bluuebunny/crossref_metadata_2025 huggingface dataset:
Intermolecular Forces and Absorption in Solids
Authors: Liebermann Leonard , Rasmussen Robert A.
Published: September 2005

Published theory of resonance absorption in crystals [L. N. Liebermann, Phys. Rev. 113, 1052 (1959)], while adequate for establishing the absorption mechanism, is not suitable for precise calculations. If the theory could be improved, acoustical absorption measurements could yield intermolecular force constants in solid crystals. Van der Waals forces in liquids and gases are known, but data on the solid state are practically nonexistent. One critical approximation in the present theory is the assumption that the Debye spectrum ρ(ν)=9Nν2/νm3 represents the actual vibrational modes of the lattice. Unfortunately the Debye maximum frequency νm occurs as νm7 in the present theory, thus making its numerical value extremely critical. Instead, solutions to the lattice vibrational modes can be given purely from vibrational constants of the lattice; for the cubical lattice, the vibrational modes resemble the acoustical modes of a rectangular room. The distribution function of the modes is considerably more complex than the Deybe function given above, but it is a function solely of the intermolecular force potential. Thus the critically uncertain Deybe parameter has been eliminated. Other improvements in the theory also are discussed.
An Experiment on Sound Absorption in Porous Materials
Authors: Bies David Alan
Published: September 2005

A theory of sound absorption in porous materials has been given by C. Zwikker and C. W. Kosten [Sound Absorbing Materials, Elsevier Publishing Company, Inc., New York, 1949] in terms of a mean pore radius, the kinematic coefficient of viscosity, and the ratio of specific heats. In order to investigate the theory, an experimental investigation has been carried out in which the kinematic coefficient of viscosity and the ratio of specific heats have been varied by using various gases. The normal specific acoustic impedance and the complex propagation constant of various samples of steel wool have been measured. The results are presented in terms of the complex compressibility and the complex density. These quantities are compared with the theoretical values predicted by the theory, and a frequency range from approximately 100 cps to 5000 cps has been covered in this investigation.
Single-Number Rating for Sound Isolating Structures
Authors: Watters Bill G.
Published: September 2005

The architect and other users of sound isolation test data need a single number rating which properly accounts for frequency, angle of incidence, and all of the other variables which determine the TL. To be of most utility, such a rating must correlate closely with the average subjective evaluation of the structure. A suggested system for calculating a rating number which applies to speech privacy will be discussed.
Preliminary Study of Requirements for Music Isolation
Authors: Watters Bill G. , Farrell William R. , Hirtle Parker W.
Published: September 2005

In many sound isolation problems, transmitted music is the disturbing factor. Examples of this are music practice and rehearsal spaces, recording studios, apartment houses, etc. The results of some recent experiences in this area, in particular, recording studios and music practice rooms, are discussed. As in the problem of speech privacy, it appears that, to achieve adequate music privacy in most cases, the noise reduction provided by the construction must be matched to the background sound levels in the receiving space. Further, the frequency distribution of the required noise reduction appears to vary significantly from one type of music source to another.
Damping of Flexural Waves in Plates by Homogeneous Fibrous Material
Authors: McQuillin R. J. , Kerwin Edward M.
Published: September 2005

The present study treats the interaction between porous blankets and the reactive near fields associated with flexural waves on plates. For the frequency range below the coincidence frequency it is shown that the damping produced by this interaction may be considerable. The amount of damping obtained is found to depend on such properties of the fibrous material as porosity, flow resistance, and structure factor. In the present studies, two cases were considered: one in which an infinitely thick fibrous blanket was near but not touching the plate, and the other in which an infinitely thick fibrous blanket was in direct contact with the surface of the plate. The results of numerical calculations performed by a digital computer (programmed to handle complex numbers) are shown to be in reasonably good agreement with experimental data, (This work was sponsored in part by the U, S. Air Force, Wright Air Development Division.)
Solution of Acoustic and Vibration Problems in over-the-Road Restaurants
Authors: Hardy Howard C.
Published: September 2005

On the Illinois Tollway the restaurants are placed over the highway with a panoramic view in both traffic directions. Pace Associates were the architects and engineers. This construction introduced numerous acoustic and vibration problems: (1) Prevention of “shimmying” of tables caused by structure-borne vibration; (2) isolation of traffic noise; (3) reverberation control (the ceiling was an unusual design of cast concrete with 3-ft by 3-ft concave openings); (4) optimum background noise control; and (5) control of ventilation system noise from under-the-floor ducts. The solutions of these problems will be illustrated and measurement data shown. In the finished structures the loudest vehicles are hardly audible and there is no perceptible vibration.
Reproducing the Cocktail Party Effect
Authors: Kaiser James F. , David Edward E.
Published: September 2005

