Showing papers in "Journal of the Acoustical Society of America in 1937"

A Scale for the Measurement of the Psychological Magnitude Pitch

Abstract: A subjective scale for the measurement of pitch was constructed from determinations of the half‐value of pitches at various frequencies. This scale differs from both the musical scale and the frequency scale, neither of which is subjective. Five observers fractionated tones of 10 different frequencies at a loudness level of 60 db. From these fractionations a numerical scale was constructed which is proportional to the perceived magnitude of subjective pitch. In numbering the scale the 1000‐cycle tone was assigned the pitch of 1000 subjective units (mels). The close agreement of the pitch scale with an integration of the differential thresholds (DL's) shows that, unlike the DL's for loudness, all DL's for pitch are of uniform subjective magnitude. The agreement further implies that pitch and differential sensitivity to pitch are both rectilinear functions of extent on the basilar membrane. The correspondence of the pitch scale and the experimentally determined location of the resonant areas of the basilar membrane suggests that, in cutting a pitch in half, the observer adjusts the tone until it stimulates a position half‐way from the original locus to the apical end of the membrane. Measurement of the subjective size of musical intervals (such as octaves) in terms of the pitch scale shows that the intervals become larger as the frequency of the mid‐point of the interval increases (except in the two highest audible octaves). This result confirms earlier judgments as to the relative size of octaves in different parts of the frequency range.

The Dependence of Hearing Impairment on Sound Intensity

Abstract: This paper discusses the measurement of hearing loss for levels of sound that were well above the deafened threshold and hence were audible to the deafened person. In the tests, observers having unilateral deafness, i.e., one impaired and one normal ear, balanced a tone heard with the deafened ear against the tone heard with the normal ear. For some people, the impaired ear heard less well than the normal ear for all sound levels. For others, tones which were well above the deafened threshold were heard about equally well with either ear. In other words, such deafened ears tended to hear loud sounds with normal loudness. It was found that this type of deafness could be represented quantitatively on the assumption that it was due to nerve atrophy. Loudness judgments for a normal ear in the presence of noise were found to be similar to judgments by a nerve deafened ear. Relations, based on the loudness properties of normal ears, have been extended to represent the loudness heard by deafened ears.

Relation Between Loudness and Masking

Abstract: A functional relationship between the loudness of a sound and the degree to which it masks single frequency tones, that is, the masking audiogram of the sound, is developed. A loudness masking function is determined experimentally. From this loudness masking relationship the loudness of a sound can be computed by simply integrating the area under the masking audiogram plotted on a special chart. Comparisons of computed and observed loudness levels are shown for a number of sounds and serve to illustrate the precision to be expected from the method. Finally, the results of a large number of masking tests are given in the form of masking contours, which enable one to predict the masking audiogram of a sound from measurements of its intensity spectrum.

On Hearing by Electrical Stimulation

Abstract: The well‐known fact that the ear generates an electric potential in response to stimulation by a sound wave has its counterpart in the fact that, when an alternating current is passed through the head, an auditory sensation results. The observer hears a tone whose pitch is determined by the frequency of the alternating current.Measurements were made of the power needed to elicit a sensation using currents of various frequencies. The power, rather than the simple voltage or current was measured, because the body presents a complex impedance to the current. The total impedance, when the electrodes are applied in a standard manner, decreases with increasing frequency. The power factor varies slightly with frequency. When the power is increased about 20 db above the threshold value, the threshold of electric shock—a stinging sensation—is reached. This effect severely limits the size of the auditory area under electrical stimulation.The amount of distortion present makes it difficult to understand speech when ...

Factors in the Production of Aural Harmonics and Combination Tones

Abstract: The magnitudes of the aural harmonics and combination tones produced in the ears of cats and guinea pigs in response to pure tonal stimuli were measured electrically The cochlear potentials were sampled by an electrode applied to the round window and thence conducted through suitable amplifiers to an electrical wave analyzer (General Radio) The wave analyzer measured the energy present at any frequency in the cochlear response The functions relating the magnitudes of the first five harmonics to the intensity of the pure tonal stimulus were determined The harmonics first appear at about 50 db above the threshold and thereafter grow more rapidly than the fundamental as a function of intensity Several differences in the behavior of the odd and even harmonics reveal the characteristics of the constraining mechanisms responsible for the production of the aural harmonics Simultaneous stimulation of the ear by two tones (700 and 1200 cycles) produces a cochlear potential out of which not only the several h

Sound Waves in a Moving Medium

Abstract: A theoretical approach is made to the problem of the behavior of sound waves in a pipe through which the medium is moving in a unidirectional flow with uniform velocity V. Calculation indicates the resonances of pipes to be affected by the steady flow so that the resonance peaks are flattened, while the separation between nodal points is reduced by the factor 1 − (V/c)2.

