bluuebunny/crossref_metadata_2025 huggingface dataset:
A Chronographic Method of Measuring Reverberation Time
Authors: Wente E. C. , Bedell E. H.
Published: September 2005

A description is given of apparatus which measures the rate of decay of sound density in a room. A loud speaker, energized from an oscillator, is preferably used as the source of sound. Current is sent through the speaker until the sound in the room has reached a steady state, whereupon the speaker is disconnected from the oscillator and the time required for the energy density in the room to decay to a definite value is recorded by the apparatus.
The Measurement of Sound-Absorption by Oscillograph Records
Authors: Chrisler V. L.
Published: September 2005

A sound decay curve in a reverberation room was photographed by means of an oscillograph. Computing the rate of decay from this film the total absorption in the room can be computed. The average results obtained by this method may be in close agreement with those obtained by the ear using the usual reverberation method, but the method as at present developed requires a prohibitive amount of time and labor.
An Audiometric Method for Measuring Sound-Insulation
Authors: Waterfall Wallace
Published: September 2005

The audiometric method of measuring the sensation level of sounds can be readily adapted to sound insulation measurements. The equipment consists of an electrical oscillator and amplifier which, by an automatic switch, is connected alternately to a loud speaker and to an attenuator and telephone receiver. The loud speaker is placed on one side of the partition to be measured and, by varying the attenuator a loudness match is made between the sound from the loud speaker and from the telephone on each side of the partition. The attenuator is graduated in decibels so the difference in the readings gives the reduction factor of the partition. Tones of 256, 512, 1024 and 2048 cycles are used. For field work, the audiometric method has the advantage that noises usually encountered do not seriously interfere with measurements.

As a check on the audiometric method, eight adjoining rooms, each an eight foot cube, have been constructed. Walls of different types separate adjoining rooms. Measurements on these partitions by the audiometric and an instrumental method show good agreement. They also agree well with measurements by the reverberation method on an identical partition tested by Paul E. Sabine at Riverbank Laboratories.
A New Acoustic Analyzer—Determination of the Sound Spectra Produced by Aircraft in Flight
Authors: Delsasso L. P.
Published: September 2005

An Electro-Mechanical Frequency Analyzer, previously reported (Physical Review, August 1, 1929) has been adapted to the determination of the sound spectra of aircraft in flight. The complex source of sound is converted into potential fluctuations by a microphone and high quality amplifier. The output of the amplifier is applied to a modified quadrant electrometer, the needle of which forms part of a sharply resonant mechanical circuit. The natural period of the mechanical circuit is made continuously variable by a tri-filar suspension and can be determined from a single micrometer reading. An analysis of a complex source is made by observing the amplitude of vibration and natural period of the mechanical circuit for each component. By a previous calibration of the instrument these observations are sufficient to determine the amplitude and frequency components of the complex sound. The instrument has been used to measure the sound spectra of typical passenger and military planes in flight.
Measurement of the Constants of a Single Reed Wind Vibrator
Authors: Wegel R. L. , Riez R. R.
Published: September 2005

Single reed wind instruments are represented by certain organ pipes, by the harmonica, clarinet, saxophone, duck call and the artificial larynx. In all of these the sound is produced by the periodic modulation of a stream of air which, when passing through a “glottis” or narrow passage between the reed and a juxtaposed stationary surface or “bed,” energizes the device. The forces concerned are the attraction of the reed to its bed due to the constriction of the air stream at the glottis according to the principle of a venturi meter, the pressure of the air on the reed and on the air stream in the glottis. Vibration results when the air flow is such that the proper relative magnitudes and phases of these forces occur. These forces have been measured in a model artificial larynx and the calculated vibration conditions checked against measurements of pitch and amplitudes.
Music as a Humanizing Agent
Authors: Lomb Henry C.
Published: September 2005

Among the many possible applications of acoustics, the practical application of music to the humanizing or betterment of all elements of our populations stands in the front rank.

Such application presupposes an influence of music on human behavior. Of this influence we find daily corroboration in the playing of martial and sacred music and in the melodies and harmonies of song and symphony.

The cause of this effect has until recently baffled scientific investigation. But the tremendous potency of music is doubtless largely due to its appeal to all classes of humanity. As the sole universal language of mankind, far transcending speech in range and power, it should be possible to employ it as a great humanizing force for the benefit of mankind.

The effectiveness of music is not limited here by its character of a language of feelings, since all mental and physical activities are determined greatly, even though unconsciously, by our emotions.

