bluuebunny/crossref_metadata_2025 huggingface dataset:
Loud Speaker Sound Pressure Measurements
Authors: Kellogg Edward W.
Published: September 2005

Methods of taking frequency-response curves of loud speakers have tended to become prematurely standardized within commercial organizations, and inadequately standardized in the industry as a whole. Characteristics taken by different experimenters are not comparable. Each may have a good defense to make of his system, and it is the writer's plea that such discussion should be “A free for all, and not a private affair.” More general discussion would promote education if not standardization. A critical attitude on the part of all is desirable, and a demand that published curves be accompanied by information as to method of test.

Two valuable contributions on the subject have so far been published, in which the result obtained by several methods of test are compared. This paper makes additional contribution to the experimental evidence, suggests some other methods of measurement, and criticises the several methods from a theoretical standpoint. One of the difficulties arises from the fact that it is desired to show a single curve whose flatness is an indication of the general merit or fidelity of the loud speaker, whereas the differences in directive properties as well as in total sound output make it impossible to describe the properties of a speaker in a single curve. Only in as far as it is possible to specify the exact conditions under which the loud speaker will be used, can such a single curve have significance.
An Efficient Loud Speaker at the Higher Audible Frequencies
Authors: Bostwick L. G.
Published: September 2005

This paper describes a loud speaker designed for use as an adjunct to existing types for the purpose of extending the range of efficient performance to 11,000 or 12,000 cycles. A moving coil piston diaphragm structure is used in conjunction with a 2000 cycle cut-off exponential horn having a mouth diameter of about 2 inches. Motional impedance measurements on this loud speaker indicate an average absolute efficiency of about 20% within the frequency range from 3000 to 11,000 cycles. The variation in response within this band does not exceed 5 db. By using a high frequency loud speaker of this type the efficiency and power capacity of the associated low frequency loud speaker can be improved and a uniform response-frequency curve from 50 to 12,000 cycles can be obtained.
Masking Effects of an Interfering Tone Upon a Deafened Ear
Authors: Guttman John , Ham L. B.
Published: September 2005

These experiments were made to test the masking function of deafened ears by means of two tones. The threshold intensity of the person examined is obtained for the one tone and then this intensity is increased 50 decibels. This tone we have called the interfering tone. The threshold intensity of the other tone (i.e., the primary) is found with and without the interfering tone. The difference between the two threshold intensity values of the primary tone is called the differential threshold.

We have found the differential threshold to be smaller for deafened people than for normal people. The greater the deafness in the primary tone, the smaller the differential threshold. These findings were found for both the so-called conduction as well as perception deafness. In conduction deafness the effect may be a little more pronounced.

An analysis of the results, especially for the more deafened cases, indicates a supplementary explanation to Paracusis phenomena.

An explanation of the results is given, based upon the supposition of a very sensitive mechanism for damping the transmission of strong sounds. This mechanism acts by reflex action of the cochlea nerve and the nerves supplying the intra-auricular muscles.
The Amount and Type of Auditory Stimuli Which Influence Stomach Contractions
Authors: Smith E. L.
Published: September 2005

A scientific explanation is needed to account for the observed ill effects of noise on health and efficiency. The hypothesis that noise causes fear reaction has been advanced to give such an explanation. This paper will report experimental observations of changes in stomach tonus, which has been shown to be an aspect of the fear reaction, under various acoustic stimuli. Human beings were experimented on and records of stomach tonus obtained from balloons in the stomach.
The Effect of Noise Intensity and Pattern on Locating Sounds
Authors: King W. G.
Published: September 2005

A sound cage with a seconds pendulum regulating the intervals between stimuli was used to determine the threshold of two-point discrimination of the position of sound. Observations will be reported on the change in threshold with change in decibel level and absorption in the test chamber, the intensity and character of the discriminated stimulus remaining constant. Bearings of the data on annoyance, fear reaction, and “third dimensional sound” will be pointed out.
Acoustics of Lincoln Hall Theater at the University of Illinois
Authors: Watson F. R.
Published: September 2005

Recent theory indicates that perfect acoustics in an auditorium may be obtained by observing conditions leading first, to the perfect generation of sound, and second to the perfect reception of sound. In the generation of sound, it is of great advantage to place reflecting surfaces near the performer to allow him to “hear himself” and thus adjust his sound for best effect. For perfect listening, it appears desirable to reduce as far as possible all reflection of sound about the auditors, since practically all the defects of echoes, reverberation and articulations may be traced to this reflection.

