bluuebunny/crossref_metadata_2025 huggingface dataset:
Importance of Frequency Range in Dichotic Speech
Authors: Schubert Earl D.
Published: September 2005

Of particular interest is the increased intelligibility of dichotic over diotic speech when each is nearly masked by diotic noise. Since speech can be viewed as a sequence of quasi-sinusoids and nonsinusoids, it may continue to present a sufficiently characteristic envelope for binaural signal-selection, even when severely filtered. To test this hypothesis, three frequency ranges of speech, each calculated to yield an articulation index of 0.5, were compared for difference in intelligibility between homophasic and antiphasic listening. The ranges were: 200–1660 cps, 880–2200 cps, and 1660–6100 cps. Measurements were made on fifteen listeners who repeated back as much as they could of running speech in each of the three frequency ranges under three listening conditions: homophasic speech and noise, antiphasic speech and noise, and speech delayed in one ear by 0.5 msec. In the low-frequency range the intelligibility gain attributable to either interaural difference is very nearly equal to the gain reported from previous experiments using the entire speech range. It may run as high as a 35% increase in number of words heard under the most difficult conditions (low intelligibility). For the mid-range and high-range speech signal, the increase averages 15 to 20% for low-intelligibility performance, but appears to vanish (statistically) when intelligibility reaches even 50 to 60%. (Supported in part by National Science Foundation.)
Digital Data Processing for Underwater Acoustics
Authors: Worley R. D. , Bronzo J. A. , Zuvich J. J.
Published: September 2005

Patterned after an earlier system developed by David, Mathews, and McDonald for speech analysis, a digital data translation system has been built to investigate the statistical properties of underwater acoustic signals and noise. Analog data is converted to digital form on magnetic tape in a format compatible with the IBM 704 computer. The maximum sampling rate is 14.2 kc for a single channel using a 6-bit binary code or 7.1 kc for a 10-bit binary code. For either code two channels can be sampled alternately at half the corresponding rate. Digital-to-analog conversion is provided to check the faithfulness of the digital recording. A sound spectrogram of a signal converted to digital and then back to analog form will be compared with the original spectrogram. The system has been used to prepare data for statistical studies of the detection of sine waves in broadband sea noise. The results of the computer program were read out on magnetic tape and played back through the digital-to-analog converter onto a Western Union Telefax recorder. Detection at a particular frequency is represented as a line on the facsimile chart. A typical chart will be illustrated. (This work was supported by the Office of Naval Research, Navy Department.)
Acoustics of the Auditorium and Convention Center for Austin, Texas
Authors: Lane R. N. , Mikeska E. E.
Published: September 2005

A 3700-seat, general purpose auditorium was included in the convention center for the City of Austin, Texas. The hall is designed with removable, upholstered seats on the main floor, with the hall opening out into the exhibition area so that the auditorium proper can be converted into a dining area for 5000 people. The acoustical problems in this type of all-purpose design are discussed and measurements presented on the reverberation time, echo structure, and articulation in the building. Since the auditorium is also used as a concert hall, subjective remarks by various musicians using the building also will be presented. Some particular problems in the use of a large auditorium by Broadway theater casts will also be discussed.
Acoustics of the Queen Elizabeth Theatre, Vancouver
Authors: Johnson B. C. Russell
Published: September 2005

The Queen Elizabeth Theatre was opened in July, 1959. This 2813-seat multipurpose auditorium is owned and operated by the City of Vancouver and is rented for religious meetings, fashion shows, jazz concerts, symphony concerts, conventions, amateur and professional dramatic productions, etc. The hall is quite wide and relatively shallow, with a large balcony and a low, average ceiling height. The cubage is approximately 650 000 cu ft. The side walls are of wood laminated to plasterboard to decrease low-frequency absorption. The stage house is equipped with a demountable plywood concert enclosure. This paper describes general design objectives and aspects of the acoustical design of the theatre and reports reverberation measurements. The architectural firm of Affleck, Desbarats, Dimakopoulos, Lebensold, Michaud, and Sise won this commission during a competition in 1954–1955. Professor Stewart Marshall of McGill University served as the acoustical adviser to the architects during the competition. Bolt Beranek and Newman Inc. worked with the architects from August, 1955, through completion of the building.
Acoustical Design of the Pan American World Airways Terminal at New York International Airport
Authors: Cardinell Richmond L. , Goodfriend Lewis S.
Published: September 2005

The new Pan American World Airways Terminal in New York has a 400-ft umbrella roof that protects passengers from rain or snow and the aircraft from high heat loads during periods it is standing at the terminal. The building also has an air-curtain door 100 ft wide. Acoustical studies were undertaken to determine (1) the effect of absorptive materials on the underside of the slab, (2) the thickness of glass required to provide satisfactory interior noise levels (NC55 with jets taxiing at the gate), (3) the shielding required for the air-curtain door to limit the interior levels to the same level as that allowed by the glass walls, (4) noise control measures needed at gates, and (5) noise control measures required for the air-conditioning system and for the air-curtain door equipment. Scale-model tests indicated that a high-absorption treatment of the canopy would reduce the levels inside the building by 6 to 10 db. A new material, acoustical cellular glass, was found for this application. Screens for the doors were investigated also using the model. The resulting 10-ft high screens are an adequate compromise. Other measures were based on conventional sound control techniques. Full-scale tests on the completed terminal indicated the adequacy of the acoustical design.
Considerations on the Reverberation Times of Concert Halls
Authors: Shankland R. S.
Published: September 2005

