bluuebunny/crossref_metadata_2025 huggingface dataset:
Rain Noise on Building Structures
Authors: Hirtle P. W. , Watters B. G. , Dyer I.
Published: September 2005

Rain noise is a frequent problem in light-weight building structures within which there are critical listening activities. Music tents aluminum domes, and light sandwich constructions are examples in which such problems arise. All experimental program has been undertaken to measure the rain noise on a plastic hyperbolic-paraboloidal roof intended for classroom application. The experimental arrangement consists of an 8 ft × 8-ft × 10-ft room roofed by the plastic structure. Measurements were made in the room with simulated rain having known water-flow rates, droplet sizes, and terminal velocities. Measurements also were made with actual rainfalls. An evaluation of the rain noise in terms of interference with speech is made. The measurements also are compared with calculations based on random excitation theory in which it is assumed that rain is a stochastic process of vanishingly small spatial correlation. (Supported in part through a grant-in-aid-study to MIT by the Educational Facilities Laboratories of the Ford Foundation, and in part by the Office of Naval Research.)
Performance of Acoustical Materials at High Sound Intensities
Authors: Allen C. H. , Westervelt P. J. , Doelling N.
Published: September 2005

The results of a study on the properties that influence the performance of acoustical materials at high sound levels is reported. Experimental data for nonlinear acoustic resistance of simple structures such as screens and perforated plates agree well with theoretical calculations. Similar data obtained for more complex structures such as fibrous or cellular materials indicate that in general the performance of an acoustical material at high intensities is determined by the conventional parameters such as its dc flow resistance R0, applicable at low intensities, plus a resistive term that depends on the particle velocity v. The dynamic flow resistance can in general be described as R = R0(1 + v/vcr), where vcr is the velocity at which the resistance becomes twice the low velocity value. Other properties of several acoustical materials, including dynamic, mechanical, and thermal performance at high intensities, are reported. (Supported by the U. S. Navy Bureau of Ships.)
Recent Advances in the Soundproofing of Large Openings
Authors: Munchhausen H. V.
Published: September 2005

A novel method of moving operating partitions is presented. The design, developed over the past two years, reduces acoustical leaks, both at the edges and at the panel section buttings, to a negligible value. It can be used both for “folding” partitions and for large window fronts: easy manual or semi-automatic operation is provided. Primarily designed for the moving of high-TL panels of comparatively low mass, the system also can be used in conjunction with panel units ranging from a 30-db design to a heavy wall. The TL of such applications is discussed. Photographs, schematics, and drawings depict this design and show its adaptability to a large variety of field conditions.
Internal Friction in Copper as a Function of Frequency and Temperature
Authors: Mason W. P.
Published: September 2005

The internal friction of a face-centered metal such as copper, measured at low-strain amplitudes, can be divided into a low-frequency region and a high-frequency region. Available data show that, in the low-frequency range, the internal friction is nearly independent of the frequency. The internal friction and the modulus change, caused by neutron irradiation, can be analyzed to show that the low-frequency region is caused by a series of relaxation processes. In the high-frequency region, the internal friction increases in proportion to the frequency, and the modulus change is nonrelaxational in character. It is shown that the variation of this component over a temperature range is consistent with the variation of phonon viscosity and not consistent with phonon scattering or thermoelastic damping of dislocations.
Ultrasonic Attenuation in Vanadium at Low Temperatures
Authors: Brewster John L.
Published: September 2005

Longitudinal elastic wave attenuation measurements have been made in a vanadium single crystal in the frequency range of 45 to 435 Mc in both the normal and superconducting states, using pulse echo techniques. Novel experimental features include the use of a superconducting niobium electromagnet (supplied by Stanley H. Autler, Lincoln Laboratory, Massachusetts Institute of Technology). Throughout the frequency range the product ql<<1 where q is the elastic propagation constant and l is the electronic mean free path. The data is in good agreement with the BCS prediction for the ratio of the attenuations in the superconducting and normal states, although this prediction is based on ql>>1. (Supported by Office of Naval Research.)
Boundary Layer Excitation of Plates
Authors: Dyer I. , Maidanik G.
Published: September 2005

In a previous theory of boundary layer excitation of plates [I. Dyer, J. Acoust. Soc. Am. 31, 922–928 (1959)] it was assumed that the boundary layer pressure field could be represented by a vanishingly small spatial correlation convected along the plate surface. A result of the theory was that the plate modes were statistically independent for small enough values of the convection speed. A re-evaluation of the theory shows that under some conditions mode coupling may be of importance when the convection speed is unrestricted and when the size of the correlated pressure field is not allowed to shrink to zero. The convection effect is shown to be far more important in producing mode coupling than the finite size of the field. It is likely, therefore, that the delta-function approximation used in the previous theory adequately describes the boundary layer pressure field and that the extension to the theory with unrestricted convection speeds makes the calculations more precise. (Supported by the Office of Naval Research.)
Transmission of Plate Flexural Waves through Reinforcing Beams
Authors: Ungar Eric E.
Published: September 2005