The Cocktail Party Effect allows the binaural listener to concentrate on speech from one talker, suppressing others in his environment. As contrasted to the monaural listener, the binaural auditor gains between 5 and 15 db signal-to-noise ratio necessary for 50% intelligibility. A gain of this magnitude cannot be reconciled with linear array theory which prescribes addition of the two available aural inputs. An alternative accounting can be made by postulating signal processing based upon properties of binaural hearing. In this modal the binaural processor derives a temporary signal which is used to gate the aural input. In effect, the gating signal leaves the major portions of the preferred talker's speech envelope intact while suppressing sound from other talkers or background noise when these do not overlap with the preferred speech. A preliminary circuit version of such a processor which derives the gating signal by cross correlation has been built and tested. Subjective measurements in two- and three-speaker environments yielded increases of 9 and 5 db, respectively, in signal-to-noise ratio.
Message Context and Speech Frequency-Weighting for Intelligibility
Authors: Pickett J. M.
Published: September 2005

A message from a small set of known speech messages can be transmitted over a much narrower band of frequencies than can a message from a much larger set. The present experiment is designed to measure this relation to a limited extent and to determine whether or not there are radical shifts in the importance of different regions of the speech spectrum with shifts in the size of the message set. Transmission of speech messages was measured under various band-pass filter conditions in the presence of a random noise having a spectrum approximately parallel to the long-time rms spectrum of speech. Three classes of speech context were examined: (1) CVC nonsense syllables constructed from 24 consonants and 14 vowels; (2) English monosyllabic words chosen from a set of 256 PB Words known to the listeners; and (3) words chosen from sets of 2 known words drawn from the 256-word set of (2). The results show no radical changes in the importance of different speech frequency regions over the three types of context. Implications are discussed for calculating a frequency-weighted index of intelligibility such as Articulation Index.
Segment Inventories for Speech Synthesis
Authors: Sivertsen Eva
Published: September 2005

Speech synthesis may be based on a segmentation of the speech continuum either into simultaneous components or into successive time segments. The time segments may be of varying size and type: phonemes, phoneme dyads, syllable nuclei and margins, half-syllables, syllables, syllable dyads, and words. In order to obtain an estimate of the size of the segment inventory for each type of segment. a phonological study was made of the particular phoneme sequences which occur in English, particularly in relation to the immediate constituents of the syllable (nucleus and margin) and to the syllable. An estimate was also made of the number, of prosodic conditions required for each type of phoneme sequence. It was found that in general there is a direct relationship between the length of the segment and the size of the inventory. However, when the borders of the proposed segments do not coincide with the borders of linguistic units, the inventory has to be relatively large. The value of using the various types of segments for speech synthesis is discussed both for basic research on speech and for practical application to a communication system with high intelligibility.
Role of Loudness in the Speaker's Judgment of Vocal Effort
Authors: Catania A. C. , Lane H. L. , Stevens S. S.
Published: September 2005

A previous paper noted a surprising difference between the exponent of the loudness function (0.6) and the exponent that describes the apparent growth of vocal effort (1.1). The fact that perceived loudness plays no more than a minor role in a speaker's judgment of his vocal effort is further demonstrated by these experimental findings: 1. The form and the exponent of the subjective scale for vocal effort remain relatively invariant under large changes in auditory feedback. When all auditory feedback was suppressed by an intense masking noise (110 db SPL), the exponent was about 1.3. (This larger value is partly an artifact caused by the speaker's tendency to raise his voice in an effort to override the masking.) When the “side tone” from the speaker's voice was amplified to a very high level, the exponent turned out to be approximately 0.9. 2. In order to show that the nature of the vocal sound (the phoneme ɑ) does not account for the results, listeners estimated the loudness of a live voice and of different levels of a recorded speech sample. For both types of sound the measured exponent was approximately 0.7. This compares with the exponent 1.1 obtained when the listener judges his own speaking level.
Problems Associated with the Measurement of Ambient Noise Directivity by Means of Linear Additive Arrays
Authors: Stone Julian
Published: September 2005

The problems associated with determining the angular distribution of continuous and discrete noise sources by means of a linear array are discussed. Among the problems considered are the effect of fluctuations in the received signal upon the reliability of the estimate of the angular distribution of the noise. It is shown that smoothing due to side lobe pickup results in a large reduction in the ability of an array to pick out small peaks in the angular distribution. The relationship is shown between optimum array length and the angular size and power of the noise sources making up the distribution. The discussion is given in terms of considering the array as a collection of correlators operating simultaneously. Special purpose arrays, such as Arsac-type arrays, are discussed briefly. Extensive use is made of techniques and knowledge available from radio astronomy. (This work was supported by the Office of Naval Research.)
Spatial Correlation of Ambient Noise
Authors: Berman Alan
Published: September 2005

