bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Wave Propagation through a Tidal Bore
Authors: Barakos P. A.
Published: October 2005

Large thermal fluctuations associated with internal tidal waves can lead to highly asymmetric wave profiles having the characteristics of internal tidal bores. An acoustic wave propagated through a medium in which such a phenomenon is in progress can undergo amplitude variations exceeding 30 dB. Synoptic time and space series of environmental and acoustic data are obtained from sensor arrays fixed in space, in shallow water off southern California. The acoustic source radiates CW pulses every 3 sec at 30 kHz to a fixed hydrophone 150 m away. Time series are obtained of temperature from vertical thermistor space arrays, and wave height is obtained from a wave staff and water motion obtained using EM current meters. A sampling interval of 3 sec was used. The large-scale acoustic amplitude fluctuations are investigated using acoustic ray techniques while the small-scale events are looked at from the statistical point of view.
A Review of Some Developments in Ray Tracing at SACLANTCEN
Authors: Krol H. R.
Published: October 2005

If the sound-speed profile is obtained by Cubic Spline interpolation, the intensity calculations become very accurate; for instance, the problem of false caustics does not arise. However, the ray equations need to be solved numerically, as theoretical solutions do not exist for a cubic. This idea has been applied to both range-independent and range-dependent ray tracing. Some numerical differential equation solvers are compared with regard to computer time and accuracy. A special test method, for the range-dependent case, that makes use of complex function theory checks ray and intensity calculations. Some computer results are shown.
Nomograms of Low-Frequency Transmission Loss
Authors: DiNapoli F. R. , Ryan D.
Published: October 2005

In the design or operation of sonar systems it is required to know under what conditions optimum performance can be achieved. The subject of this paper is a technique which should be useful in dealing with one term in the sonar equation, namely, transmission loss. Since the amount of energy lost depends on many parameters (e.g., the sound-speed profile, source and receiver depths, frequency, bottom loss, etc.), the process of determining the optimum mix of these parameters is cumbersome even if a validated transmission loss model is available. The approach utilizes the Fast Field Program (FFP) to generate transmission loss values for typical sound-speed profiles of the major ocean areas. It is assumed that at a sufficiently large range the mean propagation loss is represented by A+10 logr+αr where r is horizontal range and α is Thorp's attenuation coefficient. The constant A is then determined from a linear least-squares fit between this expression and the FFP values. The FFP is rerun for various combinations of the input parameters and the value of A are then combined to form a collection of nomograms which display the dependence of the mean transmission loss upon the input parameters. This work supported by the Chief of Naval Material.]
A Comparison of Ray Theory, Modified Ray Theory, and Normal Mode Theory for a Deep Ocean Arbitrary Velocity Profile
Authors: Blatstein I. M. , Newman A. V. , Überall H.
Published: October 2005

Modified ray theory [D. A. Sachs and A. Silbiger, J. Acoust. Soc. Amer. 49, 824 (1971)] can be used to calculate transmission loss near caustics and in shadow zones where ray theory fails. Normal mode theory is an approach that should work equally well in every region. For an arbitrary linear-gradient profile, results of ray theory and modified ray theory have been compared near a convergence zone caustic. It was found that these two approaches do not always agree in the double arrival region associated with the caustic. Results from a normal mode program using finite difference methods for an arbitrary profile [A. V. Newman and F. Ingenito, NRL Memo. Rep. 2381 (1972)] will be compared where possible with the results from the above-mentioned techniques. [Supported in part by ONR and DNA.]
Computing Power Spectra with FFT
Authors: Bogert B. P.
Published: October 2005

This is a tutorial paper describing the fast Fourier transform and practical aspects of the digital computation of power density spectra using FFT. Discussed first is the relation of the discrete Fourier transform (DFT) to the Fourier integral. Then we describe an FFT algorithm, showing its computational saving over the naive calculation of the DFT. We then consider the estimation of the power density spectrum, describing briefly the indirect method (used before FFT) and then the direct method of power spectrum estimation via the periodgram estimate now commonly used. We continue with a discussion of bandwidth and stability of spectral estimates and how these properties are related to the time and frequency windows used to smooth the periodgram estimates. Finally, we consider briefly the estimation of cross spectra and coherency and discuss some of their properties.
Some Applications of the Fast Fourier Transform
Authors: Theilheimer F.
Published: October 2005

Examples of applications of Fourier transforms are chosen from a variety of topics. Roughly, those topics can be classified in a few categories: problems that lead to partial differential equations and can be solved by certain methods of separation of variables; other problems that lead to ordinary differential equations or systems of such equations with constant coefficients, which are solved by subjecting the equations to Fourier analysis; and finally, many processes which become more intelligible to us if we study them not as functions of time but as functions of frequency. All these problems were previously attacked by standard Fourier analysis. Special emphasis is placed on pointing to the modifications brought about by the introduction of the fast Fourier transform. As far as physical subject matter is concerned, the applications are chosen largely from the field of ship design and ship operation.
Survey of Hybrid Spectral Analysis Hardware
Authors: Rothschild Richard S.
Published: October 2005