Opportunity to test this theory was given in the construction of a small theater at the University. A huge cyclorama on the stage gave the reflecting surface for performers, while upholstered seats and a very absorbent ceiling treatment reduced reflection for auditors. The acoustic outcome is good.
Approximations in Determining the Total Absorption of a Room
Authors: Andree C. A.
Published: September 2005

In the formulae for the decay of sound in a room the total absorption is customarily taken equal to Σi ai si, where ai is the absorption coefficient for any uniform area Si. It is shown that this method of determining the total absorption is an approximation requiring the assumption “that sound which is reflected from material having a given reflection coefficient has a probability of encountering, on its next reflection, material with a like coefficient which probability is equal to the ratio of the area of that material to the total area present.” This assumption requires in general an amount of “bending” of the lines of propagation in excess of what may normally be expected from dispersion phenomena. The author suggests a method of attack which permits one to account for varying degrees of dispersion and applies this method of attack to the simple case of a cubical room. Numerical values of, à, the average absorption coefficient are determined which shows the effect of assuming different degrees of dispersion, and the effect of altering the distribution of the absorbing material in the room.
Movies of Vocal Cord Speech and Voice Quality Vocal Cord Function
Authors: Russell G. Oscar
Published: September 2005

These are the first moving picture experiments to be obtained, bearing on the fundamental problems involved in a consideration of speech and voice quality vocal cord function.

Most of our theories of speech have heretofore assumed a harmonic complexity of tones produced by the actuator or vocal cords. The moving picture photographs of the heretofore inaccessible interior larynx interior and lower throat now show for the first time that this is an impossible postulate.

Speech and voice quality differences have heretofore been ascribed to a function of the total air volume cavity capacities above the vocal cords—in other words to a cavity tone modificatory influence. These pictures likewise prove that these theories are untenable and that a large part of the voice quality and many vowel quality differences may be traced to a function of the interior larynx.
Absorption of Adjoining Volumes in Reverberation Calculations
Authors: Sette W. J.
Published: September 2005

Theatres with balconies present a different aspect to reverberation calculations than the single volume type. The space under a balcony may contain more absorption in square feet of equivalent open window space than the area of the face opening into the main volume. Heretofore arbitrary values ranging from .25 to 1 have been assumed for the coefficient to assign this connecting area. To obtain a more accurate idea of the absorption effective in the main volume random distribution of sound energy was assumed and equations were derived expressing the percentage absorbed of the energy incident on the area. The apparent coefficient is a function of the average coefficient behind the area and the ratio of the area to the total surface enclosing the space in question, and is different for different assumptions made as to the manner in which reflections occur. The use of the coefficient in reverberation calculations is discussed.
THEORY OF THE ELECTROSTATIC LOUD SPEAKER
Authors: Hanna C. R.
Published: September 2005

In the electromagnetic driver the force per unit current has been shown to be a function of the inductance and the negative stiffness resulting from the presence of the steady magntic field. In this paper it is proven that the force per unit voltage in the electrostatic device is a similar function of the capacity and the negative stiffness due to the steady electrostatic field.

A new concept called Motional Admittance is introduced for the electrostatic loud speaker and this is shown to be similar in its mathematical form to the Motional Impedance of the electromagnetic driver.

A calculation of the ultimate theoretical efficiency that may be obtained with an electrostatic speaker having a pure resistance radiator and covering a given frequency range is given. It appears that efficiencies between 5 and 10% may some day be obtainable with good fidelity of reproduction.
BINAURAL LOCALIZATION OF PURE TONES
Authors: Wightman E. Russell , Firestone F. A.
Published: September 2005

Pure tones of frequency 256 cycles per second were presented binaurally to eight different observers, the phase difference and amplitude ratio of the acoustical pressures at the two ears being known and adjustable. The observers were asked to state the direction and distance of the apparent source of sound. Only three of the eight observers were influenced their judgment of direction by the phase difference and even they were rather inaccurate. All were influenced more or less in judging direction, by the amplitude ratio. None was able to tell the distance of the source by the amplitude ratio.
AUDITION BY BONE CONDUCTION
Authors: Dean C. E.
Published: September 2005

Audition resulting from vibration of the skull is investigated in various respects using audiometers with bone conduction receivers and other equipment. Applying the driving element at any point sets the entire skull into vibration, and the stimulus in one ear resulting from driving the skull on that mastoid is found to exceed the stimulus in the other ear by only 3.4±2.2 decibels. The statistical accuracy of bone conduction observations is found and compared with published air conduction results. The sensitivity on the mastoid exceeds that on the forehead by 5 db on the average. Tests of instruments for measuring air conduction and bone conduction sensitivity to determine the amount of desired over undesired type of stimulation are described and the results given. The effect of a telephone receiver in producing hearing in the opposite ear is observed with two available cases of assured total deafness on one side and the data given. Beats involving bone conduction are observed. The fact that bone conduction sensations often seem in one ear is compared with similar results for air conduction stimuli under certain conditions and a general statement of all results is made. The problems of apparent hyper-sensitivity resulting from abnormality and occlusion are discussed in the light of the foregoing results.
PROBLEMS SUGGESTED BY AN UNCERTAINTY PRINCIPLE IN ACOUSTICS
Authors: Stewart G. W.
Published: September 2005