Research, particularly in the psychology of music, to bring about larger actual and personal participation in musical activities, not merely passive contemplation thereof, is here indicated.
Sound Concentrator for Microphones
Authors: Olson Harry F. , Wolff Irving
Published: September 2005

A sound concentrator is described having the shape of a parabolic horn, with a microphone at the focus and an associated acoustic network for equalizing the response. Amplification is obtained at low frequencies due to action as commonly attributed to horns and at high frequencies due to the reflections of sound from the walls to the focus. The theory for the parabolic horn attached to a microphone is developed and compared with the experiment.

In order to determine the frequency at which the reflection from the walls becomes of importance, a comparison of the parabolic horn with a double conical horn of approximately the same size is made. Experimental results on these two horns show that reflection from the walls begins at 1500 cycles and increases in importance with frequency. The directional pick-up properties of this parabolic horn have been investigated and determined as a function of the frequency of the impinging sound. The characteristic peaks of the short parabolic horn are reduced to an optimum value by means of Helmholtz resonators loosely coupled to the horn at the receiver end.
Optimum Reverberation Time for Auditoriums
Authors: MacNair W. A.
Published: September 2005

Up to the present, the acoustics of auditoriums has rested on a purely empirical basis. A more satisfactory situation would be reached if we knew a physical quantity which had some definite value for all rooms, regardless of size, which are considered acoustically good. Such a condition is that ∫ t0t1 Lt dt = −32.6 where t0 is the time a sustained source of sound, Ē, is cut off; t, the time the sound becomes inaudible: and Lt, the loudness of the sound at any instant t. For a test tone of 1000 cycles we take Ē to be 35.3×1010 cubic feet of sound of threshold density per second, which is a fair average of sources met with in practice. All rooms which have been considered acoustically good satisfy this condition. This implies that the ear is a ballistic instrument during the period of hang over of a sound, and suggests that rooms should be adjusted so that the loudness of all pure tones shall decay at the same rate, independent of frequency. The absorption material used must have a definite frequency characteristic to obtain this result. This characteristic turns out to be very near to that which an audience of people exhibits. An audience is recognized as being nearly ideal absorption material.
Audible Frequency Ranges of Music, Speech and Noise
Authors: Snow W. B.
Published: September 2005

This paper describes the use of an electro-acoustic system, transmitting the audible frequency range almost uniformly, in determining by ear the frequency ranges required for faithful reproduction of music, speech, and certain noises.

Sounds were reproduced alternately with and without filters limiting the frequency range transmitted by the electrical circuit. The filter cut-offs producing just noticeable changes in the reproduction were deduced from judgments of listeners as to the presence or absence of filters. It was found that for absolute fidelity all musical instruments except the piano require reproduction of the lowest fundamentals. The frequencies above 5,000 cycles were shown to be important, some instruments and particularly noises requiring reproduction to the upper audible limits.

Tests were made in which experienced listeners judged the degradation of “quality” produced by a series of filters. The judgments showed definitely that the quality continues to improve as the frequency range is extended down to 80 or up to 8,000 cycles. Although somewhat indefinite on cut-offs outside these limits, they indicated that reproduction of the full audible range was considered most perfect.
Reduction of Noise in Subways
Authors: Watson F. R.
Published: September 2005

A new consideration in the reduction of the disturbances of noisy machines recently occurred to the author. The matter arose in connection with a study of subway noises, in which it appears that the sources of disturbance are traceable to the following sources—the impact between car wheels and the rails that causes both of these elements to vibrate; the grinding of the gears that communicate the power from the motor to the car axles, together with the vibration of the gear wheels; and finally the vibration and rattle of the loose parts of the car.

A simple experiment showed that the rail vibrations could be deadened effectively by clamping pads of felt on the web of the rail. In actual use, however, the use of such deadened rails produced no noticeable effect—an apparent paradox. Consideration of the action of the ear gives a simple explanation of the paradox. Suppose that each of the five sources of noise mentioned has approximately one billion units of threshold intensity, the total intensity thus being 5,000,000,000 threshold units, with a loudness of 97 decibels. If now the rail noise is completely eliminated, the intensity is reduced to 4,000,000,000 threshold units, but the loudness is reduced only one unit to 96 decibels, and therefore would not be detected by the ear. By the same reasoning it is apparent that to reduce the noise appreciably, say to 50 decibels it is necessary to reduce all the disturbing elements to at least 100,000 threshold units. If only one remains with an intensity of 1,000,000,000 threshold units, the loudness still has the high value of 90 decibels. In other words, it is waste of effort to quiet any one element of a noisey machine; it is necessary to reduce the vibrations of all the disturbing elements, assuming them to be of about the same intensity.
A Device for Direct Measurement of Sound Absorption Coefficients
Authors: Sabine Paul E.
Published: September 2005