Hybrid techniques were successfully applied to real-time spectrum analyzers more than ten years ago. The use of digital time compression was pioneered by the U. S. Navy, but it did not find wide acceptance in commercial frequency analyzers until the advent of high-speed integrated circuits. Unlike FFT processors, which perform a Fourier transform by digital calculation and thereby achieve great flexibility, the hybrid analyzer produces only the amplitude of the Fourier transform. However, it is extremely efficient, because it utilizes the advantages of digital time compression and high-speed analog spectrum analysis. Processing speeds equal to or greater than FFT units are achieved at a fraction of the cost. Hybrid analyzers, although operating differently in theory, share the same natural constraints as all-digital FFT processors—these are (1) the necessity to match sampling rate to input low-pass filtering to prevent aliasing; (2) the dependence of real-time throughput and nominal resolution upon the length of the time segment processed; and (3) the compromises necessitated by processing segments rather than continuous data. Various approaches to the solution of these problems as well as ways of utilizing the real-time capabilities of hydrid analyzers are discussed.
A Building Code for Exterior-Noise Isolation
Authors: Young Robert W.
Published: October 2005

A building code has been formulated to describe various constructions to cause a specified noise-level reduction in a given noise zone in the city of San Diego. Noise-level reduction means reduction in average A-weighted sound level from outside to inside a building. The average noise level is that called the annual community noise equivalent level according to now effective “Noise Regulations for California Airports”; this average is a mean-square A-weighted sound-pressure level obtained with the noise levels existing between 7 p.m. and 10 p.m. increased by five decibels and the noise levels between 10 p.m. and 7 a.m. increased by 10 decibels. A noise zone is an area of the city bounded by contours of annual community noise equivalent level, at intervals of five decibels. Noise-level reduction is required by the code such as to limit to 45 decibels the average noise level inside a residential building due to outside noise of whatever source. For calculating noise-level reduction from room size and construction materials, a noise spectrum is specified that is typical of aircraft and other noise in one of the noise zones. If needed to verify compliance with the building code, a simple test of noise-level reduction is provided that can be performed with noise generally prevailing outside the building.
Field and Laboratory Certification Testing for Compliance with the New York City Building Code
Authors: Wolf Steven
Published: October 2005

The Noise Control Section of the New York City Building Code contains specific acoustical requirements for indoor and outdoor mechanical equipment servicing multi-family dwellings. Acoustical requirements are also specified for partition and floor-ceiling constructions separating dwelling units from each other, and from corridors and mechanical equipment spaces. As of 19 June 1972 the Housing and Development Administration, New York City Department of Buildings, issued a directive specifying the methods of compliance with the Noise Control Section of the New York City Building Code. The methods outlined are field testing or laboratory certification for Building Department approval to obtain a certificate of occupancy. An examination of both methods will be emphasized with selection and application of the most likely test method for compliance with the New York City Building Code and other federal, state, or local EPA codes.
Insertion Losses of Acoustic Louvers
Authors: Brittain F. H. , Salter C. M.
Published: October 2005

Manufacturers of acoustic louvers usually publish transmission loss data, measured in the laboratory according to ASTM E90-70, for their products. Since field conditions rarely match those specified in ASTM E90-70, insertion loss data would generally be more valuable. Normally, an acoustic louver is used as an alternative to a standard louver. The data usually needed is not the insertion loss of an acoustic louver by itself, but the difference between the insertion loss of an acoustic louver by itself, but the difference between the insertion losses of an acoustic and standard louver. Octave-band measurements under field conditions of insertion losses for both acoustic and standard louvers were conducted. The results are presented as octave-band spectra of insertion loss for both acoustic and standard louvers. For design purposes the measured insertion losses are compared to manufacturer's transmission loss data.
Dynamic Stiffness Testing of Neoprene Mountings
Authors: Wolf Steven
Published: October 2005

Neoprene mountings are primarily used for vibration isolation of mechanical equipment and floating floor constructions. The composition of a neoprene mounting has a direct influence on its ability to reduce vibration transmission and attain a specific natural frequency for vibration isolation. The standard characteristic of static loading is not the only parameter for selecting a neoprene mounting. Dynamic stiffness [static deflection/dynamic deflection] is more useful. We have tested two sets of neoprene mountings—30, 40, 50, 60, and 70 durometer each. The results of our tests indicated that the amount of carbon black and the chemical composition of the neoprene had a direct bearing on the change in the dynamic stiffness.
Hospital Design Procedure Incorporating Early Acoustical Inputs
Authors: Salter C. M. , Barnecut R. J.
Published: October 2005