An infinite plate to which a narrow infinitely long beam is attached rigidly and continuously may be considered as an idealization of some typical flight vehicle structures. Reflection, transmission, and near-field effects, associated with a straight-crested flexural wave impinging on one side of the beam are presented as functions of the properties of the plate and beam and interpreted in terms of trace-matching of the flexural waves in the plate with flexural and torsional waves in the beam. Upper bounds on the resulting dynamic strain concentration factors and implications pertaining to the design of beam-reinforced panel structures with favorable fatigue properties are discussed. (Supported by Wright Air Development Division.)
Bending Wave Propagation on Periodic Structures
Authors: Heckl Manfred
Published: September 2005

The propagation of bending waves on periodic beam-plate systems (a plate with many parallel beams attached to it) can be calculated fairly easily if the bending wave propagation on a plate with one beam is known. Calculations show that, in the frequency bands surrounding the resonance frequencies of the beams, the wave is unattenuated. These results also may be applied to point-driven beam-plate systems. Experiments show no attenuation except at the beam closest to the source. The wave propagation on periodically loaded cylinders and on gridworks consisting of beams (grilles) also will be discussed. (Supported by the Office of Naval Research.)
Maximum Damping Attainable in Composite Structures Incorporating Viscoelastic Interlayers
Authors: Ungar Eric E.
Published: September 2005

Damping of structures by viscoelastic materials, in the form of homogeneous layers, constrained layers, or inserts, is reviewed. The effects of geometry and of viscoelastic material properties are discussed, and optimum geometries are described. The maximum amount of damping of composite structures attainable with available materials is compared to the theoretical maximum.
Comparison of Propagation Measurements Made Using Explosives and Sinusoidal Acoustic Signals
Authors: Hasse R. W.
Published: September 2005

A great many underwater acoustic propagation measurements have been made using either sinusoidal acoustic signal generators or explosives which generate very wide-band impulsive type signals. Because of the extremely different characteristics between the two signals and the fact that the shock wave of the explosive signal does not follow the propagation theory developed, considering only infinitesimal displacements, considerable concern has existed as to whether the results obtained by the two methods are comparable. An experimental study was conducted to compare propagation measurements made using explosives with continuous and pulsed sinusoidal signals. By using available source level values for explosive charges, a comparison is made between the various type signals, and the results are shown to be in agreement within about 3 db.
Fixed Path Acoustic Transmission in the Presence of Internal Waves
Authors: Lee Owen S. , Batzler William E.
Published: September 2005

Results from several sources have indicated that internal (thermal) waves might cause significant fluctuation in sound transmitted through the ocean. A series of experiments at sea was begun in September, 1959, to study direct evidence of sound field distortion produced by the internal waves. The experiment consisted of acoustic transmission of 0.2-msec pulses at 92 kcps over a horizontal range of 400 to 500 ft. The source was supported 50 ft from the bottom, being attached to a fixed stable platform; the hydrophone was supported 3 to 10 ft from the bottom on a tripod. Thermistors in the field and isotherm followers on the platform provide data to determine the position, direction, speed, and amplitude of the waves. The platform (an oceanographic tower) is located about one mile off the coast at San Diego, California, in 60 ft of water where the bottom is rippled sand. A large volume of data has been collected for comprehensive coverage of many different thermal situations. Analysis of part of the data has led to the following preliminary results: (1) internal waves are always accompanied by marked fluctuation in sound pressure; acoustic fluctuation, above normal and longer than the normal period, can be reasonably attributed to each internal wave that passed through the sound field; the fluctuation in acoustic level is about 10 db; (2) acoustic fluctuation is also present when the water is isothermal, but in this case the maximum to minimum variation is only about 4 db.
Future Trends in Acoustic Environment of Manned Space Vehicles
Authors: Sutherland L. C.
Published: September 2005

The acoustic environment of current rocket vehicles has been reported in sufficient detail within the last few years to provide a limited basis for extrapolation to future rocket-propelled vehicles. Such an extrapolation is carried out to indicate the expected trends in rocket engine noise and boundary layer noise that may be expected on the external surface of future vehicles. The analysis considers the expected influence of clustering engines on over-all power level of rocket engines. A characteristic frequency of engine noise, as indicated by a typical jet diameter and jet velocity, is related to known characteristics of the rocket engine. The expected influence of the blast deflector is considered on the basis of available full-scale data and previously unreported model data. Based on the assumption of a constant ratio of acoustic pressure to free stream dynamic pressure, the expected trend in boundary layer noise is analyzed in light of the probable restraints in the flight path of manned vehicles. Flat plate boundary layer theory is utilized as a basis for indicating the trend in a characteristic frequency of the boundary layer noise.
Noise Radiation from Rocket Motor Clusters
Authors: Dorland Wade D.
Published: September 2005