An uncertainty principle in acoustics, arising wholly from classical views, is presented. This principle is that Δν.Δt∼1, where ν is the intrinsic frequency of an acoustic signal and Δt is its time duration. Applying this principle one finds that it is consistent with experiments on the change in frequency in the vibrato and the failure to detect it by ear, with recorded tests on minimum perceptible differences in frequency, and with the minimal time for tone perception. The problems suggested by the principle are: (1) variations in Δt and Δν by an artificial vibrato with aural observations of detectable Δν, (2) redetermination of minimum perceptible differences in frequency as dependent upon Δt and (3) an examination of Δt required for tone perception with varied values of Δν
TRANSMISSION OF SOUND THROUGH APERTURES
Authors: Ritchie Earland
Published: September 2005

This investigation was an attempt to obtain experimental data to justify a prediction made by Lamb concerning the fractional transmission of sound through an aperture in a very thin plate of approximately infinite boundaries. The effects upon the actual transmission of varying the lengths of the apertures, of changing the number of the apertures, and of increasing the aperture sizes were investigated.

The work was done in the Sound Absorbing Acoustic Laboratory since it approximates outdoor conditions. The purest tones available were used as sources of sound. The apertures tested varied in lengths from one thirty-second of an inch to twelve inches, and in diameters from one-fourth of an inch to one and three-fourths inches. These were circular apertures cut through large plates three feet square. Equations were established to express the observed relationships found existing for the lengths of apertures, and for a variation of the number of apertures.

The theory given by Lamb for plates of infinitesimal thicknesses was found to be in agreement with experimental results. Apertures of different lengths showed an exponential relationship when compared with the per cents of transmission. The greatest transmissivity of an aperture can be obtained by using one aperture only. Increasing the number of apertures gave an ever diminishing result per aperture. The transmission through apertures of any length is directly proportional to their respective cross-sectional areas.
INVESTIGATION OF GAMMA IN A MIXTURE OF GASES
Authors: Barnes Garnett F.
Published: September 2005

The velocity of ultra-sonic vibrations was measured in gas mixtures and from this data the ratio of the molecular heats of the mixture was calculated. The vibrations were produced by a quartz crystal driven by a thermionic oscillator. The method employed was essentially that used by G. W. Pierce.

Mixtures of carbon dioxide and helium, air and helium, oxygen and helium, and nitrous oxide and helium were used. The molecular heat at constant pressure was taken from the International Critical Tables and the molecular heat at constant volume of the gas mixtures calculated.

It was found that the ratio of the two molecular heats of the gas mixtures as determined by experiment agrees well with that obtained by calculation.
An Efficient Miniature Condenser Microphone System
Authors: Harrison H. C. , Flanders P. B.
Published: September 2005

It has been shown recently that microphones and contiguous amplifiers distort the sound field in which they are placed by reason of their size and the cavity external to the diaphragm of the microphone. For frequencies such that the size is large compared to the wave-length of perpendicularly incident sound, reflection causes the actuating pressure to be double that which would exist in the undisturbed field. If the direction of the incident sound be along the plane of the diaphragm, the increase of pressure due to reflection is not as great; but there may be a substantial reduction in effective pressure due to differences in phase across the diaphragm. In addition, cavity resonance produces an increase of pressure at frequencies usually within the working range of the microphone.

This paper describes a laboratory model of 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.
USE OF PRESSURE GRADIENT MICROPHONES FOR ACOUSTICAL MEASUREMENTS
Authors: Wolff Irving , Massa Frank
Published: September 2005

The operation of the pressure gradient microphone is compared with that of the pressure microphone It is shown that the pressure gradient microphone may be used to measure particle velocity in a sound wave. The advantages of the pressure gradient microphone in making loudspeaker measurements, particularly outdoors, are pointed out and experimental data are given for some arrangements which were tried out. The characteristics of the distribution of particle velocity in a complex sound field are studied theoretically and experimentally with a ribbon microphone. A method is described for measuring the energy density in a sound field and some measurements which were taken in complex sound fields in rooms are discussed. It is shown that a combination of three pressure gradient or velocity microphones with a pressure microphone, placed adjacent to each other, may be equivalent in eliminating interference patterns to four pressure microphones placed at distances large compared to the wavelength and with random distribution. A microphone for measuring energy flow in a sound field is described.
THE SUPERSONIC INTERFEROMETER AND ABSORPTION MEASUREMENTS
Authors: Hershberger W. D.
Published: September 2005

The previously developed theory of the supersonic interferometer is extended with the particular view of utilizing it for absorption measurements in gases. It is shown that the mechanical impedance of the interferometer is Z = Z0 + Z(l) where Z0=j(mω − s/ω) + rZ(l)=Acρ/tanh 2αl + (Acρ/sinh 2αl)eiθ=− arc tan sin 2kl sinh 2αlcos 2kl cosh 2αl − 1.