Measurements of the reverberation times in Severance Hall at Cleveland during the past several years have provided sufficient data to give an insight into certain problems related to reverberation times, especially in halls designed primarily for symphony orchestras. In the course of recent extensive changes in the hall [R. S. Shankland and E. A. Flynn, J. Acoust. Soc. Am. 31, 866 (1959)] large areas of heavy lined carpet have been removed and replaced by vinyl tile. The areas changed include aisles, promenade areas, stairs, and areas under upholstered seats and in the boxes. Analysis of the reverberation time data [H. L. Ormestad, R. S. Shankland, and A. H. Benade, J. Acoust. Soc. Am. 32, 371 (1960)] taken over a wide-frequency range makes it possible to show in general terms the effect of these areas on the sound absorption in a hall, specifically in and near areas occupied by the audience. Another major change in Severance Hall was the construction of a heavy and acoustically tight wooden stage shell to replace one of light construction. Studies of the acoustical behavior of the hall both before and after this modification permit an estimate to be made of the effect of such a structure on reverberation times. especially at low frequencies.
Reverberant Concert Halls and Churches Can Be Good for Speech
Authors: Little Edward M.
Published: September 2005

An intermediate frequency tweeter placed high above the rostrum and fed with frequencies 1000 to 10 000 having correct vertical and horizontal angular distribution beamed on the audience and not on walls and ceiling will crisp up consonants without adding to reverberation. Kuhl recently found (by tape recordings to eliminate prejudice) that optimum reverberation of concert halls for symphony music is 1.6 to 2.1 sec independent of size, contrary to the usual idea that it is proportional to the cube root of volume. Two seconds also is probably optimum for churches when full and adds much to inspirational effect of both the music and the sermon. For plays it is desirable to have a reverberation of under 1 sec to avoid overlapping of syllables, but in a sermon the speech is much slower so that 2-sec reverberation usually does not blur the words. However, for the occasional fast-speaking minister, the above P.A. system will make the speech quite audible despite long reverberation. Even plays can be put on if several microphones are distributed along the front of the platform. A 10-μf condenser should be put in series with the speaker to protect it from accidental frequencies below 1000.
Effect of High Pressure on Sound Absorption in Water-Dioxane Solutions of Magnesium Sulfate
Authors: Fisher F. H.
Published: September 2005

Measurements are being completed in the 100- to 500-kc region on the effect of pressure and dielectric constant on sound absorption in 0.5 molar solutions of magnesium sulfate at 25°C with the following solvents: (1) pure water, D = 78.5; (2) 13% dioxane-water, D = 67.0; (3) 25% dioxane-water, D = 56.5. The effect of varying dielectric constant is most pronounced for D = 67.0 for which the relaxation frequency decreases markedly from 160 kc to 105 kc as pressure increases from atmospheric pressure to 15 000 psi. The corresponding change for D = 56.5 is from 200 kc to 187 kc, and no change from 192 kc was observed [F. H. Fisher, J. Acoust. Soc. Am. 30, 442 (1958)] for D = 78.0. The behavior at atmospheric pressure at this high concentration is as puzzling as, and exactly opposite to, that observed by D. A. Bies [J. Chem. Phys. 23, 428 (1955)] for lower concentrations (<0.02 molar) of MgSO4 where relaxation frequency first increased, then decreased as D was lowered. The earlier work at D = 78.5 is being repeated in order to secure more accurate results. (This work represents one of the results of research carried out under contract with the Office of Naval Research.)
Ultrasonic Absorption in Toluene
Authors: Cerceo M. , Meister R. , Litovitz T. A.
Published: September 2005

Investigators have studied the absorption of sound energy in toluene from 30 kc to 200 Mc in an effort to determine the causes of the excess absorption. The results to date have raised many puzzling questions. For example, Verma and Yeager (private communication) have reported a resonance peak at 50 kc, the existence of which is quite difficult to explain. R. T. Beyer reports a relaxation peak at 150 kc, the mechanism of which is not clear. We have made ultrasonic absorption measurements in toluene using the reverberation method and the pulse method over a frequency range from 150 kc (overlapping Beyer's [J. Acoust. Soc. Am. 27, 1 (1955)] frequencies) to 55 Mc and a temperature range from 6°C to 44°C. The high-frequency megacycle attenuation is studied as a function of temperature, and it is found that the temperature dependence is different than that reported by G. S. Verma [J. Chem. Phys. 18, 1352 (1950)]. The results in the kilocycle region show that the absorption per wavelength has a resonance type peak at approximately 210 kc independent of temperature with a magnitude that increases with increase in temperature. The Q of this loss mechanism is about the same as the Q of the resonance type loss reported by Verma and Yeager in the 50-kc region. The position and magnitude of the peak at 210 kc is unaffected by the introduction of methyl alcohol as an impurity up to concentrations of 10% by volume. The existence of one resonance peak in toluene is sufficiently confusing. The existence of two resonance peaks strains the limit of credibility. We are skeptical, but it will not go away! (Sponsored by Office of Naval Research.)
Resonance Tube for High-Pressure and Low f/p Ratios
Authors: Henderson Malcolm C.
Published: September 2005

