bluuebunny/crossref_metadata_2025 huggingface dataset:
Underwater Acoustic Transmission Variations Caused by Thermal Layers—Theoretical
Authors: Murphy S. R. , Potter D. S. , Garrison G. R.
Published: September 2005

A perturbation calculation on the eikonal equations by Bergmann [Phys. Rev. 70, 486 (1946)] is extended to apply to acoustic transmission in a medium with a single horizontal layer in which the deviation of the index of refraction from unity is very small. Numerical calculations for the sound level deviation for transmission in such a medium are presented. A temperature layer about 2 yd thick with a maximum temperature deviation from the surrounding water of 0.02°C can produce sound level variations of 2.2 db at 500-yd range. Excellent agreement is obtained in a comparison between these results and direct acoustic transmission measurements in an underwater medium closely approximating these assumptions. (This work was supported by the Bureau of Ordnance, U. S. Navy, under Contract NOrd 12937.)
Acoustical Plenum Chambers
Authors: Wells R. J.
Published: September 2005

Sound-treated plenum chambers have been successfully used for sound control of the exhaust gases of jet engines. Probably the earliest reference is Dr. Hardy's paper [“Design characteristics for noise control of jet engine test cells,” J. Acoust. Soc. Am. 24, 185 (1952)]. Such chambers also may be employed to reduce ventilation system noise, etc. This paper presents measured data of a series of tests showing the effect of plenum geometry and absorption. The interaction of adjacent plenums is also considered. Several methods for an approximate calculation of plenum attenuation are examined and correlated with experimental data.
Two Methods of Measuring Recovery following Short-Duration Fatigue
Authors: Byers Vincent W.
Published: September 2005

Recovery to a tone one-half-octave above a 4000-cps, 3-min, 90-dB SL, fatiguing exposure was measured by the methods of continuous-tone Békésy audiometry and determinations of threshold following periods of silence. Such a high-level exposure results in a two-part recovery function. The first is a rapid recovery occurring in the 1st min, and the second is a slower gradual recovery occurring after the 1st min. These types of recovery have been labeled R-1 and R-2, respectively, by Hirsh and Bilger. The study was divided into four experiments. Experiment 1 revealed a difference at the end of 6 min between the two methods on the order of 7 dB in favor of the method of periodic determinations of threshold as the more accurate descriptive measure. The subsequent experiments attempted to determine if this difference occurred primarily in R-1 or R-2. The results were confusing and contradictory. The immediate introduction of silence rather than continuous tone trace resulted in faster recovery. However, of the periods of silence studied in R-1—20, 40, and 60 sec—the longest period resulted in the slowest recovery. Ignoring R-1 recovery, silent periods resulted in faster recovery than continuous tone trace in R-2 recovery, but the design was unable to detect any critical differences in the length of silent periods used. The results of these experiments may have been confounded by the finding that repeated exposures to the fatiguing stimulus, while not seeming to effect the pre-exposure threshold, do modify the pattern of recovery in the direction of no change in the fatigued threshold after the 1st to 6th min of recovery. After repeated exposures, the sensitivity of the ear following high-level exposure is changed. Other relevant findings are discussed, such as the bounce phenomenon and the index of fatigued threshold.
Elastic Wave Radiation from a Fault
Authors: Press Frank
Published: September 2005

A two-dimensional ultrasonic model study of the radiation of compressional and shear waves from an impulsive strike slip fault is described. The variations with azimuth of amplitude, direction of motion, and spectrum of the elastic wave pulses are described. The behavior of the compressional wave follows geometric theory. Diffraction effects are pronounced for the shear wave, producing significant motion where nodes are expected on the geometric theory.
Nonlinearity of the Middle Ear as a Possible Source of Subharmonics
Authors: Pong William , Marcaccio William
Published: September 2005

The asymmetric restoring force of the middle-ear structure is considered as a possible source of subharmonics in the hearing system. A theoretical estimate of the required intensity of acoustical excitation to generate the subharmonic can be calculated in terms of the parameters describing the mechanical characteristics of the middle ear. It is found that, for damping characterized by a decay modulus of about 50 msec, the minimum sound-pressure level must be greater than 122 dB in order to produce a subharmonic having a frequency one-half that of the stimulating signal.
On Physical Equivalents to Spectra Notions
Authors: Trent Horace M.
Published: September 2005

The notion of a Fourier spectral equivalent of an arbitrary function has been known for a long time in its basic mathematical form. Calculations of these spectral quantities are conventionally based on the Fourier integral. It is not so well known that the Laplace transformation also yields a spectral notion of which the Fourier form is a special case. In addition, vibration engineers have made extensive use in recent years of the concept of a shock spectrum. Simple physical experiments are described which yield direct quantitative spectral values at specified frequencies for any of the three spectra mentioned in the foregoing. These equivalents are useful in assigning physical significance to the quantities under discussion.
Errors in Spectrum Analysis by a Set of Narrow Band-Selecting Filters
Authors: Haase K. H. , Vilbig F.
Published: September 2005

