bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflection of Sound from Coastal Bottoms
Authors: Mackenzie K. V.
Published: September 2005

A number of sea trips were made during the summer of 1950 and through the spring of 1951 to measure 1-kc sound-reflection losses over several bottoms as a function of the grazing angle. The results agree with Rayleigh's expressions as modified by R. W. Morse to allow for the attenuation in the bottom. The agreement appears best when the attenuation is assumed to vary as the first power of the frequency from E. L. Hamilton and G. Shumway's 30-kc data. Curves computed for typical bottoms are presented which show the ratios of reflected to incident pressures with corresponding phase changes.
Comparative Study of Three Types of Cylindrical Reflectors for Narrow Beam Sonar Transducers
Authors: Innis George , Owen Tom
Published: September 2005

This paper presents a comparison between circular, parabolic, and elliptic cylinder sections used in large aperture reflector systems designed to achieve acoustic beamwidths of a fraction of a degree. An analytic analysis of each type reflector shows the shift in optimum focal point and the phase relations at the focal element as a function of range from a test point on the axis in the near field of the transducer system. Depth of focus due to the phase discrepancies in the focal region is also derived for the three types of reflectors. Experimental results show that near field focusing is possible and the predicted shift in optimum focal point is verified for the parabolic and elliptic reflectors. Aperture shading using both reflector masking and focal element beam control is described in which minor lobe levels are suppressed 18 db below the main beam. Experimental results illustrating several degrees of lobe suppression are shown.
Lloyd's Mirror Test of a Wedge-Lined “Anechoic” Tank
Authors: Yingling A. , Medwin H.
Published: September 2005

In the experimental modeling of continuous wave sound propagation in shallow water, one must verify first that the wedge-lined, open-surface, tank properly represents an infinite half-space. A direct test of this condition uses the Lloyd's mirror development for the source and its image to describe the sound field. Observation and comparison with theory of the interference maxima and minima and the far-field 1/r2 pressure dependence than serves as a measure of the adequacy of the tank treatment. Advantages of the technique are (a) an integrated tank response for the complete wedge assembly, (b) an increase in the useful tank depth by the elimination of the layer of wedges usually floated at the top surface, and (c) the ability to decrease the extent of the complex near field by adjustment of the depth of the probe hydrophone. (This work was part of a project supported by the Office of Naval Research.)
Frequency Selective Characteristics of Arrays of Parallel Tubes having Sound-Soft Walls
Authors: Bohls Fred , Hillery Herbert
Published: September 2005

Arrays of parallel tubes having sound-soft walls and immersed in water are shown to possess frequency selective transmission and reflection characteristics at ultrasonic frequencies. No real propagation of sound waves of wavelength greater than a certain limiting wavelength is possible through a tube having walls made of material of zero acoustic wave impedance. The maxitnum wavelength which can be propagated through such a tube is determined by the cross-sectional dimensions of the tube. Experimental results are presented which demonstrate the relationship that exists between the transmission and reflection characteristics of arrays of parallel tubes and the cross-sectional areas, lengths, distributions, and departures from perfect sound-softness of wall of the tubes.
Studies of a Method for Digital Voice Communication
Authors: Smith Caldwell P.
Published: September 2005

The approach to speech compression evolved at AFCRC attempts to exploit in a maximal way the constraints that govern speech at the acoustic level. The problem requires a method for statistical encoding and decoding of voice signals in two stages. First, it is necessary to quantize speech patterns and encode these in terms of a minimal set of patterns, based on criteria of speech intelligibility, quality, and talker recognition. After converting speech to a code that specifies a sequence from the limited catalog of patterns, the data must be further reduced by recoding in terms of pattern clusters, that is, pattern sequences in pairs, triples, quads, etc. Since successive speech patterns measured every one-fiftieth of a second are not independent events but highly interrelated, recoding in terms of clusters, new patterns in which time is one of the dimensions, will markedly economize on the data rate requirement. Although these message units are purely statistical, it is anticipated that their correlation with phonetic elements of speech will be high. A digital computer has been utilized in studying some statistics of speech patterns, and these results will be presented. To expedite the study of this voice communications system concept, a real-time digital data processing equipment is being fabricated that will sort and accumulate statistics of speech patterns in real time. The occurrences of single patterns as well as clusters of up to five patterns in a sequence will not only be accumulated, but can be utilized in simulating a minimum data-rate digital speech system operating in real time. Some features of the logical design of the system will be discussed.
Fricative Production by a Dynamic Analog Synthesizer
Authors: Rosen George
Published: September 2005