By adapting F. A. Angona's [J. Acoust. Soc. Am. 25, 1111 (1953)] construction to H. Oberst's [Akust. Z. 2, 76 (1937)] method—essentially the Kundt's tube—resonance tubes have been constructed that are capable of going to several hundred atmospheres of pressure at 300°C. The tubes are, conveniently, about 2 ft long with a fundamental frequency of 250 to 300 cps, depending on the gas. By casting the basic tube in a lead or die-casting alloy jacket the annoying mechanical vibrations of the tubes are suppressed or moved to high frequencies above the region of interest—500 to 10 000 cps. The plane modes are used exclusively, from the 2nd to the 20th harmonic, though the 55th and higher can be recognized and measured. The width of the resonances at the 3 db points is proportional to the absorption, after allowance for the tube effect (Kirchhoff). Relative velocity can, of course, be measured accurately also. The work of H. and L. Knötzel [Ann. Physik 2, 393 (1948)] with oxygen has been repeated to test the method, and their results are completely confirmed both as to magnitude of the absorption and the value of the relaxation time. It is intended shortly to apply this method to nitrogen at high temperatures. A minimum f/p of perhaps 1 cps-atm should be attainable. (Work supported by the Office of Naval Research.)
Velocity of Sound Measurements in High-Pressure, High-Temperature Steam
Authors: Woodburn James
Published: September 2005

Experimental information concerning the acoustic velocity in steam as a function of pressure and temperature is quite limited. Yet it is of particular interest to steam turbine designers who are now planning units as large as 400 000 kw, operating at 4500 lb/sq in. and 1200°F, so as to increase thermal efficiencies of such units. Apparatus is now in operation for measuring the acoustic velocity up to 2000 lb/sq in. and 750°F using a variable path acoustic interferometer. Measurements are taken at 200-lb/sq in. intervals along a given isotherm using a sound frequency of 750 kc. A special experimental high-pressure boiler is used to generate the steam at the desired pressure, and the stem is then increased in temperature by means of a stainless steel superheater before entering the interferometer. The interferometer, also of stainless steel, is enclosed by an insulated steel vessel maintained at a given constant temperature by another separate steam system. Future work is now being considered up to 6000-lb/sq in. steam pressure based upon results of present experiments.
Shock and Vibration as It Affects Air-Frame Design
Authors: Rogers O. R. , Dunn W. P. , Maurer O. F.
Published: September 2005

Although secondary reasons can be found for the influence of shock and vibration on air-frame design, the primary current reason is the prevention of structural failure. In attaining such a goal, the primary requirement is to keep the material stresses (sometimes strains) within safe limits. This is accomplished by providing additional material, by using damping or detuning, or by isolation of the source from the structure. To apply these measures rationally, the structural designer must be able to recognize those sources of shock and vibration which are potentially critical and have methods available to analyze their seriousness. This paper reviews those sources now known to be significant, as well as the methods available to determine the degree to which each is critical. The sources considered include landing impact, taxi, gusts, turbulent air flow, rotating and reciprocating mechanisms, and acoustically induced vibration.
Longitudinal and Flexural Modes of Propagation in a Circular Bar: Numerical Calculations and Experimental Investigation
Authors: May Joan E.
Published: September 2005

An investigation of the factors affecting the selective propagation of elastic waves in the lowest longitudinal mode of a cylindrical bar, originally conducted under Ordnance Corps contract, has been continued and expanded to include a general study of all the lower longitudinal and flexural modes. The Pochhammer-Chree frequency equations for these modes have been programmed for solution by computing machine. Both phase and group velocities have been calculated as functions of the diameter-frequency product for a range of values of Poisson's ratio. Flexural modes having several nodal diameters have been included. The group velocity calculations have been compared with the experimentally observed velocities of elastic wave pulses excited and detected in circular cylinders by piezoelectric transducers. Velocities in cylinders of fused quartz and various metals with diameters ranging between 0.05 cm and 0.2 cm in diameter have been measured at frequencies up to several megacycles. Results of these measurements will be discussed and related to the theoretical calculations.
Accuracy of the Bernoulli Theory of Bending for Rods and the Theory of Plates
Authors: Lange James N.
Published: September 2005

