bluuebunny/crossref_metadata_2025 huggingface dataset:
The Application of Modern Instruments to the Study of Phonetic Problems
Authors: Steinberg J. C.
Published: September 2005

A description of the flow of speech, one that shows how the different physical properties of the waves change with time, and also how the changes are interpreted by the ear as changes in sensation, is of considerable importance in the study of phonetics. Theoretically, such a description can be obtained by analytical methods from an oscillograph record, but the labor involved is very great indeed. Consequently, it would be desirable to have instruments to show these changes directly. An oscillograph record of a short phrase has been analyzed to show how the frequency of the voice fundamental, the intensity of the wave, and the resonant frequencies and damping of the vocal cavities changed with time as the phrase was spoken. From these properties, the time variations in the corresponding sensations, i.e., pitch, loudness and quality, were obtained. These results indicate some of the problems that are encountered in applying instruments to the study of phonetics.
Exhaust Mufflers for Automotive Engines
Authors: Nelson C. E.
Published: September 2005

The important frequencies encountered in the exhaust noise of an automotive engine are discussed and the means described by which these frequencies are attenuated. An analysis is made of the baffle muffler as compared to the direct flow absorption and resonator type of muffler.
Motional Impedance Diagrams
Authors: Littler T. S.
Published: September 2005

The paper discusses the significance of impedance measurements on a telephone receiver. It shows how these measurements, taken when the diaphragm is prevented from vibrating, set a limit to the impedances when the diaphragm is free. From the two series of measurements, it is possible to determine the mechanical energy supplied to the vibrating diaphragm.
Recording Instruments for Frequency and Intensity
Authors: Hunt Frederick V.
Published: September 2005

An inexpensive recorder which employs a spark to puncture a moving strip of chart paper has been constructed. One of the sparking electrodes is a light pointer attached to a short-period D'Arsonval galvanometer element. The other is a curved metal guide which bends the chart paper to the arc described by the tip of the pointer. In conjunction with the logarithmic vacuum-tube voltmeter already described (Rev. Sci. Inst. 4, 672, 1933) this instrument comprises a level recorder having a uniform decibel scale (60 db) and capable of following sound decay curves as steep as 150 db/sec.

A new electronic frequency meter has been developed which is capable of following rapid variations of frequency. This device employs gas-filled discharge tubes and yields an output that is strictly linear with frequency from zero to 8000 cycles and independent of the input intensity over a range of at least 35 db. The instrument is flexible and any portion of the frequency range may be fitted to the indicating instrument permitting high sensitivity to small frequency changes. In combination with the spark recorder, or any other type of recorder, this instrument places the delineation of time variations of frequency on an equal footing with time variations of intensity. For example, the melodic curves or intonation of speech and music, vibrato, and attack may be recorded directly.
Acoustics of the Rooms at the Bureau of Standards
Authors: Chrisler V. L.
Published: September 2005

A study has been made of the acoustical treatment in two rooms of the same shape and volume. In one room the material was applied only on the ceiling. In the other room the total amount of absorption applied was smaller but the material was distributed over the upper part of the walls as well as on the ceiling. Owing to the distribution of the acoustical material, this room is acoustically the better of the two, although as usually computed, the total absorption was not as great as in the other room.

A third room which is used as a cafeteria was also studied. In this room about twice the customary amount of material was installed. Curves are given showing the variation in noise level with the number of people present, both before and after treatment.
Report of Committee on Sound-Absorption Measurements
Authors: Watson F. R.
Published: September 2005

The Acoustical Society Committee on Sound Absorption presents a report for the information of the members of the Society. After preliminary experiments on a variety of materials, using different methods, a plan was evolved by which each of the various laboratories would be furnished a sample of the same material, with the expectation that the results obtained would be more strictly comparable than the data for different samples. The Celotex Company volunteered to make up a special run of BBB Celotex and furnish it gratis to the laboratories. The results of this experiment are shown (lantern slides) and exhibit a wide variation in the values of the coefficients. The reverberation method was used in all the tests, but there was considerable difference in the electrical instruments used. One chief reason for the variation in results was found in effect of area of material used; for instance for the frequency of 500 cycles per second, 12 sq. ft. of material gave a coefficient of 1.55, where 192 sq. ft. gave 0.44.