A speech band is analyzed by scanning the spectrum through a single filter or applying it to a set of contiguous filters connected in parallel. Each filter in the set may be one tuned circuit or a combination of such circuitry. With the time constant neglected, the sectional spectral analysis obtained with a filter set will be correct if each filter band-passes only one spectrum line, showing as a rectangular transmission curve. The line amplitude can be indicated by linear rectification at the filter output. If the slope of the skirts in the filter curve is flat, it will extend to other spectrum lines and introduce an error. This error depends on the ratio of the line distance (pitch) to the filter bandwidth, on the shape of the filter curve, and on the kind of rectification in the outputs, where all ac voltages appearing as pitch frequency have to be suppressed by another filter. The more the lines comprehended by one filter passband, the more the error increases. The influence of bandwidth, skirt slope, rectification, and time constant on the resulting spectrum envelope are discussed. To simplify calculations, the complex values of a tuned circuit are tabulated in steps of 1/1000 in half-bandwidth units.
Transients in Signal Analysis
Authors: Corliss Edith L. R.
Published: September 2005

The design of analyzers can be computed to distribute transient error in a way compatible with the needs of the experimenter. Equations derived on the basis of a limiting power discrimination factor provide a measure of the largest number of bandpass filters that can be overlapped on adjacent channels to yield meaningful information about a rapidly changing signal. The function of a scanning filter can be compared to a parallel channel set of bandpass filters by calculating the effective number of bandpass filters providing the same resolution as the scanning filter. Various types of scanning functions are considered. The results are applicable to autocorrelation analyzers.
Some Secondary Effects Related to Impact Wave Forms
Authors: Nisbet J. S. , Brennan J. N.
Published: September 2005

The approximations used in characterizing impact pulse wave forms, e.g., half-sine, exponential blast, square, square with triangular rise, square with exponential rise, etc., are discussed. Distortion of high-frequency response, caused by introduction of discontinuities in the approximation, can result in marked disagreement between theoretical prediction and experimental results. Also, the neglect of high-frequency mechanical ringing is not always justified since it can produce effects that may be particularly harmful. It is shown that in some cases such ringing may excite resonances of the structure being tested, with an “amplification factor” as great as 4. This compares with a value of 2 reported by others for effects associated with rise time and with pulse duration. The conclusions are verified by oscillograms of dynamic response of a direct electrical analog of a single degree of freedom, linear mechanical system with damping. (This research was sponsored by the Quartermaster Corps, U. S. Army.)
Synthesis of Dispersive Delay Characteristics by Thickness Tapering in Ultrasonic Strip Delay Lines
Authors: Fitch Arthur H.
Published: September 2005

Tapering the thickness of a dispersive strip delay line operating in the first longitudinal mode can yield a variety of delay characteristics unobtainable with strips of uniform thickness. A strip whose thickness varies in some manner along its length may be thought of as a number of strip sections of constant thickness in series. The additive delay of these series sections can produce an over-all delay characteristic completely different in form from the delay characteristics of the individual sections. A design procedure involving the methods of linear programming has been developed which allows a unique determination of the taper required to produce a given delay function.

As a basis for comparison, the delay of a strip delay line of constant thickness departs from a straight-line characteristic by 1.5% of the nominal delay over a fractional frequency bandwidth of 15%. A tapered strip line designed for the same nominal delay and the same delay slope departs from linearity by only 0.5% over a 25% band. A tapered line designed to approximate an increasing parabolic delay characteristic exhibits a delay deviation of only 0.5% over a frequency band of 13%. An “image” line was fabricated having a decreasing parabolic delay characteristic approximating the mirror image of the increasing parabolic characteristic mentioned above. Although most of the applications of delay synthesis have employed the first longitudinal plate mode, the design procedure has also been applied to shear modes in a strip. For delay lines having nominal delays of 1000 μsec, typical insertion losses are 16 to 25 dB, with discrimination against unwanted signals of 35 to 40 dB.
Noise Generation by Open Turbulent Flames
Authors: Smith T. J. B. , Kilham J. K.
Published: September 2005

In order to provide fundamental data on the acoustic energy released by combustion processes, measurements were made of the aerodynamic sound generated by premixed open turbulent flames. Studies are described that relate the characteristics of the noise to the various geometric and flow parameters defining the flame, and it is shown that the sound radiated may be considered to arise from a statistical distribution of monopole sources throughout the zone of combustion. Examination of the combustion-noise spectra indicated that their peak frequencies may be expressed by a constant value of a Strouhal number, in terms of the burner-port diameter, the mixture flow velocity, and the flame speed. The acoustic power radiated by a turbulent flame was found to be related to the flow parameters by the expression per P ∝ (ρU4D2/c)(Ub/U)2. This relationship is shown to be similar to the basic equation for the acoustic-power output of a monopole source.
Acoustics of the New York Philharmonic Hall
Authors: Shankland R. S.
Published: September 2005