Traditionally, an architect initiates the work of the mechanical, electrical, and acoustical consultants during the preliminary design phase of a project. At this time the location of spaces in the building has been almost entirely finalized. Thus, the consulting engineers are often forced to incorporate their systems and equipment into the already formalized building layout in an uneconomical manner. This paper enumerates the specific benefits an architectural firm expects to derive by involving the acoustical consultant during the schematic and design-development phases of each project. Case histories of hospital projects are presented to illustrate cost savings due to acoustical consultant involvement in the first phases of design. A suggested acoustical check-list and the phasing of this information are also presented.
Electroanatomy of the Cochlea
Authors: Honrubia V. , Strelioff D. , Sitko S.
Published: October 2005

Measurements of the resting and acoustically evoked potentials in the cochlea are dependent upon the nature of the potential generators and the electrical properties of the cochlear structures. We have recently determined (1) the average characteristics of the acoustically evoked cochlear potentials (AECP) inside the scala media, (2) the resistances of the cochlear structures, and (3) the effects on the AECP of variations of the magnitude of the resting potentials of the scala media. This information has been used to evaluate current theories of generation and distribution of cochlear potentials with the aid of newly developed computer models. The effect of the electrical properties of the cochlea on the longitudinal distribution and magnitude of the potentials will be illustrated. It was found that the characteristics of the cochlear microphonics and summering potentials in the scala media could be accounted for by a generator with nonlinear properties. In addition, the models demonstrated that some, but not all, of the AECP could be produced by resistance changes in the hair cells.
Auditory Responses of Single Cells in the Inner Ear of the Alligator Lizard
Authors: Weiss T. F. , Mulroy M. J. , Altmann D. W.
Published: October 2005

Micropipets were used to record electric responses to sound in the basilar papilla of the inner ear of the alligator lizard. This organ is considered to be equivalent to the mammalian organ of Corti. Intracellular responses were less than 3 mV peak-to-peak. Responses to acoustic clicks and tone bursts were asymmetrical: the positive (depolarizing) portion was generally larger than the negative (hyperpolarizing) portion. Responses to 50-msec tone bursts showed an “ac” response superimposed on a positive “de” shift. Two types of intracellular responses to acoustic clicks were identified: Type A has dominant large oscillations that interleave in time for condensation and rarefaction clicks; Type B has a dominant component that occurs almost simultaneously with the initial, negative (N1) component of the compound action potential of the auditory nerve. We tentatively conclude that Type-A responses occur in hair cells and Type B in supporting cells. Certain features of the response to clicks appear to correlate with the morphological direction of polarization of hair cells in the papilla. Fourier transforms of the intracellular responses to acoustic clicks exhibit frequency selectivity (tuning). We used the method of intracellular dye marking to infer the cellular recording site. [Supported by NIH grants and the Joint Services Electronics Program.]
Tails of Tuning Curves of Auditory-Nerve Fibers
Authors: Kiang N. Y. S. , Moxon E. C.
Published: October 2005

Békésy's interest in improving telephone communication led him eventually to make observations on the mechanical properties of the basilar membrane. For apical parts of the membrane he obtained resonance curves with steep high-frequency slopes and gradual low-frequency slopes. Tuning curves for auditory-nerve fibers in anesthetized cats also show significant low-frequency tails. Even fibers with high characteristic frequencies (CF) respond to tones throughout a wide range of low and middle frequencies. For low-frequency tones at moderate and high stimulus levels, the responses of high-CF fibers tend to be time locked either to the same phase of the stimulus or to a phase that differs by a half cycle. For complex stimuli such as speech, which contains many low-frequency components, these fibers behave as broadly tuned elements, discharging with time patterns that are principally determined by the temporal characteristics of the acoustic waveform. Results of experiments using low- and high-frequency masking stimuli reinforce the view that responses of high-CF fibers to low-frequency stimuli should not be ignored in theories that seek to describe the role of the auditory nerve in speech communication. [Supported by NIH grants and the Joint Services Electronics Program.]
Coding of Amplitude- and Frequency-Modulated Tones and Noise in the Cochlear Nucleus
Authors: Møller Aage R.
Published: October 2005

The discharge pattern of single units in the cochlear nucleus of the rat was studied in response to tones the frequency of which was changed over a large range (sweep tones) and to tones the amplitude or frequency of which was sinusoidally or noise modulated to a low degree (AM and FM tones). Sweep tones were found to evoke more nerve impulses within a narrow range of frequency of the tone when its frequency was changed at a certain (high) rate compared to a steady or slowly varying tone. This sharpening of the response area of a unit becomes more pronounced when the sound intensity is raised well above threshold. The threshold is usually not significantly different within a large range of change in sweep rates. Narrow-band noise, of which the center frequency was varied, gave similar response pattern. Small changes in frequency and amplitude of tones and noise gave rise to modulation of the discharge frequency with about the same waveshape as the modulation of the sound. The degree of modulation of the discharge frequency varied with modulation frequency and a more or less pronounced peak was seen within a modulation frequency range from 50 to 200 Hz. When two tones were applied simultaneously, one inhibitory and one excitatory, modulation of the inhibitory tone usually gave rise to a lower degree of modulation of the discharge frequency than did modulation of the excitatory tone. The degree of modulation varied with modulation frequency in about the same way as it did when the excitatory tone was modulated.
Resolving Power of an Optimum Array Processor
Authors: Cox Henry
Published: October 2005