Positions of Stimulation in the Cochlea by Pure Tones

Abstract: The relation between tone frequency and position of stimulation on the basilar membrane has been calculated from data on differential pitch sensitivity. The calculations involve assumptions concerning the choice of the upper and lower pitch limits of hearing and the choice of tone levels which should be used in obtaining differential pitch sensitivity data. It is shown that for quite different assumptions the positions of stimulation for tones in the range from 500 to 10,000 cycles are not greatly affected. Outside this range the positions depend on the assumptions. The calculated positions for tones of 1000, 2000 and 4000 cycles fall, respectively, at points on the membrane about 13, 12 and 23 of its length away from the helicotrema. The calculated positions are compared with positions obtained from post‐mortem studies of human cochlea and with positions obtained from electric response measurements on the cochlea of anesthetized guinea pigs. The differences between various methods for the most part are n...

Sound Propagation in Ducts Lined with Absorbing Materials

Abstract: In ventilator and exhaust systems it is desirable to provide a high degree of attenuation for audio frequency sound waves while offering low resistance to continuous or slowly pulsating air flow. For that purpose ducts lined with absorbing materials frequently are used. This paper deals with sound propagation, particularly with its attenuation constant, in such ducts. A method for computing the propagation constant in terms of the acoustic constants of the lining and of the duct dimensions, is given. Two types of lining are considered, nonvibratile and vibratile, the former admitting of no wave motion propagated in the direction of the duct axis within the lining itself. Experimental data are presented for a duct lined with rockwool, and are compared with computed attenuations. It is concluded that the computational procedure is fairly valid up to a frequency at which the sound wave‐length is about twice the internal duct diameter.

The Vibrating String Considered as an Electrical Transmission Line

Abstract: An analogy is drawn between the piano string and an electrical transmission line, utilizing a different correlation than is customary in usual electro‐acoustical analogs. The current in the line is compared with the displacement and the voltage is compared with the momentum. With this correspondence the highly developed treatment of transmission lines becomes applicable to the piano string. The various cases discussed include: Open circuited line with and without attenuation (i.e., ideal and actual string with ends rigidly fixed), terminated line (string affixed to bridge of sound board), electrical impulse introduced (impact of piano hammer). A relation is derived giving the optimum position of striking point for a given ratio of hammer mass to string mass, and this is shown to agree with the results of George and Beckett. The appearance of the nth harmonic when the string is struck at 1/nth of its length is explained, likewise the advantages of the modern practice of high string tensions. Conclusions are drawn concerning impedance matching (string to soundboard) and the velocity of propagation for different frequencies.

An Investigation of Subjective Tones by Means of the Steady Tone Phase Effect

Abstract: Two strong pure tones, of frequencies in harmonic relation, when heard together have a sound depending in loudness and quality on the phase relation between the tones. This dependence may be observed either by the method of beats or by the method of steady tones. The phase effect is closely linked with pitch perceptions contrary to Ohm's law of acoustics, with subjective tones, and in general with the nonlinearity of the ear—i.e., the way the ear responds to sounds of large amplitude. A careful quantitative study of the steady tone phase effect was made with frequencies up to 500 cycles per second. The results indicated a need for important revisions in the concept of aural nonlinearity. These revisions are summarized in the proposal of a definition for the previously undefined and promiscuously used term, “subjective tone.”

A Direct‐Reading Pitch Recorder and Its Applications to Music and Speech

Abstract: An electrical arrangement was devised, by means of which rapid variations in pitch with time, such as occur in music or speech, could be directly recorded even in detail. The arrangement consisted of amplifiers, a wave form adjuster, an automatic volume control, and a frequency meter. The frequency meter itself is essentially the same as the two‐tube thyratron inverter, which was first described by Hull as one of the applications of thyratron, and recently modified by Hunt. Efforts were made to utilize the frequency meter in conjunction with the wave form adjuster and the automatic volume control in order to make it suitable for indicating the rapid pitch variations, accompanied by large intensity variations, in music as well as in speech. The final indication of pitch is made in logarithmic scale, several applications of the arrangement to music and speech being given.

