bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study of the Propagation of Sound over Water in Fog
Authors: Wiener Francis M. , Ball J. H. , Gogos C. M. , Hess R. L.
Published: September 2005

In the course of a basic study of signaling over ocean waters in fog by means of audible signals carried out by Bolt Beranek and Newman Inc. under contract with the U. S. Coast Guard an extensive series of field experiments were undertaken on a location off the coast of Maine. These experiments consisted of measurements of the sound transmission over water in the frequency range between about 200–2000 cps under a variety of atmospheric conditions, including fog. Simultaneously, measurements were carried out of the vertical wind and temperature gradients in the first 30 ft of the atmosphere above the water, and the liquid water content and the droplet size distribution of the fog were determined. This paper presents representative samples of the sound attenuation characteristics obtained and a résumé of the more important general results. The instrumentation and the results of the micrometeorological and acoustical measurements will be discussed in more detail elsewhere.
Sequential Effects in the Signal Detection Situation
Authors: Speeth S. D. , Mathews Max V.
Published: September 2005

Signal detection theory has provided a very useful statistical model for characterizing the behavior of human observers in situations such as the four-interval forced choice experiment. Here the observer must indicate in which of four intervals a signal, added to a background of noise, is presented. The observer's response depends on the external signal and noise and on other incompletely defined factors which have been called “internal noise.” This study examines some of the sequential effects which constitute some of these internal factors. The observer's past response, his past performance level, and the indication of what his last response should have been have all been found to exert a significant control over his behavior. This influence decreases as the signal intensity is increased. The sequential effects introduced by these variables can be characterized by finite state diagrams. A modification of the basic signal detection model to include the sequential influences is discussed. Better understanding of the conditions which shape these effects should allow the experimenter to control more completely this aspect of the subject's behavior.
Parametric End-Fire Array
Authors: Westervelt Peter J.
Published: September 2005

A high-power modulated sound beam acts like an end-fire directional array for the modulation frequency. This occurs because the nonlinear terms in the equations of motion cause such a beam to act like a distribution of sources for the modulation frequency. If the sound beam is unmodulated, it behaves precisely like a parametric amplifier for any sound traveling in the direction of beam and thus can be used as a highly directional receiver. In order to test this concept, two carrier beams having approximately the same frequency ω1 ≈ ω2 ≈ ω were superposed on each other. The modulation frequency is then the difference ω8 = /ω1 − ω2/. If the pressure of each carrier is the same and equal to P0 the modulation percentage will be 100. The expression for the radiated intensity Is at a distance R0 far from this source is Is=ωs4P04S02[1 + 12ρ0c0−1(d2p/dρ2)]22(8π)2ρ03C09R02 × 1α2 + k2sin4(θ/2) in which S0 is the cross-sectional area of the carrier beam, α is the pressure attenuation coefficient for the carrier beam, θ is the angle measured from the axis of the carrier beam, and k = ω8/c0. Maximum radiation occurs at θ = 0 in the forward direction of the carrier. Experiments, described in an accompanying paper, agree well with the theoretical expression which, incidentally, shows the same angular dependence as Rutherford scattering in atomic theory. (Supported by the Office of Naval Research.)
Korotkoff Sounds in Humans
Authors: Wallace John D. , Lewis David H. , Khalil Sami Abou
Published: September 2005

Direct monitoring of Korotkoff sounds from the brachial artex with vascular pressure, cuff pressure, and external sounds has been carried out. Lowering cuff pressure from above systolic brings the onset of intravascular sounds with the first pulse through the cuff. External sounds appear at this or the next lower beat. As cuff pressure is lowered, external sounds usually disappear before diastolic pressure is reached. Internal sounds disappear at the diastolic level. Recording of internal sounds from within the artery indicates sounds directly beneath or distal to the cuff but not proximal to it. It is suggested that Korotkoff sounds are the result of the sudden opening of the blood vessel. The discrepancy between direct and indirect blood pressure measurement will be discussed.
Use of Spheroidal Wave Functions to Predict Far-Field Radiation Patterns
Authors: Horton C. W. , Innis G. S.
Published: September 2005

The problem of predicting the farfield radiation patterns from near-field measurements is attacked by using wave functions in spheroidal coordinates. By using this coordinate system, one is able to make measurements of pressure alone over a coordinate surface that fits closely a transducer whose shape is either a cylinder or a circular disk. This approach represents a generalization of a paper by J. Pachner [J. Acoust. Soc. Am. 28, 86–90 (1956)]. Comparison with experimental data is presented. (This work was supported by contract with the Bureau of Ships.)
Electrostatic Transducers for Ultrasonics
Authors: Wright Wayne M.
Published: September 2005