The classical concept of resolution consists of recognizing that an observed effect is due to two separate sources. The resolving power of an optimum array processor which is based on the inversion of the signal-plus-noise cross-spectral matrix is examined. Exact conditions are presented for resolution of closely spaced sources by an optimum beamformer. These results are applied to a line array and compared with the resolution capability of a conventional beamformer. For equal strength sources it is found, for example, that an output signal-to-noise ratio of about 47 dB is required to achieve a resolving power with an optimum processor which is ten times that given by the classical Rayleigh limit. Conditions are also presented for the resolution of two sources of unequal strength. It is shown that two closely spaced sources of unequal strength will be resolved by the optimum beamformer if the strength of the weaker source is slightly larger than that required for resolution of two equi-strength sources in the same geometric configuration.
Sensitivity to Mismatch of Optimum Array Processors
Authors: Cox Henry
Published: October 2005

Mismatch in a beamformer occurs when the knowledge of the signal directional properties is imprecise. The effects of mismatch on a conventional beamformer and two optimum beamformers are compared. One optimum beamformer is based on inversion of the noise cross-spectral matrix while the other is based on inversion of the signal-plus-noise cross-spectral matrix. When there is mismatch the inclusion of the signal in the matrix inversion process can lead to dramatic reductions in the output signal-to-noise ratio when the output signal-to-noise ratio of a perfectly matched beamformer would be greater than unity. However, the corresponding effect on the total beamformer output is less dramatic since an increase in the noise response partially offsets the decrease in signal response.
Precise Tracking of Suspended Hydrophone Motion
Authors: Spindel R. C. , Porter R. P. , Jaffee R. J.
Published: October 2005

A Doppler tracking system has been developed to enable continuous real-time measurement of the motion of suspended hydrophones. The system consists of three bottom-moored CW beacons, a phase detector for each beacon signal, and a computer processing scheme. Displacements as small as 1 cm have been detected in ship-mounted, ship-suspended, sonobuoy-deployed, and bottom-moored hydrophones at ranges up to 10 km. The system was used to coherently phase detect low-frequency acoustic transmissions by using displacement information to correct the Doppler shift due to hydrophone motion; however, its applicability extends to any environment where highly accurate mooring motion must be measured. An analysis of the combined effects of surface and forward volume scattering shows that these phenomena do not compromise the tracking system. Random phase fluctuations in beacon signals attributable to these effects were estimated to be less than 0.2 rad. An analysis of hydrophone motion derived from data obtained during two ocean tests of the system is presented in this paper.
A High-Speed Third-Octave Filtering Algorithm for Real-Time Noise Analysis
Authors: Borgioli R. C.
Published: October 2005

An efficient third-octave digital filtering algorithm has been designed and implemented, meeting ANSI S1.11-1966, Class III, for real-time applications. The approach is seen to produce significant savings in computational effort compared to recursive realizations (by as much as a factor of 10 on constant confidence limit configurations spanning 10 or more octaves) while avoiding extensive data storage and response inadequacies associated with FFT (fast Fourier transform) methods. Results taken from a prototype program implemented on a high-speed computer show the response to pure tones and white noise over a 10 Hz to 50 kHz bandwidth. Adaptations for real-time applications are discussed for tailoring measurement confidence limits to the data bandwidth and speed of the machine.
Envelope Structure of Surface-Generated Noise in the Ocean
Authors: Anderson Victor C.
Published: October 2005

The directional and temporal spectra of ambient noise in the ocean have been observed with a 48-element acoustic array mounted on the research platform FLIP. A fully digital DIMUS multi-beam processor is used for on-line processing of ambient-noise data. Off-line processing of digital tapes with an FFT analysis provides a representation of the ambient-noise envelope statistics. Data collected over a 30-day observation period in the open ocean shows an envelope power spectrum which reflects an increase of power in the vicinity of 0.1 Hz corresponding in general to the period of surface waves. The overall envelope power spectrum is strikingly higher than that predicted from a simple isotropic stationary Gaussian noise field. [This represents results of research sponsored by the Office of Naval Research.]
Sounds from Seaquakes
Authors: Northrop J.
Published: October 2005