This paper describes a small scale device for direct comparison of the intensity of sound reflected from a surface of unknown coefficients with that reflected under identical conditions from surfaces whose coefficients have been determined by reverberation methods. It consists of means for producing sound of fixed intensity and frequency at an angle of incidence of 30°, and measuring the energy reflected at this same angle. Calibration is effected by measuring the intensity at the “pickup” of sound reflected from a highly polished marble surface, and from surfaces of known coefficients, and finally when no reflecting surface is interposed in the path of the incident sound. These measurements show a strictly linear relation between the intensity of the reflected sound and the reflection coefficient of the reflecting surface. The intercept of this line on the coefficient axis shows the percentage of the stray energy directly from the source to pickup. This percentage is very constant as the intensity in the incident beam is varied.

Coefficients obtained by this method show excellent agreement with reverberation coefficients obtained by measurement on identical samples.
A Critical Study of the Precision of Measurement of Absorption Coefficients by Reverberation Methods
Authors: Sabine Paul E.
Published: September 2005

This paper is the result of a careful comparative study of the coefficients obtained by various methods used for the measurement of absorption coefficients employing the equations of the reverberation theory. Both organ pipes and an electro-dynamic loud speaker were used as sources of sound. With the latter, both steady tones and flutter tones were employed. Absorbing power was measured by determining the rate of decay from measurements of the reverberation time for known relative values of the steady state intensity, using the loud speaker source. The results indicate that a loud speaker operated at a fixed value of the input current sets up a steady state intensity that is constant, independently of the absorbing power of the room. The measurements with the organ pipes confirmed the assumption that the latter acts as a source of constant acoustical power output, setting up a steady state intensity that is inversely proportional to the total absorbing power of the room.

Comparison of the results using steady and flutter tones shows that with a frequency range of a semitone above and below the mean frequency the measured values agree within the limits of experimental error. As between the organ pipe and the loud speaker, the former shows consistently higher values on four materials tested at the tone 512 vibrations per second, although the difference is only slightly greater than the experimental error. At other frequencies there is no consistent difference.

The experiments showed that although total absorbing power scan be measured with a precision of the order of 2% or 3% yet errors of this magnitude, if cumulative, may result in variations of about 10% in the value of the absorption coefficient, computed from the difference in absorbing powers of the reverberation chamber with and without the test sample present.

Comparison of results with result on identical samples tested in other laboratories show that at the frequency 512, the agreement between different laboratories is within the limits of accuracy of the methods so far developed.
Acoustic Adjustment of Curved Walls in Auditoriums
Authors: Watson F. R.
Published: September 2005

The modern trend among architects to use curved walls in auditoriums brings into considertion the adjustments that are helpful in reducing the resultant echoes and concentrations. Coffering these curved surfaces breaks up the reflected sound somewhat, but usually leaves more or less concentrated echoes. The application of absorbing material in a checkerboard pattern, with bare wall between the absorbing pads is promising. The pads absorb sound and change the phase of the reflected waves which interfere with the waves from the bare spaces, so that this arrangement appears more effective than coffering.

A more drastic treatment is to make the entire surface of grill work, whereby the incident sound passes through without reflection to a space behind the wall which may be used as the plenum chamber of the ventilation system. The appearance of the wall can be made satisfactory if the holes in the grills are not large, and if the surface is suitably decorated. This plan was tried in a New York auditorium with successful results, so that it now appears possible to use such curved walls, and allow architects freedom in the design of auditoriums with curved interiors.
The Muscial Scale and Its Tuning
Authors: White William Braid
Published: September 2005

The accepted system of tuning divides the octave into a succession of twelve tones, of which the frequency relations are such that if n be any tone n : n + 1 = 1 : 2112 from which also it follows that n : n + 12 = 1 : 2

This system, however, is purely artificial and was adopted in the eighteenth century in order to effect a practical compromise between the growing demand for freedom of tonal combination, and the limitations of a keyboard which had fastened itself upon practical musical performance. The paper discusses the nature of the musical scale and the anomalies which arise when an attempt is made to evoke intervals and chords in accurate relations of frequency with only twelve separate tones available in each octave. Some of the acoustical defects of equal temperament are pointed out especially in relation to music as heard. A thorough reconsideration of the subject is suggested for the general benefit of the reproducing arts and of the future of Music as a living form of expression.
Characteristic Sound Producers of the Organ
Authors: Leet Leslie N.
Published: September 2005

Description and demonstration of the factors that influence the tone quality of organ with a brief outline of the general structure of the organ. Illustrated by actual pipe examples played on a miniature laboratory organ.
Standardization in Teaching the Control of the Human Voice in Speech and in Song
Authors: Simmions Louis
Published: September 2005