No standard method is approved at the present time, but certain recommendations have been adopted for guidance in absorption tests. In the meantime, several different methods are being investigated, with the expectation that a solution of the present difficulties will be found.
The Timbre of Orchestral Instruments
Authors: Seashore C. E. , Rothschild Donald
Published: September 2005

Harmonic analysis has been made of ten representative instruments with two variables: (1): a sampling of pitch throughout the normal register of the instrument, and (2), for each tone, a loud and a soft rendition. The results give a graphic picture of the characteristics of each instrument and its range of variability dependent on pitch and intensity.
The Interpretation of Sound Measurements Used as a Tool in Machinery Noise Reduction
Authors: Abbott E. J.
Published: September 2005

The recent reports of standardization committees on acoustical measurements and terminology will be of very great value in eliminating confusion which has existed on account of differences in the use of terms, in different references levels, equal loudness contours, etc. This work is highly commended. Unfortunately, however, these standardizations valuable as they are, do not eliminate all the confusions which exists; not only with workers in acoustics but more especially with engineers and executives whose primary interest is not acoustics but who are vitally interested in noise reduction and similar problems. It also appears that this confusion is hardly a matter which can be cleared away by committee action but which must be worked out in practical application.

At present there are at least seven scales used for indicating the magnitude of a sound, namely: sound pressure, sound pressure level, above threshold level (sensation level), intensity, intensity level, loudness level, and loudness. All of these scales are recognized by standardization and there seem to be definite reasons why each of these scales is valuable in practice. However, since four of them are expressed in decibels and often without further identification, great confusion results, particularly among engineers and others who are interested in noise, but who are not primarily acousticians.

This paper states the advantages and disadvantages of these various scales, together with suitable illustrations drawn from practice of the difficulties which arise in putting these scales to practical use in machinery noise reduction problems.
An Application of the Doppler Effect to Avigation
Authors: Delsasso L. P.
Published: September 2005

A short pulse of sound of frequency ns emitted from a ship moving with velocity v and making an angle α with a reflecting surface is shown to be received at the ship as an echo of frequency nR = nsp2−cos2 α+sin α(p2−cos2 α)12p2−:cos2 α−sin α(p2−cos2 α)12 where p is the ratio of the velocity of sound to that of the ship. An experimental check was obtained from observations made in an airship, by recording on an oscillograph samples of the transmitted sound and its echo. The agreement with the theory is within the experimental error.
An Acoustic Spectrometer
Authors: Hickman C. N.
Published: September 2005

A series of tuned reeds are mounted so that they may be electromagnetically driven. Each reed carries a small concave mirror with which light from an illuminated slit is brought to a focus on a screen. These slit images are lined up in the order of the reed frequencies. When a current having a complex wave, such as the speech current from a microphone, is passed through the electromagnet, the reeds and in consequence the slit images on the screen will oscillate. The driving system and the reeds are so designed that the amplitude of oscillation of each image is proportional to the strength of the corresponding harmonic component in the driving current. Therefore, by observing or photographing the slit image amplitudes, the frequencies and the relative energy content of the components of a complex current may be determined. A spectrometer of this type covering a small frequency range (50 to 3109 cycles) was built for demonstration purposes. The range of such an instrument can be extended to higher and lower frequencies.
The Doppler Effect for Sound in a Moving Medium
Authors: Young Robert W.
Published: September 2005

An alternate derivation of the Bateman formula for Doppler's principle is described. A method is given for the evaluation of the direction cosines which appear in this formula, so that in the special case of constant velocities of sound, and of the medium ν′ν = u[a2−(v2+w2)]12+a2−v2−w2−[a2−(v2+w2)]12U1+vV1+wW1u[a2−(v2+w2)]12+a2−v2−w2−[a2−(v2+w2)]12U0+vV0+wW0 where u, v, w are component velocities of the medium, a is the velocity of sound, U0, V0, W0 the component velocities of the source, and U1, V1, W1 those of the observer. The x-axis here connects source and observer, and ν and ν′ are, respectively, the original and observed frequencies. The case of a stratified medium is also considered.
The Relation of Pitch to Intensity
Authors: Stevens S. S.
Published: September 2005

Measurements were made of the amount by which the pitch of tones ranging from 150 to 12,000 cycles is changed by an increase in intensity. Observers were presented alternately with two tones of different frequency and required to make them sound equal in pitch by varying the intensity of one of the tones. The results, when plotted as equal pitch contours, show (1) the pitch of high tones increases with intensity, (2) the pitch of low tones decreases with intensity, (3) the point at which the effect reverses varies with intensity level. The fact that the points of reversal correspond quite closely with the points of greatest sensitivity of the ear, as shown by contours of equal loudness, suggests that the change in pitch with intensity is due to the resonant characteristics of the ear.
A Loudness Scale for Industrial Noise Measurements
Authors: Churcher B. G.
Published: September 2005