Signals from fixed, spatially separated hydrophones were filtered into half-octave bands, infinitely clipped, and cross correlated in a polarity-coincidence type of detector. The output of the correlator was measured as a function of hydrophone separation in both the horizontal and vertical. In general, the result was found to have a null at 12 wavelength of the midband frequency and was zero for distances greater than 1 wavelength. Theoretical interpretations of the results are given. (This work was supported by the Office of Naval Research.)
Radiation Field of a Dipole near a Wedge
Authors: Yildiz M. , Mawardi O. K.
Published: September 2005

In connection with a study of the vibratory pressures excited on a ship's hull by a propeller, a study is made for the idealized case in which the hull is represented by an infinite rigid wedge and an element of the propeller by a point dipole. The direction of the dipole axis is arbitrary. When the wavelength is much larger than the distance of the dipole from the wedge, then a low-frequency approximation considerably reduces the mathematical complexity of the problem. This simplified formulation is discussed in detail. (Work supported in part by Bureau of Ships.)
Attenuation of Torsional Waves in Teflon
Authors: Leonard R. W.
Published: September 2005

Measurements of the attenuation of torsional waves in a cylindrical rod of circular cross section have been made. Temperature, crystallinity, and axial stress (tension) are varied, and the transmission loss is measured as a function of these variables. The results of the measurements and a description of the experimental technique will be presented.
Vibration Sensitivity of Condenser Microphones
Authors: Rule Eric , Suellentrop Fred J. , Perls Thomas A.
Published: September 2005

The problem of operating condenser microphones in a vibration environment is considered, and it is pointed out that there is a precise relation between the vibration and pressure response for any given transducer. This relation is shown to be dependent on the mass per unit area of the microphone diaphragm, and graphs are given from which the suitability of a given microphone to perform its function in a vibration environment can be assessed. The results of measurements on a well-known type of condenser microphone are presented to support the theory, and the usefulness and disadvantages of vibration-isolating mounts and of systems using two transducers are discussed. A proposed design of a condenser microphone to be insensitive to vibration is described.
Lead Metaniobate in High-Pressure Transducers
Authors: Sims Claude C. , Groves Ivor D.
Published: September 2005

The characteristics of lead metaniobate make it peculiarly suited to hydrophone applications where high hydrostatic pressures are encountered. Some hydrophone design parameters are discussed, properties of various materials are compared, and the measured performance of hydrophones containing lead metaniobate elements is presented.
On Some Factors Affecting the Estimation of Loudness
Authors: Hellman R. , Zwislocki J.
Published: September 2005

The effect of several factors on the loudness estimation was explored in a series of experiments. It has been found that the numerical estimation of loudness ratios by listeners without auditory pathology depends on the sensation level, when the number assigned to the standard is kept constant, and on the number assigned to the standard when the sensation level is invariant. Only when the sensation level and the number are varied simultaneously in an appropriate way is it possible to maintain an approximately constant loudness function. The experiments have led to the determination of the loudness function near the threshold of audibility. In general. the results are in agreement with the data obtained by Robinson, Zwicker, Scharf. and J. C. Stevens and with those of S. S. Stevens at medium and high sensation levels. (Work supported by a contract between the Office of Naval Research and Syracuse University.)
Binaural Summation of Loudness
Authors: Reynolds G. S. , Stevens S. S.
Published: September 2005

The common assumption that a given stimulus sounds twice as loud in two ears as in one turns out to be both true and false It is true for a particular level (roughly 90 db) but false for all other levels. The power functions governing the two loudness scales have different exponents: binaural is approximately 0.6 (the sone scale), monaural is approximately 0.53. These relations were determined in five kinds of experiments: (1) monaural-binaural loudness matching, (2) magnitude estimation, (3) magnitude production, (4) cross-modality matching between loudness and apparent strength of a vibration on the finger tip, and (5) halving and doubling of loudness, monaural vs binaural. Binaural loudness ranges from about 1.4 times as great as monaural loudness at about 40 db to 2.3 times as great at about 100 db.
Temporal Discrimination in Different Types of Auditory Patterns
Authors: Kinney Jo Ann S.
Published: September 2005

Discrimination functions for temporal differences within auditory patterns were measured under two experimental conditions. One of these was the frequency separation of the elements in the pattern; the other was the type of pattern or the way in which the elements were combined. All of the auditory patterns utilized a basic unit consisting of two tones of different frequency separated by a variable amount of silence. This basic unit was presented alone and in various combinations of other tones so that the discrimination results with the various patterns could be compared directly. Discrimination of the temporal differences between the two tones was measured by the ABX technique. The results showed that discrimination of differences in time of onset was consistently better when the frequency separation of the tones in the pattern was small than when the tones were widely separated. There was a further difference in discrimination in the various types of patterns, the same temporal difference being much easier to discriminate in some patterns than in others. These results are compared with those from a visual experiment in which the same patterns were formed by using the spectrographic transformation between audition and vision. (Work supported in part by the Haskins Laboratories and the Air Force Cambridge Research Center.)
Auditory Discrimination and Sleep Deprivation
Authors: Cohen Alexander , Fine Bernard J.
Published: September 2005