At low frequencies the Bernoulli theory of bending accurately describes damping in rods; however, at higher frequencies the theory no longer holds and the loss factor assumes a different value. A similar situation exists in the case of the theory of plates which is based on similar approximations as for rods. Experimental results are presented to verify both the agreement and disagreement with the Bernoulli theory for rods and the theory for plates. (This work was sponsored by the U. S. Atomic Energy Commission and the Bureau of Naval Weapons.)
Stratigraphy of the Hudson Submarine Canyon Area
Authors: Barakos P. A.
Published: September 2005

Pressure waves generated at different ranges in the continental shelf and slope by explosions of one pound of TNT charges were received by hydrophones connected by sea cables to a fixed station in the ocean. An extensive analysis of the dispersion in the water wave was made, covering five different courses within a 150-mile radius from the receiving station, all the seasons of the year, and over 400 charges. In general, for shallow water the received pressure wave displays certain features which are characteristic of the depth of the water, the velocity-depth contour in the water, range, and the structure of the bottom. Dispersion in the water was also observed in a surface channel formed in moderately deep water. The observed dispersion phenomena were studied quantitatively, and the data were interpreted in terms of the bottom structure. Two- and three-layer liquid models are used to interpret the experimental results.
Propagation of Low-Frequency CW Sound Signals in the Deep Ocean
Authors: Guthrie A. N. , Shaffer J. D.
Published: September 2005

This paper continues a study on which a preliminary report previously was made [J. Acoust. Soc. Am. 32, 645 (1960)]. The acoustic field of a low-frequency CW source, towed at slow speed at a depth of 25 m, was measured by a stationary hydrophone, 460 m below the ocean surface, at ranges between 64 and 122 km. Frequencies of 10.04 and 13.89 cps were used. Tangential and reversed radial runs were made to test range dependence of observed signal intensity fluctuations and to test the repeatability of fluctuation patterns. Both range dependence and repeatability of fluctuations were verified. Theoretical calculations for comparison with experimental results are planned. (This work was supported by the Office of Naval Research.)
Fluctuations in Short-Range Propagation of Sound from a Fixed Source to a Fixed Receiver in Deep Water
Authors: Nichols R. H.
Published: September 2005

Acoustic signals at 270 cps were produced by a projector on the ocean bottom at a depth of about 200 fathoms at a point off the coast of an island in the Bahamas. The signal was received at bottomed hydrophones about 2 nautical miles and 20 nautical miles away at depths of 200 fathoms and 2500 fathoms, respectively. Over a period of several weeks, the average received level of CW signals did not vary greatly, but there were continual short-term fluctuations of 1 to 10 db with periods of perhaps 5 to 10 sec. It is suspected that these fluctuations are associated with surface waves, and measurements are being made with pulsed signals to determine the acoustic paths involved. The degree of correlation of level variations at separate hydrophones is being investigated. (This work was supported by the Office of Naval Research, U. S. Navy Department.)
Effects of Ocean Waves on Acoustic Signals to Very Deep Hydrophones
Authors: Beckerle John C.
Published: September 2005

Amplitude fluctuations of surface reflected signal pulses from a 1-kc source at a depth of 50 ft were recorded by two bottom-mounted hydrophones 500 ft apart and 2600 fathoms deep. Some features of the observations are attributed to ocean wave focusing effects. It is shown that the surface-reflected pulse amplitude distribution may be described by using a Rayleigh distribution for noise modified by adding a single-focused contribution of random phase. An observed delay in the envelope of the signal pulse amplitudes recorded by the two receivers that is greater than the wave-front delay is explained as resulting from the sweeping action of an acoustic caustic produced by the ocean waves. These effects should depend on the direction, wavelength, and speed of the ocean waves as well as on the orientation of the hydrophones and the source location. Auto- and cross-correlation functions were computed from the data. (This work was supported by the Office of Naval Research, U. S. Navy Department.)
Signal Amplitude and Phase Fluctuations Induced by Surface Waves in Ducted Sound Propagation
Authors: Scrimger J. A.
Published: September 2005

The effect of surface waves on sound propagated from a continuous wave source over a range of 300 ft in water 10 ft in depth has been examined. It is found that the surface waves induce regular amplitude and phase fluctuations in the received signal. The dependence of the amount of amplitude and phase fluctuation on crest to trough height of the surface waves has been obtained for acoustic frequencies in the range 1 to 10 kc. Frequency spectra of the fluctuations, for values of the ratio of sound wavelength (λ) to wave height (A) above 18, are the same as the surface wave spectra. For values of λ/A less than 18, the fluctuation spectra are broader and show well-defined second and sometimes third harmonic components. Wave packet experiments in which the bow wave of a small boat is propagated across the length of the otherwise calm duct surface show that in the case of the uniformly rough surface the fluctuations are produced only by surface waves near the source and near the receiver.
Panel Response to Boundary Layer Turbulence
Authors: Tack D. H. , Lambert R. F.
Published: September 2005