Both on technical grounds and from experience in industrial noise measurements, it is recognised that the decibel scale, used as a loudness scale, does not yield numerical values proportional to the loudness sensation. In many spheres of work this occasions great inconvenience and there is need for an agreed rule for converting the decibel observations of practical noise measurements into loudness values on a linear loudness scale. A survey has therefore been made of published data with a view to deducing the most probable law for the relation between stimulus and sensation for a 1000 cycle pure tone. Relations derived from mental estimates of loudness, from data on monaural-binaural listening and from data on the properties of tone combinations are discussed. The evidence indicates that not only does the nerve-impulse theory of audition provide an explanation of the faculty of making mental estimates of relative loudness and of the monaural-binaural listening phenomena, but that stimulus-sensation relations deduced by the two methods are in substantial quantitative agreement. On theoretical grounds it is not thought that tone combination data are admissible for this purpose and an important divergence between these and monaural-binaural data appears to exist. Consequently the suggested relation put forward (Proposed Standards for Noise Measurement, J.A.S.A. 5, 109 (1933)) is not felt to be the most probable law. For the final relation derived in the present paper from the available data, the number 100 is assigned to the loudness evoked by an intensity of 100 db above 0.0002 dyne per sq. cm reference pressure. For practical industrial noise measurements, the relation is expressed sufficiently nearly by a simple power law between the limits of 30 and 115 db. Over this range, the loudness L is given by L = d5 × 10−8, where d is the number of decibels above reference pressure. In addition to its being more in conformity with introspective judgments of relative loudness, this simple rule is thought to be preferable to the suggested curve because it is easily remembered, accurately definable and easily used with the aid of a slide rule.
On the Use of Sound Measurements in Machinery Noise Reduction
Authors: Abbott E. J.
Published: September 2005

Noise has long been an important problem in many kinds of machinery but the use of sound measurements in dealing with it has not been very extensive. Engineers generally seem to regard machinery noise as one of those things which does not follow the rules of logic and common sense and, in a number of cases, attempts to use noise meters have increased rather than diminished this feeling. The difficulty seems to be that here is a new and complicated field in which the fundamentals are rather unusual, somewhat complicated, and not generally recognized. As a result, engineers do not know what can be expected from sound measurements, and quieting experiments are often illogically planned or improperly interpreted. On the other hand, experience has proved that even the most complicated noise problems can be untangled and cleared up with sound measurements which definitely indicate methods of noise reduction. Often quieting can be obtained with little or no increase in cost of production, in ways which were not at all apparent at the outset. Several practical noise problems are outlined, together with their difficulties and methods of solution.
Response Measurement and Harmonic Analysis of Violin Tones
Authors: Abbott R. B.
Published: September 2005

Output intensity measurements and harmonic analyses were made on the open strings of a series of twenty-one violins ranging in price from $25 to $10,000 each. To secure standardized conditions, a mechanical bowing device was used, and the pressure, speed, and relative position of the bow maintained constant. A crystal harmonic analyzer, operating synchronously with an automatic level recorder, furnished a graphical record of the desired tone structures. The measured responses, tone centers, and tone structure factors were plotted against the retail prices of the violins and correlations found to exist.
Influence of Experimental Technique on the Measurement of Differential Intensity Sensitivity
Authors: Montgomery H. C.
Published: September 2005

The lack of agreement among previous measurements of differential intensity sensitivity indicates that the values obtained depend to a large extent on the experimental conditions. An attempt was made to assess the importance of various factors and to discover the conditions which would lead to the smallest values of differential intensity sensitivity. The values thus obtained were of the order of 0.1 db at high levels above threshold, and were consistently smaller than any previously reported. Certain psychological aspects of the measurements are considered, and it is suggested that the observer's response is essentially variable, and should be measured by statistical means.
The Electrical Phenomena of the Cochlea and the Auditory Nerve
Authors: Davis Hallowell
Published: September 2005

The electrical phenomena of the ear and of the auditory nerve are described. One component of the electrical disturbance is generated by the sensory cells of the organ of Corti and reflects accurately the fluctuations of mechanical pressure which they undergo. The other represents the action potentials associated with the nerve impulses in the auditory nerve. Recent work, particularly that carried on at the Harvard Medical School, is summarized and the following conclusions are drawn: Nerve impulses appear synchronized with the stimulating sound waves up to an extreme limit of 4000 per second, but the correspondence is fortuitous, depending simply on the intermittent character of the stimulus and on the nature of nerve impulses, and it plays no part in the perception of pitch. Stimulation is associated with outward, but not with inward, movement of the tympanum. The basilar membrane is progressively “tuned” from end to end, resonating at its basal end to high tones and at its apical end to low tones, and thus serves as a harmonic analyzer. The sensation of pitch depends upon which group of nerve fibers is activated and not upon their frequency of discharge. Loudness depends upon the total number of nerve fibers activated and not upon the total number of impulses per second traveling to the brain. Masking does not appear in the electrical response of the cochlea, but is present in the response of the auditory nerve and depends ultimately on the necessity of a recovery period following the passage of each nerve impulse. Masking is modified by changes in the phase relations of the competing stimuli.
The Absorption of Sound in Gases
Authors: Knudsen Vern O.
Published: September 2005