The voice teachers of the past and the present have been trying and are tying to standardize their work in teaching the control of the human voice. Without a standard of measurement this was not possible. The acoustical scientists have evolved a standard of measurement in the art of the reproduction of the human voice. The speaker through practical demonstration believes he can prove that the same standard of measurement can be applied to the training of the human voice in speech and in song. With this end in view the speaker has evolved and applied in his teaching an acoustic measuring apparatus with which the student of voice can hear his own voice amplified and measure the right pressure of the vowel continuant through the deflection of a sensitive meter.
Measurement and Frequency Analysis of Sound from Large Reduction Gear Units
Authors: Abbott E. J.
Published: September 2005

In order to determine noise specifications in absolute units for a certain type of large reduction gear measurements were made of the sounds produced by ten machines in operation at a large central generating station. An average weighted total intensity, and a frequency analysis were made of the noise of each machine. It appears that these data are suitable and sufficient for absolute noise specifications on this type of machine.

It was found that 1 db. represents an important difference in loudness in these machines which places quite rigorous requirements on the apparatus and the methods of measurement in order to eliminate errors due to wave patterns, location, load, speed, etc. Data on these points are given.

A very close check was obtained between the observed frequencies of the various notes, and the movements of certain parts of the machine. By a comparison of the frequency analyses of the different machines it was possible to locate which part of the machine was responsible for the noise, and something of the nature of the defect producing the noise.
The Salient Features of the Functioning of the Cochlea, with Demonstration of a Transparent Hydraulic Model
Authors: Meyer Max F.
Published: September 2005

In constructing a model for demonstration of the function of the cochlea two assumptions are what we ought to keep clearly out of our mind: (1) that the living cochlea might contain dead building material of such physical properties as vulcanized rubber or tensile metal, (2) that the cochlea might contain contractile tissue, muscle tissue, that is, building material, which, in itself or in the supports in which it is inserted, could, from time to time at least, actively produce any stresses.

A mechanical theory must recognize four salient features: (1) that any sound pervades the cochlea no matter whether the window flexibility is considered in theorizing or put down as negligible in theorizing or is actually (pathologically) impaired—just as any sound pervades any building with all its rooms and partititions, and that such a primitive function is almost certain to have at least a weak and otherwise limited stimulating effect; (2) that the main and more adequate (but not exclusive) stimulating effect in mammalian animals (having an elongated cochlea tube) is likely to result from displacements of the phragma due to pressure differences between the windows, which are unsymmetrical to the meatus; (3) that the bulge formed by the displaced phragma can not travel, but can only lengthen itself, as is demonstrated by inspection of the hydraulic model; (4) that the formation of a bulge on either side of the average location of the phragma is succeeded by the development of stress in the phragma, as is demonstrated by inspection of the hydraulic model.
The Technique of Microphone Calibration
Authors: Ballantine Stuart
Published: September 2005

The distinction between pressure and free wave calibration of the microphone will be brought out and two or three methods using electrostatic actuator, thermo-phone and piston-phone will be described. Experimental precautions required in use of each of these will also be given.
Plane Sound Waves of Finite Amplitude
Authors: Fay R. D.
Published: September 2005

The principal object of the analysis is to find the change in type of periodic plane waves of sound of finite amplitude propagated in free air.

A solution of the exact equation of motion is obtained as a Fourier series. Due to the nonlinear relation between pressure and specific volume there is found to be a gradual transfer of energy from components of lower frequency to those of higher frequency. Since the effect of viscosity is to attenuate the higher frequency components more than the lower, there is always a wave form having the harmonic components in a stable relation such that the decrease in relative magnitude of any component due to viscosity is compensated by the relative increase due to non-linearity. The conditions for stability vary with intensity. There is therefore no permanent wave form, but the stable wave will change its form more gradually than any other wave of the same intensity and wave length. The change in type of any wave is toward this stable form. There is a marked departure from the sinusoidal in the stable type even for waves of very moderate amplitude.
Some Uses of Pressure Gradient Microphones for Acoustic Measurements
Authors: Wolff Irving , Massa Frank
Published: September 2005

The difference between microphones whose action depends on the pressure and those whose action depends on the pressure gradient in the sound wave is pointed out, and illustrations are given of each type. The characteristics of the pressure gradient in a complex sound field is discussed. It is shown that under certain conditions the pressure gradient gives a measure of the particle velocity in the sound wave. Illustrations and experiments are described which show how the vector characteristics of the pressure gradient may be used to advantage in making acoustic measurements.
The Determination of Absorption Coefficients for Frequencies up to 8000 Cycles
Authors: Hopper F. L.
Published: September 2005

The necessity for the determination of coefficients of sound absorption for frequencies up to 8000 cycles has been brought about by the improvements being effected in increasing the range of recorded and reproduced frequencies in sound pictures and broadcasting. Naturalness and intelligibility are enhanced by the addition of these higher frequencies which further increases the effect of realism. Consequently, with the development of apparatus capable of handling a wider frequency band, a knowledge of acoustical conditions over an equally wide band of frequencies is required.