The displacement response of a simple panel (bar) to turbulent boundary layer pressure fluctuations has been investigated experimentally and the results compared with theoretical predictions based upon a decaying and convecting correlation field as proposed by R. H. Lyon [J. Acoust. Soc. Am. 28, 391–398 (1956)]. The response is interpreted in terms of a locus of natural frequencies of the turbulence and the panel in the complex frequency domain with special attention focused on hydrodynamic considerations. The importance and interpretation of parameters such as eddy decay frequencies and eddy convection frequencies as obtained from correlation studies will be emphasized. (This work was sponsored by the U. S. Air Force.)
Base Pressure Fluctuations
Authors: Eldred Ken
Published: September 2005

The intense vibration accompanying the extension of dive brakes and other high drag devices on aircraft and missiles has been observed for many years. Recently, considerable vibration has been experienced at the fundamental longitudinal mode and at other internal resonance frequencies of a vehicle which had a blunt base during the maximum dynamic pressure phase of flight. In both cases the vibration is believed to result from the turbulent fluctuations in the wake of the base or drag device. The base pressure fluctuations have been measured at two base positions on a small body of revolution at eleven points in the velocity range of 68 to 352 ft/sec. The results show that (a) the ratio of (〈p2〉)12/q varies between 0.007 at the center of the base to 0.015 at 65% radius; (b) the spectrum of the pressure fluctuations is a function of the body Strouhal number; (c) the variation of observed vibration response with flight parameters can be predicted from the base pressure fluctuation data. (Work performed jointly with Norair, Division of Northrup Corporation in conjunction with U. S. Air Force contract.)
Segmentation Scheme for Use of a Speech Recognition Computer Program
Authors: Forgie James W. , Forgie Carma D.
Published: September 2005

A segmentation scheme is being developed to operate as a first step in a general speech recognition program. Input to the segmenter is sampled, quantized spectral data (35 frequency channels scanned every 5.5 msec). The output is a sequence of boundary markers together with a rough classification of the enclosed segments. The segments are generally phonemic, or smaller, in size, and the classification corresponds either to type of phoneme (e.g., fricative, nasal, vowel) or to sound characteristic (e.g., silence, aspiration). The segmenter operates by first classifying each 5.5-msec scan of the spectral data. This classification is obtained by computing a number of measurements of different attributes of the spectral pattern and combining the results with suitable weighting functions. The number of such measurements is made larger than the logical minimum to avoid placing too much dependence on any one measurement. Segments are then built by grouping together scans which have the same individual classifications. Finally these primitive segments are subjected to an editing process which modifies and merges together certain of the primitive segments according to rules based on length, amplitude, the classification of neighboring segments, etc. The effect of the editing process is to insure that the output segment sequence does not violate any simple articulatory rules for the language. (Lincoln Laboratory is operated with support from the U. S. Army, Navy, and Air Force.)
Automatic Extraction of Fundamental Period of Speech by Auto-Correlation Analysis and Peak Detection
Authors: Fujisaki H.
Published: September 2005

A digital computer has been used to simulate schemes for automatic extraction of the fundamental period of speech by analysis of the waveform in the time domain. The basic principle is to apply 1-bit quantization to the signal samples followed by a short-time auto-correlation analysis with an averaging interval as short as one period of a low-pitched male voice. The peaks of the auto-correlation function corresponding to the period are then detected. In the determination of each period, reference is made to the immediately preceding decision, and several logical operations are introduced to reject minor peaks. Measures of accuracy and reliability for various types of utterances are presented and discussed. [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 Air Force Cambridge Research Center.]
Anechoic Sonar Test Pool
Authors: Green Charles E.
Published: September 2005

The free-field calibration of sonar transducers requires a test environment free of echoes. This paper describes an anechoic pool designed to channel all sound out of the central area where tests are performed. Sound is reflected from the water surface into surrounding sound trap areas where special materials absorb and dissipate the energy. The system permits steady-state operation. The pool consists of a central bowl and surrounding shallow. The bowl is generated by the rotation of an ellipse about a vertical axis, the ellipse being oriented so that one focus is below the water surface and the other focus is above the surface and at a distance half as great. The surrounding shallow region that constitutes the sound trap is of a constant depth equal to that of the virtual image. Three different models employing this technique have been constructed and evaluated to prove the theory. Sound originating near the focus is attenuated more than 60 db before returning to this position. The full-size pool will have a bowl 160 ft in diameter and 38 ft deep: the outer absorbent traps will occupy an additional surface area to form a pool 200 ft wide by 300 ft long.
Broadband Transducer Composed of Three Elements with Proportionately Spaced Resonant Frequencies
Authors: Hueter T. F. , Elston A. W.
Published: September 2005