Two series of formal listening tests were conducted with fricative consonants generated by a dynamic analog of the vocal tract. The consonants were generated using a fricative configuration consisting of a uniform tube with a single constriction and were presented in CV context, always with the vowel /ɑ/. The variables studied in the first test series were the place and degree of constriction and the position of noise excitation relative to the constriction. Listeners were required to make one of six fricative responses in forced and nonforced tests. Responses of /s,∫,f/ better than 95% were obtained for some stimuli. The second series of tests was made to determine how closely the temporal relations between articulatory change and buzz and noise excitation need to be specified. Stimuli were presented in pairs and subjects were asked to vote for the more “natural” stimulus in each pair. A supplementary identification test showed a sharp change of response from voiceless to voiced fricative as buzz excitation was initiated at progressively earlier times. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research, Air Research and Development Command), and the U. S. Navy (Office of Naval Research) and in part by Air Force Cambridge Research Center Contract AF 19(604)-2061.]
Effects of Multiple, Narrow Pass Band Filtering on the Intelligibility of Speech
Authors: Kryter Karl D. , Wiener Francis M. , Gogos C. M. , Flanagan Gail
Published: September 2005

It was reported [J. Acoust. Soc. Am. 29, 1262 (A) (1957)] that speech passed through several half-octave band pass filters spaced at intervals along the speech spectrum was more intelligible than one would predict on the basis of the Articulation Index. The present study is a further exploration of communication over this type of a multiple, pass band system. PB word and sentence intelligibility tests were conducted with unfiltered speech and with speech filtered (1) by a 1600-cps low pass filter, (2) by a 500–2000-cps band pass filter, (3) by a 1000–2500-cps band pass filter, and (4) by various configurations of one, two, or three band-pass filters, each 500 cps wide. The positions of the center frequencies of the 500-cps band pass filters were systematically varied during the tests. If we use constant speech intelligibility as our criterion, the results indicate that the total “effective” band width required for the multiple pass band system is less than that required for the best contiguous pass band systems by a factor of 2 or 3. Also, a feature of the signal resulting from this multiple sampling in the frequency domain is that it sounds “natural” and the identity of a talker's voice appears to be maintained. (This study was performed under Contract No. Da-36-039 SC-78078 with the U. S. Army Signal Research and Development Laboratory, Fort Monmouth, New Jersey.)
Report on an Investigation of Certain Flute “Blow-Hole” Parameters
Authors: Voots R. J. , West P. L.
Published: September 2005

The modern transverse (or side-blown) flute has not been changed appreciably since its development by Boehm (ca 1832). Mechanized manufacturing techniques have resulted in a fairly standardized set of dimensions for the body, foot joint, and the tube of the head joint. The final shaping of the blow-hole (or embouchure) in the head joint remains, however, as essentially a hand-crafted operation. The considerable variation found in the configuration and dimensions of this somewhat critical area may sometimes be attributed to design but is probably more often the result of whim, carelessness, or the lack of skill on the part of the craftsman performing this operation. The authors have constructed several head joints of identical tube dimensions but with a variety of blow-hole parameters. These have been investigated in the laboratory for their possible effect on the spectral distribution of the resulting flute tones with a view toward standardizing an optimum blow-hole design.
Intonation of an Alto and a Tenor Saxophone
Authors: Young Robert W.
Published: September 2005

In common with other reed instruments, the intonation of the saxophone is distorted because only two octave holes are used: the interval between the two registers may exceed on octave by as much as 20 cents for the note D served by the lower octave hole. The intonation of a saxophone can be markedly affected by the mouthpiece: a large cavity therein lowers the intonation whereas a small cavity raises the intonation. The effect is not uniform throughout. The difference in intonation for a metal mouthpiece having a large cavity and a rubber mouthpiece (bearing the same brand name) having a small cavity was found to be as great as 50 cents on some high notes. The common method of tuning by sliding the mouthpiece back and forth on the corked mouthpipe thus functions by change of mouthpiece cavity as well as by change of length of the air column.
Pitch Shifts with Pure Tone Masking
Authors: Small Arnold M.
Published: September 2005

While gathering data on the masking of one pure tone by another, marked pitch shifts in the signal tone were noted. This paper presents preliminary results of a systematic investigation of this phenomenon. Signals of five frequencies and two levels were used together with eight masker frequencies for each signal frequency. For a given condition signal level was constant, but the signal was effectively raised above masked threshold by lowering masker level. For three masker levels listeners adjusted a matching tone, heard in the contralateral ear, to the pitch and loudness of the masked tone. Stimuli were presented alternately to each ear. The results indicate that with no masking a just noticeable difference (JND) in frequency is much larger when the stimuli to be discriminated are presented to opposite ears rather than to the same ear. Further, this JND increases rapidly for frequencies above about 3200 cps. Under conditions of masking, the results are similar to those obtained using a narrow band noise masker. In general, the pitch of the signal is shifted away from the frequency region of the masker. The maximum shift occurs when signal and masker frequencies are nearly equal. Also, as signal threshold is approached the amount of pitch shift increases. Possible relations between the slope of the masking function and the magnitude of the pitch shift are discussed.
Pitch and Tonal Masking
Authors: Ehmer Richard H.
Published: September 2005