There is continuing interest in electrostatic transmitters and microphones for applications which require a relatively flat frequency response in the ultrasonic range. This paper presents an analysis of a class of electrostatic transducers for use with gases at frequencies up to several hundred kilocycles. with emphasis on the relations of the resonance frequency and the transmitting and receiving responses to the mechanical parameters. The transducers considered utilize a thin metalized plastic diaphragm over a very thin air film and behave as systems having a single degree of freedom. The performance capabilities of such transducers are summarized, and the theoretical predictions are compared with experimental results obtained by the author and by others. (This work was supported in part by the Office of Naval Research.)
Transducer Beam Control with Plane and Conical Reflectors
Authors: Baird D. L. , Wallace R. H.
Published: September 2005

It is well known that a large plane reflector directly above and normal to the axis of a cylindrical transducer can have a rather drastic effect on the beam patterns of such a transducer. The degree of such an effect is, of course, dependent on size and material of the reflector, distance above the active face of the transducer, and the size of the active face of the transducer in wavelengths. Experimental data will be presented indicating some of the precautions one must take to guard against such effects or to use these effects to one's advantage if desired. Information will be presented, for both plane and conical reflectors, as to the beam depression, beam width, effective hydrophone sensitivity, and minor-lobe structure as a function of reflector dimensions and for various distances of the reflectors above the active face. (This work is supported by the Bureau of Ships.)
Some Effects of Missing Elements on Sonar Beam Patterns
Authors: Tucker E. A. , Wittenborn A. F.
Published: September 2005

An interesting variation of the classical problems involved in synthesizing desired sonar transducer beam patterns is to examine the effects caused by missing acoustic radiating elements. Beam patterns were calculated for a multi-element circular array using discrete frequencies and a composite beam pattern was calculated for a decade bandwidth. The same beam patterns were then calculated omitting single elements and groups of elements for analog and polarity sampling beam forming networks. The results are discussed in terms of rotating and fixed beam sonar systems.
Underwater Exponential Horn Transducer
Authors: Duderstadt D. Worth , Wittenborn A. F.
Published: September 2005

An audiofrequency underwater transducer utilizing a folded exponential horn has been designed, developed, and tested. The horn is driven by a lead zirconate titanate piezoelectric bimorph driver, producing a sound output of 74 db re 1 dyne/cm2 at 1 yd. The radiated sound pattern is essentially omnidirectional, with a Q of about 4. The horn length and mouth diameter are about one-third of the wavelength of the center frequency. The transducer can operate at great depths since the horn and driver are free flooding. A physical description of the driver and horn is given. This is followed by a comparison of calculated impedance and frequency response curves with experimental results. (Represents work performed under subcontract to SIE Division, Dresser Electronics, for the Bureau of Ships.)
Finite 90-Deg Biconical Surface as an Acoustic Target
Authors: Barnard G. R. , King W. R.
Published: September 2005

It is often desirable for an acoustic target to have a large target strength independent of target aspect. A sphere is considered to have a low target strength that is independent of target aspect, whereas a cylinder is considered to have a high target strength for a particular target aspect but low target strength for other aspects. The measured target strength in water of a finite 90-deg biconical surface as a function of target aspect is compared to similar data for a finite cylinder and sphere with the same relative dimensions. The biconical surface targets are two metal cones, having a common axis, and joined at their vertices with the vertex angles equal to 90 deg. The finite 90-deg biconical surface is shown to have a lower maximum target strength than the cylinder but has a target strength that is less dependent upon target aspect than that of the cylinder. Target strength data for four right-circular conical surfaces measured in water at two frequencies in the plane normal to the conical axis are compared to the empirical formula T = 10 logR3/3λ, where R is the radius of the base of the finite 90-deg biconical surface and λ is the wavelength of the incident acoustic wave. (This work is supported by the Bureau of Ships.)
Behavior and Properties of Clarinet Reeds
Authors: Backus John
Published: September 2005

Previous work has shown that the clarinet reed is primarily stiffness controlled, its motion reproducing the pressure variations in the mouthpiece fairly closely [J. Acoust. Soc. Am. 33 806 (1961)]. Subsequent investigations have provided more information on the properties and behavior of the reed. The Young's modulus for the cane from which reeds are made varies by more than a factor of two among samples, even for strips of the same cane. The density also varies, but over a smaller range. These variations make finding a good clarinet reed an unpredictable matter. The reed, when wet (as under playing conditions), has a smaller modulus and larger density than when dry. The deviations from the simple stiffness behavior mentioned above are important to the performance of the instrument. The damping provided by the player's lip is important in reducing the tendency to produce high-frequency vibrations. The mass of the reed is an important factor determining the production of higher harmonics and is thus of considerable importance to the quality of the tone produced. (This work is supported by a grant from the National Science Foundation.)
Semiconductor Transducers—General Considerations
Authors: Mason Warren P.
Published: September 2005