The diffraction and interference effects produced by the “clouds” suspended from the ceiling of the new Philharmonic Hall at Lincoln Center in New York are investigated, and reasons are given for concluding that they are in part responsible for the observed deficiency in low-frequency sound in the hall.
Pitch-Induced Spectral Distortion in Channel Vocoders
Authors: Gold Bernard , Tierney Joseph
Published: September 2005

A hypothesis is advanced that severe spectral distortion can be expected in a channel vocoder driven by unsmoothed pitch pulses during those intervals when the pitch is not constant. A vocoder-synthesizer configuration is proposed that minimizes this effect. The question of the smoothing of the excitation periods is related to our hypothesis.
More on Noise Produced by Boundary-Layer Turbulence
Authors: Powell Alan
Published: September 2005

The question of possible sound produced by stresses at a rigid surface is again discussed. It has been previously pointed out that these stresses are effective sources, being the reaction to momentum fluctuations in a contiguous flow and with which the true sound sources are to be associated. There is no error in the original general formalism, and no confusion need exist between hydrodynamic pressure and sound-field pressure in the limits of very small surfaces (when net forces are to be directly associated with dipole radiation) and of very large plane surfaces (when the surface pressures merely represent reflections of the quadrupole flow noise).
Comments on “Moments of the Output of Linear Random Systems”
Authors: Samuels J. Clifton
Published: September 2005

It is shown how the various moments of a random system can be obtained directly from the governing dynamical equations. An equation is given for the n-point probability distribution of dynamical systems.
Comments on “Theory of Stochastic Linear Systems with Gaussian Parameter Variations”
Authors: Samuels J. Clifton
Published: September 2005

It is argued that equations obtained a previous paper are approximately valid under wide conditions. Some conditions are discussed under which the equations are exact.
Precision of Oceanographic Data for Sound-Speed Calculations
Authors: Fofonoff N. P.
Published: September 2005

The precision of sound speeds calculated from oceanographic data, consisting of measurements of temperature and salinity at various depths, depends on systematic errors of the empirical formula relating sound speed to the oceanographic variables and on the errors of the measured variables. Estimates of precision, defined as twice the standard deviation, range from 0.021°–0.025°C for temperature, 0.016‰–0.072‰ for salinities determined by titration, and 7–12 m for depths to 1000 m. Systematic errors of the sound-speed formula are estimated to be about 0.5 m/sec.

In a homogeneous layer of the ocean, the errors of measurement of temperature and salinity limit the precision of sound speed to 0.12 m/sec. In a stratified layer, the precision less (larger standard deviation) because of the uncertainty in the depth determination.
Transmission Loss of Leaded Building Materials
Authors: Ostergaard Paul B. , Cardinell Richmond L. , Goodfriend Lewis S.
Published: September 2005

A number of architectural-partition materials have been tested for sound-transmission loss with and with- out a 0.125-in. lead sheet adhesively bonded to one side. A series of tests with and without lead on panels with and without 2×4-in. wood studs indicates that a new series of building products having high TL is practicable, using conventional building materials with a lead sheet adhesively bonded, as well as the imaginative combinations of lead with many new substrate materials. Evaluating methods for new lead-bearing materials are outlined.
Low-Frequency DL's: Effect of a High-Frequency Noise
Authors: Campbell Richard A.
Published: September 2005

A high-pass filtered noise will increase the difference limen (DL) for frequency for a simultaneously presented, low-frequency, unmasked sinusoid. Since only the basal end of the basilar membrane should be interfered with by such filtered noise, this would seem to indicate the participation of the basal end in the perception of a low-frequency sinusoid, contrary to a traditional place theory. These data are from 20 normal-hearing listeners making either unilateral alternate-pitch matches or constant-method judgments for a 150-cps sinusoid at a 5- to 50-dB sensation level (SL). Two interfering noises, one periodic and one aperiodic (either unilateral or contralateral to the sinusoid), were presented at the maximum level possible without masking the sinusoid at its threshold. Both noises contained essentially no energy below 400 cps. The frequency DL's were increased approximately 20% by all the noises, regardless of ear of presentation. The increase would thus appear to be attributable to a general, bilateral phenomenon, such as distraction, rather than the interference with the basal end of the ear receiving the sinusoid.
Cumulation of DL's for Intensity Change at Low Sensation Levels
Authors: Dallos Peter J. , Carhart Raymond
Published: September 2005

Data which appear in the literature on normal DL's for intensity change lead to the hypothesis that, for pure tones through a sensation level of 40 dB, a linear function relates 1/jnd to the sensation level. A nonlinear difference equation expressing this hypothesis is developed here. A resultant formula allows the number of jnd's which cumulate within a range of sensation levels to be compared, provided one knows the DL magnitudes at the two limits of that range. The adequacy of this procedure was tested on six normal hearers. It was found that the number of jnd's which each subject exhibited when DL's were successively cumulated experimentally at 1000 and 4000 cps corresponded to within an average error of 4.0% to the number predicted from the formula. The maximum single error of prediction was 6.6%.
New Standard for Measurements of Certain Piezoelectric Ceramics
Authors: Martin Gordon E.
Published: September 2005