Several investigators have shown recently that if the changes in the internal energy of a gas take place so slowly that they cannot follow the adiabatic changes which result when a sound wave passes through the gas, sound dispersion and anomalous absorption of observable magnitudes occur. Experimentally, it is found that the absorption in the air, for example, not only depends upon temperature and humidity in a characteristic manner, unsuspected by classical theory, but at frequencies above 1000 cycles is so great as to require consideration in such technical problems as architectural acoustics and sound signaling. The findings are in good agreement with the new theory. The presence of small impurities (less than one percent) in gases may change the speed of sound at certain frequencies as much as several percent: and the absorption coefficient as much as several hundred percent. Absorption measurements for frequencies between 1000 and 40,000 cycles in O2 containing small impurities of H2, He, H2O, H2S, NH3, CO, CO2, O3, C2H2, or one of many other hydrocarbons throw light on the nature of molecular collisions. A new device is thus available for studies in molecular physics, and acoustics has become a potent ally of the quantum theory.
Performance of Telephone Receivers as Affected by the Ear
Authors: Olson Harry F. , Massa Frank
Published: September 2005

An analysis is made of the impedance characteristic of the ear when coupled to a telephone receiver by means of an ear cap which introduces an acoustic leak at the junction. A vibrating system is also described which causes constant sound pressure to be generated in the ear cavity under such conditions. Experimental data as obtained on an artificial ear are given showing the effect of the acoustic leak on the response of various types of receivers. Subjective tests are also described and data given which corroborate the data obtained on the artificial ear.
Acoustical Instruments
Authors: Wente E. C.
Published: September 2005

Previous to the development of amplifiers most of the instruments used in acoustical research depended for their operation upon purely mechanical principles. This paper includes a brief survey of such of these instruments as are still of interest in connection with the investigation of technical or research problems in acoustics, but it deals primarily with the more recent electrical devices used in the study of air-borne sound waves. The limitations and fields of application of various electrical instruments, including microphones, particularly adapted to definite types of acoustic measurements, are discussed.
Influence of Experimental Technique on the Measurement of Differential Intensity Sensitivity of the Ear
Authors: Montgomery H. C.
Published: September 2005

The lack of agreement among previous measurements of differential intensity sensitivity indicates that the values obtained depend to a large extent on the experimental conditions. The relative importance of various factors is indicated, and a procedure is suggested which was designed to give the smallest possible values of differential intensity sensitivity. Intensive measurements made by this method upon a single subject, using a pure tone of 1000 cycles gave values consistently smaller than any previously reported. There is no sharp division between intensity changes which can be perceived and those which cannot. The response of the subject is essentially variable and can only be described by statistical methods.
Dust Figures in a Kundt's Tube
Authors: Hastings R. B. , Ball D. H.
Published: September 2005

An experimental investigation of Kundt's tube phenomena has been performed with the primary purpose of investigating the actual motions and appearances of the striations under different conditions. No attempt was made to formulate rigorous theories explaining the figures. Very clear photographs of the particles in a striation were made by causing the striation to move out to the end of the tube and remain stationary long enough to be photographed. Photographs were also taken through the eyepiece of a microscope. From these it was evident that the particles in a striation did not, in general, touch each other. Striations on either side of a long metal rod on the bottom of the tube usually showed different spacings and occurred in different numbers on either side. This could not be caused by overtones since it is unlikely that more overtones could exist on one side than on the other. An electrostatic charge in motion near the tube prevented the figures from forming. A stationary charge in no way prevented their formation. Figures destroyed by the motion of a charge would slowly build up again when the charge was brought to rest, even with the charge present.
Sound Control and Isolation in the Design of Broadcast Studios
Authors: Nixon G. M.
Published: September 2005

The paper contains a discussion of the necessity for making relatively elaborate provisions for sound control and isolation of broadcast studios, particularly studio groups as large and complex as the NBC studios at Radio City. A description is given of the methods of isolating a studio from those adjacent and also from surrounding spaces; of sound control and isolation details of windows, doorways, vestibules, foyers, corridors, electric light and power wiring, and the installation of isolating partitions. The paper also contains a discussion of the control of noise in an air conditioning system; layout and isolation of duct work; choice of sound absorbing material and manner of installation in duct work; design and choice of air velocities in supply and return outlets; and isolation of rotating machinery. A discussion is also given of anticipated noise levels and those obtaining after the completion of the installation.
Practical Airplane Quieting
Authors: Norris R. F.
Published: September 2005