A Study of the Effect of Frequency and Temperature on the Velocity of Ultrasonic Waves in Gases

Abstract: Measurements of the velocities of ultrasonic waves were made in carbon dioxide, nitrous oxide, and sulphur dioxide at temperatures from 30°C to 150°C. The fundamentals of seven quartz oscillators were used to obtain frequencies from 40 kc/sec. to 105 kc/sec. The gases were heated by passing them through a coil of copper tubing surrounded by a heating unit, both being wound around the gas chamber in which wave‐length measurements were made. This chamber was a modified Kundt's tube with movable reflector for producing standing waves. The reflector was carried by a screw with a pitch of one millimeter and a dial graduated in hundredths of a millimeter. As the reflector passed through the nodes and loops the varying amount of energy reabsorbed by the electric circuit made it possible to determine the wave‐length by the reaction of a radiofrequency milliammeter in the energizing circuit. The frequencies of the oscillators were determined by a frequency meter constructed for this work and calibrated by beating ...

A Chromatic Stroboscope

Abstract: A stroboscope is described which permits direct reading of any pitch with a precision greater than that of the ear. The readings are made in terms of musical scale notation instead of frequency.

The Nature and Origin of Aural Harmonics

Abstract: Problems as to the nature and origin of the aural (subjective) harmonics, tones which are heard, but which are not present in the sound wave outside of the ear, have concerned musicians and scientists for many years. It is customary to assume that these harmonics arise because of non‐linearity in the functioning of the middle ear. Their magnitudes have been measured by indirect means, such as the method of best beats, but there has been no adequate direct study.We have used several means to attack this problem. (1) The minimum amount of distortion (2nd harmonic) which the ear can detect in a tone was studied by determining the thresholds for the second harmonic when it is added, outside the ear, to a pure fundamental in various phase relations. (2) Since it is possible to pick up from the cochlea an electrical potential which gives a good indication of the functioning of the auditory mechanism, we made an analysis and measurement of the harmonic components present in the cochlear response of animals under...

Hearing of Speech by Bone Conduction

Abstract: A method for testing hearing of speech by bone conduction has been developed on the basis of Fletcher and Steinberg's articulation testing methods. High quality recordings of the articulation lists were substituted for callers. A special induction type electrodynamic bone conduction vibrator was developed from the original Barany‐Schwarz Knochentelefon. It is linear over a wide intensity range for all speech frequencies and has a frequency response characteristic which allows clear transmission of speech. The method and apparatus have been tested by a comprehensive series of measurements on an individual with hearing slightly above normal. The force of application of the vibrator necessary for best understanding of speech was found to be approximately 350–400 grams‐weight. The best area of vibrator button varied with conditions; for open ear canals a button of 0.7 sq. cm area gave higher articulations than larger ones and as high scores as smaller, less comfortable ones; for closed ear canals a larger button gave better results. Speech was heard best by bone conduction when the observer's mouth was closed, his teeth touching but not clenched, and his ear canals occluded. The variation of percent articulation with level‐above‐threshold was studied for bone conduction with both open and occluded canals and for air conduction with one ear and two. The curves obtained were coincident within observational error, indicating the same functional relation in all four cases. (The intensity levels at threshold varied for the four cases, being greater for bone conduction than for air conduction and greater for open‐canal bone conduction than closed‐canal.) A large amount of frequency distortion was tolerable without seriously affecting the articulation as long as there was no nonlinear distortion. Finally, all the results have revealed that the hearing of speech by bone conduction may attain as high a degree of perfection as that attained by the more usual method of air conduction.

An Empirical Formula for the Loudness of a 1000‐Cycle Tone

Abstract: The equation L = I(10−5/2I+1)−2/3 may be used to compute the loudness, L (millisones), of a 1000‐cycle pure tone of intensity I (in units of 10−16 watts per square centimeter). This indicates that for low intensities the loudness is directly proportional to the intensity; for high intensities it is proportional to the cube root of the intensity.