Semiconductor materials cut in particular directions have a very large change of resistance with strain. This is a consequence of the multivalley nature of the shape of the energy surfaces. Lightly doped samples have a gauge factor that varies inversely proportional to the temperature but heavily doped samples have a much smaller change in gauge factor than do lightly doped samples. Heavy doping also improves the linearity of the specimen. Silicon has the widest temperature range and the greatest sensitivity of any known material. Another pressure-sensitive device is the heavily doped p-n junction known as the Esaki or tunnel diode. A negative resistance occurs over parts of the voltage-current characteristic. The properties are pressure-sensitive because of the thickness change and because of the energy gap change under pressure. The latter usually dominates and causes a reversal of effect between silicon and germanium. The present paper discusses the general properties, while other papers in the series discuss applications.
Poststimulatory Fatigue of Masked Threshold
Authors: Bilger Robert C. , Anderson Charles V.
Published: September 2005

Temporary shift of threshold for 1400 cps and its course of recovery following exposure to a tone of 1000 cps at a sound pressure level of 120 db for 2 min was traced on a modified Békésy audiometer. Measures were taken in “quiet” and in the presence of a band of noise (500 4000 cps) at over-all sound pressure levels of 47.5 and 77.5 db. When noise was used, it was present before, during, and after the exposure. The results indicate that the slower, more stable recovery process that is dependent upon the strength of exposure, labeled R-2 by Hirsh and Bilger [J. Acoust. Soc. Am. 27, 1186 (1955)], is completely masked by even low levels of noise. On the other hand, the recovery process, labeled R-1, that is rapid and short-lived is not masked by low levels of noise and is not completely obscured by levels of noise capable of affording 60 db of masking.
Information Processing on Simultaneously Presented Auditory Tasks
Authors: Herman Louis M. , Corso John F.
Published: September 2005

This study primarily investigated the concept of a single limited-capacity channel in information processing and the role of long-term storage (memory) in controlling inputs to that channel. In a monotic pursuit situation, S's (four groups of ten) tracked a 1000-cps tone for 20 identical trials (53 sec each) during which the auditory course changed in intensity over a 35-db range, approximately. Within each trial, the course followed a random pattern, but the pattern was repeated from trial to trial. During two intervals (8 sec each) which occurred randomly within each trial, S's were required to judge simultaneously the longest in a series of five tonal pulses. The tonal pulses (four equal and one unequal in duration) were presented in S's opposite ear at either 350 or 2250 cps and were relatively easy or relatively difficult to discriminate. It was found that in the simultaneous-task situation, practiced S's transmitted more information on the auditory tracking task and less on the tonal-pulse task than did unpracticed S's. When the tracking task was of low information input, S's were able to maintain the performance level achieved on that course in the single task situation and were able to process additional information on the tonal pulse task. However, S's tracking the course of high information input were not able to maintain their prior performance level on the tracking task during the simultaneous task situation. For the more difficult discrimination of the tonal pulses, less information was transmitted on that task, but no negative effects were observed on the amount of information transmitted on the tracking task. The results of this research provide support for the single-channel hypothesis. Practice on a task results in long term storage and appears to determine the preference for selecting inputs from that task rather than from some other task. Broadbent's model requires the addition of an intertask decision loop if it is to account for the findings of this study.
Multiple-Reflection-Type Quartz Delay Lines
Authors: Konig W. F. , Lambert L. B.
Published: September 2005

The performance characteristics, such as time delay, spurious response levels and bandwidth, of multiple-reflection-type delay lines are discussed. State of the art performance is indicated, and efforts to improve these characteristics are described. The time delay is determined by the path length of a given design and size limitations on the fused-quartz blanks. Multiple symmetry designs are derived from regular polygons by rotating facets to achieve long path lengths. Typical designs are presented, and the delays that can be achieved in readily available blanks of fused quartz are indicated. Spurious responses result from diffraction at the transducer and subsequent reflecting facets, and from reflections at the transducers. “Creation angle” spurious responses characterize multiple symmetry type designs, resulting in the use of simpler designs for many critical applications. Aperturization techniques may be employed to control the size of the reflecting facets, and hence to control certain diffraction effects. The delay-line bandwidth is a function of the transducer resonant frequency, bonding techniques and delay medium characteristics. The dependence of bandwidth on bonding parameters is discussed in terms of the transducer equivalent circuit. Medium losses increase with frequency, and limit the attainable bandwidth for long delays. The ultimate performance capabilities of multiple reflection type delay lines using materials and techniques currently available are considered. Limitations imposed on the time-bandwidth product and dynamic range are discussed. Practical upper limits are considered in terms of figures of merit for communications and radar applications.
Magnetostrictive Delay Lines
Authors: Rothbart Arthur
Published: September 2005