Results are presented from an acoustic noise survey of rocket motors with 500-lb thrust, tested in configurations of one, two, four, and eight engine clusters. Information concerning sound pressure, acoustic power radiated, the directivity of the radiation, and correlation of acoustic parameters to engine performance parameters is obtained. Also, results of the survey are correlated with measurements of sound radiation from an eight engine cluster developing 1 300 000-lb thrust.
Spectrum Matching of Nasal Consonants
Authors: Fujimura O.
Published: September 2005

The important features of sound spectra of nasal consonants have been examined quantitatively with the assistance of a computer. The computer program (1) allows the experimenter to select the frequencies and bandwidths of poles and zeros of an arbitrary transfer function, (2) calculates the corresponding sound spectrum, (3) provides visual comparison between the calculated spectrum and any given stored speech spectrum, and (4) calculates measures of the goodness of fit of the two spectra. The speech samples were drawn from the materials described in a paper on vowel formants presented at this meeting. In order to match spectra of nasal consonants in the frequency range below 3000 cps, one or two pole-zero pairs attributable to the closed oral cavity must be used, together with three or four poles. The bandwidths of the poles in nasal consonants are always greater than the bandwidths found in nonnasal vowels. The locations of poles and zeros which give the best match for [m] may vary significantly with vowel environment and may change during the period of mouth closure. Theoretical considerations can explain and to some extent predict these pole-zero characteristics. [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 the National Science Foundation.]
Some Basic Considerations in the Analysis of Intonation
Authors: Peterson G. E. , Lehiste I.
Published: September 2005

This paper considers some basic problems inherent in the instrumental analysis of intonation. The problems are illustrated by a detailed analysis of one intonation contour in American English. The material studied consisted of two sets of data. The first set involved sentences recorded by one speaker with determined stress and pitch patterns. These sentences consisted of 1263 CNC words produced in an identical frame, with primary stress and the peak of the intonation contour occurring on the CNC word in the frame. The second set of frame sentences involved 70 minimally different words, uttered by five different speakers of the same general dialect. The fundamental frequency values for the various levels of the intonation contours of the sentences were measured from narrow-band sound spectrograms, and the measurements were correlated with the segmental phonetic structure of the utterances in which the intonation contours were produced. The intrinsic fundamental frequencies of the various syllable nuclei of the words from both sets of data, and the influence of preceding and following consonants on these frequencies, are described. The relationships among successive intonation levels within the sentences also are discussed.
Instrumentation for Measuring Underwater Acoustic Intensity
Authors: Boyer G. L.
Published: September 2005

Instrumentation has been developed to measure one component of underwater acoustic intensity. Acoustical intensity is defined as the rate of flow of acoustical power per unit area in a direction normal to that area. It is equal to the product of the sound pressure and particle velocity at a point averaged over a period long relative to that of the lowest frequency component present. Transducers have been developed to measure both the sound pressure and particle acceleration. The outputs of the two transducers are amplified and filtered. The voltage proportional to the particle acceleration also is integrated. Thus, two voltages proportional to the sound pressure and particle velocity whose relative phase is the same as existed between the pressure and particle velocity are multiplied and averaged to provide a measure of the intensity. This instrumentation measures the acoustical intensity in octave bands from 50 to 2000 cps. A method of calibrating the pickups in the near field of a sound projector also is described.
Electroacoustic Transducer Calibration Combined with Semi-Automatic Data Reduction
Authors: Roshon John
Published: September 2005

The absolute calibration response of underwater sound transducers is most tedious and time consuming when point-by-point calculations are employed. This paper describes an accurate means of quickly producing the characteristic frequency response of electroacoustic transducers using the three-transducer reciprocity method. This accelerated process of calibration permits the engineer not only to obtain a complete evaluation but immediately determine errors in measurement. Two techniques are employed which, as far as the author is aware, are not in general use. First, a graphic method is used to reduce reciprocity measurements to absolute calibration response curves. Second, an X-Y recorder is used to produce continuous traces that, when evaluated with the graphic method, result in an absolute calibration. The frequency and amplitude scales will match the grid of any notebook graph paper. These techniques are now in use at the U. S. Navy Electronic Laboratory's calibration station at Sweetwater Lake in San Diego, California.
A System for Measuring the Sensitivity of Hearing Aids to Alternating Magnetic Fields
Authors: Priestley J. T.
Published: September 2005