Eight subjects were given an auditory discrimination test at four separate times each day (3 a.m., 8 a.m., 4 p.m., 11 p.m.) for a four-day period in which they were deprived of sleep. The test was a tape recording of 72 groups of sounds. Each group consisted of three successive tonal bursts which were presented binaurally. The third tone in each group was identical to either the first or second tone, the unmatched tone differing in varying amounts of frequency, intensity, or duration from the identical tones. The subject had to indicate which of the first two tones matched the third. Four values of frequency (1000 cps, 1010 cps, 1020 cps, 1030 cps), intensity (70 db, 73 db, 76 db, 79 db), and duration (1.0 sec, 1.3 sec, 1.6 sec, 1.9 sec) were used in constructing the tonal groups. Compared to test data obtained under nondeprivation conditions, losses in discrimination were most prominent at 8 a.m. and 4 p.m. on each deprivation day. In contrast, the 11 p.m. tests showed relatively smaller impairments across the period of deprivation.
Wave Front Curvature in a Horizontally Stratified Waveguide
Authors: Stone Julian , Klerer Melvin
Published: September 2005

A simple procedure has been devised for determining the curvature of a wave front emitted from a point source as the wave front passes a vertical line in a horizontally stratified medium. The procedure consists of adding a correction for spherical spreading to an expression valid for any long ranges which is formally identical with Snell's Law. The wave-front curvature also may be related to travel times from the source to points on the vertical line. Numerical examples are given. (This work was supported by the Office of Naval Research.)
Fluctuations of Sound Reflected from the Sea Surface
Authors: Clay C. S.
Published: September 2005

Experimental data [Clay et al., J. Acoust. Soc. Am. 31, 1572 (1959); M. V. Brown and J. Ricard, J. Acoust. Soc. Am. 31, 1572 (1959)] suggest that the fluctuations of received signals are due to the reflection from the sea surface. These data are compared with calculations based on the theory of C. Eckart [J. Acoust. Soc. Am. 25, 566–570 (1953)]. (This work was supported by the Office of Naval Research.)
Some Results of Bottom Reverberation Tests in Deep Water
Authors: Scannell Everett H.
Published: September 2005

Measurements were made of bottom reverberation off the East Coast of the United States at various locations in water depths of 1900 and 2700 fathoms. Smooth, moderately rough, and rough bottoms were covered. The signal frequency was 4300 cycles per second and pulse lengths of 2. 6. and 10 msec were used. Grazing angles ranged from 13 to 35 deg. Results are presented as reverberation strengths vs grazing angle for various bottom areas.
Measurement of Sound Pressure Amplitude by Optical Methods
Authors: Breazeale M. A. , Hargrove L. E.
Published: September 2005

Theoretically, absolute measurement of the ultrasonic pressure amplitude in a plane progressive wave can be made using one or more optical methods. Three optical methods are described. Considerations for the use of the different methods are discussed. Experimental results obtained under identical conditions are given. These results show good internal agreement, but the accuracy of the absolute values of pressure is limited by the accuracy to which the piezo-optic coefficient is known. (This work was supported by the Office of Naval Research.)
Use of Practical Spheres as Standard Sonar Targets
Authors: Wallace Reuben H.
Published: September 2005

Spheres play a rather important role in sonar work in that they are often used as standard targets in field measurements of sonar parameters. Their theoretical lack of dependence on aspect and frequency is a strong attribute. The theoretical derivation of target strength for a rigid sphere is well known; however, there seems to be a lack of information concerning the target strength of practical spheres and the restrictions on the use of spheres in a measurement program. This paper presents the results of an experimental investigation of the target strengths of various spherical targets. Data from water-filled, air-filled, corprene-lined, and Celtite-covered spheres will be presented. (This work was supported by contract with the Bureau of Ships.)
Mean Free Path and Ultrasonic Vibrational Relaxation in Liquids and Dense Gases
Authors: Madigosky W. M. , Litovitz T. A.
Published: September 2005

Measurements of ultrasonic absorption and velocity in CO2 yielded values of the vibrational relaxation times over a range of densities from 400 to 610 amagats at 25°C and 50.2°C. On the basis that only binary collisions were important it was found that the Enskog theory for determining collision times in the dense fluid failed to account for the results. Application of the Eyring-Hirschfelder cell model of the liquid accounted well for the density dependence of the relaxation frequency but gave values of mean free path which were too large. It was proposed that for mean free path calculations a realistic cell model must not use fixed walls, as Eyring and Hirschfelder, but moving walls. When this modification was included, excellent agreement was obtained for both CO2 and CS2. It was further shown that attractive forces do not play the role in determining the collision efficiencies in a liquid or dense gas that they do in the dilute gas. After correcting for the effect of attractive forces, it was found that the collision efficiencies of the dilute gas agree with values obtained for the liquid and dense gas.
Sound Propagation in Gaseous Dissociating N2O4
Authors: Sessler G. M.
Published: September 2005