Sonobuoy recordings of underwater sounds from several swarms of seaquakes in the Central Equatorial Pacific were analyzed for signal arrival-time structure and sound-pressure level. Three acoustic waves were noted for each earthquake. Listed in order of arrival time, these are identified as (1) a crustal P wave refracted into the water, (2) a crustal S wave refracted into the water, and (3) surface reflections of these phases in the ocean. Epicentral distances as computed from these arrival times, ranged from 12 to 18 km. Estimates of the seaquake magnitudes, as computed from the received sound-pressure levels, varied from −1.9 to −3.9 on the Richter scale. The time between earthquakes varied from 1 to 8 sec. The average occurrence rate was 51 events per hour for the six hours of recording. Most of the energy in the received signal was below 100 Hz. These sounds may contribute to the low-frequency ambient noise in the ocean because the low-angle rays become RBR (refracted, bottom reflected) and are trapped in the deep-ocean sound channel. [Work supported by Office of Naval Research.]
Measurements of the Low-Wavenumber Region of the Turbulent Boundary-Layer Wall Pressure Spectrum
Authors: Jameson P. W.
Published: October 2005

Measurements of the low-wavenumber region, (ωc<k<ωUc), of the TBL wall pressure spectrum have been performed using a thin rectangular steel plate clamped at its edges and located in a wall of an open jet flow of air. The magnitudes of oscillation of individual plate modes were monitored with an accelerometer for a range of air speeds from 21 to 112 ft/sec. We concluded that the response of the plate was controlled by the low-wavenumber region since the contributions from the acoustic noise in the room and the convected pressure field scattering at the plate boundary were too small to account for the observed levels. A knowledge of the modal decay time allowed us to infer the value of the pressure spectral density. The speed dependence was about U∞3.
The Effects of Horizontally Varying Internal Wave Fields on Multi-Path Interference of Refracted-Refracted Propagation about the Deep Sound Channel Axis
Authors: DeFerrari Harry A. , Yacoub Kamal , Nghiem-Phu Lan
Published: October 2005

Fluctuations of CW signals transmitted through real ocean paths are characterized by smooth slow variations in phase and rapid noise-like variations in amplitude. These variations are the result of internal waves, which perturb the sound-speed field and thereby produce time-varying multi-path interference. This study is concerned with modeling the effects of horizontal and vertical variations in the sound-speed field on multi-path interference of CW propagation for the particular case of refracted-refracted ray paths. The vertical sound-speed profile is approximated by two layers of linear gradient and arbitrary horizontal variations are introduced by numerical methods. The travel times along individual ray paths are influenced by fluctuations of the internal wave fields with horizontal scales which are (1) approximately equal to the cycle distance of the ray paths or (2) greater than several cycle distances of the ray. Both types of disturbances induce multi-path interference but the later also produces phase shifts for all ray paths. The model approximates fixed-system experiments on CW propagation between Eleuthera and Bermuda. We show that horizontally invariant internal tide cannot cause both phase and amplitude statistics which are consistant with experiment.
Statistical Analysis and Interpretation of Fixed-System Measurements of CW Propagation Between Eleuthera and Bermuda
Authors: Yacoub Kamal , DeFerrari Harry A. , Leung Ricky
Published: October 2005

Statistical analysis is performed on a 43-day time series of fluctuations in phase and amplitude, of a CW signal propagated over a 1500-km path between Eleuthera and Bermuda. Histograms, autocorrelations, and power spectra of amplitude and phase time series are compared with similar data for a 13-km range in the Florida Straits. The principal cause of fluctuations of amplitudes is shown to be multi-path interference and statistics of the amplitude fluctuation are related to statistics of fluctuation of travel times among the various ray paths. The model of propagation through a two-layer ocean with horizontal variations discussed in the previous paper is used to interpret experimental results and to determine the characteristics of the internal wave fields which could produce the observed phase shifts and multi-path interference statistics.
Control of Impact-Excited Noise on Scale-Model and Full-Scale Box-Girder, Type Bridge Structures
Authors: Kirschner Francis
Published: October 2005

Impact noise radiated by elevated rapid-transit systems is a source of community annoyance. Noise reduction for these structures can be accomplished by reducing the amplitude of vibration of the radiating surfaces either by isolation or by viscoelastic damping materials when the structures are made of steel. Evaluations have been made in an acoustics laboratory of the impact noise radiated by scale models of (a) an all-steel bridge, (b) a composite steel box-girder concrete deck bridge, (c) a prestressed all-concrete bridge. The scale-model impact noise level tests will be presented shock excited with an ISO Standard R140 tapping machine. Noise reduction results obtained on the scale-model structures will be compared with noise reduction on full-scale bridge structures, and the effectiveness of the viscoelastic damping material and the correlation between scale-model and full-scale structures by actual test will be described.
Reduction of Several Impact Noises in Office Products
Authors: Randolph David C.
Published: October 2005