This paper describes equipment used in making objective measurements of the sensitivity of hearing aids to the alternating magnetic field associated with ac operated equipment. The hum picked up by a hearing aid depends upon its orientation in the magnetic field. Three large mutually perpendicular coils were used to set up an ac field along three axes consecutively. The signal was generated by a 60-cps source with controllable harmonics. In order to obtain an accurate measure of hum pickup it is necessary to use a field whose intensity does not overload the hearing aid. For linear response from some hearing aids the field strength cannot exceed 1 mgauss. Since the background field in the laboratory was of the order of 2 mgauss, it became necessary to attenuate the background field. A feedback arrangement was devised whereby pickup coils sensed the background field and sent through the large coils a signal of proper phase and amplitude to cancel the background field. (This work was carried out under sponsorship of Veterans Administration.)
“Colorless” Artificial Reverberation
Authors: Schroeder M. R. , Logan B. F.
Published: September 2005

An artificial reverberator is described which has a flat amplitude-frequency response and therefore does not alter the spectral balance or “color” of the reverberated sound. Neither does the reverberator add any extraneous hollow, reedy, or metallic qualities or flutter echoes of its own. The number of echoes per second increases with time according to the same law governing the echo statistics of a real room. Thus, it is compatible with the most exacting fidelity requirements in sound recording, home use, and the electroacoustic conversion of auditoriums and theaters, designed primarily for speech, into concert halls. In the last application, the flat amplitude-frequency response of the reverberator minimizes acoustic feedback problems associated with other artificial reverberation devices.
Experimental Full-Range Electrostatic Speaker
Authors: Priestley J. T.
Published: September 2005

The transient nature of speech makes it necessary to test hearing aids for transient response. To carry out the tests, the sound source used must reproduce transients faithfully. This paper describes development of a sound source suitable for transient measurements. An experimental push-pull full range electrostatic speaker was built and tested. The speaker is of the small area, long excursion type rather than the conventional large area, small excursion type. In order to achieve the high compliance necessary for long excursion, a diaphragm suspension was devised in which a square diaphragm was suspended only by tabs at the corners. Because of the light weight of the diaphragm material and the compliance of the mounting, radiation damping was dominant. The fundamental resonance for an 8-in. square occurred at about 20 cps. The frequency response was flat within ±5 db down to 150 cps, with no individual peak greater than 2 db. The transient response was observed by making oscilloscope photographs of the output of the speaker to pulsed sine waves. (This work was carried out under sponsorship of Veterans Administration.)
Evaluation of the Effectiveness and Acceptability of Masking Noise for Providing Speech Privacy in Buildings
Authors: Farrell William R.
Published: September 2005

Data will be presented showing the results of both laboratory tests and field experiences. The feasibility of using a terminal air delivery device to generate masking noise will be discussed. The information presented will be based on a large number of background noise measurements made in both older and newer buildings and on approximately 150 test subjects in the laboratory tests. The conclusions drawn are two-fold: (a) it has been found that the noise levels required to mask speech are lower than the average of the noise levels encountered in spaces where masking noise was not planned; and (b) to obtain the design masking noise level from air delivery devices requires more precise balancing of air flow than is normally done for temperature control reasons.
Thresholds of Audibility for Periodic Pulse-Trains
Authors: Flanagan James L.
Published: September 2005

Thresholds of audibility are determined by the Békésy technique for four periodic trains of rectangular pulses. The pulses of a given train are uniform in amplitude and duration. The trains differ in their periodic patterns of pulse polarity. The parameters investigated are pulse rate (20 to 1000 pps), pulse duration (20, 100, and 500 μsec), and polarity pattern (+, +−, ++−−, ++−+−−). The stimuli are presented binaurally, in quiet, over good quality headphones. Data for four subjects are reported. The results show the thresholds to be little dependent upon the polarity pattern of the train. Below a pulse rate of about 100 pps, the thresholds also are little dependent upon pulse rate. They approach constant values apparently determined by pulse duration. The threshold is lowest for the longest pulse duration. Above 100 pps, the threshold for a given pulse duration diminishes monotonically at a rate of about 3 to 6 db per doubling of pulse rate. The possibilities for analytically specifying the thresholds are discussed.
Limits of Tolerance to an Intense Tone under Water
Authors: Strickland J. F. , Montague W. E.
Published: September 2005

Data on the threshold of audibility of underwater sound have been published, but virtually no data are available on the upper threshold of tolerance to underwater sound of high intensity. The present experiment was undertaken to obtain such data. Twenty-three listeners, UDT (Underwater Demolition Team) and scientific personnel, were given audiometric tests preceding and immediately following exposure in a high-intensity underwater sound field. The stimulus was a 1500-cps tone of 1-sec duration that was increased in 1-db steps from 161 db (re 0.0002 d/cm2) to 180 db. Masking from breathing noise of the open circuit SCUBA (Self Contained Underwater Breathing Apparatus) was eliminated by having the listener breathe during the 2-sec interval between steps. The listeners indicated to the experimenter their “tolerance” limits by means of an electrical signaling device. Tests were run with and without foam neoprene hoods. The data indicate that the threshold of discomfort to underwater sound at 1500 cps is approximately 173 db for divers without hoods. A comparison is made with similar data for airborne sound. A shift in the visual field which occurred at the onset of the sound is discussed.
Naval Aviation Hearing Conservation Program Aboard Aircraft Carriers
Authors: Ades Harlow W.
Published: September 2005