Sound absorption and dispersion in a gaseous equilibrium mixture of N2O4, and NO2 has been calculated under the following assumptions: 1. The N2O4 molecule dissociates when it has collected the dissociation energy in 6 out of its 12 vibrational degrees of freedom. This collection of energy results from collisions with other molecules and occurs (in the approximation) in two steps; the energy first rises to an intermediate value and then to the dissociation energy 2. The absorption and dispersion caused by the translational, rotational and those vibrational degrees of freedom which do not influence the dissociation is additive. The calculations show that the total absorption can be smaller than that predicted by Einstein's theory [Sitzber. Akad. Wiss. Berlin 380–385 (1920)], which considers only a one-step dissociation process. Measurements at 20 and 53°C, at pressures between 1 and 200 mm Hg and at frequency/pressure values between 105 and 108 cps/atm are in good agreement with the calculations. The measurements have been performed with an acoustic interferometer consisting of two electrostatic transducers with solid dielectric. The measurements yield for the second-order rate constant of the N2O4 dissociation at 1 atm and 20°C 1.7⋅105 sec−1 and at 1 atm and 53°C 8.4⋅105 sec−1. (This work was performed at the III. Physikalisches Institut der Universität Göttingen, Germany.)
On the Problem of Sound Absorption in Air Caused by the Presence of Water Vapor
Authors: Wiley D. R. , Watson R. B.
Published: September 2005

The one-chamber method of evaluating the absorption in air caused by the presence of water vapor has been investigated, with especial attention to the variation in absorption of the wall materials of the chamber and to the methods of measurement of humidity in the range from 0–15% relative humidity. Conventional measuring techniques are discussed and the need outlined for a convenient humidity meter for the range mentioned. The absorption of the chamber walls is evaluated as a function of the humidity of the air in the chamber, using in fact nitrogen in the chamber to avoid the molecular effects arising from oxygen. A mechanism is suggested for the explanation of the quadratic dependence of the absorption in air on water vapor content.
Estimating Structural Response to Noise
Authors: Smith P. W.
Published: September 2005

Expressions are given for estimating the rms response of a general mechanical structure, vibrating in individual modes, when exposed to noise. The noise field is characterized by the free-field rms sound pressure. Linearity is assumed in air and structure. The principles of reciprocity and superposition are employed. As an extreme case, it is assumed that all damping is due to radiation to the far field. The mean square velocity for a uniform distribution of sources (alternatively, the ensemble average for all angles of incidence) is particularly simple; for given sound spectrum level, it varies inversely with modal stiffness but is independent of the acoustic-mechanical coupling. Under the same assumptions, the mean square dynamic strains in fundamental modes of plates. designed to the same static strain under fixed pressurization, are approximately proportional to spectral density of free-field noise multiplied by mass and divided by the square of surface area. Modifications for other conditions are discussed. (Supported by Wright Air Development Division.)
Vibration of a Plate at Low Frequencies
Authors: Greene David C.
Published: September 2005

The normal mode method of analysis correctly predicted the high-frequency driving-point impedance and background sound radiation of point-excited flat plates for both damped and undamped conditions. Evidence now has been obtained that the same methods also correctly predict the behavior of the plate in the lower frequency range, wherein the resonances are well separated. Effects resulting from the position of the driving point are examined theoretically and experimentally.
Rapid Method for Evaluation and Design of Structures with Viscoelastic Interlayers
Authors: Ungar Eric E.
Published: September 2005

A simple method is presented for rapid approximate determination of stress-vs-frequency and power absorbed-vs-frequency curves for plate and beam structures incorporating viscoelastic shear damping. The utility of this method is illustrated by applying it to the design of damping for the wall structures of the Wright Air Development Division sonic fatigue test facility. Some conclusions are drawn concerning damping material properties desirable for obtaining favorable stress-vs-frequency trends. (Results presented grew out of studies supported by the U. S. Air Force. Wright Air Development Division.)
Equipment Testing to Sonic Environments—Facilities and Techniques
Authors: Hill James A.
Published: September 2005

A general description, along with details, for the equipment qualification sonic testing facility at North American Aviation, Inc.. Columbus. Ohio, is presented. Methods of sound generation, control, and monitoring and testing techniques are described. A unique method of generating noise at the open end of a large catenoidal horn (11 ft at the open end, 10 ft long, and 3 ft at the throat) and concentrating such noise at the throat to increase SPL is utilized in this facility.
Automatic Equalization of Resonances in Sonic Fatigue Chambers
Authors: Boynton Richard
Published: September 2005