That is, if reactance is plotted against resistance we obtain an impedance spiral with center (Acρ/tanh 2αl, 0) and radius Acρ/sinh 2αl. The action of the interferometer is studied in terms of the properties of the spiral. Absorption measurements are effected by compensating for the changes in the equivalent series electrical resistance because of changes in l by adjusting a shunt resistance across the crystal so the e.m.f. is held constant, irrespective of l. Absorption in the medium is calculated from the values of shunt resistance for the path lengths of interest. Measurements were taken at three frequencies in the range 899.0 kc to 2514 kc. The quantity 2αλ2 as measured by the interferometric method is not constant but shows a systematic change with frequency.
ON MINIMUM AUDIBLE SOUND FIELDS
Authors: Sivian L. J. , White S. D.
Published: September 2005

The minimum audible field (M.A.F.) has been determined from data taken on 14 ears over the frequency range from 100 to 15,000 c.p.s. The observer is placed in a sound field which is substantially that of a plane progressive wave, facing the source and listening monaurally. The M.A.F. is expressed as the intensity of the free field, measured prior to the insertion of the observer. Similar data are presented for binaural hearing, over the range from 60 to 15,000 c.p s., obtained with 13 observers. At 1000 c.p.s. the average M.A.F. observed is 1.9 × 10−16 watts per cm2, corresponding to a pressure 71 db below 1 bar. Included are data showing how the M.A.F. varies with the observer's azimuth relative to the wave front. Another type of threshold data refers to minimum audible pressures (M.A.P.) as measured at the observer's ear drum. The differences obviously to be expected between M.A.F. and M.A.P. values are due to wave motion in the ear canal and to diffraction caused by the head. The M.A.F. data are discussed in relation to the M.A.P. determinations from several sources. Some possible causes of difference between the two, which are due to experimental procedure and may add to the causes already mentioned, are pointed out.
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 loud speaker 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 − 0 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.
A New Portable Meter for Noise Measurement and Analysis
Authors: Osbon W. O. , Oplinger K. A.
Published: September 2005

This paper describes (1) a portable noise meter, the development of which is based upon several years experience in the field of industrial noise measurements, (2) a new superheterodyne analyzer attachment for the noise meter which permits analysis of noises with a high degree of selectivity and (3) a moving coil type of pick-up for making vibration measurements. The principle considerations in the design of the various units have been ruggedness, simplicity of operation, portability, and accuracy. A general discussion of the factors involved in the design and use of noise measuring instruments is given.
The Determination of the Acoustical Output of a Telephone Receiver from Input Measurements
Authors: Fay R. D. , Hall W. M.
Published: September 2005

The paper describes how an analysis of the functioning of a telephone receiver can be made by measuring the terminal electrical impedance of the receiver as a function of the length of a closed tube into which it works. With these data it is possible to calculate the excess pressure and the velocity of the air at the mouth of the receiver in relation to the voltage across the input terminals for any load condition. The analysis therefore furnishes means both for measuring acoustic impedance and for producing sound of known intensity.
Physical Methods of Exploration for Oil-Bearing Structures
Authors: Shepard E. R.
Published: September 2005

Modern scientific methods of prospecting for oil will be described and illustrated. These employ both natural and artificially produced forces. The former include gravitation, magnetism, galvanic potentials, radioactivity, and heat generation; while among the more important of the latter are seismic waves caused by an explosion and electric currents used in the study of the electrical resistivity of the earth.

A detailed description of the seismic method will be given particularly as it is used for determining the location of oil bearing salt domes on the Gulf Coast. In this method a charge of dynamite is exploded in the ground and the resulting waves through the earth are picked up by geophones at several points and recorded on an oscillograph film. The ground waves travel with different velocities, depending upon the character of the strata through which they pass. Because of the relatively high velocity of the waves through salt and stone, such mediums are easily detected.