Reduction of impact noises in office equipment constrained by nontechnical factors as well as acoustical/functional tradeoffs. Typewriters and electrostatic copy machines require different approaches. Long-term and short-term approaches sometimes differ also. Impact printing is the traditional typing process; the Selectric typewriter mechanism also uses many impacts to stop and start motions. Noise reduction at the source must encompass all these impacts; the major redesign required can yield only long-term results. For immediate results, path control is chosen. Attenuation of high-frequency airborne energy depends on the degree of enclosure. Low-frequency structurally borne excitation of the covers and desk top is reduced by resilient mounting. Copiers have many nonimpact noises, and impact is not basic to machine operation. This plus different nontechnical constraints suggests impact noise reduction at the source. Fluid damping is used to reduce major impacts in the IBM Copier II. In one instance, both functional and acoustical improvement results from control of mechanism dynamics.
Use of a Damping Alloy Rotation Chuck in Development of a Quiet Pneumatic Rock Drill
Authors: Jensen James W. , Visnapuu Aarne
Published: October 2005

The modification of a percussion drill, of the type used in mining, to reduce the noise to permissible levels requires drastic reduction of exhaust noise, drill-steel resonance noise, and machine noise from the drill mechanism. Efficiency and utility of the portable tool must be retained in the quiet version. The impact of the piston on the drill steel generates excessive airborne and structure-borne noise, and containment and suppression of this noise at or near its source is vital. A rotation chuck machined from manganese—copper damping alloy, when substituted for the standard steel chuck, enclosing the impact area within the drill, very effectively suppressed the shock noise from the impacting surfaces. Test-stand data show that greater noise reduction was achieved by this method than was obtained by some external covers when the steel chuck was in use.
Comparative Study of 20 European Concert Halls—A Preliminary Report
Authors: Schroeder M. R. , Gottlob D. , Siebrasse K. F.
Published: October 2005

Using reverberation-free magnetic-tape recordings of various musical selections as source material, comparative sound transmission studies were undertaken in 20 European concert halls. The sound signal, radiated from the stage by a multi-loudspeaker system, was recorded at the “eardrums” of a specially designed dummy head with realistic surface impedances of the ear canal and pinnae. These recordings were electronically processed such that, when played back over two loudspeakers in an anechoic chamber, nearly identical acoustic signals were recreated at the eardrums of a human listener. This method of recording and reproduction, although far from perfect, makes possible practically instantaneous comparisons of the acoustic qualities of different halls. Subjects of different degrees of musical training served in paired-comparison tests for musical preference and also made triadic similarity judgments of acoustic quality. The raw data were processed by appropriate multidimensional scaling programs which preserve individual judgment differences [J. C. Carroll and J. J. Chang, “Analysis of Individual Differences,” Psychometrica (1970)]. The correlation of the subjective dimensions, found in this manner, with physical and geometrical parameters of the halls has not been completed at this writing. [Research supported by Deutsche Forschungsgemeinschaft.]
New Methods in Architectural Acoustic Investigations to Evaluate the Acoustic Qualities of Concert Halls
Authors: Plenge G.
Published: October 2005

In recent years, efforts in architectural acoustics investigations have concentrated upon correlation between the physical data of a concert hall, on the one hand, and hearing events and judgments in the hall on the other hand. Contrary to earlier investigations in this field, these efforts do not concentrate upon finding the subjective correlate to an individual physical characteristic, e.g., reverberation time versus frequency early decay time, “Deutlichkeit,” and so on; nowadays, instead, the total hearing impression of an observer in a concert hail—the “Hörsamkeit”—s correlated with the total set of physical data measured in this room. L. Beranek, who started his work in architectural acoustics with exact calculations and measurements of rectangular rooms at the laboratory of F. V. Hunt, Harvard University, described the first important effort in this direction about 10 years ago. A deficiency of this and similar trials is the uncertainty of the subjective observations and judgments. In this respect in recent years, a great improvement has been attained by refining the collection of subjective judgments and by the aid of improved electro-acoustic transmission systems. A survey of these systems—especially head-related stereophonic systems—will be given and preliminary results will be reported. [The material in this paper is shared with this session and the F. V. Hunt Memorial Session I.]
Some Acoustical Features of Byzantine Churches
Authors: Shankland R. S.
Published: October 2005

Byzantine (Greek Orthodox) Churches in Greece and elsewhere vary greatly in size and were built over many centuries. Their construction strongly suggests the development of a tradition in acoustical design especially adapted for services employing no musical instruments, but depending entirely on speaking, chanting, and singing. The chancel construction is highly efficient for propagating sound from altar into nave. Its ceiling is a quarter sphere prolonged into a smaller and then a larger half cylinder. Its rear is a vertical half cylinder. These surfaces act approximately as elliptical or parabolic reflectors but with sufficient diffusion to prevent sharply focused sound images. The acoustical effects are similar to the Cathedral at Agrigentum in Sicily, long ago noted by John Hershel and Wallace Sabine as a remarkable “whispering gallery.” The domes in Byzantine Churches interfere little with sound propagation from chancel to nave, but do contribute essential reverberation for singers located nearby. Thus, the architectural features helpful for singing are only weakly coupled to those essential for speaking, to the great advantage of both forms of communication.
The Effect of Late-Arriving Reverberation on Perception of Spectrum
Authors: Queen Daniel
Published: October 2005