The Standards on piezoelectric ceramics provide for the evaluation of the longitudinal parameters such as k33 only for short bars and thin cylinders electroded at the ends. In view of the restricted polarization thicknesses of materials, ceramic bodies are often formed by cementing together a number of pieces of shorter dimensions. This note gives the equations for the evaluation of all parameters of such a multiply segmented ceramic body for which the length is large as compared to the lateral dimensions.
Elastic Constants of Silicon Carbide
Authors: Einspruch Norman G. , Claiborne Lewis T.
Published: September 2005

The elastic constants of polycrystalline silicon carbide were measured using the ultrasonic pulse-echo technique. The high moduli [E = 36.0, μ = 14.8 (1011 dyn cm−2)] are consistent with measurements on other hard materials.
Effects of Uranium Salts on Sound Cavitation in Water
Authors: Messino D. , Sette D. , Wanderlingh F.
Published: September 2005

Uranium salts have a large effect on ultrasonic cavitation when dissolved in water. The effect seems due to the creation of large nuclei by fission induced by cosmic neutrons thermalized in water.
Extension of the Concept of Equivalent Eulerian Boundary Conditions
Authors: Kessler Henry C.
Published: September 2005

The statement of a Lagrangian boundary condition at the face of a vibrating piston in terms of an approximately equivalent Eulerian condition is examined to second order in the particle velocity. The second-order correction to the boundary condition is explicit but complicated.
Reduction in Convective Heat Transfer due to Vibration
Authors: Nevill G. E. , Commerford G. E. , Raben I. A.
Published: September 2005

Experimental results demonstrating the occurrence of reductions in forced convection heat transfer due to vibrations of a heated tube in water have been obtained. A description of the study, together with a tentative qualitative explanation of the phenomenon and suggestions as to its possible importance, is presented.
Out-of-Plane Vibration of a Clamped Circular Ring Segment
Authors: Nelson Frederick C.
Published: September 2005

The fundamental out-of-plane symmetric and antisymmetric frequencies of a clamped ring segment are obtained as a function of opening angle via the Rayleigh-Ritz procedure. Particular attention is paid to its behavior at large opening angles.
Ultrasonic Absorption and Relaxation Times in Nitrogen, Oxygen, and Water Vapor
Authors: Fujii Y. , Lindsay R. B. , Urushihara K.
Published: September 2005

The absorption coefficient α is measured in nitrogen, oxygen, and water vapor by a direct traveling-wave method that employs a pulse modulated signal of about 65 kc/sec. The apparatus used is a modification of that previously reported by C. Ener, O. Herbjørnsen, Y, Fujii, and L. Nyborg. The rotational relaxation times in nitrogen and oxygen for 22°C and 1 atm are obtained as (7.6±0.6) × 10−10 to sec for nitrogen and (5.1±0.4) × 10−10 sec for oxygen. The coefficient α in water vapor is measured for temperatures between 42° and 183°C and over the range of angular frequency/pressure from 1 to 50 Mc/sec/atm. Part of the observed excess absorption is probably due to rotational relaxation, but the larger part, especially at the higher temperatures, is considered to be due to vibrational relaxation. On the latter assumption, calculation of the relaxation time yields a value of the order of 1.5 × 10−8 sec. This is of the same order of magnitude as that reported by other observers for higher temperatures.
Acoustical Measurements with 3- and 10-Gc/sec Quartz-Cavity Resonators
Authors: Stewart Ellen S. , Stewart James L.
Published: September 2005

Employing principles outlined previously by the authors, quartz-cavity resonators were built which operate in the 3- and 10-Gc/sec regions at room temperature. Their properties agree well with theory. In order to resonate, the crystals must be very thin and accurately plane-parallel. There is no dispersion in the longitudinal velocity of sound in X-cut quartz to 10 Gc/sec within 0.005%. The attenuation is (4±0.4) Np/cm at 3.2 Gc/sec and (33±6) Np/cm at 9.6 Gc/sec. The specific acoustic impedance of water is (1.5±0.6) × 106 g⋅cm−2 sec−1 at 3.2 Gc/sec. The efficiency for radiation into water is 10%. Sound has been transmitted into water through an aluminum film 3 μ thick.
Mechanical Input Admittance of Ultrasonic Delay Lines Operating in Torsional or Shear Modes
Authors: Onoe Morio
Published: September 2005

The mechanical input admittance at the end face of an ultrasonic delay line operating in torsional modes for a rod or shear modes for a plate is analyzed. The analysis is based on the facts that SH waves in a plate constitute a Fourier series and torsional waves in a rod constitute a Dini series, and consequently any stress distribution on the end face can be expanded in terms of these waves. It is shown that modes below cutoff contribute to the susceptance, and modes above cutoff contribute to the conductance. Three transducer configurations are discussed: namely, a single transducer for exciting symmetric modes in a plate, two push-pull transducers for exciting antisymmetric modes in a plate, and a hollow coaxial transducer for exciting torsional modes in a rod. Modes below cutoff decay exponentially along the direction of propagation. The distance from the end face at which these modes have significant effects is discussed. As the frequency becomes successively higher than cutoff frequencies, successively more modes become propagating. The amplitude distribution among these propagating modes is also discussed.