Ordinarily the criterion of the masked threshold is the detection of any signal besides the masking tone. This criterion is perhaps satisfactory for signal detection and communications purposes, but for inferring the excitatory pattern of a tone in the auditory apparatus, it does not indicate the full area activated by the tone. In the present experiment, therefore, the criterion adopted was the detection of the characteristic pitch of the pure tone signal. The new criterion leads to a masking pattern much higher than the conventional masked threshold and much sharper on the high-frequency side as well as on the low-frequency side. On the other hand, the pitch threshold curve may not have a well-defined peak.
Balanced Hydrophone with Isolated Shield
Authors: Greene David C.
Published: September 2005

A balanced hydrophone intended for use at frequencies below 1000 cps was designed, constructed and tested. The design is believed to be novel in that the shield surrounding the sensitive elements is isolated electrically from the hydrophone case and from the water. The hydrophone has an open-circuit sensitivity of approximately −75 db reference 1 v per μbar, a source capacity of 530 μμf, and no directionality below 1000 cps. It may be used at depths to 500 ft. The same principles may be used in designing hydrophones for higher frequencies.
Voicing Cues: Perception of Stop Consonants after Removal of a Preceding Fricative
Authors: Lotz John , Abramson Arthur S. , Gerstman Louis J. , Ingemann Frances , Nemser William J.
Published: September 2005

One of the differences between English /p t k/ and /b d g/ is the presence of aspiration in the former and its absence in the latter. When the stops occur as the second element of initial s clusters, they are unaspirated, whatever other phonetic characteristics (voicing or voicelessness, laxness or tenseness, etc.) they may have. If the s friction is removed by tape cutting, American listeners hear the stops as /b d g/. This may be because initial stops must be aspirated to be perceived by these listeners as /p t k/. Alternatively, it is possible that stops after initial /s/ are voiced, and that the voicing feature is the basis for their assignment to the /b d g/ series. One test is to find out how these sounds are perceived by listeners whose native languages have stops with characteristics different from those of English. Both Puerto Rican Spanish and Hungarian have unaspirated voiceless stops opposed to voiced stops in initial position. Speakers of these languages tended to hear the residual stops as voiceless. Thai has a three-way distinction of voiced-voiceless unaspirated-voiceless aspirated stops. Thai speakers tended to hear the residual stops as voiceless unaspirated. These results support the first interpretation above.
Pressure Reciprocity Calibration of Condenser Transducers to 50 kc in Air
Authors: Hickmon Floyd O.
Published: September 2005

A procedure for obtaining a pressure reciprocity calibration in air of a condenser transducer in the frequency range from 8000 to 50 000 cycles per second has been devised. The method is particularly useful in studying the response of the transducer diaphragm at short wavelengths without the effects of diffraction being present. A discussion of the basis for the calibration is presented to some extent, with emphasis on (1) the design and construction of a suitable calibrating chamber and (2) the nature of the calibrating acoustic field along with a presentation of some of the techniques and results of the calibration.
Electronically Modulated Air Valve
Authors: Fiala Walter T. , Hilliard John K.
Published: September 2005

A new design of an electronically modulated air valve on the dynamic principle, which will generate acoustic power in excess of 1.5 kw for small electrical input, will be discussed in detail. Applications of this device for generation of high intensity random noise will be described. Measurements in reverberant environment, free field, and for sonic fatigue tests of structures will be presented. A number of new applications, some of which may involve speech, such as in disaster warning systems, signal systems, communication systems, and psychological warfare are suggested.
Sonic Failure Research Facility
Authors: Kamperman G. W. , Allen C. H. , Sharp J. R. , Williams L.
Published: September 2005

A unique facility has been constructed for testing flight vehicle structures and electronic systems in the presence of high intensity sound. The siren sound source will produce pure tones or narrow bands of noise throughout the frequency range from 50 to 10 000 cps with controlled modulation from 0 to 50 cps. The maximum acoustic power output is 25 000 w to produce a sound pressure level of approximately 174 db in the 1 ft square progressive-wave test section. This paper discusses the performance of the facility. (The design and construction of this facility was sponsored by the Electronic Technology Laboratory and the Aircraft Laboratory of Wright Air Development Center.)
Propagation of Sound between a Fixed Source and a Fixed Receiver in the Ocean
Authors: Clay C. S. , Blaik M. , Sherry H. B. , Tyson L. , Weber P.
Published: September 2005