From a knowledge of absorption coefficients at the lower frequencies it appears to be impracticable to predict coefficients at the higher frequencies, consequently a resort to measurements is the only satisfactory solution. The apparatus and technique for the determination of coefficients of absorption for frequencies up to 8000 cycles by the chamber reverberation method are discussed. Factors affecting these measurements, such as sound absorption in air, size and methods of mounting the test samples, and so on, are described. The absorption coefficients for a number of commercial materials for these higher frequencies are shown. Since materials having different types of frequency absorption characteristics, as well as absolute absorption, are required for such work as: the reduction of noise, the acoustical treatment of theatres and auditoriums, and the treatment of rooms or stages used for the electrical recording of speech or music, such information is necessary in order to intelligently design such acoustical treatment.
Reverberation Characteristics of Sound Pictures Sets and Stages
Authors: Hanson R. L.
Published: September 2005

In this paper are presented the results of reverberation measurements made in about sixty motion picture sets and sound stages together with a theoretical consideration of the behavior of residual sound in motion picture sets. The paper points out that, on the basis of the experimental results and the theoretical considerations a uniform decay of the intensity level of residual sound in a motion picture set having large areas opening into a sound stage would not be expected. The initial decay rate is approximately that which would exist in the set located in the open, but changes with time and approaches that which would normally exist in the stage itself. The detrimental effect which such characteristics have on the quality of the reproduced sound depends upon various factors such as the volume range which can be accommodated by the system, the relative intensities to be recorded, the type of set and stage, etc.
The Acoustics of Large Auditoriums
Authors: Wolf S. K.
Published: September 2005

Laws of acoustics known to apply to smaller volumes may not always be taken as true for large auditoriums. For example, computed reverberation times are radically different from actual measured times. In the case of Madison Square Garden, 6,200,000 cubic feet in volume, the calculated time of 35 seconds at 500 cycles contrasts with a measured time of 7.65 seconds. Use of the formula recently proposed by Knudsen reduces the discrepancy, but insufficiently. At 2000 cycles the computed time was 13 seconds; whereas, the measured value was 5.4 seconds. Some general possible causes of the anomaly are suggested.
The Apparent Reduction of Intensity Level of Noise
Authors: Taylor Emory W. , Laird Donald A.
Published: September 2005

Practical observations indicating that a small reduction in noise appears vastly larger than it actually is have been verified and the degree of apparent reduction measured. Naïve observers were given a 3-A audiometer stimulus to listen to, immediately following which they were to indicate the one of several other loudnesses which reduced the original stimulus by one-fourth, one-half, or three-fourths. The audiometer sound was heard in one ear, and in other phases of the study was amplified to bathe the subject, with results that are practically identical. An intensity level of 80 decibels appears to be reduced by one-half when it is only reduced by 23 decibels, etc. Lantern slide charts of results (5 minutes).
The Influence of Noise Stimuli upon the Normal Secretion of Saliva and Gastric Juices
Authors: Graham Henry T. , Stephen James W. , Laird Donald A.
Published: September 2005

Partial confirmation of the hypothesis that the ill effects of appropriate noises are due to the generation of a biological fear reaction was sought in the effects of noises upon these secretions. The complicated noise of the 3-A audiometer at an intensity level of 50 decibels or more was found to cut down the secretion of saliva by 50% or more. Similar noises of 40 decibels or more cut into the secretion of gastric juices. Possible methods of overcoming these effects are discussed. Lantern slides of methods and findings (8 minutes).
A Uni-Directional Ribbon Microphone
Authors: Olson Harry F.
Published: September 2005

Directivity has been found to be desirable in sound pickup systems to improve the ratio of direct to generally reflected sounds and to otherwise discriminate against undesirable sounds. The ribbon microphone is a simple directional system in which the directional characteristics are independent of the frequency. The response is a function of the angle between the normal to the ribbon and the direction of propagation of the incident sound. The ribbon microphone is a pressure gradient microphone and the response is a measure of the velocity component in a sound wave. Using a mass controlled element the velocity of the ribbon is in phase with the velocity in the sound wave. By a suitable combination of this microphone with a pressure operated ribbon microphone a uni-directional microphone may be obtained. The pressure ribbon microphone should be resistive controlled and the response is then a measure of the pressure component in the sound wave. The velocity of the ribbon in this microphone is then in phase with the pressure. By combining the outputs of two such microphones the response as a function of the angle θ between the normal to the ribbon and the direction of propagation of the incident sound is expressed by R = R0(1+cos θ) where R0 is the sensitivity of the pressure and velocity ribbon microphone for θ=0. Preliminary experimental results verify the theory with respect to the phase relations and the directional characteristics.
On Sound Diffraction Caused by Rigid Circular Plate, Square Plate and Semi-Infinite Screen
Authors: Sivian L. J. , O'Neil H. T.
Published: September 2005