Improved performance and reliability of magnetostrictive delay lines have resulted in their increasing military and commercial use in aircraft navigation, radar, data processing, and automation. This trend has been particularly evident in the small digital computer where the advantages of this type of pulse storage, namely, economy, temperature stability, high operating speed, and expandable capacity, have enabled magnetostrictive delay lines to displace magnetic drums and cores. This paper presents the characteristics and design features of commercial delay lines. Particular attention will be paid to the following areas: 1. Transducer design. 2. Choice of delay-line materials for transducer operation and as propagation media. 3. Materials and techniques for mechanical terminations. 4. Heat treatment of wire to obtain low temperature coefficients of delay. Because of the rapid growth in the use of magnetostrictive delay lines, there has been insufficient time for industry to agree on standard definitions and measurement procedures for such delay-line parameters as resolution, signal-to-noise ratio, input impedance, terminating impedance, and attenuation figure. A presentation will be made of logical concepts on which such standardization might be based.
Hydrophone Installation for the Study of Marine Animals and Preliminary Results
Authors: Steinberg John C. , Kronengold Morton , Cummings William C.
Published: September 2005

A hydrophone assembly has been installed on the east bank of the Gulf Stream, with terminals in the Lerner Marine Laboratory, Bimini, Bahamas. This assembly is being used to study the feasibility of combining acoustical, biological, and electronic techniques for information on soniferous animals in the natural environment. Sounds from two bottom-mounted hydrophones, one in 100 ft of water and the other in 1200 ft are recorded on dual-track magnetic tape on a 24-hr basis. The tapes are played back at eight times recording speed and monitored for sounds of possible marine animal origin. More than 25 categories of sounds were observed during the initial period from November, 1960 to June, 1961. In general, sound categories at the shallow and deep sites are different. Usually, only a single category is present at a hydrophone at one time. A number of repetitive, diurnal patterns and possible seasonal patterns of soniferous activity are discussed. Some tentative identifications are made. Expansion of the installation is currently in progress; this includes additional hydrophones for the localization of sound producers and for information on migratory behavior of short duration. Demonstrations of the categories are presented from tape recordings. (This work was supported by the Office of Naval Research, the Bureau of Ships, and Bell Telephone Laboratories.)
Nonacoustical Means of Communication
Authors: Pierce J. R.
Published: September 2005

The human voice is a favored means of communication because we are all trained to use it face-to-face, and we can speak over the telephone without any further training. Nonetheless, writing, typing, diagrams, and pictures play an important role in human communication, and today we have data communication between machines. All of these nonvocal forms of communication will come increasingly into use. This paper will discuss some of their possible uses and some of the obstacles in their path.
Speech Projection and Reception Systems—Developments, Characteristics, Prospects
Authors: Christoff Jerry P.
Published: September 2005

The search for transducers which would permit reduction in the encumbrance of communication equipment for use in high-altitude long-range missions has led to the discovery of new techniques for the projection and reception of voice communication. Absolute and quantitative measurements have been made of the relative performance of speech projection methods—conventional and radical—to define speech spectral sensitivity, noise spectral sensitivity, speech articulation capability, and noise tolerance as a function of speaking effort. Similarly, speech reception techniques have been studied quantitatively to find promising new approaches to eliminate head contact or discomfort while maintaining adequate noise tolerance. The performance of two new approaches, the forehead contact transmitter and the horn-coupled receiver, are described in detail.
A Military Semi-Vocoder for Analog Telephone Transmission
Authors: Howell A. S. , Schneider G. O. K. , Stump T. M.
Published: September 2005

A semi-vocoder for telephone speech is described. It was developed for an Air Force envisioned system of multiple analog vocoders fed from any telephone line to operate over a single voice frequency channel. Such a semi-vocoding plan is shown to offer advantages in the maintenance of voice quality, an important factor in user acceptance. It comprises 500 cps of unvocoded baseband and 250 cps, or 13 spectrum channels, of vocoded information. The direct baseband provides spectrum and excitation information; it facilitates the derivation of pitch when the fundamental frequencies of talkers are missing. Also, the processing of the direct baseband to provide automatic voice excitation obviates the need for an arbitrary voiced-unvoiced decision and excitation by buzz-hiss switching. Errors associated with the latter method are accentuated by the limited frequency range of telephone inputs. The vocoded information is processed by the direct time sampling of the unrectified spectrum channel energy. This method of identifying the speech spectral pattern is entirely feasible when certain requirements are recognized. The frequency occupancy of the complete semi-vocoded speech channel is directed toward multiplexing within a 900-cps total bandwidth inclusive of guard space.
Word Reading Device: Design Considerations
Authors: Cooper Franklin S.
Published: September 2005