This paper presents the results of an investigation conducted to determine the feasibility of a compact, lightweight, multi-element broadband transducer. The basic element used was a low resonant frequency transducer characterized by small size and high-power output. High-power output is possible because of the high mechanical compliance of the plate. The large excursions of the plate are necessary because of inadequate acoustic loading resulting from the small size of the single transducer element compared to the wavelength. The principal limitation of this transducer is the restricted frequency band, Q≐9. To overcome this limitation and still retain the desirable characteristics of the single element, three elements with proportionately spaced resonant frequencies were assembled. Careful acoustic tests were conducted on the transmitting properties. The array proved capable of radiating from 1.75 to 2.70 kc with not more than ±1.5-db power variation. Tests indicated that the maximum distance between the elements should be approximately a quarter-wavelength for any frequency radiated. The wavelength at 1.75 kc is 33 in., resulting in a package size 5 in. in diameter and 8 in. in length with a total weight of 14 lb. This investigation demonstrated that low Q devices can be constructed from a combination of high Q elements provided that a proper orientation and spacing are observed. Such arrays should prove useful for applications requiring broadband underwater transmission.
Analysis of the Effects of Nonlinear Elements upon the Performance of a Back Enclosed Direct Radiator Loudspeaker
Authors: Olson Harry F.
Published: September 2005

A theoretical analysis of the nonlinear suspension and the nonlinear compliance of the air in the cabinet has been carried out. The results of the analysis have been applied to the development of a back enclosed, direct radiator loudspeaker with low distortion.
Calibration and Equalization of the Western Electric 640AA Microphone to 100 kc
Authors: Ortega Jose
Published: September 2005

Model testing of jet engine noise control devices has spurred high-frequency microphone development because of the importance of the high-frequency bands in the full-scale noise reduction. Calibration of the Western Electric 640AA microphone to 100 kc by free-field reciprocity has become routine in our laboratory. Some essential details of the technique and results of repeated calibration over a long period are reported. Use of reciprocal equalization in the complementary circuitry facilitates the use in noise analysis. Sensitivity and noise threshold of the 640AA microphone are excellent for model jet measurements.
Personal Microphones
Authors: Olson H. F. , Preston J. , Bleazey J. C.
Published: September 2005

The term personal microphone is used to designate a microphone worn by a speaker with the resultant sound pickup inherently limited to the person wearing the microphone. The operational characteristics of personal microphones will be described. Various types of microphones suitable for personal applications will be described.
Uncertainties in Frequency Analysis of Short Duration Random Signals
Authors: Galloway William J.
Published: September 2005

It has been shown previously that statistical uncertainties in frequency analyses of short duration random signals can be estimated from chi-square distribution functions. This approach has been used to compute confidence limits, in decibels, for various statistical degrees of freedom. The information has been utilized to compute confidence limits for the analysis of short-duration random signals with several commercially available constant-percentage bandwidth filter sets.
Comparison between Predicted and Observed Satisfaction for Speech Privacy in Buildings
Authors: Watters B. G. , Farrell W. R. , Hirtle P. W. , Cavanaugh W. J.
Published: September 2005

The notion of a single number rating for speech privacy problems in buildings [B. G. Watters, J. Acoust. Soc. Am. 32, 917 (1960)] has been developed further. The resulting system rates both the measured noise reduction of the isolating construction and the background (masking) noise levels. It also takes into account those other factors that determine the acceptability of speech privacy between spaces such as the size of the rooms, the level of speech effort in the spaces, and the degree of privacy needed by the occupants. The ratings calculated, using this system, are compared with observed subjective evaluations of the occupants in a large number of field situations.
Articulation Testing in Moderate Sized Rooms, II
Authors: D'Eustachio D. , D'Eustachio I.
Published: September 2005

By using the technique described in the previous paper, articulation scores were measured in a typical school classroom having a volume of approximately 10 000 cu ft, as a function of reverberation time and distribution of absorbing material. It was found (1) that articulation scores were significantly affected by the placement of the absorbing material and (2) that reverberation time could be increased to as much as two seconds at 500 cycles per sec with little effect on the articulation scores, provided that the absorbing material was distributed on the room surfaces in relatively small patches.
Noise, Enzymes, and Hearing
Authors: Angeluscheff Z. D.
Published: September 2005

Vibratory energy perceived by the ear is subjectively interpreted as hearing. Without the ear there would not be any acoustics. How the vibrations are translated into hearing, we don't know. Studies on invertebrate and monocellular organisms indicate the enzymes as a factor involved in this phenomenon. Enzymes are organic compounds, the nature of which is not well understood. They are present in the living matter and play a role in synthesis and decomposition of protein. Exposure of cerebral tissue to ultrasound is followed by an increase of the floating enzymes (cholinesterase). The shaking of the molecular structures provokes liberation of enzymes. Nerve cells depleted of enzymes are deprived of the “ignition” for synthesis of amino-acids into high polymer protein (RNA, DNA). Enzymes containing chemosensory receptors receive incoming stimuli which then are referred to the nerve; the nerve does not possess enzymes. In the receptors the stimuli generate potentials which in contact with specific amino-acids produce frequencies of various order. The recorded spike, conditioned by presence of salts and acids, are large, those by the presence of carbohydrates are small. Sustained noise presents heavy taxation to the chemoreceptors. Depleted of enzymes, electrolytes (potassium), etc., the synthesis of high protein in the nerve cell is disrupted and the function of the cochlea inhibited. The inhibition would be averted by solving the problem of fixation of nitrogen by amino-acids.
Review of Musical Frequency
Authors: Martin Daniel W.
Published: September 2005