Of the three problems named above, a theoretical solution due to Sommerfeld is known for the case of the semi-infinite screen when the wave front is plane and parallel to the edge of the screen. For the other two problems no theoretical solutions have been given. Both these cases are of interest in connection with the types of diffraction caused by a number of practical acoustic devices. Hence it was thought worthwhile to present some experimental data and to indicate a calculating procedure which, though not at all rigorous, accounts for a number of the observed facts. In the semi-infinite screen problem the theoretical solution is restated in forms suitable for numerical evaluation. Several graphs showing the sound pressure amplitudes in regions of particular interest are given.
On the Loudness of Noise
Authors: Marvin H. B.
Published: September 2005

In order to determine the usefulness of pure tone data in design of noise meters intended for measurement of complex sound, a reference tone of 1000 cycles at various levels was compared with noises typical of electrical machinery. The comparison was made on the basis of equal loudness determined by ear and also by noise meter. A description of the method and preliminary results are given. The results show good agreement between ear and meter in the noise levels covered by two frequency weighting networks designed from pure tone data. Need for a third network in the higher noise levels is shown.
Control of Pitch in Wind Instruments
Authors: Taylor John Bellamy
Published: September 2005

A statement often heard or read as coming from some prominent musician is to the effect that of all the orchestral instruments only the violins (including the larger members of violin family) and the slide trombones can play in perfect intonation. The absence of frets on the finger-board permit performer to nicely determine vibrating length of string and sliding tubes of trombone give similar opportunity for precise determination of air column length. Coupled with the claimed pitch superiority of violins and trombones there is also an implication that a better “ear” is required for acceptable playing of these instruments than is needed for playing other orchestral instruments, viz., flutes, oboes, clarinets, bassoons, horns, and trumpets.

While the wind instruments do have a limited tuning range, it is misleading to speak of them as of “fixed pitch,” and erroneous to assume that uncovering the proper vents, or depressing the proper pistons assures a tone of definite pitch. This is because the air column of instrument is, through mouthpiece or reed, sufficiently coupled to lips and oral cavity of player to give him an appreciable control of the air column time of vibration. This allows sounding the tone either definitely “out of tune” or, within reasonable limits, raised or lowered in pitch to come in close accord with the tones from other instruments. To exercise this pitch control musically and artistically the wind instrument player is as dependent on a good “ear” as is the performer on the strings.
Liveness of Rooms
Authors: Hanson R. L.
Published: September 2005

Experience has shown that the sense of liveness of reproduced sound cannot always be correlated with the reverberation period of the region in which the sound originates. A series of experiments have therefore been carried on which show that the liveness of reproduced sound is not a function of the reverberation period but is dependent upon the irregular fluctuation of the sound intensity at the microphone. This fluctuation which often appears during sustained as well as growing and decaying tones is a function of the size, shape, and abxorbing power of the room in which the microphone and sound source are located. It explains the effect of monaural pick-up, microphone distance, etc., on liveness. The conditions which give rise to a high degree of intensity fluctuation and hence liveness are often such that a long reverberation period results. It is pointed out in the paper that if there is an optimum reverberation period for listening in a room, that period should also be optimum for recording. The intensity fluctuation due to shifting interference patterns should, in the case of a monaural pick-up pe reduced to a degree comparable to that which is apparent to a two ear listener.
Acoustic Measuring Instruments
Authors: Hanson R. L.
Published: September 2005

During the past few years great advances have been made in various laboratories toward the development of instruments for making quantitative measurements of acoustic phenomena. Among the instruments of this type which have been developed at the Bell Telephone Laboratories, are a reverberation meter, a sound meter, an automatic level recorder, a rapid record oscillograph, and three types of audiometers. Although these instruments have previously been described in detail elsewhere this paper will be a summary of their main features and the purposes for which they are adapted. It will be followed at the close of the session by an exhibit of the instruments in operating conditions.
Laryngoscopic Observations on the Parabolic Action of the Epiglottis in Controlling the Directional Power of the Low, Middle and High Frequencies of the Singing Voice
Authors: Simmions Louis
Published: September 2005