One way to obtain a spoken version of printed text is to fabricate connected speech from voice recordings of single words stored in a random-access memory and assembled under control of the text. The construction of such a word reading device (WORD) is within reach of current technology in the electronic data processing field; however, feasibility depends also on the quality and intelligibility of the output speech. An experimental approach to this “language problem” is the subject of a companion paper; the present discussion deals with over-all design problems, some of the interrelationships between language and machine constraints, and an experimental WORD for evaluation studies and use by the blind. The voice library of the experimental device employs tape recordings of word addresses (digital) and spoken words (analog), arranged in pairs. This method provides compact storage, but it may be desirable, in a full-scale WORD, to use an all-digital memory. This appears to be feasible if the voice entries am stored as instructions for synthesis. Thus, certain parallels can be drawn with a type of reading device that will generate speech by the use of rules for synthesis operating on subphonemic units [A.M. Liberman et at., J. Acoust. Soc. Am. 31, 1490–1499 (1959)]. (Research supported by the Prosthetic and Sensory Aids Service, Veterans Administration.)
Word Reading Device: Experiments on the Transposability of Spoken Words
Authors: Gaitenby Jane H.
Published: September 2005

Individual sentences and paragraphs of text have been constructed artificially from prerecorded spoken word units. This was done to test methods of recording a vocabulary adaptable to the requirements of the word reading device for the blind described in the preceding paper. High intelligibility and a modicum of naturalness have been achieved for both statements and questions of normal syntactic construction, using a vocabulary of several hundred words. The words were spoken by a male speaker who followed rigid intonational prescriptions when reading the word list. The intonation for each word was assigned “automatically” in two steps: (1) the word was classified grammatically according to its most probable functional role and (2) a particular intonational pattern was designated for each of six major grammatical categories. The parameters specified in the instructions were relative starting pitch, pitch slope, duration, and intensity. Because a speaker cannot be precisely “programmed,” the compatibility of his productions depends not only on the aptness of the instructions but also on the speaker's skill, his insight into the linguistic aspects of the recording problem, and, of course, upon his voice quality and diction. An accompanying tape demonstrates progressive results obtained with three speakers. (Research supported by the Prosthetic and Sensory Aids Service, Veterans Administration.)
Pitch Extraction on the TX-2 Computer
Authors: Gold Bernard
Published: September 2005

A man can quite readily detect the periodicities in a speech wave by visually inspecting the wave. It has been demonstrated by Swaffield that Vocoder quality is clearly improved by using as buzz source a set of pulses marked by eye from the original speech wave. The aim of the program described here was to extract pitch markers from speech using eye-extracted markers as the “ideal.” The four basic features of the program are (1) voiced-unvoiced decision, (2) three separate pitch detection rules, (3) a “regularity” test which combines the three rules to make better decisions than can be made by any of the individual rules, (4) an editing procedure, which fills in gaps and removes spurious markers. The speech (band-limited from 30 cps to 4 kc) from two women and two men, each saying five sentences was processed. The average length was about 212 sec per sentence. For more than 50% of the sentences processed, the program was “perfect” in that it agreed wholly with the result obtained from visual inspection. The total percentage error was less than 1%. (Lincoln Laboratory operated with support from the U. S. Army, Navy, and Air Force.)
Capabilities of Speech Communication in Noise
Authors: Webster J. C. , Thompson P. O. , Klumpp R. G.
Published: September 2005

Over the past year numerous communications systems have been evaluated in the NEL High Level Noise Facility. This system, consisting of 16 low-frequency and 38 high-frequency horns driven by a 10 000 w amplifier, can reproduce jet aircraft noises to a group of six listeners at levels up to 140 db (over-all, C weighting). Two different mobile (flight deck) radio communications systems, a series of developmental sound powered phones, and a Helicopter PA rescue announcing system have been evaluated. In addition, limits of face-to-face communications have been established. Satisfactory communications using the best available acoustic components can be carried on in jet noise when both talkers and listeners are in 135-db levels. Flight deck radio communication sets now in use in the fleet are usable up to levels of 125 db. Developmental models of sound powered phone equipments are usable up to 120 db, although present equipment is good only to 100 db. With no electronic or acoustic aids satisfactory face to face communications between a talker and listener are possible in jet noise up to 97 db at 3 ft, 91 db at 6 ft, and 85 db at 12 ft. Selected data (1) on different noises, (2) when either talker or listener are in quiet, and (3) when ear protection is used also will be discussed.
On the Relations between VU-Meter Readings and the rms and Peak Values of Speech
Authors: Wathen-Dunn Weiant
Published: September 2005

In articulation testing, the signal-to-noise ratio is very often one of the parameters against which one wishes to plot the articulation score, and ideally this S/N should be the ratio between the long-time rms value of the signal and a similar measure of the noise. When speech is the signal, however, it is difficult, if not impossible, to determine its true rms value with any great accuracy by means of the instruments usually available unless one has established relationships between the readings of these instruments and the desired measure of the signal which are valid for the particular conditions of the test. Since the VU meter is most often used to monitor the level of the speech in articulation test work, it is particularly desirable to know the relation between its readings and the true rms value of the signal. An alternative method of arriving at this figure would be to take peak-value readings of the signal from an oscilloscope from which the rms value could be calculated provided the peak factor were known. The present paper is concerned with measuring the relation between the average value of peak VU-meter readings and the rms and peak values of both wide- and narrow-band samples of continuous speech recorded by several adult male and female talkers.
Some Aspects of Concert Hall Acoustics
Authors: Beranek Leo L.
Published: September 2005