As constructed, all acoustical chambers and most acoustic transducers exhibit sharp resonant peaks, resulting in a concentration of energy over a few narrow frequency bands. Furthermore, these resonant frequencies vary for different specimens placed in a chamber. In order to achieve the desired “flatness” with respect to frequency it is necessary to create electronically the inverse of this frequency characteristic at the input to the system. Early types of equalizing circuits required laborious manual adjustment of many interacting controls to achieve equalization for each new specimen. The instrument described in this report automatically compensates the chamber for both sine and random wave testing. The system consists of 27 separate closed servo loops, each one controlling a 13 octave segment of the total frequency band. The resulting amplitude-controlled segments are then summed and applied to the acoustic driver. The problem of phase cancelation between adjacent 13 octave bandpass filters is overcome through the use of special linear-phase bandpass filters and a toroidol phase compensating transformer. By using a unique solid-state circuit to compensate each frequency segment, it is possible to equalize all resonance occurring in a 200-cu-ft acoustic chamber within 10 sec after the application of a wide-band random noise input.
Automatic Processing System for Acoustical Data
Authors: Parker Winston E.
Published: September 2005

An improved instrumentation system has been developed to analyze the dynamic pressure field produced by jet aircraft. The system is automatic and utilizes analog computer techniques to obtain an accuracy of ± 0.2 db in its readout. The method used is to secure a true rms value of octave band segments of the jet noise spectrum and to convert this to decibels by the use of a dc logarithmic amplifier. The transition to acoustical decibels is made by obtaining the difference between this voltage and another voltage obtained from a reference oscillator. This signal has been converted to equivalent electrical decibels (reference 1 v). The value of this reference oscillator in acoustical decibels is known. A value of approximately 150 db is used. The dynamic range of the system, 18 db, has proved more than adequate for greater than 90% of the data processed by this unit during the past six months.
Mathematical Detectability Limits and Signal Perception
Authors: Mathews Max V.
Published: September 2005

Several theoretical limits on detectability of a known signal in Gaussian noise have been obtained. They differ in their characterization of the noise as being Fourier series bandlimited, being spectrum bandlimited, or having a rational spectrum. Some of the resulting limits differ widely, and the question may be asked which should be applied to perception experiments. This discussion will present evidence for the opinion that none have a priori pertinence; that only by experiment could a connection be established; and that presently reported results do not consistently support any of the limits. All these limits depend on arbitrary assumptions concerning stimulus properties such as the period of the noise in the Fourier series bandlimited case or the energy at boundless frequencies in the rational or spectrum bandlimited case. These parameters have not been demonstrated to have significance in perception. Need for comprehending the mathematics involved puts an unnecessary burden on experimenters, which both discourages the nonmathematically inclined and diverts the attention of the mathematicians from the basic theory of perception as a hypothesis test, a theory which has great merit. It is proposed instead that effort be directed toward developing more specific models which are closely tied to experiment and to a more complete evaluation of hypothesis testing behavior. Many interesting investigations concerning, for example, factors other than the stimulus affecting subjects' responses remain to be done.
Acoustical Design Goals for Hospitals
Authors: Goodfriend Lewis S. , Cardinell Richmond L.
Published: September 2005

To achieve NC30 levels in hospital bedrooms and NC35 levels at nurses stations (as recommended in our final report) requires considerable care in the planning and selection of hospital equipment in all areas of the hospital. (Wall TL is not a problem.) This paper presents a schedule of maximum sound levels for hospital equipment according to equipment location and room absorption. Two limits are provided, the first making use of sound pressure levels, the second stated in terms of maximum permissible sound power levels. The sound pressure level method is to be dropped at a future date. Specifications also have been drawn with regard to vibration isolation based on the NC30 and NC35 curves and, finally, damping specifications for all sheet metal units including sinks, cabinets, and carts. Doors are not included since they are seldom closed. (This paper is based on the report Noise in Hospitals. This work was supported by the U. S. Public Health Service.)
Factors Determining Cruise Flight Noise Levels in a Turbojet Transport Airplane
Authors: Bishop D. E.
Published: September 2005

Results of inflight measurements in the Convair 880 airplane show that of the major external sources, engine noise and boundary layer noise, the latter is the predominant factor in determining cabin noise levels under most cruise conditions. From flight measurements in an airplane lacking interior trim, with microphones placed inside the fuselage near the outer skin at four positions along the length of the passenger cabin, plus fuselage noise reduction values based upon laboratory measurements using a section of a fuselage placed in reverberant sound field [D. E. Bishop, J. Acoust. Soc. Am. 31, 116(A) (1959)], a generalized spectrum of boundary layer noise has been derived. Predictions of changes in cabin noise levels with variations in flight conditions, based upon this generalized spectrum, are compared with noise measurements taken at several cruise conditions in an aircraft with complete interior trim.
Sound Transmission of Circumaural Ear Defenders
Authors: Shaw E. A. G.
Published: September 2005