Recordings of a sample sentence by four talkers were processed so that each talker sample was available in either original or spectrum-distorted form. Sequences were presented, each having first one spectral form of the talker, then the other; then the two were mixed, with one of them delayed 65 msec and reverberated. The sequences were mixed and the samples randomly selected. Each subject was instructed to choose, for each sequence, the spectral sample he perceived in the third, mixed sample. Since either spectral form could appear in either the early or delayed sound, the choice would indicate from which sound the subject received spectral cues. Initial results favor the early sound, indicating that equalization of sound systems in large rooms should affect the direct field of the system transducers only.
Sound Amplification Systems for Orange Bowl Stadium, Miami, Florida
Authors: Kaye David H.
Published: October 2005

Sound amplification systems designed and installed within a five-month period in 1972 at the 80,000-seat Orange Bowl Stadium combine a high-level central loudspeaker cluster with distributed loudspeakers digitally delayed in 13 30-msec steps. A gain-shifting and visual monitor arrangement aids operators in keeping amplified sound levels matched to crowd-noise levels, to reduce annoyance of the residential community surrounding the stadium. Control facilities are tailored to the stadium users' operating requirements. The system design emphasizes simplicity and reliability, including convenient means for substitution of spare amplifiers. A flexible portable amplification system can be used independently of the main system, or as a supplementary on-field monitor in conjunction with the main system. [Thomas R. Horrall of BBN collaborated with the author in the design of the system. Project coordination and structural and electrical design were by the Department of Public Works, City of Miami, Florida.]
Design and Analyis of Reverberant Room Experiments
Authors: Ingalls Douglas J.
Published: October 2005

Accurate measurements of sound power in a reverberant room using the substitution technique require that the means of the squared sound-pressure level (SPL) of the known source and unknown source be determined. Careful design of an experiment permits the errors due to the microphone traverse, the instrumention, and the source location to be separated. The technique of two-way analysis of variance with replication applied to a measurement of the SPL established by an air-conditioning condensing unit with only the fan operating reveals that (1) the observed variance in SPL is considerably greater than that observed for the Ilg Reference Sound Source and (2) strongly dependent on source location, with a small change of source location causing noticeable changes in the measured SPL. The variance due to source location for the 250-Hz 13-oct band suggests a pure tone exists in this band. Further experimentation shows that changes of a few degrees in the room temperature can also cause appreciable changes in the measured SPL for this band. Investigations of the details of the fan spectrum are continuing. Results of these experiments indicate that accurate measurements in a reverberant room require careful attention to details.
Effect of Absorption and Rotating Vanes on Qualification Procedure of Reverberation Chamber
Authors: Tichy J.
Published: October 2005

The new ANSI Standard 1.2-1972, “Methods for the Determination of Sound-Power Levels of Small Sources in Reverberation Rooms,” and ASHRAE 36–72, “Methods of Testing for Sound Heating, Refrigerating and Air-Conditioning Equipment,” define criteria for the reverberation chamber which have to be satisfied in order to qualify for the measurements of sound power at discrete frequencies. As it has been found by measurements of existing reverberation chambers with no additional treatment, the criteria for measurements of sound power with only one source position are not satisfied. However, when applying absorption and rotating vanes, it is possible to achieve the qualification. At low frequencies the addition of absorption is substantial. The rotating vanes are very useful at middle and high frequencies where the increased absorption must be avoided. The effect of absorption can be explained by its influence on modal overlap. The rotating vanes modulate the sound field. This paper presents practical data on qualification procedure.
Oblique-Angle Determination of the Reflection Coefficient R of Flat Sound Absorbers
Authors: Jaeger E. W.
Published: October 2005

Methods for determining the reflection coefficient R usually involve the procedure of insonifying the absorbing material at a fixed frequency at the desired angle of incidence. Then, the quantities required for the calculation of R are either measured with a movable receiver probing the interference field in front of the absorber or with a fixed receiver at the proper point to receive specular reflections. (In the latter case, direct rays from the source must be shielded from the receiver.) The method proposed in this paper combines both of the above approaches but is simpler and quicker than either. The receiver is fixed in space and receives both the specular reflections and the direct rays, as the sound source transmits with steadily increasing (or decreasing) frequency. A level recorder connected to the receiver produces a frequency-dependent interference diagram. Keeping the source-receiver configuration unchanged, one generates another such diagram with a perfectly reflecting plane substituted for the sound-absorbing sample. Comparison of the two sets of data yields the quantities necessary for the calculation of R versus frequency. Frequency response and beam pattern of the loudspeaker and microphone used need not be known.
Formulae for Estimating Minimum Measuring Distance, Bias, and Variance in Semireverberant Fields
Authors: Lubman David
Published: October 2005