The status of present knowledge in the domain of musical frequency is reviewed against the background of past experience, hypotheses, and conjecture, in an attempt to identify areas where additional research is needed.
Enzyme Systems of the Cochlea—Succinic Acid Dehydrogenase
Authors: Mundie J. Ryland , Johnson Marion T.
Published: September 2005

A histochemical technique that has been employed on guinea pig cochlea for demonstration of the enzyme, succinic acid dehydrogenase, will be described. The method employs the conventional chemical agent Nitro BT to develop a blue diformazan which is deposited at the enzyme site in the form of fine rods and granules. Since this enzyme is involved only in the Krebs cycle, its presence in a cell indicates oxidative metabolism taking place at that point. The stain developed is proportional to the quantity of enzyme present, so it is possible to draw conclusions as to the relative metabolic rates of various cells within an organ. Because the cochlea is completely surrounded by bone, a technique of direct perfusion of the cochlea via scala vestibuli and scala tympani was developed to bring the substrate into closer contact with cochlear structures. Slides demonstrating the distribution of this enzyme in the guinea pig cochlea will be shown.
Nonlinear Response of a Simple Panel
Authors: Smith P. W. , Malme C. I. , Gogos C. M.
Published: September 2005

Measurements have been made of the nonlinear steady-state response of a 2-in. by 12-in. strip of 2024 T3 aluminum, 116 in. thick, which was clamped on the short side and free on the long side. Vibrations were excited by the sound of a siren at the end of a duct in whose side the strip was mounted. Measurements were made in a broad range of frequencies around the fundamental resonance and at sound pressure levels up to 150 db, re 0.0002 microbar. Skewed response curves typical of a hard-spring oscillator were obtained. The data can be reasonably interpreted by means of a theory which includes the effects of in-plane tension generated by large amplitudes of bending displacements. when allowance is made for a number of interesting experimental complications. (Supported by Wright Air Development Division.)
Application of Modulated Sinusoids in Vibration Testing
Authors: Galef A. E.
Published: September 2005

Narrow band random vibration, which is frequently observed in air and land vehicles, cannot be reasonably simulated in the laboratory by means of sinusoidal vibration testing or by white noise vibration testing. An alternate test technique is proposed which results in a more nearly correct simulation than either of the vibration test techniques in common usage and which may be performed using any electrodynamic exciter system, with minor and low-cost modifications.
Stress and Strain Limits on the Attainable Velocity in Mechanical Vibration
Authors: Hunt F. V.
Published: September 2005

The maximum peak velocity which can be developed at the free end of a slender rod driven at resonance in a normal mode of longitudinal vibration is given by v0 = c0 Sxx, where c0 is the Young's modulus speed of sound (E/ρ)12 and Sxx is the limiting value of extensional strain for the rod material. In a similar way, the ratio of allowable stress to the maximum peak velocity is given by Txx/v0 = ρc0, where the characteristic specific acoustic impedance plays in this case the role of a transfer impedance relating the stress at a node to the velocity at an antinode. Similar expressions, modified only by numerical factors which range from 12 to 2, describe the relations between the maximum allowable stress or strain and the normal component of velocity at the antinodes of displacement for thin bars or plates vibrating in flexure.
Movement of the Lips in the Generation of Bilabial Consonants
Authors: Fujimura Osamu
Published: September 2005

The movement of the lips during the pronounciation of bilabial stops and nasals in various contexts has been studied by means of a stroboscopic technique. A rate of 240 frames/sec was used for the major part of this study. The results show that, for initial [p], [b], and [m] when not followed by [r], the separation of the lips reaches about 30% of the maximum value in the following vowel, and the width of the mouth opening reaches about 50% only about 5 msec after the separation begins. It is predicted from the results that about half of the total traverse of the formant transitions might well occur within about 5 msec after the plosion. The speed of the motion depends on the context. It is markedly slower for [p] preceded by unaccented [ə] than for initial [p]. An oscillatory tendency in the motion of the lips generally was observed after the plosion of the stops; this was particularly apparent when [p] was followed by [r]. The data suggest that the lips are blown apart by the air pressure behind the occlusion in the case of initial [p] and [b] but not in the case of [m]. (The 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), the U. S. Navy (Office of Naval Research), and the National Science Foundation.)
Some Allophones of /l/ in American English
Authors: Lehiste I. , Peterson G. E.
Published: September 2005