In the course of routine measurements over a considerable period, information has accumulated which may be of general interest. In the current objective method of measurement, the ear defender is placed over a microphone mounted in a box which serves as an artificial head. When necessary, the effect of the circumaural flesh impedance is simulated by a layer of gelatin placed under the sealing cushion. Such a layer of “artificial flesh” has proved stable over a period of two years. By using a sound field of wide-band noise, which may be either uni- or omni-directional, the sound transmission loss is defined as the difference in measured levels of 13-octave bands of noise with and without the defender in place. With certain sealing cushions the low-frequency transmission loss has been found to change significantly over a period of many hours, indicating elastic relaxation. In such cases the protection afforded becomes largely indeterminate. Above 2 kc there may be as much as 10 db difference in attenuation between normal and oblique incidence. The magnitude of this effect appears to depend on cup material.
Determination of the Ratio B/A from Optical Measurements
Authors: Breazeale M. A.
Published: September 2005

The ratio B/A used to characterize the nonlinearity of a liquid in the study of the propagation of sound waves of finite amplitude can be determined from the change of index of refraction of the liquid with pressure. Calculation of this quantity from existing experimental data will be discussed. (This work was supported by the Office of Naval Research.)
Transients in Pipe Organ Tones
Authors: Ingalls Clyde E.
Published: September 2005

A critical study of pipe organ sounds has been initiated by by recording transient and steady state waveforms and harmonic analyses of tones photographically from oscilloscope traces, with some magnetic tape recordings. Microphones are located from 34 to 112 in. from the mouth or open end of the pipe. Observations show that reed pipes usually reach maximum output in a fewer number of cycles than flue pipes, the number increasing with frequency at a rate less than proportional to frequency. Wave shape is roughly constant with time in reed pipes and in flue pipes with low harmonic content. Tones with higher harmonic content are usually initiated by an inexact harmonic, which grows and then often reduces in amplitude as the fundamental grows. In diapasons (open) this is second harmonic; in the Nason Flute (stopped) it is third. Third harmonic rise and early decay produces a “chiff” sound, less obvious with second harmonic. Reed pipe sounds approach impulse excitation of bandpass filters, with or without pronounced peaks. Flue pipes have peaked formants with regenerative excitation less rich in harmonics. The research objective must determine what is important in waveform as well as harmonic content, resulting in a better understanding of how we hear.
Relationships between Wind Instruments Timbre and Sound Spectra
Authors: Hall Jody C. , Kent Earle L.
Published: September 2005

The sounds of nearly all wind instruments are characterized by formant-like patterns that are identified by musicians with descriptive terms such as superior or unacceptable, dark or bright, and the like. This study contributes to the basic understanding of the relationship between the sound spectra of wind musical instrument tones and the terminology used in describing those tones. The basic patterns of all common wind instruments are included. Tape recordings will be used to demonstrate the relationships presented.
Relationships between Electronic Organ Timbre and Sound Spectra
Authors: Kent Earle L.
Published: September 2005

The timbre of tones having a given spectra can be modified by other factors in the tones such as attack, release, vibrato, dynamics, and tonal combinations. The relationships between these factors and timbre will be demonstrated with an electronic organ.
Studies of the Vibrations of Clarinet Reeds
Authors: Backus John
Published: September 2005

The vibrations of the reed of an artificially blown clarinet are being studied by means of a photoelectric technique. Light from a source placed at the bell of the instrument passes through the opening between the reed and the mouthpiece and enters a multiplier phototube whose output is observed on an oscilloscope. Results at present indicate that the motion of the reed is quite simple and has very nearly the same pattern for all tones over the range so far studied. For loud tones in the chalumeau register the aperture between the reed and the mouthpiece is completely closed for nearly one-half cycle and completely open for the remaining half cycle. For softer tones the aperture does not close completely and the motion becomes nearly sinusoidal. (This work is being supported by a grant from the National Science Foundation.)
“Facilitating” Effect of the Prior Member of a Monaural Click Doublet
Authors: Guttman Newman , Frishkopf L. S.
Published: September 2005

This experiment delineates a range of intensities and monaural time separation intervals at which the second member of a monaural click doublet is displaced forward in time. (Displacement is the interaural time difference under the null criterion for binaural fusion of the second click of the doublet with a single contralateral click.) It had been found that, in most of the conditions of an earlier experiment, the second click was internally depressed: either it could not be fused or at fusion it was displaced backward in time. This corresponded to known refractory behavior of peripheral (N1) neural latency (increase) and amplitude (decrease) due to presence of a prior click. In a few cases, however. the second click was displaced in the other direction, a phenomenon which would correspond to a neural facilitation that has not yet been found. This experiment indicates that, to effect forward displacement, the prior click must occur largely within 2–10 msec of the second and must be weaker. The most sensitive time separation is 4 msec, and, under certain conditions, a prior-click level of even −6 db SL can be effectual. The measured magnitudes of the induced interaural time shift were up to about 0.2 msec.
Interaural Correlation and Earphones
Authors: Tobias Jerry V. , Jeffress Lloyd A.
Published: September 2005