The fluctuations of the phase and amplitude of sound propagated between a source and receiver both on the bottom of the ocean were studied. The sound produced by the source was a continuous wave signal at 107 cps. The source was placed at a depth of 155 fathoms on a slope and the receiver was 1.1 nautical miles from the source at a depth of 760 fathoms. The phase and amplitude of the signal were each observed to fluctuate with an average period of about 10 sec. The maximum amplitude fluctuation from the mean level was about 10% and the maximum phase fluctuation was about 3°. Similar measurements were made with a receiver at 23.1 nautical miles from the source at a depth of 2700 fathoms. The receiver at this distance and depth was in shadow region because of the increase of the velocity of sound in water with increasing depth. The phase and amplitude fluctuations could not be studied in detail because of poor signal-to-noise power ratio at this receiver. The average amplitude of the sound observed at this receiver changed slowly, i.e., by a factor of two in a time of about 2 hr. This will be compared with what might be expected on the basis of travel paths calculated with several different sets of oceanographic parameters. (This work was supported by the Office of Naval Research.)
Side-Scattering of Sound in Shallow Water
Authors: Urick R. J.
Published: September 2005

When a sound beam travels through the sea, it is scattered in all directions by inhomogeneities of various sorts in the sea and on its boundaries. In the backward direction, the aggregate of all the scattered contributions is called “reverberation.” In other directions, the “side-scattering” can be studied by using two directional transducers, oriented so that the beams cross each other, to measure the sound scattered out of one beam and received on the other. This method was employed in an off-shore area in the Gulf of Mexico having a particularly uniform bottom. Using two-bottomed transducers a mile and a half apart, the intensity of scattering was measured at 22 kc for different angular orientations of the two beams. The measurements were reduced to the coefficient, scattering strength, without requiring either transducer calibrations or direct measurements of transmission loss. The results indicate a bottom scattering strength between −30 and −40 db having no appreciable dependence on angle between the two beams. Within the angular range from the backward direction around to 150° in the forward direction, the scattering appears isotropic. This indicates that isotropic bottom scattering may be safely assumed in applications utilizing separated transmitting and receiving transducers at kilocycle frequencies.
Behavioral Evidence in the Rat on the Question of Frequency Modulation and Amplitude Modulation
Authors: Allen Clark E.
Published: September 2005

This study was designed to test the ability of the Harvard strain of albino rats (three month old males) to make auditory discriminations between modulated and nonmodulated tones, based on differential responding in an instrumental conditioning situation. Rats trained to a criterion level of responding in a Skinner-box food-lever association were then subjected to modulated and nonmodulated tones of 4 kc at 70 db SPL. The tones were randomly arranged on tape to constitute a 3-min trial period. If the rat made the characteristic response during the time the tone was modulated, he was rewarded with a standard pellet. Responses during nonmodulated presentations of the tone were unrewarded. Beginning with examination of tones modulated at 5% in frequency or 5 db in amplitude, the study was planned so that the degree of modulation is progressively reduced till no discriminatory behavior is exhibited. The rat's performance in these stages of the over-all problem will be discussed. Comment will be made on the direction of further work in this area and its implications for the theory of primary auditory abilities. [This study is supported in part by Contract No. AT(30-1)-2398 of the U. S. Atomic Energy Commission.]
Masking of Tones by Noise for the Cat
Authors: Watson Charles S.
Published: September 2005

Masked thresholds were obtained by the method of behavioral audiometry for each of four cats at each of nine frequencies (octave steps from 125 to 32 000 cps). Masking stimuli were bands of noise centered about each test frequency. Estimates of critical band width (K) were obtained from data on frequency discrimination for the cat reported by Elliott et al. (MPA, 1959). The noise bands were adjusted in width to be 3 to 10 db wider than these estimated K's. Since preliminary data at 2000 cps show the signal-to-noise ratio at threshold to be constant for the cat when masking exceeds 10 db, the intensities of the noise bands were chosen to produce 20 db or more of masking. K is defined as the signal-to-noise ratio at the masked threshold. The function relating K to frequency for the cat parallels that for man, but is 4 to 5 db larger at most frequencies. The estimates of K based on the frequency-discrimination data for the cat are in reasonable agreement with these findings. [This research was supported by the U. S. Air Force under Contract No. AF 33(616)-3844, monitored by Aero Medical Laboratory, Directorate of Research, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio.]
Permanent Deafness after Continuous and Spaced Exposures to Noise
Authors: Miller James D. , Watson Charles S.
Published: September 2005

The auditory sensitivity of the cat as measured by the behavioral audiogram is severely impaired after a 2-hr exposure to a broad band (about 200–4000 cps) of thermal noise at an over-all level of 115 db. An exposure at this level with a duration of only 7.5 min produces no permanent change in the cat's auditory sensitivity. In the present experiment, four groups of four cats each were exposed according to the following schedule. Group I received a 2-hr exposure to the noise which was continuous in time. The other groups received the noise in sixteen, 7.5-min doses. These doses were spaced at one hour intervals for group II, 6-hr intervals for group III, and 24 hr intervals for group IV. Since the over-all level of the noise was 115 db for all groups, anc since all cats were exposed for a total of 2-hr, all cats were exposed to the same total noise energy. Persistent threshold shifts averaged over the frequency range from 125 to 16 000 cps are approximately as follows: group 1, 38 db; group II, 16 db; group III, 8 db; and group If, 0 db. Details of the audiograms, of the changes in the threshold shifts during a series of exposures, and of the recovery after the cessation of the exposures will be discussed. [This research was supported by the U. S. Air Force under Contract No. AF 33(616)-3844, monitored by Aero Medical Laboratory, Directorate of Research, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio.]
“Oxidative” Microelectrodes: A Technic for Measuring Metabolism and Permeability in Cochlear Scalae
Authors: Misrahy G. A. , Spradley J. F. , Beran A. V.
Published: September 2005