According to the terms of U. S. Navy BUMED Instruction 6260.6A, given a noise environment of certain dimensions, a hearing conservation program must be instituted. Whether or not this instruction can be accomplished feasibly depends upon assessment of noise environment, determination of volume of audiometry required, and evaluation of equipment and test rooms under ship's operational conditions to determine whether the given volume of testing can be accomplished. There have been several surveys of the noise environment on carrier flight decks. These have usually entailed sample measurements of SPL at peak levels and representative locations on the flight deck during launching of aircraft. In addition to this type of measurement, it is necessary to know the duration of SPL above certain levels in order to complete the exposure data so that all variables, including time, intensity, and spectrum, are known for each work location. Given accurate data on the noise environment, the individuals whose hearing must be monitored can be determined. It then becomes possible to specify the time and facilities necessary to conduct the necessary testing. This has been done on USS Saratoga on which a special testing room and several types of single and group audiometers have been installed. Data described in the next two papers will show that more than adequate hearing testing is feasible, even during air operations, and a hearing conservation program is possible.
Maximum Power Criterion for the Vibrating Free Edge Disk
Authors: House Raymond N.
Published: September 2005

A criterion for the maximum radiated power delivered by a high-efficiency piezoelectrically driven free edge disk, vibrating in the first symmetrical mode, has been developed. The maximum power emitted from such a transducer is necessarily limited by the maximum stresses and strains to which the disk is subjected when undergoing transverse vibrations. A complete solution of the stress and strain distribution is given for this mode of vibration. Maximum values for these stresses and strains occur at the center of the vibrating plate. Assignment of a safe stress level, dependent on material, which the center of the vibrating plate must not exceed then yields a unique value of maximum center velocity at which disk fracture occurs. The maximum power criterion is then established by the maximum safe center velocity, which is shown to be independent of plate geometry, and the radiation resistance of the disk in its operating medium. Experiment shows, as anticipated, that fracture occurs at the geometric center of the vibrating plate, with power values consistent with the theory.
Radar Target Identification by Aural Display
Authors: Pew Richard W.
Published: September 2005

Experiments were performed to determine the discriminability of radar target characteristics when the modulations of the radar echoes were presented in an aural display. Sample signals were obtained from three monitoring locations in a C-band pulse-doppler radar. A noncoherent signal was extracted by detecting the range-gated i.f. signal, and two coherent signals were derived from the range-gated bi-polar video. Two radar operators experienced in listening to and using the aural displays and five inexperienced radar operators were asked in each of two sessions to make several two-alternative discriminations on each of 84 samples of typical radar signals. When reduced to a symmetrical two-alternative decision matrix. experienced operators' discrimination between aircraft with one turbojet engine vs aircraft with two turbojet engines was correct with probability 0.73. Discrimination between one aircraft and two aircraft was correct with probability 0.76. Detection of target velocity change occurred with probability 0.97, and no errors were made in detecting the occurrence of a 180° turn. Results with operators unfamiliar with aural radar signals indicated that a training problem similar to that of sonar must be solved before aural displays can be used to provide reliable target identification information.
Two Recording Studios—One for Fun and One for Profit
Authors: Sepmeyer L. W.
Published: September 2005

Two recording studios will be described: one, an addition to the home of an audio hobbist; the other, the new studio, control room, and echo chambers for a large commercial recording company.
Vibration of Complex Systems at Low Frequencies
Authors: Skudrzyk E. J.
Published: September 2005

The high-frequency behavior of complex mechanical systems can be predicted with relatively great accuracy on the basis of the asymptotic frequency difference between successive resonances, the effective mass of the system, and its damping. It is shown that the same theory, with slight modifications, also describes the low-frequency behavior of mechanical systems of any complexity, at least as far as the theory of vibration insulation is concerned. The conclusions are illustrated by theoretical computations and experimental results. (This work was partially sponsored by the U. S. Atomic Energy Commission.)
Statistical Studies of Digital Voice Data
Authors: Smith Caldwell P. , Walter Charlton M.
Published: September 2005

The results of some statistical data processing techniques which have been applied to the study of digital voice data are discussed. Speech signals were analyzed in an 18-channel spectrum analyzer and converted to a digit stream at a data rate of 3000 bits per second. The digital data were recorded on tape and processed on general purpose digital computers by various methods in order to examine the underlying structure of the speech information. Exploratory studies have included the compilation of tables of relative frequencies of occurrence of various voice spectrum pattern modes and groupings. The cross correlatior of voice spectrum amplitude information as a function of both frequency and time was investigated, along with the effect of transforming from frequency spectrum coordinates to a new set of uncorrelated coordinates.
Auto-Correlation Vocoder
Authors: Schroeder M. R. , Crystal T. H.
Published: September 2005