In a recent paper, J. V. Tobias and E. D. Schubert [J. Acoust. Soc. Am. 31, 1595–1605 (1959)] suggested an “effective onset-duration” of 1–3 msec which they related to the “on-effect” and to the minimum refractory period of fibers of the VIIIth nerve. In the present experiments, an attempt was made to measure the critical duration by playing pairs of binaural stimuli with interaural correlations of +1 and −1 (or −1 and +1) and determining the duration below which the two conditions could not be recognized as different. For both noise-burst and click stimuli through PDR-8 earphones, stimulus durations were varied down to 0.09 msec. Judgments were 100% correct for all conditions. Acoustic measurements showed that, although waveform varied with varying duration of electrical input, the acoustic period remained at least 1 msec long. Indeed, for a given short-duration (less than a millisecond or so) burst of electrical noise, the acoustical waveform was surprisingly constant. The same sort of experiment, done with a comparison of +1 and 0 (uncorrelated) stimuli, produced similar results. The basic finding, then, is that stimuli delivered via PDR-8's cannot be changed enough electrically to produce acoustically an “unsolvable” interaural-correlation problem. It is apparent that the binaural system can solve any duration-sensitive transform that is transduced through standard earphones. (This work was partially supported by the Bureau of Ships.)
Binaural Interaction of Clicks of Different Frequency Content
Authors: Deatherage Bruce H.
Published: September 2005

Observers were required to adjust the interaural time relation of dichotically presented clicks to place the click image in the median plane. A check on the adequacy of the adjustment was made by commutating the dichotic signals. If the image did not appear to shift location on commutation, the interaural time difference was recorded. The “standard” click was generated by ringing a band-pass filter set at 250–500 cps. The filter for the “variable” click was set either at the same or at one of four higher octave bands. The two clicks were adjusted to the same level of five different peak equivalent sound pressure levels. For small frequency separations only one clearly localizable click-image could be heard. At higher frequency differences there were two images, one sounding high and the other low in pitch-like quality. To place the high-pitched image in the center of the head, the high passband click was set to lead the low and was set to lag to place the image of low-pitch quality in the midline. An explanation of this peculiar phenomenon will be attempted.
Response of Cochlear Models to Random Noise
Authors: Tonndorf Juergen
Published: September 2005

In most experiments reported here responses were recorded from a single-scala model at various points along the partition by means of a condenser probe after Bekesy (1941). It was ascertained by direct observation that the events as recorded occurred in the same manner in the usual dua-scala model. It was found that the models acted with distance as low-pass filters in response to random noise in the same way as to sinusoidal frequencies; also that responses were purely random; furthermore, locations of displacement maxima were determined in response to various noise bands in reference to those of sinusoidal frequencies equal to the center frequencies of these bands. The experimental results permitted the following conclusions: Each individual transient contained in the noise sets up its own traveling bulge. These bulges are superimposed randomly; thereby their original time sequence is not necessarily preserved with distance due to differences in propagation velocity. Even when the original noise band did not contain energy at low frequencies because of high-pass filtering, displacement occurred along the most distal portions of the partition, although at a reduced rate, since each individual bulge traveled the entire length. The latter fact may explain the phenomenon of remote masking (Bilger and Hirsh, 1956). (This work was supported by a Public Health Service grant.)
Evidence of Neural Activity below Standard Audiometric Threshold
Authors: Derbyshire A. J. , Groen J. J.
Published: September 2005

These experiments support the hypothesis that a standard audiometric threshold is not equivalent to a measurement of all auditory information available in the ear and the neural paths. They demonstrate the influence of audiometrically “inaudible” tones on the responses of human subjects. A weak tone (5- to 30-db sensation level) is passed through an attenuator. This attenuator can be bypassed for measurable periods to create a pulse of the background tone. Subjects signify their detection of the pulse by pressing a key. The shortest duration of a consciously detectable pulse is found to vary as a complex inverse function of the intensity of its background tone. An effect is present even when the background intensity is as much as 40 db below the pulse intensity (or 20–30 db below the subject's “conscious” threshold for that tone). The effect also occurs binaurally. The reaction time also shows a similar function in relationship to intensity of background. These data suggest that something more is necessary to cross the “conscious threshold” than a simple arithmetical addition of the energies of pulse and background. Instead, some complex function exists involving the factor of time and the degree of contrast between background and pulse.
Determination of Far-Field Radiation Patterns from Near-Field Measurements
Authors: Innis G. S. , Horton C. W.
Published: September 2005

The Helmholtz formula for the wave equation is used to determine the far-field radiation patterns of large transducers from measurements of the near-field pressures. It is shown that under suitable circumstances the normal component of velocity that is required in the formula can be related to the pressure. With the aid of this approximation, the far-field radiation pattern is computed from near-field pressure measurements for two transducers of different shapes. It is shown that the resultant patterns agree closely with the observed far-fields. (This work was supported by contract with the Bureau of Ships.)