The study reported in this paper deals with the acoustic characteristics of the various allophones of the /l/ phoneme in American English. Four positional variants are included in the study: initial and final allophones of /l/ occurring in monosyllabic words, medial allophones occurring in disyllabic words, and allophones of /l/ forming the second syllable of certain disyllabic words. The mutual influences of the positional variants of the /l/ phoneme and the preceding and following vocalic syllable nuclei are explored and discussed. It appears that the second formant of the initial allophone of /l/ anticipates to a certain degree the second formant position of the following vowel, but that the first and third formant of the vowel are in turn influenced by the preceding /l/. The final allophone of /l/ shows a much smaller range of variations and is essentially independent of the preceding vowel, but it exerts a strong influence on the second formant of the preceding syllable nucleus. The acoustic characteristics of the medial allophone appear to depend to some degree upon the morphological structure of the word: the allophone is closer to the initial allophone, if the word contains a derivative suffix beginning with /l/, but more like the final allophone when it contains a derivative suffix beginning with a vowel, added to a base ending in /l/. Syllabic /l/, redefined as postconsonantal final allophone of /l/, resembles a postvocalic final /l/ in formant structure but has certain duration and intensity characteristics that distinguish it from the former.
Spectrographic Technique for Discerning Formant Frequencies
Authors: Foulkes J. D.
Published: September 2005

A human observer readily can track the formant positions in a conventional spectrogram. This paper describes a simple way of modifying a conventional spectrograph so that the machine attempts to extract this information directly and produce a spectrogram in which only the formant traces are present. The technique employed is based on a result of S. O. Rice. It involves counting the zero crossings of the signal output of the analyzing filter and using this information to estimate the positions of local maxima of the amplitude spectrum.
Segmentation of Speech into Voiced Sounds, Unvoiced Sounds, and Silence
Authors: Lochbaum Carol C.
Published: September 2005

A study of the segmentation of speech into silent, voiced, and unvoiced sections has been carried out by digital computer simulation. The divisions are made on the basis of normalized zero and first moments of the short-time speech spectrum. The set of segmentation rules is based on correlation of speech and silence with high and low values, respectively, of the zero moment (total energy). Portions of speech for which the first moment, the center of gravity, is high are noted as unvoiced, and those portions with a low center of gravity are called voiced. These rules were programmed for the IBM 704, and speech samples in the form of digitalized spectrograms were segmented for several combinations of high- and low-pass filtering of the data. These same utterances were segmented by reading a computer print-out of the spectrographic information. The normalized zero and first moments and the hand-segmented data were used to obtain the distributions of the zero moment for silence and speech and of the first moment for voiced and unvoiced sounds. From these distributions percentage errors in classification for given high-pass and low-pass filter combinations were obtained.
Periodic Variations in Low-Frequency Underwater Ambient Noise Levels
Authors: Wenz Gordon M.
Published: September 2005

Variations in underwater ambient noise spectra, from 20 to 1000 cps, were studied by use of a statistical filter technique to examine the spectral density functions in the range from 1 to 80 cycles per week. At frequencies below 100 cps narrow band components at 7 and 14 cycles per week were observed in the spectral density function. The cyclic variations agree more closely with the rotational period of the earth than with tidal cycles. The maxima occur at approximately midnight and noon, local time. These periodic changes in the ambient noise levels were not correlated with changes in local wind speed.
Ambient Noise as a Function of Depth
Authors: Berman Alan , Saur A. J.
Published: September 2005

Ambient noise measurements were made with a hydrophone which could be made almost neutrally buoyant at any desired depth. Signals were transmitted via a very light and very flexible cable to the laboratory, where they were band-filtered, rectified, and integrated. Spectra are presented for various depths from 30 to 4200 ft, and curves are shown for the intensity in half-octave bands as a function of depth. (This work was supported by the Office of Naval Research.)
Ambient Seismic Signals in Deep-Hole Geophones
Authors: Blaik Maurice
Published: September 2005

Low-frequency ambient seismic disturbances in the frequency range from 4 to 50 cps have been detected and recorded by use of 7-cps geophones and suitable electronic instruments. The geophones are in deep uncased holes within 1000 ft of the Fire Island Beach line of the Atlantic Ocean near Bellport Coast Guard Station, Long Island, New York. These detectors are pressed against the walls of the holes by means of spring clamps at various depths below the surface from about 400 ft to 2000 ft. A detailed description of the area and installation has been reported by Blaik, Northrop, and Clay [J. Geophys. Research (February, 1959)]. The variation of spectrum levels with depth and frequency will be shown and some interpretations will be given relating to the generation and propagation of this seismic energy. (This work was supported by the Office of Naval Research.)
Mechanical Resonance Dispersion and Plastic Flow in Crystalline Solids
Authors: Fitzgerald Edwin R.
Published: September 2005

Experimental observations of mechanical resonance dispersion in solids will be reviewed. Results of complex shear compliance measurements on single crystals, polycrystalline metals, and crystalline polymers will be presented. A theoretical explanation for the existence of the resonances on an atomic basis will be adduced. The theory allows the calculation of the critical shear stress or yield strengths for crystalline materials which deform by plastic flow or alternatively predicts the breaking stress for materials exhibiting brittle fracture. Good agreement with experimental values is obtained.