In an auto-correlation vocoder system, samples of the short-time auto-correlation function of a speech signal are transmitted over a reduced bandwidth channel and converted into a time wave that is properly periodic and a replica of the auto-correlation function. By Wiener's theorem, the amplitude spectrum of the thus synthesized signal is the power spectrum of the analyzed speech signal. Phenomenologically, this spectrum squaring has four distinct effects: 1. Doubling of dynamic level fluctuations. 2. Doubling of formant level differences. 3. Deepening of spectral minima (“zeros”). 4 Reduction of formant bandwidths. The most serious of these spectral degradations have been removed by a variable equalizer preceding the auto-correlation analyzer. The remade speech quality produced by this technique exceeds that of known frequency-channel vocoders and of a previously described cross-correlation vocoder [J. Acoust. Soc. Am. 31, 852 (A) (1959)]. Bandwidth (or time) compression is about 10:1 (before multiplexing). Tape-recorded speech samples from the equalized auto-correlation vocoder will be played.
Analog Measurements of Sound Radiation from the Mouth
Authors: Flanagan J. L.
Published: September 2005

Free-field measurements of the sound radiated from the mouth of a life-size manikin are described. A transducer installed in the head of the dummy is calibrated to produce a known acoustic volume velocity through the lips. The sound field in vertical and horizontal planes through the head is explored with a pressure microphone. Directivity patterns are determined for frequencies of 250, 500, 1000, 2000, and 4000 cps. Radiation of sound from the mouth is compared with that from a small piston set in a rigid sphere of 9-cm radius.
Pitch Synchronous Spectral Representations of Voiced Speech
Authors: Miller J. E. , Mathews Max V. , David Edward E.
Published: September 2005

A number of reduced-information rate spectral representations of voiced speech, analyzed pitch-synchronously, have been examined by digital simulation. The experiment consists of spectral analysis of each period of the voiced portions of connected speech, averaging the spectral information in several ways, resynthesizing the speech from the averaged information, and finally evaluating the result with listening tests. The first method transmits only every other component of the harmonic amplitude spectrum and employs various interpolation functions to recover the absent harmonics. Next, formants are located in two different ways and resynthesis carried out with various numbers and bandwiths of formants. Finally, time averaging is introduced by representing a formant track over a speech event by a polynomial function of time which is the best mean square fit to the track. The resynthesis is carried out varying the number of formants and the degree of the fitting polynomials. The resynthesized samples are evaluated in the listening tests as to their quality and intelligibility. These factors are compared with reduction of information.
Spoken Digit Recognition Using Time-Frequency Pattern Matching
Authors: Denes P. , Mathews Max V.
Published: September 2005

A study of the machine recognition of the spoken digits zero through nine has been carried out by a digital computer simulation. The spoken utterances are converted to time-frequency patterns of spectral energy. Recognition is done by cross-correlating the pattern of an unknown utterance with a test pattern for each digit and selecting the digit having the highest correlation. Time normalization could be applied to all patterns, thus reducing utterances to a standard duration. Six male and one female speakers provided 38 samples of each of the ten digits. Pauses were made between successive words for segmentation. No errors were observed recognizing a single speaker using test patterns from his own speech with time normalization. A group of 5 male speakers and test patterns averaged over the group produced 6% errors with time normalization and 12% without. A 25% rate occurred for the woman matched against male patterns. The study indicates both the effectiveness and limitations of this simple recognition procedure for limited vocabulary and limited number of speakers. Time normalization improves performance in all cases.
Study of Ambient Noise in the Deep Ocean
Authors: Miller Norman D.
Published: September 2005

An understanding of the characteristics and nature of the ambient noise is fundamental to the design of long-range submarine detection systems. During the summer of 1959 a series of deep-ocean ambient noise measurements were made with a 10-element vertical hydrophone array suspended to a depth of 500 fathoms in 2000-fathom water. Measurements were made over the frequency range of 5 to 25 cps. All data were recorded on magnetic tape and returned to the laboratory for analysis. The objectives of the measurements were to determine the spectral nature of the ambient noise and any special properties such as directionality that the ambient noise might have. By use of a magnet drum delay line, the array was steered in a vertical sense about the center of the array. The intensity and frequency spectrum of the beams was recorded. Broadband spectrum analysis was made, and both frequency and power spectrum plots were obtained of the ambient. A considerable amount of biological noise was recorded, and some classification of these signals was made. This paper describes the method and instrumentation used in recording the raw data and a description of the data analysis techniques. The results of the data analysis program are then discussed in detail.
Resonance Absorption in Solid Cyclohexane
Authors: Rasmussen Robert A.
Published: September 2005