The noise problem as found in an actual plane is stated, the method of attack outlined, and the actual treatment described. Sound-level readings are given before and after remodeling and the results discussed.
Transmission of Plane Sound Waves Through Multiple Partitions
Authors: Kimball A. L.
Published: September 2005

The transmission ratio, and thus the transmission loss in decibels, has been determined from a theoretical consideration of this problem, based on certain simplifying assumption such as zero stiffness compared with mass, an air layer between partitions small compared with the wavelength, etc. Three cases in particular are considered, the transmission loss being expressed as a function of wavelength of sound, weight per square foot of partitions, and distance between them: (1) Double partition wall; (2) Single wall (noting check with previous work); (3) Double partition and single partition loosely fixed to vibrating surface as a means of reducing sound radiation from that surface. Certain limitations of the theory are explained briefly.
On the Auditory Sensitivity of Animals Relative to Man
Authors: Steinberg John C.
Published: September 2005

This note abstracts from recent literature a comparison of the auditory sensitivity of four different animals—the chimpanzee, the monkey, the cat, and the guinea pig—as obtained recently by four different experimenters using four different methods, with that of man. The work represents painstaking attempts at a quantitative determination of animal sensitivity. The data indicate that for tones of frequency of 1000 cycles or less the auditory sensitivity of the animals did not differ significantly from that of man. The cat and the guinea pig appear significantly less sensitive than man for tones of 4000 cycles and higher. For tones of 8000 cycles and higher, the monkey and the chimpanzee appear more sensitive than man.
Apparent Duration of Sound Perception
Authors: Lifshitz Samuel
Published: September 2005

With the aid of a vacuum tube “impulsator” the limits for which the integral law of apparent duration holds true, were determined; they are expressed by the value ∫t1t2 log Idt, for the extent of the apparent duration. Experiments with different impulses of tones of 1000 vib./sec., showed that the law holds true for limits of from 2 to 50 units of apparent duration. As a unit of apparent duration we take the apparent duration of a pure, constant tone which has sounded for one second at a loudness level of 1 db. Further experiments with tones of 50, 100, 500, 1000, 2000 and 4000 vib./sec. showed that the integral of apparent duration holds true for these tones and does not depend on the frequency of the tone. The musical optimum of reverberation corresponds to 37 units of apparent duration. As a result of the limits determined as indicated above, we can consider that the integral law of apparent duration in its unvaried form is applicable for the determination of the musical optimum of reverberation for halls up to 80,000 cu. m in volume.
Relating to the Physics of Speech Sounds
Authors: Trendelenburg F.
Published: September 2005

It is difficult to find the composition of sounds which are aperiodic, especially those that change rapidly with time, such as those which occur frequently in spoken sounds. The methods of automatic electrical analysis cannot easily be used because they require too much time. Fourier-analysis by graphical and mechanical means cannot be recommended since too many single analyses have to be carried out in aperiodic occurrences. One obtains a very graphic picture of the time function of the sound composition by taking oscillograms of the single octaves of the sounds by use of band pass filters. The paper reports the results of such oscillographic analyses of speech sounds. The oscillograms obtained make it easy to recognize by inspection the various harmonic and nonharmonic components of speech sounds. From the photographs, conclusions are drawn with regard to the theory of voice.
An Analysis of Some Artistic Elements in Singing
Authors: Seashore Harold G.
Published: September 2005

A skeletal job-analysis is presented of the content of a scientific esthetics as applied to singing with tentative formulation of some laws of artistry in intonation, rhythm, phrasing, dynamics and tone quality, determined from objective measurements of the performances of accepted artists.
Preliminary Study of the Vibrations of a Violin
Authors: Saunders F. A. , Hall H. H.
Published: September 2005

It is well known that the vibrations of a violin are produced by those of the string, transmitted through the bridge, but that what we hear comes mainly from the top and back of the body, and from the enclosed air mass through the f-holes. The resonant pitches of the body and of the air column are examined by a method due to Raman. With an automatic player which produces a steady tone the least weight needed to make the instrument “speak” properly has been measured at each frequency. A curve of these weights drawn against the frequency discloses the resonant frequencies. A simple method is described whereby the main air-mass frequency can be distinguished from that of the body. The effect of the resonant pitches on the tone quality is briefly discussed, with reference to a few analyses obtained with the analyzer described at this meeting. Loading the bridge is shown to affect some of these resonant points; also the tension to which the whole instrument is subjected by the strings. Variations of the sound energy emitted in a definite direction with bow pressure, speed and distance from the bridge are given by graphs.
The Noise Problem in the Application of Fans
Authors: McMahan K. D.
Published: September 2005