A transducer which covers the whole cross section can excite the fundamental nondispersive mode in plates and rods without generating higher modes. Hence, this configuration is recommended for delay line design in order to avoid possible complications due to higher modes in the delay line characteristics.
Optimization of the Mass Distribution and the Air Spaces in Multiple-Element Soundproofing Structures
Authors: Mangiarotty R. A.
Published: September 2005

A method is evolved for predicting the transmission loss of soundproofing multiple-element configurations containing any number of elements. The optimum distribution of mass between the impervious elements (fuselage skin panel, blanket septa, trim panel) is determined for a general theoretical configuration and for a typical aircraft structure. The theoretical improvement obtained by mass distribution optimization (approximately uniform distribution between the impervious elements) is about 3 to 6 dB in the low frequencies (below 500 cps) and 8 to 14 dB in the speech interference range (600 to 4800 cps).

It is shown that a large increase in air spaces between elements is required to obtain only about 8- to 10-dB improvement (in theory), neglecting contact flanking paths between the elements. Also, replacing air spaces with acoustical blankets produces small improvements (2 to 8 dB) at the cost of possible structural flanking transmission between the elements.

It is also shown that covering a hard terminating trim panel with an acoustical blanket increases the overall transmission loss by about 2 to 6 dB in the 300- to 4800-cps frequency region.

Finally, it is shown that reducing the ambient pressure in a fuselage reduces the sound attenuation properties of soundproofing, viz., the decrease in transmission loss due to pressurizing an aircraft to an equivalent altitude of 8000 ft is about 3 to 6 dB.
Analysis of the Middle-Ear Function. Part II: Guinea-Pig Ear
Authors: Zwislocki J.
Published: September 2005

An electrical network analog is developed for the guinea-pig ear. The analog is similar to that developed previously for the human ear. The network is based on the anatomy and on impedance measurements. Its input impedance and transmission characteristic are in approximate agreement with those of the real ear. It is shown how the analog can be used for the determination of transient responses.
Intensity Discrimination, the “Pedestal” Effect, and “Negative Masking” with White-Noise Stimuli
Authors: Raab David H. , Osman Eli , Rich Edward
Published: September 2005

Miller's data on masking and intensity discrimination with white-noise stimuli are reanalyzed. Since the masking and increment stimuli in Miller's study were, in fact. correlated, their sound pressures (rather than sound powers) were added. Recalculation of the extents of masking from the relative DL's shows that there was less masking than had originally been computed. The masked increment is 25 dB (not 12 dB) less than the masker when the latter is at 25 dB SL or above. Below 25 dB. there is “negative masking,”
Transducer Measurement Platform on Seneca Lake
Authors: Miller Harry B.
Published: September 2005

A large mobile platform is now in operation for underwater acoustic measurements in Seneca Lake. The noise level is very low. and the available water depth is nearly 600 feet.
Comments on “Transient Response of a Thin Elastic Cylindrical Shell to a Moving Shock Wave”
Authors: Brogan W. L.
Published: September 2005

Radial vibrations of thin cylindrical shells have been the topic of several recent papers. Bhuta has considered a simpler version of the problem partially solved by Brogan. It is implied that the more recent paper contradicts and, therefore, disproves the earlier results. The purpose of this note is to show that there is no contradiction. In fact, it is possible to calculate analytically the “critical velocities” that were found numerically. The calculation depends directly upon the conclusion of Brogan which was subjected to the strongest criticism.
Mutual Coupling with Dipoles in Arrays
Authors: Toulis W. J.
Published: September 2005

Mutual coupling between transducers in a plane array may be eliminated completely if thin oscillating disks are used as radiators. The radiation resistance of such dipoles is very low unless the diameter is about a half-wavelength in the fluid medium or the disk is bordered with a finite rigid baffle. Alternatively, a pseudodipole type of transducer may lead to low mutual coupling without impairing seriously the radiative self-impedance.
Sound Propagation in Homogeneous Deciduous and Evergreen Woods
Authors: Embleton T. F. W.
Published: September 2005

The sound attenuation due to trees has been measured (under atmospheric conditions requiring no corrections) at about twenty locations, representing four selected types of woods. A constant excess attenuation of 7 dB/100 ft was found at frequencies below 2000 cps, in disagreement with previous workers. With the sound source in the open at the edge of the woods, effects due to change of medium were observed, viz. an increase of sound-pressure level in the woods and a distinctive S-shaped curve of attenuation vs frequency. This is suggestive of resonant absorption, although a theory developed according to such a hypothesis, while having the correct frequency dependence, fails to predict the magnitude of the observed results by a factor of 103. Transverse modes of vibration of the branches were shown to be the oscillators active in the frequency range of interest, 250 cps in the lower branches to about 1100 cps near the top of the tree; indications were that trunk resonances might also be important.
The Marina as a Two-Dimensional Auditorium
Authors: Morrow Charles T.
Published: September 2005