A minimum distance between source and microphone is necessary for practical measurements of reverberant sound power and sound transmission loss. This is intended to limit error due to contamination by the direct field. An experimental/graphical procedure for its determination is prescribed in two important measurement Standards (ANSI S1.21-1972 and ASHRAE 36–72). To supplement this procedure, we offer a simple formula for estimating this minimum distance. It is useful when the source directivity factor can be estimated. Also intended for these cases, an experimental procedure for spatial averaging in semireverberant fields is described wherein the direct field bias can be precisely estimated. This procedure requires spatial averaging on a segment of a straight line passing through the acoustic center of the source. Finally, a formula is given for spatial variance measured in this region of a semireverberant field.
Lecture Demonstrations in Sound
Authors: Pinkston E. R. , Crum L. A.
Published: October 2005

For the past three years the National Science Foundation has supported at the Naval Academy a summer short course in lecture demonstrations in physics. This short course is intended to acquaint teachers with lecture demonstrations available for use in introductory physics courses. The demonstrations to be shown have been selected from a lecture on sound which has been given by invitation at a number of institutions. Many of the demonstrations are appropriate for use in an introductory acoustics course.
A General Acoustics Course for Speech Pathology, Audiology, and Engineering Acoustics Students
Authors: Watson E. E. , Tichy J.
Published: October 2005

A general acoustics course covering basic material needed in speech pathology, audiology, as well as engineering acoustics, has been taught for the last two years at The Pennsylvania State University under the direction of the Engineering Acoustics Graduate Program. This course is divided into two sections, one mathematically oriented and the other based on a more qualitative discussion. The two sections meet together once a week and have separate lectures two other meetings a week. A joint laboratory meets once a week to supplement the material discussed in class. This paper reports the problems encountered because of the students' diverse background in fundamental science and mathematics. These problems will be compared to problems encountered when the engineering students are not included during one term. Also, the responses of the students are discussed and their suggestions for improvement are outlined.
Session J. Peter A. Franken Memorial Lecture on Environmental Noise
Authors: Shaw Edgar A. G.
Published: October 2005

Noise increasingly degrades the quality of our living environment and therefore demands the attention of citizens and scientists alike. This lecture, for laymen as well as specialists, identifies the main sourcse of disturbing noise, describes the adverse impacts of noise on people, and illustrates many ways in which noise can be controlled. Toward achieving a quieter environment, scientists and engineers in recent years have made many technical advances, including important ones made by Dr. Franken (1930–1972), a distinguished member of the organizations sponsoring this lecture.
Responses of Squirrel Monkey Auditory-Nerve Fibers to Tones
Authors: Geisler C. D. , Rhode W. S. , Kennedy D. T.
Published: October 2005

Responses were obtained to tones from squirrel monkey auditory-nerve fibers having best frequencies between 6 and 9 kHz. The response areas were very asymmetrical, extending sometimes down to 200 Hz. Thresholds at the lower frequencies were, however, high. For frequencies below best frequency, the discharge rate data show generally consistent relationships. Plots of rate versus intensity (in decibels) are approximately parallel. Iso-rate contours are also generally parallel, with shifts along the intensity axis bringing them into registration. By contrast, for frequencies above best frequency, the rate versus intensity curves decrease in slope as frequency increases. Moreover, the intensity shifts used to bring the lower-frequency sections of the iso-rate contours into registration leave the higher-frequency sections out of registration. Period histograms were calculated at frequencies below 4 kHz. The phase of the histograms' fundamental component varies approximately linearly with frequency. These data will be compared with the measured displacements of the same region of the basilar membrane in the same preparation [W. S. Rhode, J. Acoust. Soc. Amer. 49, 1218–1231 (1971)].
A Model for Mechanical-to-Neural Transduction in the Auditory Receptor (“Hair Cell”)
Authors: Schroeder M. R. , Hall J. L.
Published: October 2005

We describe a physiologically oriented model for transduction of displacement of the basilar membrane to activity of auditory nerve fibers. In the model, quanta (“vesicles”) are added to a population inside the hair cell at a fixed average rate. They are removed from the population with a probability proportional to the number of quanta in the population and related in a simple manner to the instantaneous amplitude of the mechanical stimulation. The removal of a quantum results in an action potential with a probability related to time elapsed since the preceding neural event (“refractory period”). Apart from refractoriness, the model is completely specified by three parameters which determine spontaneous and maximum firing rates and the time constant of recovery after intense stimulation. Several fundamental properties of this model can be derived analytically and they agree well with neurophysiological observations. The most crucial among these is the astonishing level independence of period histograms for levels of stimulation above about 40 dB SPL. The model also predicts correctly the overshoot in PST histograms for tone or noise-burst stimulation and the subsequent suppression of spontaneous activity. Theoretical work by B. F. Logan and L. A. Shepp (to be published) shows that, for spontaneous activity, intervals between successive neural firings are distributed exponentially, in agreement with experimental evidence.