This paper is a continuation of a study of the acoustical aspects of concert halls and opera houses, numbering 54 halls in 16 nations, that has been underway since 1956 [L. L. Beranek, J. Acoust. Soc. Am. 32, 661 (1960)]. The present paper gives the results of lengthy interviews of fifty leading conductors and music critics in the United States and Europe and describes fifteen attributes of acoustics that play a part in the over-all acoustical quality of a concert hall. A preliminary scheme for rating concert halls from acoustical and blueprint data is discussed.
On the Development of Subjective Ratings for the Sound Reduction of Partitions
Authors: Hardy Howard C.
Published: September 2005

This paper will present some recent thoughts and experience directed toward simplification of the methods of developing subjective ratings of partition walls. Any such scheme will depend on the nature of the sound sources: speech, musical instruments, radio and television, machinery equipment, and apparatus, etc. Of these the most discussed is speech. Parkin has proposed and used a frequency weighting curve; Farrell and Watters, an articulation scoring scheme. The present paper presents somewhat simplified and similar ideas which lead to, for example, a parameter called “speech leakage index.” This evolves from a weighted average of the data taken at standard STL and NR frequencies. The same scheme with different weighting factors can be applied to other sound sources such as music and equipment noise. The measurement and evaluation of school room partition isolation given in the previous paper has presented an opportunity to check these assumptions. The results will be presented.
Contraction of the Middle-Ear Muscles in Man
Authors: Møller Aage R.
Published: September 2005

The contraction of the middle-ear muscles has been studied in normal human subjects by using the change in the acoustic impedance of the ear as a measure of contraction. The change in impedance was measured on both sides (ears) simultaneously, and various types of stimulation were employed to elicit the muscle contraction. The sensitivity of the muscle contraction is studied in response to sinusoidal signals and various complex signals. In addition, the sensitivities to ipsilateral, contralateral, and bilateral stimulation are compared. The function of the middle-ear muscles in modifying sound transmission through the middle ear will be discussed. The middle-ear muscle response is considered as a possible indicator of auditory neural activity at the level of the superior olive. Considered in this way, the response may be a convenient representation of the neural activity at a level ordinarily inaccessible in the human subject.
An Electrical Analog for the Middle Ear and Basilar Membrane
Authors: Flanagan James L.
Published: September 2005

In earlier work, mathematical models were developed for middle ear transmission [J. Acoust. Soc. Am. 32, 1494(A) (1960)], and for basilar membrane displacement [Bell System Tech. J. 39, 1163–1192 (1960)]. These models are rational, transfer-function approximations to acoustical and physiological measurements reported by Bekesy, Zwislocki, and others. They respectively relate stapes displacement to sound pressure at the eardrum, and membrane displacement to stapes displacement. Because of their rationality, they can be realized in terms of lumped-constant electrical circuits. The network representation of the analytical models is described and the design procedure is given. The response of the analog is compared with the experimental physiological data. Its applicability to the analysis of psychoacoustic stimuli is illustrated. Finally, its utility in relating subjective and physiological behavior in measurements of pitch perception, threshold detection, and binaural lateralization is discussed.
Calibration of Cardiographic Microphones
Authors: Hardy Howard C.
Published: September 2005

It has been determined that the important parameter which is detected by a cardiographic microphone is the displacement of the skin under the contained area covered by the microphone cup. This displacement amplitude is to the first approximation, the same as the skin displacement without a microphone except for a resonance at approximately 80 cps which is due to the reaction between the microphone mass and the skin stiffness. To first approximation the microphone's response is proportional to the displacement. The calibration curves for several commonly used commercial cardiographic microphones will be presented. The simplified technique developed for making these calibrations will also be shown.
Finite-Amplitude Motion of a Piston in a Shallow Cavity
Authors: Blackstock David T.
Published: September 2005

Nonlinear effects in the resonance behavior of a driven piston in a short, fluid-filled cavity are analyzed. More specialized treatments of this problem have been given previously in studies of distortion in back-enclosed loudspeakers (see, for example, H. F. Olson, Preprint No. 143, 1960 Audio Engineering Society Convention). The present work deals with liquid-filled as well as gas-filled cavities; it is assumed only that the fluid's pressure-density relation may be expressed accurately by p − po = ρoco2[s + (B/2A)s2 + (C/3A)s2], where s is the condensation and the subscript o denotes a static value. Also, the effect of finite length of the cavity is taken into account. The equation of motion of the piston, a generalized Duffing's equation, is derived. The steady-state solution of this equation contains a modified form of the small-signal solution plus second-, third-, and higher-harmonic terms. The frequency response curve differs markedly from the one predicted by small-signal theory. The results show that measurements of the piston motion might be used to determine the coefficients B/A and C/A in the fluid's pressure-density relation. A push-pull piston-cavity arrangement is also described.
Measurements of the Acoustic Properties of Sediments. I. Acoustic Velocity
Authors: Hampton L. D.
Published: September 2005