This paper stresses the noise elements in the application of fans, particularly those of the propeller type, where the apparatus must operate in quiet surroundings. The sources of such noise are divided into the inherent noise of the fan, and the five classes of noise which tend to modify this inherent noise as follows: (1) Noise increase due to improper flow conditions; (2) noise increase due to improper application or design of fan; (3) change of the inherent noise by other parts of the apparatus; (4) amplification by the fan of noise made by other parts of the apparatus; (5) noise increase due to improper mechanical design or construction. The inherent noise forms a base level for the required performance of a given design operating under the best possible conditions, and depends upon the static pressure against which the fan must operate. The first and second classes of noise result because of deviations from the best operating conditions. The third and fourth classes deal with the interrelation between the fan, its motor and the system in which it works. The result of the third class may either be an amplification or an absorption. The fifth class concerns mechanical vibrations usually in a form of resonance. Several illustrations are shown as practical examples of each class of noise.
Reducing Noise in Airplane Sound Locators
Authors: House Frank R.
Published: September 2005

The maximum distance at which an airplane in flight may be detected by aural listening through sound locators has been found to depend on the ambient or masking noise level. Ambient noises and local disturbances which contribute to increase noise level at the listener's ear were investigated. Contrast between ambient sound and that of the airplane, either as total sound or some part of the sound frequency spectrum, rather than degree of amplification of the combined sound of the airplane and ambient through the sound receiver determines audibility. There are many disturbing elements which affect sound locator range. Some are generated within the sound locator receiver and mounting structure. Their magnitude and effect increase the masking sound level at the listener's ear and considerably reduce range. Soundproofing sound receivers, their mountings and cooperating units reduces the disturbance. The distortion of sound when amplified was studied. Since range was not dependent on amplification a smaller receiver was found to provide a more comfortable and less disturbing low frequency ambient sound level at the ear. Collectively, these have reduced the effective ambient level at the listener's ear. Disturbances caused by inclement weather and specific local noise are insulated. Their tendency to raise the effective ambient is minimized and our effective average listening range is increased.
Noise Reduction Problems in Central Stations
Authors: Cellerier J. F.
Published: September 2005

Data are presented covering insulating materials, central station machinery noise characteristics and curves of sound transmission.
The Characteristics of Sound Transmission in Rooms
Authors: Wente E. C.
Published: September 2005

By means of a high speed level recorder sound transmission vs. frequency characteristics have been measured between points in rooms having different acoustic characteristics. The measurements show that by a suitable choice of measuring conditions it is possible to determine not only frequency distortion and pressure levels at different parts of an auditorium, but reverberation characteristics as well.
The Use of Loud Speakers in Groups
Authors: Petzold Ernst
Published: September 2005

The number and strength of loud speakers, their relative location, and the radiated sound spectrum must be examined relative to acoustical principles. It follows that uniform distribution throughout a room is not only uneconomical but does not lead to best audibility. In view of interfering sounds, formulae are developed allowing computation of the required number and strength of loud speakers and their most favorable location, and the intensity for each observer. It is further shown how the absorption in air is to be considered. Using different sound spectra in loud speakers, there arises a greater total loudness than would be computed on a straight energy basis. Very large auditoriums do not follow the generally accepted acoustical laws. Short examples show the practical use of the formulae.
Tests on a Recording Analyzer for the Audible Frequency Range
Authors: Hall Harry H.
Published: September 2005

The heterodyne analyzer which was described two years ago (J. A. S. A. 5, 62 (1933)) has been improved. Three analyzing speeds are provided which cover the range from 50 to 10,000 cycles in 10, 6.61 and 3.78 seconds, respectively. The resolving power may be stated as follows: At all three speeds frequency components differing by 50 cycles may be separated if they are of the same amplitude. At the medium speed, components differing by 120 cycles and by 20 decibels may be separated, while at the lower and higher speeds the resolution is correspondingly better and worse. Typical analyses of violin sounds, speech sounds, noise and various synthetic waves, designed to illustrate the performance of the instrument, are presented. The filter employed is of the magnetostrictive type (Proc. I. R. E. 21, 1328 (1933)). It consists of two resonant elements coupled by a vacuum tube. Records of the response of one of these elements to an alternating driving force of varying frequency as it passes through the resonance frequency of the element show the presence of fluctuations on the decay side as observed by Barrow, Ann. d. Physik 11, 147 (1931) and by Shuck, Proc. I. R. E. 22, 1295 (1934). In the response of the double filter, however, these irregularities are largely averaged out. The effect of imperfect matching of the resonance frequencies of the two elements, as well as the effects of damping and of the rate of frequency variation of the driving force, are shown and discussed. It is concluded that for a given rate of frequency variation there is a value of damping of the resonant element which results in a response of minimum width.
Internal Dissipation in Solids for Small Cyclic Strains
Authors: Wegel R. L.
Published: September 2005