A number of slides will depict different geologic formations with which oil is associated, while others will show seismic apparatus and the technique employed in locating the oil-bearing structures.
Recent Developments in Generators and Receivers of Directive Sound Signals in Air
Authors: Hayes H. C.
Published: September 2005

Certain problems peculiar to the Navy in process of solution at the Naval Research Laboratory, Anacostia, D. C. have called for the generation and reception of powerful directive sound signals in air. This paper describes apparatus developed for this purpose, and discusses briefly some of the applications. A working model of the apparatus will be demonstrated.
Sound Ranging at the U. S. Coast and Geodetic Survey
Authors: Dorsey Herbert Grove
Published: September 2005

At this Bureau sound ranging is utilized in both the vertical and horizontal directions. The former, or echo method of depth measurement, was started in 1923 with the Sonic Depth Finder, which uses a method of regulating the rate of sending signals until the outgoing signal is binaurally heard to coincide with the incoming echo. From the rate of sending the depth is calculated. This method was displaced by the Fathometer when it was placed on the market in 1925. The Fathometer is direct reading by visual indications, the time elapsed between the outgoing signal and received echo being measured by the angle through which a neon tube has rotated during the interval. Fathometers are now used on practically all Coast Survey Ships.

The success of sound ranging in the vertical direction suggested its use in the horizontal direction and the method was developed early in 1924 with the cooperation of the Bureau of Standards. By this method a chronograph on the surveying ship records the explosion of a small bomb of TNT, the sound of which goes to two or more hydrophone stations and automatically causes the emission of radio signals which are recorded on the same chronograph. Such methods are now extensively used by Coast Survey Ships to locate their position in areas beyond the sight of land.
Measurement of Sound Absorption by a Modified Tube Method
Authors: Morrical K. C. , Watson F. R.
Published: September 2005

Measurements of the sound absorbed by small samples of material one foot square were obtained for five pitches,—4096, 2048, 1024, 512, 256, with numerical calculations of coefficients for the three higher pitches. Diffraction effects at the pitches 512 and 256 made the calculations uncertain. Sound from an electrodynamic loudspeaker passed through a cast iron tube 8 inches in diameter and 2 feet long where it impinged on the material placed at an angle of 45° to the axis of the tube. It was thus reflected so as to pass at right angles to its original direction through a side opening in the tube to a condenser microphone where it was measured. The path from the material to the microphone was enclosed by a tube of ground cork 2 inches thick held in place by porous metal screening. Additional measurements were taken with the sample removed (theoretically, 100 percent transmission, 0 percent reflection) and also with a thick glass plate replacing the material (100 percent reflection). Further experiments are in progress to get coefficients at the lower pitches.
Measurement of the Rate of Decay of Sound in Small Chambers for Frequencies to 11,000 cycles, and a Determination of the Effects of Temperature and Humidity on the Absorption of Sound in Air
Authors: Knudsen Vern O.
Published: September 2005

A modification of the Norris-Andree method of measuring the rate of decay of sound in small chambers has been developed which operates satisfactorily for frequencies up to 11,000 cycles. The rate of decay, in db per second, in cubical chambers 6 feet and 2 feet on an edge, is accurately linear over a range of at least 60 db. The equipment has been used to determine the effects of temperature and humidity on the absorption of sound in air. The results obtained confirm those obtained by the author two years ago, but the measurements have been extended to higher frequencies, to dryer air, and to temperatures between 0 and 70°C. The results exhibit further evidence of the absorption of sound owing to the transfer of energy by collisions of H2O and O2 molecules (see abstract by H. O. Kneser, Bull. Am. Phys. Soc. for Washington meeting, April, 1933). The apparatus also is convenient for measuring the absorption coefficients of small samples of acoustical materials, especially at high frequencies.
Minimum Audible Sound Fields
Authors: Sivian L. J. , White S. D.
Published: September 2005

A paper by this title was presented at the last meeting of the society. It dealt principally with the thresholds for monaural hearing in an open sound field. Since that time the work has been extended to include the field thresholds for binaural hearing. The present paper is to report on the new data and to indicate how the threshold is modified by the observer's azimuth relative to the wave front of the sound field.