Among the tools available to measure permeability of membranes and metabolism in the cochlea, a promising one appears to be “oxidative” microelectrodes. This method is based on the principle that “active” metals at a given electrical potential will oxidize certain compounds. Current flow reflects concentration of oxidizable substances present. In general, current flow was greater in endolymph than in perilymph. Passage of oxidizable substances through membranes can be determined by this technic. Passage of ascorbic acid, sodium iodide, and chlorpromazine has been measured in all three scalae as well as in the brain, kidney, and liver. Preliminary results indicate marked differences in passage through the different membranous cochlear partitions. Implications of some of these results and problems involved in preparing the electrodes will be discussed.
Frequency Discrimination after Section of the Brachium of the Inferior Colliculus
Authors: Goldberg Jay M. , Dalen Betty Ann , Neff William D.
Published: September 2005

After complete bilateral section of the brachium of the inferior colliculus, cats cannot relearn an auditory frequency discrimination, a task which can be easily relearned after ablation of all known auditory neocortical areas and the subsequent degeneration of the thalamic auditory nuclei (the medial geniculate body and the posterior nucleus). The problem can be relearned when a small part of the brachium remains intact; the rate of relearning depends upon the anatomical locus of the remaining fibers. These results suggest that the brachium may contain fibers that do not end in the medial geniculate body and that these fibers, which probably come from the inferior colliculus and/or the nucleus of the lateral lemniscus, play an important role in the neural mechanisms underlying frequency discrimination. (This research was supported by the Office of Naval Research and the Air Force Office of Scientific Research.)
Effect of Memory for Amplitude on Amplitude Discrimination
Authors: Tanner Wilson P.
Published: September 2005

A two alternative forced-choice experiment (2 AFC) in which the observer is asked to state which is the larger of two segments of tones presented sequentially in time, is analyzed as an experiment involving only amplitude memory. Frequency, phase, starting time, and duration information is provided each trial by the stimuli. The 2 AFC experiment is conceived as one in which a measure of the intensity of the first signal serves to establish a cutoff value against which the measure of the second can be compared. If the measure of the second exceeds the cutoff then it is reported to be larger. If the measure of the second is less than the cutoff then the first is reported to be larger. The variable in these experiments was the time interval, τ, between the two signals. Intervals from 50 to 9600 milliseconds were studied. The efficiency in these experiments varied as the produce (1 − e−A τ)1/1 + A τ, where C is a damping constant and A is a constant describing the variance of the cutoff. (This study upon which this paper is based was sponsored by the Air Force Office of Scientific Research.)
Driving Point Impedances of Cylindrical Structures
Authors: Franken Peter A.
Published: September 2005

This paper continues the study of a point-excited infinite cylindrical shell in vacuum [J. Acoust. Soc. Am. 31, 115(A) (1959)]. Each nonaxisymmetric modal impedance is found to contain a resistance and a mass of equal magnitude, as in the case of an infinite bar. The impedance decreases with increasing mode number up to a “cutoff” mode. Stiffness effects become important for modes above the cutoff mode. The analysis has been extended to finite shells and rings. Couplings between the impedances in practical problems are considered. [Supported by Office of Naval Research Contract No. Nonr-2322(00).]
Sound Radiation from a Finite Cylindrical Shell with Rigid End Caps
Authors: Brigham Gerald A. , Borg Matthew F.
Published: September 2005

Utilizing the concept of a point source omnidirectivity, two separate approaches are derived to the problem of far field sound radiation from a finite cylindrical shell source with rigid end caps vibrating in one of its normal modes. An additional approach is derived by taking the expressions of Laird and Cohen [D. T. Laird and H. Cohen, J. Acoust. Soc. Am. 24, 46 (1952)] and expending them into a shell band source on an infinite cylinder. For all three above approaches, three separate boundary conditions are considered. Case I, finite cylinder in a free field; case II, finite cylinder resting normal on a rigid plane reflector with zero phase shift between incident and reflected wave; case III, similar to case II except for a 180° phase shift between incident and reflected wave. All nine approaches are compared to one another, together with a case III comparison to experimental values.
Analytic Study of the Vibrating Free Disk
Authors: House Raymond N. , Kritz Jack
Published: September 2005