Measurements of the acoustic absorption in monocrystalline cyclohexane have been made in the frequency range 3 to 9 Mc. Absorption coefficients in this range are unusually large, being of the order of 0.1 cm−1 and the absorption increases as the square of the frequency. Although the absorption is large, its measurement is difficult unless large single crystals affording long path lengths are available. A method for growing single crystals of cyclohexane having linear dimensions of 10 cm has been developed; the method and the absorption measurement technique are described. Both the magnitude of the absorption and its frequency dependence are in good agreement with the resonance absorption theory [L. N. Liebermann, Phys. Rev. 113, 1052 (1959)]. These results for cyclohexane, together with previously reported data for benzene, offer support for the existence of this absorption mechanism. As a further test of the theory, absorption was measured as a function of temperature in the range 0 to −150°C. The results are described in light of the theory.
Recent Studies of Line-Source Loudspeakers
Authors: Klepper David L. , Gardiner Martin F.
Published: September 2005

From the theoretical treatment in the literature, it appears that line-source loudspeakers should find more extensive use in auditorium and church sound reinforcement systems. The application of practical line-source loudspeaker systems to two spaces is discussed. One system, installed in the Harvard Memorial Church in Cambridge, Massachusetts, consists of an array of five 8-in. loudspeakers positioned and adjusted on a “try and fit” basis. A second system is currently being designed for the Metropolitan Boston Arts Center Theater in Boston, Massachusetts. This theater has a three-quarter round seating layout under an inflated nylon roof. The proposed configuration for the theater loudspeaker array was determined using data obtained from a small array of six special 3.5-in. loudspeakers which was constructed and studied experimentally in an anechoic chamber. The laboratory data showed the effect of attenuating the signals to the different loudspeakers and of curving the array. One important limitation of such a system is that the system acts as a series of point sources, rather than as a continuous line source. This causes the formation (at frequencies when the wavelength equals the speaker spacing) of large lobes at 70°–90°, both sides of the axis. To minimize these lobes, two rows of loudspeakers, side by side, but staggered, are used.
Spectrographic Determination of Vowel Quality
Authors: Ladefoged Peter
Published: September 2005

Thirty-one sets of eight equivalent vowels were analyzed on a modified Kay Sona-Graph. The formant frequencies of vowels such as [e, ɛ, a]) usually could be determined unambiguously by visual inspection and measurement of the spectrographic displays. But the spectrograms of [i, ɑ, ɔ, o, u] often provided inadequate data for determining the precise formant frequencies. The analysis indicated that it is generally true that the quality of a vowel can be specified in terms of the relationship between the pitches of its first three formants and the pitches of the first three formants of other vowels spoken by the same speaker. But in very high vowels, like [i, u] where it is difficult to determine the formant frequencies (and hence the pitches) from spectrographic data, the quality may be specified in terms of other auditory attributes such as the pitch of formant two and the relative loudness of formants two and three (the precise pitch of formant one being of less relevance). For very back vowels like [ɑ ɔ, o, u] the chief auditory quality may be the mean pitch of formants one and two and the comparative absence of energy in the upper part of the spectrum.
Effect of the Size of the Sound Receiver on the Received Noise Level for Boundary Layer Flow Noise
Authors: Skudrzyk E. J. , Haddle G. P.
Published: September 2005

The noise level recorded in the boundary layer of a moving body depends greatly on the size of the receiver and on the homogeneity of the turbulence. Doubling the length of a rectangular hydrophone may decrease the noise level by 6 db; doubling the diameter of a circular hydrophone may decrease it by 9 db if the width of the hydrophone is small in comparison to the lateral correlation length of the eddies that produce the noise. If the hydrophone is large in comparison to the lateral correlation length of the noise pressure, doubling its linear dimensions reduced its flow noise level by 12 db. If the turbulence is inhomogeneous, increasing the diameter of the sound receiver may even increase the recorded noise level. The theory will be presented in conjunction with experimental results.
Measurements of the Vortex-Induced Vibration and Sound Spectra Generated by Water Flowing over a Cavity Orifice
Authors: Bland R. E.
Published: September 2005

When water flows over an orifice of a water-filled cavity, pure tone vibrations are detected on the lips of the cavity, and radiated sound is detected in the surrounding medium. A series of measurements conducted at the Ordnance Research Laboratory's Garfield Thomas Water Tunnel are reported. The measurements were made at tunnel velocities of 30, 40, 45, 50, and 60 ft per sec. Narrow-band vibration spectra of the upstream and downstream lips of the orifice are shown along with sound pressure spectra in the cavity and immediately adjacent to each side of the downstream lip. The behavior has a marked similarity to air and water jet edge-tone systems even though the flow is nonsymmetrical and the orifice size is 3 in. A scheme for the study of the vortex-shedding transit and stagnation using the Schlieren technique is discussed briefly. (The work is supported under the Fundamental Hydrodynamics Program of the David Taylor Model Basin.)
Dislocation Contribution to the Attenuation of Ultrasound in Ferromagnetics
Authors: Bratina W. J. , Mills D.
Published: September 2005