Work has begun on the measurements of the acoustic properties of uncompacted sediments. This paper describes some of the preliminary work on the measurement of the velocity of sound in sediments. A pulse technique is used and measurements have been made over the frequency range from 50 to 200 kc/sec. Results are reported for several artificial sediments containing a wide range of particle sizes and for sediments composed of relatively pure clay minerals. Velocity measurements in these sediments were made as a function of frequency and as a function of particle concentration. A slight dispersion has been measured and this dispersion is compared to existing theoretical predictions. (This work is supported by the Bureau of Ships.)
A Note on Signal Interferences in a Medium with Multipaths
Authors: Clay C. S. , Liang William
Published: September 2005

Signals can travel from the source to the receiver by many paths in the layers of the earth. Many of these paths have nearly the same travel time; thus the arrivals interfere. The effect of the mean frequency of band-limited signals upon interfering arrivals has been studied. The total signal arrival with low-mean signal frequencies is simpler than with a high-mean frequency. The “classical uncertainty” principle ΔωΔτ⩾1 is used to estimate a desirable relation between the mean frequency and bandwidth of a signal. With the assumption of very many paths, the minimum signal bandwidth is estimated to be about 0.6 of the mean frequency. (This work was supported by the Office of Naval Research.)
Signal Detection in a Multipath Medium by M.E.S.S. Processing
Authors: Parvulescu Antares
Published: September 2005

A brief pulse sent through a multipath medium is received as a long and complicated signal. All the arrivals are important, and any detector will be far from optimum unless it can recombine all such arrivals. The “ideal detector” must have an impulse response which is in some sense the inverse of the multipath impulse response. The design of such a detector being very difficult, we have modified the problem and sought to construct a complicated signal which would be recombined by the medium itself into a single impulse at the receiver. A good approximation to the desired “inverse signal” in a room is the matched equivalent-space signal (M.E.S.S.) which is extremely easy to generate by recording the multipath impulse response and playing it back in reverse direction. The use of the M.E.S.S. yields a considerable gain in detectability, directivity in both angular and radial coordinates, and noise rejection, as verified experimentally. Among the applications to be discussed are those to architectural acoustics and public-address systems; to geophysical studies; and to the psychoacoustic problems of the cocktail party effect and the extinction of room resonances. (This work was supported by the Office of Naval Research.)
An Estimate of the Offshore Ambient Noise Spectrum Produced by Pounding Surf
Authors: Saenger R. Alfred
Published: September 2005

At previous meetings it was shown that when a water wave breaks onshore a seismic pulse, or “surfseism,” is communicated to the sandy bottom. The spectral character of pulses measured on the beach at Fire Island, New York, were accounted for in terms of statistical parameters characterizing the surf “noise generator” and geophysical parameters characterizing the intervening “earth filter.” Using experimental values derived from these beach measurements, an estimate has been made of the absolute output levels of the surf noise generator under certain physical assumptions which will be discussed. Expected pressure spectrum levels from pounding surf were computed at several ranges offshore using a simple two-layered liquid half space as an approximation to coastal conditions off Fire Island. Between 22.5 and 65 cps, where only first mode propagation need be considered, the spectrum levels produced by breakers several feet in height at a range of 1000 ft from shore are less than the extrapolated values obtained from Knudsen's spectrum level curve for the ocean at zero sea state. For coastal areas of the type considered here, surfseism, contributions to the ambient spectrum a few thousand feet offshore appear to be completely negligible. The effect of different geophysical conditions on these contributions will be discussed in conjunction with the specific calculations. (This work was supported by the Office of Naval Research.)
Noise from Convected Turbulence
Authors: Williams J. E. F.
Published: September 2005

The work reported concerns an extension of Lighthill's acoustic analogy to cover the supersonic as well as subsonic range of .Mach numbers. A theory is developed from Lighthill's moving axis equations and stated in a manner that illustrates both the effect of aircraft motion and eddy convection. The singularities normally associated with this analysis, at (1 − M cosθ) = 0, are shown to be finite when retarded time differences are taken into account and this condition corresponds to a Mach wave emission of quite a different character to the quadrupole radiation. The strength of this emission depends on M3, contrasting vividly with the M8 dependence at low speeds. Detailed application of the theory at high speeds is not contemplated relying as it does on the complicated density dependent stress tensor but dimensional reasoning is used to develop the more general aspects of acoustic radiation in the transonic and supersonic speed range. The general theory is illustrated with an example which shows the analysis to be continuous throughout the speed range and displays many of the features described by Phillips in the supersonic regime.
Near Field of a Shaded Radiator
Authors: Martin Gordon E.
Published: September 2005