Variations in Absorption Coefficients as Obtained by the Reverberation Chamber Method

Abstract: Absorption coefficients determined by the reverberation chamber method on the same material in different laboratories are not in agreement. The discrepancies were noted with several materials tested in both the NBC and J‐M laboratories. An investigation, involving comparative measurements on materials of different absorbing efficiencies, was undertaken to determine the reasons for the variations. The results indicate that the order of agreement depends on frequency and the absorptivity and size of the sample under test. Various reverberation time formulas have been proposed and of these the Millington formula tends to give the best agreement and most reasonable results under the test conditions. An attempt is made to define the limiting assumptions of the formula empirically from absorption vs. sample area data obtained during the investigation.

Finite Acoustic Filters

Abstract: Most of the previous theoretical work on acoustic filtration has dealt with idealized infinite structures. The present paper is a theoretical study of finite filters such as are used in practice. Considering an acoustic structure with air as the medium with main line impedance Z and with n branch impedances Zb (pure reactances) equally spaced at intervals 2l, it develops that one can express the power transmission ratio for the structure in the simple form Pr = 1⧸(1 + Z24|Zb|2⋅sin2 nWsin2 W), (1) where cos W=cos 2kl+iZ/2Zb⋅sin 2kl, (2) the familiar parameter of the transmission theory of filtration (reference 2). The plot of Pr in (1) as a function of frequency shows the presence of transmission and attenuation bands which approach those of the corresponding ideal infinite case as n becomes large compared with unity. Comparison of (1) with the actual transmission measurements of Stewart (reference 2, pp. 170, 175) shows satisfactory agreement.The phase change which occurs between successive sections in a ...

A Method for Evaluating Compliant Materials in Terms of Their Ability to Isolate Vibrations

Abstract: A method is given for evaluating by dynamic means the stiffness and resistance of a vibrating system. By using this method, compliant materials not readily evaluated by static means may be investigated. The actual efficiencies of isolating systems are compared with the efficiencies predicted from a theoretical one‐degree‐of‐freedom treatment. The comparison is favorable, but certain limitations of the theoretical treatment are discussed.

The Measurement of Timbre

Abstract: Research designed to measure timbre as a function of harmonic structure, frequency level, and intensity level is in progress. This paper, the first of a series of projected reports, includes a description of apparatus, a brief discussion of problems of measurement, and a summary of some of the data already secured.The apparatus consists mainly of an electrostatic generator, described in part elsewhere. This instrument produces complex tones constituted of desired combinations of any or all of sixteen consecutive harmonics, the frequencies, intensities, and phase relationships of which are subject to control. Each harmonic is reasonably free from stray components. A calibrated Western Electric 555 receiver is used with the generator. The current flowing through the receiver (current being proportional to the r.m.s. value of pressure developed in the ear canal) is measured with a vacuum tube voltmeter. As many as five different test tones, each to be paired a required number of times with a suitable standar...

Spherical Torsion Pendulum as Supersonic Radiation Pressure Meter in Liquids

Abstract: Following King's theoretical work, a series of measurements has been carried out with bronze spheres varying in diameter from 14 to 112 inches. In plane stationary waves in water at frequencies between 100 and 200 kc. King's predicted dependence of radiation pressure on the location of the spheres relative to the position of nodes and loops is verified. Neglecting the viscosity of the medium and the compressibility of the spheres, it was found that the radiation pressure approximates inverse variation with the radius a of the sphere when the latter's size is such as to make 2πa/λ greater than unity and less than four.Considering the spherical torsion balance a likely laboratory acoustic standard in liquids, it is possible to calibrate as secondary standards any pressure microphone for subaqueous use in the supersonic range. Such calibration was effected upon tourmaline crystal microphones by the usual resonance tube method. The piston source was telescopically fitted into the end of a horizontal rigid cyl...

Combination Horn and Direct Radiator Loudspeaker

Abstract: A loudspeaker is described consisting of a long horn coupled to one side of a small dynamically driven cone for the reproduction of low frequencies and an acoustic filter for changing the output from the horn to the open side of the cone for the reproduction of the mid and high frequency range. A theoretical analysis shows the action of the system. Experimental data substantiates the theory.

Detection and Location of Laminations in Steel Plates

Abstract: Laminations in the plating and other members of fabricated steel structures cause weaknesses and failures in present welded junctions that did not occur in the case of riveted joints. Thus the need has arisen for some effective method and means for detecting such flaws in structural steel material. Simple theoretical considerations predict that the presence and location of such laminations can be determined by the distortion which they produce in sand patterns formed on the plates when they are thrown into various types of mechanical resonance. Practical tests have substantiated these predictions in the case of plates of different form and thickness.