A piezoelectrically driven free disk vibrating in the first symmetrical mode has been shown to possess advantageous properties as a sonic generating source. Proper transducer design requires an evaluation of the disk properties together with a development of the equivalent circuit. An expression for the deflection surface is presented which satisfies the necessary boundary conditions for a vibrating free circular plate. The potential and kinetic energies are derived which in turn lead to expressions for the equivalent stiffness and mass, respectively. Expressions for the radiation impedance are developed using equivalent piston concepts. A derivation of the electromechanical transformer is given together with an evaluation of the constants for quartz. The equivalent circuit referenced to center displacement is constructed and the results are then compared with experimentally obtained data.
Vibration Measurements of a Cylindrical Shell in Air and Water
Authors: Lott G. B. , Bland R. E.
Published: September 2005

An experimental system is described for vibration measurements on a 21-in. diam cylindrical shell. The measurements were conducted in both air and water at water depths up to 50 ft. The shell was excited by a pure-tone constant force over the audible frequency range. Data are presented to compare the shell vibration levels in air and in water. No appreciable change in vibration level is shown with submergence depth. The vibration levels of various points on the shell and the mechanical impedance of the driven point is also presented. Radiated sound pressure measurements are compared to vibration levels on the shell. The inherent difficulties with this type of experiment are discussed.
Theory of Sound Transmission through Suspended Ceilings over Partitions
Authors: Mariner T.
Published: September 2005

Two adjoining rooms are considered to be separated by a perfect partition extending only to a suspended ceiling. A source in one room produces there a reverberant field of energy density D1. In the other room an energy density D2 is produced by sound which originates in the source room and travels the path : source room ceiling, plenum, receiving room ceiling. A theory is developed which relates the ratio (D1/D2) to the transmission coefficient of the suspended ceiling, the absorption coefficients of the plenum boundaries, the total absorption of the receiving room, the lateral dimensions of the two rooms, and the depth of the plenum. The ratio (D1/D2) is found to be quite sensitive to variation of both the transmission coefficient of the suspended ceiling and the absorption coefficients of the horizontal plenum boundaries. For three types of suspended ceilings calculated values of (D1/D2) are compared with experimental values obtained by Hamme, some of which he published in NOISE Control [5, 64 ff (January, 1959)]. Agreement between theory and experiment is encouraging.
Measured Noise Transmission Characteristics of Lightweight Partitions Used in Recently Constructed Music Buildings
Authors: Lane R. N. , Mikeska E. E.
Published: September 2005

Measured values of noise reduction achieved between classrooms, teaching studios, and practice rooms for four new music buildings are presented. Data on double plaster walls set on cork isolation, and on concrete alone are presented, along with data on double and single concrete block walls.
Comparison of the Vibration Damping Effectiveness of Free and Constrained Viscoelastic Layers
Authors: Kerwin Edward M. , Ross Donald
Published: September 2005

Two important treatments for the damping of flexural waves in plates are the free viscoelastic layer [H. Oberst, Acustica 2, Suppl. 4 (1952)] and the constrained viscoelastic layer, sometimes called “damping tape” [E. M. Kerwin, Jr., J. Acoust. Soc. Am. 31, 952 (1959)]. In this paper we compare these two treatments in order to determine which is more useful in a given situation. For good, contemporary damping materials at lower treatment weights, and therefore lower values of damping, the constrained layer is the more effective. The free layer becomes more effective than the constrained layer for higher treatment weights. At a given fraction of the plate weight, the performance of a given free layer depends on the plate material (e.g., steel vs aluminum). On the other hand, if the constraining layer has the same modulus-to-density ratio as the plate material, the maximum effectiveness of a constrained layer at a given fraction of the plate weight is practically independent of the plate material. (This work was sponsored in part by the U. S. Navy, Bureau of Ships, Code 375, under Contract NObs-72452.)
Relation between the Compensatory and Pursuit Modes of Display in Auditory Tracking of Loudness
Authors: Pikler Andrew G. , Harris J. Donald
Published: September 2005

A preliminary experiment with compensatory loudness tracking convinced us that the principle is useful as a psychophysical and engineering tool. A full-scale study was then completed using five subjects given compensation, pursuit, monaural, binaural, and interaural combinations. Three taped programs were used presenting intensity changes over a 20-db range at the rate of 1 db/sec. Response was written on a paper tape recorder by means of an external voltage and a second rotary attenuator on subject's control dial in a manner analogous to certain man-machine feedback systems. Analysis of variance midway through the replications revealed no influence of particular program or of learning, with these trained subjects. For all subjects and all channels, the compensatory mode was superior to the pursuit. The average instantaneous error in db for the former was 2.5, for the latter 3.4. This superiority was maintained whether one considers the interaural channels or the monaural or binaural channels. There was only the slightest tendency for the interaural channels to be superior to the monaural or binaural channels, and then only for the pursuit mode. The monaural pursuit and the binaural pursuit averages deteriorated to 3.4 and 3.9 db, respectively.
Detection of Signals Presented at Random Times
Authors: Egan James P. , Greenberg Gordon Z. , Schulman Arthur I.
Published: September 2005