The speaker demonstrated laryngoscopic observations in the formation of primal sounds in the interior of his larynx and sang scales, arpeggios, intervals, trills, with the aid of a laryngoscope; he observed and reported the different elements which enter into the formation of the five fundamental singing vowels on open and covered position of the epiglottis; while making these observations he at the same time amplified these primal sounds and vowels into his own ears with a new acoustic device which he called a VOCALSCOPE.
An Efficient Miniature Condenser Microphone System
Authors: Harrison H. C. , Flanders P. B.
Published: September 2005

This paper describes a Wente-type condenser microphone of high efficiency and an associated coupling amplifier which are of such small size that reflection and phase-difference effects are of negligible importance within the audible frequency range; while the cavity is so proportioned that its resonance effect is an aid rather than a detriment to uniformity of response in a constant sound field.
Some Improvements on the Bells of a Carillon
Authors: Giannini G. M.
Published: September 2005

The unsatisfactory performance of the bells of a carillon from a musical standpoint is discussed and two improvements are suggested. The first is to check and regulate the amplitude of the partials of the bell with respect to the amplitude of the fundamental. The second improvement is the use of a damping device which brings the bells into the class of a musical instrument. The operation of such electrical apparatus to accomplish this second improvement is described.
The Acoustic Properties of Small Gongs
Authors: Steinberg J. C. , Farnsworth D. W.
Published: September 2005

This paper gives the acoustical properties of several types of small gongs and the relations between some of these properties and the size, shape and material of the gongs.
A Relationship between Loudness and the Minimum Perceptible Increment of Intensity
Authors: Riesz R. R.
Published: September 2005

Using previously reported data (Phys. Rev., Vol. 31, May, 1928) concerning the differential intensity sensitivity of the ear, the number of perceptible increments of intensity is calculated as a function of the intensity expressed in db above the auditory threshold for frequencies of 200, 1000, 3000 and 10,000 c.p.s. These curves are then used in an attempt to arrive at a logical explanation of the data presented by Laird, Taylor and Wille (Jour. Acoustical Soc., Jan., 1932 “The Apparent Reduction in Loudness”).
Low Frequency Thresholds of Hearing and of Feeling in the Ear and Ear Mechanisms
Authors: Wegel R. L. , Riesz R. R. , Blackman R. B.
Published: September 2005

A redetermination of the hearing threshold in the frequency range 35 to 1000 cycles shows the minimum audible pressure in the ear canal to be inversely proportional to the cube of the frequency up to about 500 cycles. This is interpreted to mean that the form of vibration of the basilar membrane does not change appreciably and that the amplitude of its motion varies inversely as the square of the frequency in this range. It follows from this that the threshold stimulus for the nervous tissue is a constant acceleration. This observation also shows that the efficiency of the ear at high frequencies is principally due to the properties of nervous tissue and that the maximum mechanical efficiency occurs in the frequency range at 1000 to 2000 cycles. A redetermination of the threshold of feeling shows a nearly constant pressure at low frequencies which corresponds to a constant amplitude of motion at the ear drum and ossicles, suggesting that this sensation originates in the middle ear.
An Experimental Determination of the Equivalent Loudness of Pure Tones
Authors: Munson W. A.
Published: September 2005

The intensity levels at which pure tones of different frequency sound equally loud have been determined by comparison with a thousand cycle reference tone. A frequency range from 62 to 16,000 cycles and an intensity range from near threshold to uncomfortably loud sounds was covered. The tones were impressed upon both of an observer's ears by means of telephone receivers, and were of short duration to avoid fatigue effects. The comparisons were made by eleven observers. From the intensity levels which were found to produce equality of loudness, the equivalent loudness of all points in the normal auditory sensation area were determined in terms of the 1000 cycle reference.
Estimating Room Errors in Loud Speaker Tests
Authors: Kellogg E. W.
Published: September 2005

Reflections from the walls, ceilings and floors of loud speaker test rooms are likely to be much greater than would be judged from listening tests. Simple calculations will show whether the errors resulting from these reflections are likely to be serious, and will also indicate how they may be most easily reduced.
Acoustics of Broadcasting and Recording Studios
Authors: Stanton G. T. , Schmid F. C.
Published: September 2005

This paper describes the acoustic design of broadcasting and recording studios wherein the type and location of acoustic treatment is selected to permit a monaural pickup to represent, when reproduced, the acoustic conditions normally anticipated for the type of program presented. Acoustic conditions surrounding musicians and performers and those surrounding the microphone more nearly conform to established ideal relation between performers and audience under actual listening conditions. Certain examples of studios treated in accordance with this plan are described.
Some of the Factors which Affect the Measurement of Sound Absorption
Authors: Chrisler V. L. , Snyder W. F. , Miller Catherine E.
Published: September 2005

Curves have been drawn showing the effect of water vapor and temperature on the total absorption of a reverberation room. At 4096 cycles changes in barometric pressure seem to have an appreciable effect.