It also gives a further discussion of the relationship between the two types of threshold: the above minimum audible field (M.A.F.), and the minimum audible pressure (M.A.P.) as measured at the observer's ear-drum. It has been established that the two are different at frequencies so low that diffraction caused by the head and wave motion in the ear canal cannot be assigned as causes. Some new experimental evidence bearing on this point, is presented.
The Relation of the Reference Level for Loudness and Intensity Measurements of Sound to the Thermal Noise Level in Electric and Acoustic Circuits
Authors: Fletcher H.
Published: September 2005

The reference level for comparing loudness and intensities of sound which is being considered for adoption by the American Standards Association is a sound intensity of 10−16 watt per square centimeter in a freely travelling wave front. It has been shown by H. Nyquist (Thermal Agitation of Electric Charge in Conductors, Phys. Rev. July, 1928) that the fluctuating voltage V created at the terminals of a resistance R is the same as would be caused by a power P being consumed in the resistance where P = V2R = 10−16T303 Δf6000. The quantity T is the absolute temperature and Δf is the frequency band being transmitted. For an area A large compared to the wave-length the sound intensity due to thermal agitation is given by JA = 10−16Δf6000 T303. For a small area compared to the wave-length Sivian and White have shown that J = 10−16f23 − f1<3150003 where f2 is the upper and f1 the lower frequency limit of the band being transmitted. By means of the loudness formula, it is shown that the acoustic thermal noise is only a few db below the threshold. of hearing and is probably what limits very acute hearing.
Discussion on the Design of a Rotating Mirror Oscilloscope
Authors: Mallina R. F.
Published: September 2005

In the laboratory and in the classroom it is sometimes useful to project the wave form of electrical or acoustical phenomena on a screen. A rotating mirror in combination with a vibrating mirror and a light source is a convenient way of showing such waves. The problem of building an instrument for such purposes is comparatively simple if a small screen is used in a dark chamber. However, if the screen is made large enough to be viewed by a dozen people or more, many difficulties arise.

The paper describes how the various parts of the apparatus may be coordinated in order to produce a comparatively bright clearly defined wave with a small incandescent lamp in a room of average illumination. The vibrator used in the apparatus may be so constructed that its response is either inversely proportional to frequency or independent of frequency. The range covered is between 100 and 3000 cycles.
The Influence of Phase on Tone Quality and Loudness; the Interference of Subjective Harmonics
Authors: Chapin E. K. , Firestone F. A.
Published: September 2005

A strong 108 cycle fundamental and one of its harmonics were impressed on one ear in various relative phases and sound pressures. The tone quality and the loudness of the combination were found to depend on the relative phase of the two components. In a certain phase relation the loudness of the combination was 3.5 db less than the loudness of the fundamental alone; varying the phase changed the loudness of the combination by about 10 db. The above observations may be explained by assuming that the ear mechanism distorts the pure components of a complex sound pressure, producing subjective harmonics which may either constructively or destructively interfere depending on the relative phases of the components. Some evidence was found in support of an assumption that the subjective harmonics due to a single low frequency pure tone actuating the ear, are in phase as cosine functions without epoch angles.
Filtration of Elastic Waves in Solid Rods
Authors: Lindsay R. B.
Published: September 2005

The theoretical studies previously made on the filtration of compressional waves in solid rods by Lindsay and White have been extended to the case of torsional waves in a rod and of compressional waves in rods having solid rods for side branches. If an infinite cylindrical rod is loaded at equal intervals of length 2l with disks (having planes perpendicular to the rod) of mass m and moment of inertia I about the axis of the rod, the resulting structure is found to act as a low-pass filter for torsional waves. The transmission bands are given by the condition +1⩾cos W⩾−1, where cos W = cos 2kl − ωI/πa4ρ0c⋅sin 2kl. Here k = ω/c = 2πν/c, where ν is the frequency of the waves. The velocity of propagation c = (μ/ρ0)12, where μ = rigidity modulus and ρ0 is the mean density of the rod. The radius of the rod is a. For given I, increase in l decreases both the cut-off frequency of the first transmission band as well as the upper limit of the first attenuation band. For given l, increase in I decreases the cut-off frequency. There is next considered the case of an infinite cylindrical rod loaded at equal intervals of length 2l with perpendicular side rods of length ls. The approximate assumption is made that longitudinal compressional waves in the main rod set up transverse flexural waves in the side rods. Calculation indicates that if the side rods have free ends the structure acts as a low-pass filter for compressional waves in the main rod. If on the other hand the side rods have rigidly clamped ends, the structure under suitable choice of dimensions (in particular l/ls≫1) can act as a high-pass filter. Numerical illustrations are given.
Acoustics of a Board of Trade Room
Authors: Watson F. R.
Published: September 2005

The acoustical problem of a board of trade room is quite different from that of an ordinary auditorium. Instead of a single speaker and a quiet audience, there is a group of perhaps 200 traders all yelling at the top of their voices, with attendant noises of a considerable number of telegraph instruments and loud calls for messenger boys. The acoustic problem is to ascertain the conditions which will promote the possibility of one trader being heard in the general uproar by other traders. Calculations are given for the loudness of one trader's voice compared with the loudness of the group, also the reenforcing effect of the ceiling and sidewalls. The conclusion is drawn that individual traders can be heard in much the same way that individual instruments are distinguished in an orchestra.
Reverberation Time and Absorption Measurements with the High Speed Level Recorder
Authors: Bedell E. H. , Swartzel K. D.
Published: September 2005