Three types of experiments measured the decrement in (de)12 that results from uncertainty in the time of onset of a sinusoid (1000 cps, 0.25 sec) presented against a continuous background of noise. (1) A light defined an observation interval during which the signal either was or was not presented [p(SN) = 0.5]. The signal, when presented, started at an instant randomly selected within the observation interval. The interval of time uncertainty during which the tone might start was systematically varied from 0 to 8 sec. After each observation interval, the listener indicated his confidence that a tone was presented by using a rating scale. (2) The sinusoid was or was not presented [p(SN) = 0.5] at a randomly selected instant. A fixed time after this instant, the listener was informed (by a flash of light) of the real time at which the signal might have occurred, and he responded with a rating. (3) The sinusoid was presented a number of times in a 2-min observation interval. The temporal intervals between the presentations of the tones were randomly selected. No further indication was given to the listener as to the times at which the tones were presented. Over a series of sessions, the listener adopted various criteria, and he pressed a single “yes-key” whenever he “heard a tone.” This situation is the most difficult one to analyze, because a trial is not defined. Nevertheless, this method of free response results in a family of curves of temporal coincidence [n(y)/sec as a function of time after onset of the signal]. These curves allow an estimate of the coordinates of the point of intersection, (de)12, of an assumed operating characteristic. Results for the three types of experiments are based on a total of around 105.3 responses. [This research was supported by the Operational Applications Laboratory, Air Force Cambridge Research Center, under Contract AF 19(604)-1962.]
Meters for Predicting the Subjective Response to Noise
Authors: Anderson Floyd C.
Published: September 2005

Two portable, battery-powered, transistorized meters have been designed to produce direct measurements for the prediction of subjective response to noise. One of these meters reads loudness (octave-band sones and total sones) and loudness level (phons) based on Steven's method. The other meter reads Speech Interference Level in decibels (re 0.0002 microbar) based on the average sound pressure level of the three octave-bands from 600 to 4800 cps. These direct reading meters are utilized to replace the sound level meter-octave band analyzer combinations customarily used for these applications. The construction and the applications of the meters are discussed.
Response of Structures to Sound
Authors: Smith P. W.
Published: September 2005

In experimental and mathematical considerations of the response of structures to sound, it is convenient to have a generalized form of Thévenin's theorem, valid for a general vibratory system with an arbitrary distribution of sources. Linearity must be assumed. One form of the theorem is useful only when the vibrational pattern of the surface of the structure can be predicted or estimated. Then a generalized force is defined as the net force acting to move the structure with that pattern. The theorem states that the generalized force due to the sources equals the difference: (1) the generalized force that would obtain when the structure is constrained from moving, minus (2) a radiation reaction. The latter can be written as a product of velocity amplitude by radiation impedance for the particular vibrational pattern. Experimental analyses of complicated problems can be designed on the basis of this theorem. One would measure the generalized force for an almost rigid structure of the same shape and the combined mechanical and radiation impedances for the actual structure. The dual form of the theorem is useful only when the pressure pattern on the structure can be predicted, and it is therefore not usually convenient. [Research supported by Wright Air Development Center under Contract No. AF 33(616)-6347.]
Response of Plates to Moving Shocks
Authors: Ungar Eric E.
Published: September 2005

Panels of high speed vehicles are likely to be subjected to shock waves passing over them or oscillating about some mean position. The present paper deals with calculations of modal responses of simply supported rectangular panels to shocks moving parallel to one pair of edges. Generalized coordinates are used to evaluate the effect of shocks which move at constant velocity or which move sinusoidally. A reasonable pressure cross-correlation function associated with randomly oscillating shocks is also discussed and results obtained by use of the concepts of A. C. Eringen [J. Appl. Mech. 24, 46 (1957)] are summarized. [Supported by Wright Air Development Center under Contract No. AF 33(616)-6217.]
Application of the Mechanical Impedance Concept to Shock and Vibration Testing
Authors: Morrow Charles T.
Published: September 2005

Until recently, the mechanical impedance concept has been ignored in connection with shock and vibration. There is no question of the importance of the concept, especially in respect to correcting vibration data for loading effects. In testing, the applications must be carefully planned so as to avoid demands for excessive amounts of data or data of a type that is difficult to obtain, excessive complexity of test equipment, and excessive complexity in the test procedures. One compromise is to operate the shaker as an approximation to an infinite-impedance or a zero-impedance source according to the relationship of the tested item of equipment to the structure to which it is attached while in use. If a zero-impedance source is favored, it is desirable to make a transition to infinite impedance at the lowest frequencies, partly because the impedance of the qeuipment is usually lower than that of the structure at such frequencies and partly because a zero-impedance shaker might have too much chance of bottoming. Impedance is controlled simply by equalization. Another compromise is to adjust the spectrum of motion prior to mounting the equipment to be tested and require that the impedance of the shaker correspond to an upper envelope of the impedance of the structure on which the item is to be used. This involves a complicated servomechanism problem which must be solved for each test fixture. Simulating the exact impedance of the structure rather than an envelope is not feasible.
Space Requirements for Airborne Equipment Excited by Random Vibration
Authors: Himelblau H. , Keer L. M.
Published: September 2005