When highly absorbent materials are placed in the reverberation room, the rate of decay is not uniform.
Position Finding by Underwater Sound Signals
Authors: Hubbard B. R.
Published: September 2005

The ability of a navigator to fix the true position of his ship at sea under the adverse conditions of storm and fog has been made possible through synchronized radio and underwater sound signals. Hydrographic survey vessels are fixing their position with ease and accuracy by means of radio acoustic sound ranging and underwater sound spotting. The point of impact of a projectile fired from coast artillery is being determined by underwater sound spotting. Ships are checking their position at sea by taking a series of echo depth soundings. Coast defense fortifications are using underwater sound direction finding for the detection and location of distant invisible ships. In each case underwater sound signals are playing an important part. The paper describes some of the more important technical aspects of these methods of position finding by underwater sound signals.
Measurement of Transmission Loss through Partition Walls
Authors: Bedell E. H. , Swartzel K. D.
Published: September 2005

This paper reviews the theory and describes the method used at Bell Telephone Laboratories of measuring the transmission loss through partition walls.

The partition to be tested is built into an opening between two adjacent but structurally isolated rooms. A loudspeaker acts as a source of sound in one room and a portion of the sound energy is transmitted into the second room through the test partition. The transmission loss is taken as TL = L1 − L2 − 10 log10 (a2/A) where L1 and L2 are the intensity levels in the source and test room respectively, expressed in db, a2 is the absorption in the test room and A is the area of the partition. The levels L1 and L2 are measured and plotted with a moving coil microphone and an automatic level recorder, and a beat frequency oscillator is used as a source of tone so that the frequency may be varied continuously. Measurements with a continuous variation in frequency enable resonances in the partition to be much more easily and quickly detected than is possible when measurements are made at discrete frequency intervals. Both pure and frequency modulated tones have been used for the measurements. Results of measurements on a few partitions are given.
The Methods and Results of Supersonic Interferometry
Authors: Hubbard J. C.
Published: September 2005

In the acoustics of audible sound the instruments of investigation, including sources and receivers, are generally small as compared with the wave-length. Diffraction effects, i.e., the spreading of the waves, becomes an all important factor. On the other hand, in the optics of visible light the instruments of investigation are in general large as compared with wave-lengths, and diffraction effects may in many cases be neglected. With Langevin's discovery of the methods of producing beams of high-frequency compressional waves in liquids, with the comprehensive investigation of their properties by Boyle, and finally, with the development by Pierce of the acoustic interferometer, acoustics has been developed in the region of short wave-lengths, the instruments and methods becoming analogous in many respects to those of optics. The field of acoustic research has thus been enlarged by the acquisition of interferometric methods. Aside from numerous applications of immediate practical interest the new methods are of great scientific value since they furnish a new working tool in a frequency region of significance in molecular physics. Various methods are discussed and a summary given of important conclusions.
Velocity and Absorption Measurements at Supersonic Frequencies
Authors: Pielemeier W. H.
Published: September 2005

Importance of Supersonics. This field is related in varying degrees to gas theory, thermodynamics, chemistry, physical chemistry, mechanics, heat, radio engineering, navigation and biology.

The author's work in this field began in 1919 and has been confined to a search for a suitable high-frequency source and to the measurement of velocity and absorption in air, in oxygen and in carbon dioxide. Quartz slabs, properly cut from the original crystal and sputtered on both faces with metal were found far superior to the other tested sources for measurements requiring constant frequency and intensity. With such crystals, there were obtained frequencies ranging from 300 to 2000 k.c.

The velocity in air was found to be approximately 331.6 m/sec. in this range. At the lower frequencies the absorption appeared to exceed that predicted by the earlier theory. No serious deviation from expected values were found in oxygen. With carbon dioxide the velocity was found to increase about 3 percent from 300 to 2000 k.c. The absorption greatly exceeds the values predicted by the earlier theory. Both velocity and absorption values are in good agreement with those obtained theoretically by Kneser.
Studies in Supersonics
Authors: Reid C. D.
Published: September 2005

The paper naturally divides itself into two parts. The first deals with experiments concerning the energy distribution in a supersonic beam in water and describes a useful visual method of determining such distribution. Diffraction and interference phenomena similar to those in light are discussed. In the second part the method used for the precision measurement of supersonic velocity in air is described and the results discussed.