The high speed level recorder described by Messrs. Wente, Bedell and Swartzel may be used in many types of acoustical measurements. It is particularly well adapted to the measurement of reverberation time, however, because with a single interruption of the test tone a continuous curve of sound intensity during the decay period is obtained on a logarithmic scale. The level recorder has recently been modified so that measurements can be made through an intensity range as great as 90 db. This paper presents some data obtained with the level recorder on reverberation measurements in a sound chamber, and includes an investigation of the accuracy of the results as affected by the intensity range through which measurements are made, the use of rotating reflectors, warble tones, a number of loudspeaker and microphone positions, and a number of microphones simultaneously, placed at different locations in the chamber.
Effect of Distribution and Location of Acoustical Material upon Its Sound Absorption
Authors: Chrisler V. L.
Published: September 2005

Experimental data are presented showing that the absorption of an acoustical material depends upon the size of the surface of the acoustical panel as well as its location and the manner in which the panels are distributed around the room. This phenomenon depends to some extent on the frequency of the sound. Most of these measurements were taken in the laboratory but a few measurements have been taken on installations in various buildings. Measurements taken in the field agreed with those taken in the laboratory.
The Absorption of Sound in Oxygen as Influenced by the Presence of Other Gases
Authors: Knudsen V. O. , Kneser H. O.
Published: September 2005

The authors recently have described experiments which show that the absorption of audible sound in oxygen is strongly influenced by the presence of water vapor. [J. Acous. Soc. (Oct., 1933).] The present work describes the effects produced when other gases are mixed with oxygen, such as He, H2, CO, CO2, NH3, H2S, CCl4, C2H5OH, C2H2, C6H6, and other hydrocarbons. Of these gases, all except CO and CO2 produced effects similar to that produced by water vapor, that is, as the concentration of the foreign gas was increased from zero the absorption coefficient m increased to a maximum and then decreased. In every instance the maximal value of m coincided with that previously obtained for oxygen and water vapor (10×10−4 cm−1 at 3000 cycles and 20×10−4 cm−1 at 6000 cycles), but the concentration at which the maximal absorption occurred was very largely dependent upon the kind of foreign gas mixed with the oxygen. Thus, a trace of C2H5OH was sufficient to give the maximal absorption, whereas concentrations of the order of 10 to 50 percent were required for such gases as H2 and He. For all admixed gases, with the exception of water vapor, the concentration at which the absorption is a maximum is proportional directly to the frequency.
History of the Use of Acoustical Materials
Authors: Berlin Harold R.
Published: September 2005

A summary of the development and use of commercial sound absorbents and some problems in their manufacture and sale.
Writing Acoustic Specifications
Authors: Wolf S. K. , Burgess G. V. T.
Published: September 2005

The writing of acoustic specifications is in such a chaotic and unformed state that it suffers enormously in comparison with the well-ordered and fundamentally sound practices which have been built up in specifying the character of other parts of a building structure. This paper discusses the several phases of the existing problem, suggests methods of handling them, and reviews the work now being done to settle many of the questions which face the acoustic engineer. The objectives sought in the specification of acoustic material characteristics for noise reduction and for control of reverberation, and in the specification of sound insulative construction, and degrees of quiet in the operation of mechanical equipment are outlined. The sound frequency range to be considered, the method of measuring and checking the performance of specifications, the probable limits of accuracy of such measurements and the units and reference values to be used are discussed. The conclusion states the need of further work by acoustic material manufacturers, research engineers, and testing laboratories to provide the specification writer with all the information needed.
Cavity-Wall Influence in Cavity Resonance
Authors: Cotton J. C.
Published: September 2005

Since the walls of the resonant cavities concerned in voice production are non-rigid in character, a study of vocal resonance might well begin with an experimental investigation of various soft walled cavities. The apparatus being used in this study was described at the Ann Arbor meeting of the Society, November 29, 1932. Results of this investigation reveal a number of important differences in behavior from that predicted by the theory based on “perfectly rigid walls.” Among these differences are: a higher fundamental resonant frequency; a radical decrease in the amplification of the driving tone at a resonant frequency; a reduction or loss of resonant response at harmonics of the resonator's natural frequency.
The Origin of the Threshold of Feeling in the Ear and Its Relation to Artificial Hearing Aids
Authors: Reger Scott N.
Published: September 2005