The problem of reducing the waveheight in a marina or artificial harbor by comparison with that of the open ocean is treated by analogy to the classical derivations of auditorium acoustics. A formula is obtained that relates the effectiveness of the marina to the breadth of the mouth and the total absorption of wave energy by the interior shoreline.
Static and Dynamic Transmission Losses of Partitions
Authors: Raes Auguste C.
Published: September 2005

The conclusions of 10 years of practical experience with a measurement method which the author published earlier sum up as follows: Static transmission losses (TL) are defined as the values obtained by standard methods using constant level sounds. Dynamic TL are measured with transients or with varying level sounds. The latter measuring conditions agree much more than the first with practical conditions. TL values measured on traditional types of partitions (e.g., masonry walls) may vary by ±10 dB from one wall to another of the same type in the same building. For prefabricated partitions, these variations drop to less than ±3 dB, even under variable boundary conditions. Tests on one sample are thus insufficient to draw definite conclusions on the TL which should be expected of a type of partition. Three to ten samples should be tested. The time lag of a partition may have a relationship with its sound insulating value. The measurement of the sound TL of any selected partition in any position in a building or a ship is a necessity if sound insulations are to be effectively guaranteed. It has now been done for 10 years.
Modification of Sensory Localization as a Consequence of Oxygen Intake and Reduced Blood Flow
Authors: von Békésy Georg
Published: September 2005

Breathing oxygen from a mask or a reduction in the blood flow through the head produced definite but temporary changes in directional hearing. Similar results were found for directional hearing and for analogous phenomena in other sense organs, such as vibratory sensations on the skin, heat sensations, and taste. Both the administration of oxygen and the reduction of the blood flow decrease the speed of nerve transmission and lengthen the reaction times.
Frequency Discrimination of Pulsed Tones
Authors: Campbell Richard A.
Published: September 2005

If a 2200-cps tone is pulsed 150 times/sec under appropriate conditions, a low pitch (periodicity pitch) will be heard corresponding to that of a 150-cps tone although there is little or no energy present at 150 cps in the signal. To account for the perception of this low pitch, it has been postulated that either (1) the cochlea acts as a mechanical envelope “detector” resulting in neural activity in a peripheral “low-frequency or pitch” channel, or (2) the cochlea performs a Fourier-like analysis resulting in neural activity in a peripheral “high-frequency or pitch” channel with this neural activity undergoing a central temporal analysis where the low periodicity pitch is “detected.” Absolute threshold measures were obtained for three stimuli: a 2200-cps sinusoid, a 150 cps sinusoid, and a 2200-cps tone pulsed 150 times/sec. Frequency discrimination measures were obtained for the same three stimuli at various sensation levels. The measures obtained for the pulses were compared, by analysis of variance and correlation techniques, to those measures for each of the sinusoids. The cochlear detection hypothesis would demand close relation between the pulse and 150-cps measures although none was found. Conversely, the central detection hypothesis would demand closer relation between the pulse and 2200-cps measures, which was found. Furthermore, a lack of monotonic relation between perceived pitch and repetition rate and a large “atonal range” was found for the pulses, indicating their perception involved mechanisms not involved in the perception of the sinusoidal stimuli, i.e., a central temporal analysis.
Detection, Discrimination, and the Loudness of Short Tones
Authors: Creelman C. Douglas
Published: September 2005

Two experiments were conducted, with the same observers in each. A method of adjustment was first used to measure the relative loudness of short tonal signals at four different durations and four intensity levels. The second experiment measured the detectability of each duration which had been used in the first, and scales were constructed on the basis of the measurements. It was shown that the relative loudness of a short tone (the level to which it will be set to sound equally loud) can be predicted from the detectability scale. The relationship is an extremely simple one: the equal-loudness settings yield signals of equal detectability.
Pitch Associated with Time Delay between Two Pulse Trains
Authors: Small Arnold M. , McClellan Max E.
Published: September 2005

If a series of equally spaced ac or dc pulses is delayed in time with respect to an identical series of pulses, a pitch will be heard corresponding to the reciprocal of the smallest delay between adjacent pulses. This study investigates the precision with which listeners are able to match the pitch of a pure tone to that produced by the time separation in a double pulse train. Ten listeners each made 50 pitch matches for six pulse delays at each pulse repetition rate of 25, 100, and 400 pps. The results indicate that the distribution of pitch matches is centered at the reciprocal of the pulse delay. The dispersion of this distribution seems remarkably small, but tends to widen as pulse delay is shortened, especially at the highest pulse repetition rate. Although the study was not designed for the investigation of all possibilities, no obvious spectral cue seems to exist which would account for the data.
Auditory Unmasking
Authors: Treisman Michel
Published: September 2005