When a solid body vibrates, the alternating strain within it induces a correlated dissipation of energy resembling internal static or rubbing friction. No material is purely elastic. Elasticity must be regarded as having a phase angle which varies little, or not at all, with frequency, and in metals is a small fraction of 1°. This friction introduces losses in acoustic apparatus in amounts depending on design, and also on choice and heat treatment of materials. Taking metals as a class, this dissipation is generally least in light materials like aluminum and duralumin, and greatest in the heaviest substances like lead. They may be varied by a factor of as much as 10 by heat treatment.
On Forced Vibrations of a Circular Plate with Free Edge by Point Excitation
Authors: Backhaus H. , Schuenemann R.
Published: September 2005

A circular Al-plate of 30 cm diameter clamped in the center is excited to vibrations in a special point by means of a loudspeaker system. This point was chosen either in 14.5 or 7 cm distance off the center. The modes of vibration of the plate were studied by varying the excitation frequencies between 575 and 1230 cycles. One natural frequency of the plate with three node diameters was found near 600 cycles, another with one node diameter and one node circle near 1230 cycles. The investigation of the mode of vibration was carried out by measuring punctually amplitude and phase by means of a “touching condenser.” The exciting voltage and the voltage of an adjustable phase required for compensation was taken from a specially built beat tone oscillator with two outlets. The measurements show that the node lines become very sharp in the neighborhood of the natural frequencies. In such node lines the phase jumps almost unsteadily about 180°. Outside of the region of the natural frequencies the node lines enlarge to node zones within which a steady phase transition takes place. There are no node lines in the sense that all their points remain at rest at all times, but only lines of smallest amplitude. The phases alongside of these lines of smallest amplitude vary in several cases from 90° to 270°. At the transition points the amplitudes become immeasurably small. Such transition points may be considered to be “true” modes of vibration. The appearance of such true node points presages a splitting up or a confluence of node lines, when the excitation frequency is increased. By increasing the frequency the mode of vibration develops in such a way that at first two neighborhood node radii flow together and form three islands at the plate edge. Then a fourth island is formed round the excitation point. These node lines then form a node circle in separating from the plate edge while two node lines form the node diameter.
A Method for Very Rapid Analysis of Sounds
Authors: Meyer Erwin
Published: September 2005

Sound analysis by a single band pass filter requires a considerable time, which is inversely proportional to the square of the frequency discrimination. Analyzers consisting of multiple resonators are cumbersome and do not cover a continuous frequency band. The paper describes a new method based on the dispersing properties of a diffraction grating analogous to those used in optical analysis and equivalent to an infinite number of resonators. The sound frequencies are modulated by a 40-kilocycle carrier, projected by a ribbon loudspeaker and reflected by a curved grating three meters long. The frequency discrimination thus attained equals that of a 125-cycle band selector; the theoretical speed of analysis approaches 0.01 second, making it possible to obtain “moving pictures” of continuously changing sound spectra.
Acoustic Impedance of Small Orifices
Authors: Sivian L. J.
Published: September 2005

Data are presented giving the measured acoustic reactance and resistance for a number of circular orifices varying in diameter from 1 cm down to 0.034 cm, and for a rectangular orifice 1.9 cm×0.075 cm. The measurements were made for various particle velocities, the corresponding Reynolds numbers varying from 0.7 to 3000, roughly. The reactance is found substantially independent of the particle velocity; a formula for computing it is given. The resistance approaches a constant value as the velocity is sufficiently decreased; formulae for computing this “low velocity” resistance are given. At larger velocities the resistance increases with the velocity. This is discussed from the standpoint of a loss of kinetic energy of flow, acting besides viscosity and turbulence.
Vortex Noise from Rotating Cylindrical Rods
Authors: Stowell E. Z. , Deming A. F.
Published: September 2005

A series of round rods of the same diameter were rotated individually about the midpoint of each rod. Vortices are shed from the rods when in motion, giving rise to the emission of sound. With the rotating system placed in the open air, the distribution of sound in space, the acoustical power output, and the spectral distribution have been studied. The frequency of emission of vortices from any point on the rod is shown to be given by the formula of yon Kármán. From the spectrum, estimates are made of the distribution of acoustical power along the rod, the amount of air concerned in sound production, the “equivalent size” of the vortices, and the acoustical energy content for each vortex.
An Effect of High Intensity Sound on Cellulose Fibers
Authors: Buckingham Stephen A.
Published: September 2005