By means of a beat-frequency audio-oscillator, amplifier and a calibrated sound reproducer capable of high acoustic output levels it was found that 27 observers with complete bilateral hearing loss, due either to congenital defect or meningitic infection, but with normal tympanic membranes, possessed average value thresholds of feeling. This finding is interpreted to signify that the threshold of feeling is not causally related to stimulation of the acoustic portion of the eighth cranial nerve. The threshold of feeling in 33 ears lacking tympanic membranes because of the radical mastoid operation or prolonged otitis media was raised 20 db or more above the average values for normal ears, which suggests that the end organs responsible for the threshold of feeling are located within the tympanic membrane and epithelium lining the combined middle ear cavity and external auditory meatus. Individuals with pronounced hearing loss and intact tympanic membranes cannot tolerate high levels of sound amplification in a headphone to enable perception of speech sounds because of the pain elicited when high amplification stimulates the threshold of feeling. Individuals with equal hearing loss but lacking tympanic membranes can use sufficiently high levels of sound amplification to enable perception of speech sounds without arousing unpleasant sensations in the ear.
Responses to Vibrations Received Through the Skin
Authors: Goodfellow Louis D.
Published: September 2005

This paper presents some of the results of research on the senses of touch and vibration and the extent to which they can be used to interpret the vibrations of speech and music when the highly developed ear ceases to function. First, the author discusses the nature of the senses of touch and vibration—their neurological basis, the limits of frequency and intensity within which they function, and their capacity to discriminate subtle differences in pitch, intensity and quality. Other data on the senses of touch and vibration such as differences in sensitivity depending upon the part of the body used, and the individual observer, illusions of hearing due to vibratory stimulation, a comparison of auditory and tactual sensitivity, and the localization of the source of a vibrating body complete the description of the senses of touch and vibration. After a review of the research of Professor Robert H. Gault and his attempt to apply these data in developing a means of communicating with the deaf through these lower senses, the author presents available data on contemporary research in this field and a description of the Gault-Teletactor, the apparatus used for transmitting the vibrations of speech and music to the finger tips of the deaf.
Interpretations of Vibro-Tactile Experiments
Authors: Gault Robert H.
Published: September 2005

Touching is primitive “hearing.” The human ear is properly described as a highly developed organ of touch. In the course of evolutionary development leading to our ear, there appeared what is probably rightly called a “sense of vibration.” The author's current experiments involve a “sense of vibration.” This suggests the following question: Has the ear concentrated in itself all the “hearing” function that in early stages of phylogenesis was very widely distributed throughout the organism? Many thousands of observations in our wide variety of experimental situations, as well as the work of Dr. Katz in Rostock and Dr. v. Frisch in Munich, point to the negative of this question and support a phrase that was used by the late Dr. Victor Vaughn in his mention of some of our earlier work: “We hear not only with our ears but with our whole bodies.” There is no possibility of answering the question whether the practiced deaf in our experiments acquire the feeling that is the quality of hearing in normal subjects. It is at least plausible. From a psychologic angle the acquisition of the rudiments of spoken language and of the ability to interpret it in our procedure go along the same lines as in the usual normal situation.
Synchronized X-Ray and Oscillographic Speech Records
Authors: Russell G. Oscar , Palomo Jose
Published: September 2005

The synchronization of physiological and physical speech studies would seem to be the logical next step in analyses of their characteristics. Not only should a study be made of the physical characteristics as manifest in the oscillographic record, but the physiological position at any exact instant should also be known if a complete understanding is to be had. It is obvious that both records will have to be automatic. The x-ray exposure time will have to be reduced to at least 1/120th of a second if a study of normal speech is to be made. Prolonged or sung vowels are not characteristic of normal speech. Consequently such x-ray procedures have long since been discarded by careful investigators. Since motion picture x-rays consisting of 1/120th of a second are not yet feasible, the instantaneous x-ray exposure used in this study is chosen as the next best technique. Sound picture records likewise synchronized therewith serve as a check back on the final resultant.
Pitch and Intensity Characteristics of Connected Speech
Authors: Tiffin Joseph
Published: September 2005

Curves of fundamental pitch and relative intensity, both graphed against time, were obtained from approximately 200 subjects. The pitch curves were obtained from oscillograms and from the strobophotographic camera (to be described briefly). The intensity curves were obtained by means of a high speed output-level indicator, equipped to give a photographic record (to be described). The subjects were divided into groups according to speech training and experience and separate analyses made of the data from each group. Spoken material both factual and informational in content was used, separate analyses again being made for each type of material. The major results consist of a statistical summary of the pitch and intensity characteristics of these voices speaking under the different conditions. A treatment of the rôle of pitch and intensity in determining emphasis, or stress, and the effect of emotional expression on these sound wave factors, will also be included.