A model of auditory perception is presented. It postulates a hierarchical system of tests, each depending on the operation of a signal detection device. A prediction is derived from the model: if a masking tone presented to one ear raises the threshold for a signal at the other ear, then adding white noise to the masking ear may decrease the contralateral masking. This prediction was confirmed, and a practice effect, a tendency for the unmasking to decrease in a naive subject's second session, was found. This was explained in terms of the model, and further predictions were derived. These were that the decline in unmasking would be shown despite changes in the masking tone or signal tone, or reversal of the ears used, and that monaural masking of a tone (of the frequency of the masking tone) by white noise would also show a decline with practice, even in the opposite ear. These predictions were also confirmed.
New Instrumentation for Making Spectrographic Pictures of Speech
Authors: Wood D. E. , Hewitt T. L.
Published: September 2005

Communication by speech involves the production and perception of elements of an acoustic code. This code can be made visible in pictures which show certain spectral patterns existing in the sound signals. A new instrumentation has been developed for making spectrographic pictures of large quantities of speech. The outputs of a bank of filters are repeatedly scanned at a high rate to produce spectral cross sections. Each cross section presents the existing spectrum as a continuous distribution of energy versus frequency. A unique process of interpolation of filter outputs maximizes the information recovered so that the frequencies of tones are accurately represented by peaks in the spectral cross sections. These cross sections may be recorded on film to provide a complete and detailed time history of signal spectra. Other picture formats include spectrograms showing amplitude by density modulation. Strip-film recording and operation in real time combine to provide a very great analyzing capability. This paper reviews the basic analyzing functions, describes some of the kinds of flexibility of analysis, and presents reproductions of films made by the analyzer.
Experimental Study of Dispersion in Ultrasonic Waveguides
Authors: Lastovka J. B. , Carome E. F.
Published: September 2005

An experimental study has been made of the velocity of ultrasonic pulses in cylindrical, water-filled, metallic waveguides. Both a pulse coincidence and a direct source-to-receiver signal travel-time method were used for measurements over the frequency range from 1 to 5 Mc/sec. The diameter of the acoustic sources and receivers was 0.5 in., and measurements were made in guides with inner diameters of 0.50, 1.0, and 1.37 in., and also under free-field conditions. At 5 Mc/sec, all of the measured velocities were essentially the same. At lower frequencies, however, the velocities in the smaller diameter waveguides were substantially below those obtained under free-field conditions, with the differences decreasing from 6 m/sec at 1 Mc/sec, to 2 m/sec at 3 Mc/sec. From a qualitative analysis of the data in terms of several idealized theories, it is concluded that these results may be explained on the assumption that the plane-wave mode is not propagated in such waveguide systems.
Effects of Transducer Alignment on Light Diffraction by Ultrasonic Waves
Authors: Mayer Walter G.
Published: September 2005

Light-diffraction patterns produced by wide ultrasonic beams of 5.235 and 8.786 Mc/sec are investigated for normal and slightly nonnormal incidence. A method for the correct alignment of the transducer is described. The results are discussed regarding agreement between experiment and theory.
Vibration Modes of Coupled Plates
Authors: Scanlan Robert H.
Published: September 2005

The present note is directed to the question of the vibration modes of violins.
Articulation Effectiveness Measure Applied to Processed Speech
Authors: Barker Boone A. , Latorre Victor R.
Published: September 2005

An area of increasing importance to the military is that of secure and jam-resistant transmission of voice information. As digital techniques are the more promising means of achieving jamming protection and secure encoding, it is necessary to consider the effects of the analog-to-digital-to-analog processing of the speech itself. The processing systems considered are compared on the basis of articulation effectiveness measure, which is a numerical measure of sound articulation, the importance of each sound being weighted by its frequency of occurrence. On this basis, the intelligibility of clipped-speech samples is about the same, while delta modulation is quite sensitive to sample rate. These results are as expected and show the usefulness of the articulation effectiveness measure in evaluating speech systems.
Articulation Index and Average Curve-Fitting Methods of Predicting Speech Interference
Authors: Webster J. C. , Klumpp R. G.
Published: September 2005

Sixteen equally speech-interfering noises were rated by using articulation index (AI) calculations and by using noise criteria (NC)-type contours as averaging, not peak-finding, devices. Articulation-index scores based on 5 or 6 weighted octave-band levels were equal to AI scores obtained by the 20-band method and predicted very well that the noises were equally speech-interfering. The use of NC-type curves (from 500 to 2000 cps) to find an average, not a peak, noise level also gave good prediction. Equally speech-interfering noises were not, however, equally “loud,” nor equally “noisy.” There was evidence to show that the frequency that divided noise-masked speech into two equally intelligible frequency regions was 850 or 1000 cps, and was not 1700 or 1900 cps, which is the dividing frequency when the speech in quiet is progressively restricted in bandwidth by high- or low-passed filtering.
Design of Sonic Amplitude Transformers for High Magnification
Authors: Eisner Edward
Published: September 2005

Using the design method described by Eisner and Seager, in which a suitable wavefunction is chosen and the corresponding profile is deduced, a new class of amplitude transformers is designed. The wavefunction used is a fourth-order Fourier series. The resulting transformers give a useful compromise between the properties of the “stepped” and the “exponential” transformers. The output amplitude produced for a given maximum strain is somewhat lower than the amplitude given by the exponential transformer of the same magnification, but is much higher than that given by the corresponding stepped transformer. While the “Fourier” transformer is slightly less stiff in bending than the stepped, it is very much stiffer than the exponential.
Finite Amplitude Distortion
Authors: Allen Clayton H.
Published: September 2005