The processes associated with deformation of annealed polycrystalline low- and high-carbon steel were investigated employing sound waves of megacycle frequency sent longitudinally through the specimen. The dislocation component of the attenuation was of primary interest. External magnetic fields were used in order to suppress the ferromagnetic component of the attenuation [W. J. Bratina, U. Martius, and D. Mills, J. Appl. Phys. 31, 241(S) (1960)] The attenuation changes during straining were related to active dislocations, taking into consideration generation, annihilation, anchoring, and pinning of dislocation loops. Stress-strain curves were determined using a “hard” tensile machine. A detailed study of attenuation vs time after straining also was made.
Progressive Wave System with Electro-Pneumatic Transducer
Authors: Hilliard John K. , Fiala Walter T.
Published: September 2005

This paper describe. a progressive wave system, 1 ft × 1 ft in cross section, employing one electro-pneumatic transducer in the frequency range 37.5–1200 cps. The unit is capable of generating sound pressure levels in excess of 160 db over-all sound pressure level. High-frequency energy is generated by conventional compression-type dynamic transducers. The high-frequency energy is combined with the low-frequency energy in a mixing unit which consists essentially of a 45° acoustic mirror. By means of appropriate slots, the mirror is made transparent in the low frequency range and reflective at the higher frequencies. Design data on the acoustic mirror and measurements of over-all and octave band sound pressure levels as well as variations in sound pressure over the cross section of the tube, particularly in the transition range iron the plane to the progressive wave condition, are presented. The capability of the system when four electro-pneumatic transducers are employed is also discussed.
Stereophonic Sound Considerations
Authors: Olson Harry F.
Published: September 2005

Studies in the field of stereophonic sound have been carried out on the following subjects: auditory perspective, reverberation and room acoustics, information capacity, ideal sound reproducing systems, cross-talk between channels, and applications in the home and the automobile. The results of these considerations will be described.
Automatic Nyquist Plotter for Feedback Analysis of Acoustic Systems
Authors: Weiss Erwin
Published: September 2005

For some time now devices have existed for automatically plotting the Nyquist amplitude phase characteristics of feedback devices where the significant frequencies were below 100 cycles. These devices were largely electro-mechanical in nature. There has been a need for a device to plot the Nyquist amplitude phase characteristics of devices which operate at frequencies where electro-mechanical techniques are no longer usable. The application of the Nyquist criteria to audio amplifiers, and more particularly to the complex feedback paths of modern hearing aids, is discussed as a useful method of analyzing their operation and synthesizing improved designs. For this purpose an electro-mechanical Nyquist plotter has been constructed which automatically plots the amplitude phase characteristics of feedback devices in the audio frequency range. Details of this device are explained.
Loudness Summation under Masking
Authors: Scharf Bertram
Published: September 2005

Loudness summation has been shown to be greatest at SPL's between 40 and 70 db. The present experiments show that a decrease in loudness summation occurs also when a complex is heard in a uniform masking noise. The loudness of a 4-tone complex centered at 2000 cps was matched to that of a 2000-cycle tone. Both the complex and the tone were presented with the masking noise through a single PDR-8 earphone. Three independent variables were studied: (1) the frequency separation ΔF between the highest and the lowest components of the complex, (2) the SPL of the standard signal (which was sometimes the complex, sometimes the tone), and (3) the over-all sound pressure of the masking noise. Results for six subjects show that when the standard was at either 40 or 60 db and ΔF was greater than 300 cps (the value of the critical band at a center frequency of 2000 cps), loudness summation decreased as the level of the background noise was increased. When the level of the standard was 20 or 80 db or when ΔF was less than a critical band, the background noise had, for the most part, little or no effect upon loudness summation. (This research was supported by a grant from the National Institute of Health, U. S. Public Health Services.)
Normal Mode Theory in Layered Media
Authors: Diesendruck L.
Published: September 2005

The integral for the potential due to a source in a layered medium is expressed in terms of “effective reflection coefficients,” following the method of Brekhovskikh [Soviet Phys.-Acoustics 2, 362 (1956)]. The effective reflection coefficients are given in terms of the properties of the layers in recursion form for any number of layers, both of the liquid and of the solid type. The general expression for the normal modes in terms of these properties is applied to the specific case of a three-layered medium—liquid-liquid-solid. This case is compared to the liquid-liquid-liquid case given in the literature. (Supported by the Office of Naval Research.)