser‐magnitude similar signals applied to back loudspeakers (“front source dominance”); and (4) the perceived angular coverage of the field produced by the back loudspeakers is substantially smaller than that produced by the front loudspeakers (“back image contraction”).