It is found that an effect, known in the paper industry as “hydration,” can be produced by the irradiation of an aqueous suspension of cellulose fibers with high intensity sound. Methods of production and detection of “hydration” are discussed. A comparison is given of the magnitude of the effect produced by sound with that produced by conventional methods. The relative efficiency of sound in producing the effect is considered also.
The Harmonic Analysis of Consecutive Waves in the Vowel “Ah” in Normal Voices and Before and After Surgical Removal of Nasal Polyps
Authors: Black John , Lierlie Dean M. , Tiffin Joseph
Published: September 2005

Oscillograms were obtained of the word top as spoken by nine normal male voices and by five voices before and after surgical removal of nasal polyps. Every repetition of the wave pattern from the nine normals, and the first, third, fifth, etc., patterns in the sounds of the operated subjects were analyzed by means of a Henrici harmonic analyzer. A total of approximately 500 waves were considered, the analysis in each case reaching at least to the 25th component, and if necessary to the 45th.

The results justify certain conclusions relative to (a) the nature and importance of the temporal factor and wave-to-wave fluctuations in the vowel; (b) the support of the Helmholtz theory of vowel production; (c) location and variations of the three characteristic regions of energy; (d) probable reasons for certain inconsistent results found in studies of tongue position in vowel formation; (e) effect of removing nasal polyps on voice quality.
The Psychophysics of Frequency Modulation
Authors: Ramsdell Donald A.
Published: September 2005

The auditory sensations which result from a frequency-modulated stimulus provide a method for determining certain characteristics of the auditory mechanism. A tone produced by a beat-frequency oscillator was modulated by means of a rotary condenser in order to investigate the critical rate and range of modulation at which apparent fluctuations in pitch become apparent fluctuations in loudness. The rate of modulation for ranges under thirty cycles at which observers cease to detect a change in pitch is a function of the frequency of the stimulus.

At a given frequency, 500 cycles, continuous increase in the rate of modulation shows first a critical point at about eight modulations per second followed occasionally by a second critical point at about fourteen modulations per second, beyond which changes in both pitch and loudness are detectable simultaneously. The first critical point is a linear function of the rate and range of modulation, except lot large ranges where the critical rate decreases.

The critical point phenomena can be interpreted in terms of the persistence of vibration of the basilar membrane.
Flutter in Sound Records
Authors: Shea T. E. , MacNair W. A. , Subrizi V.
Published: September 2005

Frequency modulation of a sound signal produces some very interesting and sometimes not readily identifiable auditory sensations. Distortion of this type is caused in sound records by the nonuniform speed of the record during the recording or reproducing process.

While the physical nature of frequency modulation and some of the physiological effects produced by it are discussed, the paper consists largely of demonstrations including a demonstration of the side-band nature of flutter, the influence of room acoustics on the perception of flutter, the auditory effects of flutter in single frequency tones, and a demonstration of the auditory effects of frequency modulation in speech and music.
A Nondirectional Moving Coil Microphone
Authors: Giles L. W.
Published: September 2005

This paper describes a moving coil microphone, one of the principal features of which is its nondirectional characteristic, that is, its ability to pick up with equal fidelity sound coming from all directions. This nondirectional property is attained largely by the use of an acoustic screen which is located in front of the diaphragm of the microphone. In addition, this microphone possesses the advantages of small size, light weight, and a uniform response over a wide range of frequencies.
A Compound Horn Loudspeaker
Authors: Olson Harry F. , Massa Frank
Published: September 2005

A new type of loudspeaker is described in which a single mechanism is coupled to two horns: a straight axis high frequency horn and a folded low frequency horn. A theoretical analysis of the combined system is given and experimental data are shown which indicate smooth uniform response from 50 to 9000 cycles, and an efficiency of the order of 50 percent over a large portion of this range.
Apparatus and Technique for Reverberation Measurements
Authors: Hunt Frederick V.
Published: September 2005

New apparatus has been constructed for obtaining accurate reverberation data. The conventional method of timing the decay to an adjustable threshold is made automatic by a system of relays which control the following sequence: when a predetermined sound level is attained in the sound chamber the source is turned off and an electric timer is started; when the sound level falls to the adjustable threshold the timer is stopped and the source is turned on. If this recurrent cycle is interrupted after ten repetitions the average time for a single decay can be read directly from the timer. The apparatus is entirely a.c.-operated and 80 db of decay can be recorded in the middle audiofrequency range.

Using this apparatus we have investigated the merits of employing a low pass electric wave filter to remove the rapid fluctuations in the rectified output of the microphone amplifier. This is approximately equivalent to the use of a recorder which is just capable of following the average decay rate. Determination of the average decay rate is not affected by the use of the filter but the average deviation from linearity in the decay curves can be reduced by a factor of at least two.