The problem of mount bottoming of resiliently-mounted equipment and its collision with adjacent structure when both are subjected to random vibration is solved in terms of probability of occurrence and the mean time between occurrences. The system is represented by two simple mechanical oscillators (with damping) whose relative motion is determined. A complete solution is obtained for white Gaussian excitation. This solution can also be applied to other structural problems, such as the mechanical design of electronic components, when the same representation can be used.
Dynamic Considerations for Neutralizing Shock Stresses in Buildings Subjected to Fringe-Area Nuclear Blasts
Authors: Carlisle Richard W.
Published: September 2005

Buildings subjected to fringe-area nuclear blasts having an instantaneous pressure of, for instance, 5 psi suffer fracture of windows and collapse of roofs and floors. Walls in which windows actually fracture are, however, relatively undamaged (see “The effects of nuclear weapons,” published by the U. S. Atomic Energy Commission). It is deduced that a building wall functions as an acoustical baffle to build up the pressure of the shock wave and that the fracture of windows provides instantaneous leakage, and therefore relieves the pressure. It is accordingly suggested that buildings be planned with fast-acting shuttered ports distributed on the roofs for relief of pressure. Stresses on internal walls and floors may be neutralized by providing equal ports communicating with each side of each one. The dynamics of this problem are discussed.
Some Physical Aspects of Cathodic Protection Against Cavitation Damage
Authors: Ellis A. T. , Jones I. R.
Published: September 2005

It is well known that metal surfaces may be protected from chemical corrosion by application of a negative potential. That they may be protected in this way from cavitation damage has also been established by several experimenters. The possibility that part of this protection may be due to physical rather than chemical effects is investigated by means of a pressure bar technique and high speed photography to correlate cathodic currents with bubble geometry and collapse pressures. Comparison is made with nearly pure vapor bubble behavior in degassed water. Ultrasonic cavitation generated by both barium titanate and magnetostriction transducers is studied.
Effect of Interaural Phase on the Binaural Absolute Threshold for Tone
Authors: Diercks K. Jerome , Jeffress Lloyd A.
Published: September 2005

Earlier workers have found that where monaural thresholds are equal, or where inequalities are compensated for, the binaural threshold is about 3 db lower than the monaural. Licklider in Steven's Handbook suggests that this implies a kind of power summation. Since the powers being summated are going to different ears, this summation cannot be acoustical. The summation, therefore, appears to be neural, and we should expect some of the temporal phenomena of neural summation to apply. Delaying the sound to one ear, for instance, should make conditions less favorable for summation and should raise the binaural threshold. In the present experiment a 2-msec delay (or advance) was produced by reversing the phase of a 250-cps tone. Monaural and binaural thresholds (both homophasic and antiphasic) were determined for four subjects, and the best ear was taken as reference. The results indicate that the threshold for the antiphasic condition instead of being elevated relative to the homophasic is actually lower. This suggests that we are dealing, not with neural summation, but with a masking phenomenon—that the absolute threshold is really a masked threshold. [This Work was partially supported by the Bureau of Ships.]
Clues to Sound Localization
Authors: Hanson R. L.
Published: September 2005

At the May, 1959, meeting of the Acoustical Society, the author reported experimental results which indicate that the location of a steady-state low frequency sound is well defined only when a certain relationship exists between the interaural time and pressure differentials. This is to be a demonstration to illustrate that when such a relationship does not exist, as is usually the case in a room, (a) an observer is confused as to the direction of the source and (b) by the use of suitable clues he can be influenced to hear a well-defined source but from a direction not necessarily associated with that of the actual source.
Speech Perception through Different Hearing Aids
Authors: Hirsh I. J. , Shore I. , Charan K.
Published: September 2005

In a previous statistical study, Shore, Bilger, and Hirsh found, for 15 clinical patients, that four different hearing aids, each with two different tone settings, did not yield significant differences in speech discrimination in quiet or in noise when test results were based upon four different testing days. In order to explore further whether the lack of significant difference came from a lack of acoustical difference among these hearing aids, response-frequency characteristics were obtained for the four different makes of hearing aids, each with the necessary number of combinations of tone setting, earphone, cord, and insert, to provide both good and bad “fittings” for each of the 15 patients. There are some substantial differences in the frequency response of the various hearing-aid combinations used but only rarely do these differences correspond to differences in test results based upon speech perception with patients. [This study was supported by Grant (B-1854) from the National Institutes of Health (NINDB).]