Comparisons show good agreement between empirical and theoretical relations describing finite amplitude distortion for both plane and spherical waves. Magnitudes of the harmonic components of pressure in an originally sinusoidal spherical wave can be described in terms of a parametre called distortion factor which is a simple function of wavelength distance from the source and the source intensity. Evidence for the existence of a limiting acoustic pressure both for plane and spherical waves will be reviewed and useful interpretations of this limiting pressure will be offered.
A Progressive-Wave Velocimeter and the Speed of Sound in Water
Authors: Greenspan Martin , Tschiegg Carroll E. , Breckenridge Franklin E.
Published: September 2005

The speed of sound in water at 5 temperatures near room has been determined from measurements of variation of phase with distance on the axis of a progressive wave emitted by a small piston-like radiator. The minimum distance from source to receiver was large enough to render negligible the Fresnel-type interference errors; errors arising from the finite diameter of the receiver were also negligible. Reverberation effects were reduced partly by use of absorbing baffles and partly by pulsing the sound at a rate such that the reverberation died out between pulses. Readings of the screw were taken each half-wavelength, as indicated by Lissajous figures, for 30 wavelengths (total distance of 18 mm for the frequency of 2.6 Mc). The variation of distance with phase was accurately linear; the standard deviations of the points were about 1 micron, which is also the least count of the screw. The standard deviations of the speed of sound were in the range 0.04 to 0.12 m/sec. The results agree with our earlier ones obtained by an L/T method to within 0.04 m/see (27 ppm) and disagree with those measured with ultrasonic interferometers.
New Airborne-Sound Transmission Loss Measuring Facility at Riverbank
Authors: Huntley Ralph , Richards R. L.
Published: September 2005

With the recent completion of a new 3000 cubic foot reverberation room, Riverbank Acoustical Laboratories are now able to meet explicitly all the requirements of the American Standards Association and the American Society for Testing Materials for the measurement of airborne-sound transmission loss of walls and partitions. The measuring method is explained and the several checks for accuracy are discussed. Some of these checks have been: the influence of microphone position; measurement error and repeatability; insurance against sound leaks and flanking transmission paths; interchanging transmitting and receiving rooms; and agreement of measured results with those which can be calculated.
A 90-km Sound-Transmission Test in the Arctic
Authors: Milne A. R.
Published: September 2005

A 90-km sound-transmission test on the continental slope of the Arctic Ocean north of the Canadian Archipelago is described. Spectrum levels of sounds from 1-lb explosive charges vs distance are presented for frequencies in the range 12 cps to 16 kcps. Results confirm the low-pass filtering effect of the ice canopy and assist in the determination of transmission losses.
Some Field Studies of the Transmission Loss of Lightweight Aggregate Concrete Masonry Blocks
Authors: Watters B. G. , Farrell W. R.
Published: September 2005

Hollow, lightweight aggregate concrete masonry blocks are widely used for the walls of offices, studios, dormitories, and the like. It has been found that the transmission loss provided by such walls in the field does not compare favorably with the loss which one would predict from the weight of the wall. Further, the transmission loss values which we measure in the field are often found to differ appreciably from test data reported by the National Bureau of Standards and other testing laboratories. This paper will present field data and discuss some of the reasons for the discrepancies between the theoretical mass law, transmission loss, the values measured in the laboratory, and the values actually obtained in the field.
Effects of Light Coatings on Impedance and Absorption of Open-Celled Foams
Authors: Schwartz Manuel , Buehner William L.
Published: September 2005

Light coatings of the order of 0.002 g/cm2 to 0.04 g/cm2 were applied to open-celled foams of 1-in. thickness and 97% porosity. It was found that coatings of 0.002 g/cm2 improved the absorption over a range of frequencies extending from 480 to 1500 cps or 1980 cps. The improved absorption is attributed (in units of ρc) to the resistance approaching unity and/or the reactance approaching zero. The reactance becomes large at high frequencies with increasing coating mass per unit area, thereby causing the absorption at high frequencies to decrease. The improved absorption shifts to lower frequencies with increasing coating mass per unit area.
Static and Dynamic Characteristics of Isolation Materials
Authors: Mintz F.
Published: September 2005

In an effort to determine optimum materials for use as a comfort measure under carpeting in airplanes, an experimental study was made of the static and dynamic characteristics of seven types of isolation materials and various combinations of these materials. Tests of wear under simulated use conditions were made on those materials most effective for isolation. Results (which are presented in some detail) indicate that, of the materials tested, a foam Neoprene has the best combination of isolation and durability characteristics from the viewpoint of physical measurements. Attempts to develop an approach for predicting dynamic characteristics from static measurements were partially successful. Various nonlinear effects, reported by previous observers of elastomeric material behavior, were noted.