The near field of a bizonally shaded rectangular transducer is investigated theoretically and experimentally. The theoretical radiation integral is solved first for a shaded piston using Fresnel integrals. The radiation from a shaded array of pulsating spheres is also solved exactly. Both theoretical directivity patterns are determined for a certain transducer at various near field separations using the Datatron 220 digital computer. Experimental results are also given for the transducer. Excellent agreement between theory and experiment to very short ranges is obtained.
Space-Time Limits in Acoustic Signal Processing
Authors: Stocklin Philip L.
Published: September 2005

Basic physical limitations of the quality and complexity of decisions, imposed by the volume, bandwidth, and time available for processing the acoustic field, are developed. Markov-Gauss space-time noise-probability density functions, together with several states of knowledge concerning signal waveform and wave front, are used to illustrate decibel departures of optimum minimum-average-risk space-time processors, from pattern formation and correlation processing. Volume, bandwidth, and time are related to each other and to possible processing gain. Sensitivity of both the decibel differences and these relationships to signal and noise states of knowledge is discussed.
FLIP—a Stable Ocean-Going Platform for Acoustic Experiments
Authors: Fisher F. H. , Spiess F. N.
Published: September 2005

The need for a stable platform at sea has been a long-standing one of ocean-going scientists and in particular for those who perform acoustic experiments at sea. The Marine Physical Laboratory, with the support of the U. S. Navy, is in the process of building a Floating Instrument Platform (FLIP), 355 ft long, displacing about 500 tons and which has the shape of a spar buoy. FLIP will be towed to station in the horizontal position and flooded down to a draft of 300 ft in the vertical position. Electronics, machinery, living quarters and a wet lab will occupy four decks beginning 15 ft above the waterline in the vertical position. The shape of the buoy has been chosen to minimize the effect of gravity waves. Although FLIP will be initially used for measuring effects of thermal microstructure on sound propagation, many experiments heretofore too difficult or too costly to perform can be done and under more desirable conditions. Proposed experiments will be discussed as well as details of the operation of FLIP. (This work represents results of research carried out under contract with the Office of Naval Research.)
Sound Source for ASD Sonic Test Facility
Authors: Allen C. H. , Starr E. A. , Sharp J. R. , Lansil R. S.
Published: September 2005

The sound source for the ASD Sonic Test Facility now under construction consists of two banks of independently controlled sirens designed to give sinusoidal output over a range of operating pressures. The main fixed bank of sirens (frequency range 50 to 2000 cps) employs 25 sirens, each using a 24-in. rotor; a second movable bank (frequency 500 to 10 000 cps) employs nine sirens each using a 12-in. rotor. Each siren employs a modulator which permits random or coherent amplitude modulation of the acoustic output at modulation frequencies from 0 to 25 cps for the large sirens and from 0 to 50 cps for the smaller sirens. Maximum acoustic power output of the fixed bank of sirens is expected to exceed 106 w in the midfrequency region from 200 to 800 cps. Finite amplitude limitations will be discussed. (Sponsored by Aeronautical Systems Division, Air Force Systems Command, U. S. Air Force.)
A New Jet Engine Noise Suppressor
Authors: Lane R. N. , Mikeska E. E. , Anderson C. D.
Published: September 2005

Acoustic measurements have been made on two models of a new jet engine noise suppressor, using J-57 engines in tests at Kelly Air Force Base, Texas, and Miramar Naval Air Station, California. Data are presented showing noise reduction of 10 to 30 db for the engine at military power.
Generation of Aerodynamic Sound by Dilatation and Momentum Fluctuations
Authors: Powell Alan
Published: September 2005

Physical reasoning suggests that aerodynamic sound from free flows may be attributed to local fluid dilatation coupled with local fluid accelerations, the former acting like a simple source field and the latter like a dipole field which reduces to a quadrupole field. A supporting mathematical development is given. It discloses the formal need of an additional surface integral so that the complete result takes the following form: p(x,t) − p0=14πc02∂2∂t2  ∫ V0(x̂⋅y) (x̂⋅ρ0 ∂uinc∂t)dV(y)(1*x)−14πc02∂2∂t2  ∫ V0pincdV(y)(1*x)+14πc02∂2∂t2  ∫ S00 (x̂⋅n̂) (x̂⋅y)pincdS(y)(1*x). It applies to the far field only, and the incompressible flow values for the velocity and pressure yield a good approximation for low speed flows. The surface integral, over the surface enclosing the sound generating flow, appears here in its point quadrupole approximation. This result and some other forms closely related to it are discussed in detail. (This work received partial support from the Office of Naval Research.)