bluuebunny/crossref_metadata_2025_split huggingface dataset:
Finite Acoustic Filters
Authors: Lindsay R. B. 
Published: September 2005

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 reactantes) 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. 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 and Lindsay (ibid., pp. 170, 175) shows satisfactory agreement.
The phase change which occurs between successive sections in a filter is also computed and it is shown that unlike the situation in the infinite case the phase change is a function of the section. However, at relatively high frequencies and for large n this approximates to the total phase change along the structure divided by n. Comparison with such experimental results as are at present available yields reasonably satisfactory agreement.
A Study of the Tuning of Pianos
Authors: Railsback O. L. 
Published: September 2005

Measurements of the pitch of each note on the piano were made immediately after tuning by means of the chromatic stroboscope. Sixteen grand pianos and twelve upright pianos were included in this study. Different makes of pianos were used and the tuning was done by different tuners. Averages were computed for each of four tuners, using three grand pianos by each tuner, to discover whether or not different tuners follow different patterns of tuning. The conclusion is that they follow, on the average, about the same pattern with individual differences on the extreme ends. With this established the average was then taken of sixteen grand pianos to determine the slope of average deviation from the equally tempered scale. A line drawn to true fifths much more nearly coincides with the line of averages than does the line of true octaves and is very close for the middle five octaves. At the ends the departure is considerably greater. For the twelve upright pianos the departure is still greater.
A variety of causes seem to contribute to the “stretching” of octaves. In harmonic overtones in the bass and over compensating to avoid “flatting” are probably most significant.
Measurements in the Field
Authors: Stanton G. T. 
Published: September 2005

“The absorption coefficients of materials as determined by field measurements, differ from those in the laboratory.” This belief appears general in the industry and is, in the author's opinion, based on a false premise.
There is some evidence to indicate that if in field measurements of reverberation due consideration is given to insuring the same degree of agreement with the definition of reverberation time as that in the laboratory, the absorption coefficients shay be determined in the field which will agree with those from the laboratory. However, the primary purpose of field reverberation measurements is to determine the acoustic conditions resulting from a given form of acoustic design, and measurements made with this end in view are not generally suitable for direct determination of absorption coefficients. The agreement between laboratory coefficient and that directly determined from the reverberation time in a practical room varies with the degree of diffusion of sound energy in the room.
Angular Distribution of Normal Modes
Authors: Bolt Richard H. 
Published: September 2005

As stressed by Hunt the angular distribution of normal modes must be incorporated into an adequate evaluation of the effective absorption of material in a room. Thus, approximate theory, using the “sin θ” law of random distribution, yields an average value of acoustic impedance: z̄=z0/2, where z0 is the impedance at normal incidence. Maa derived a more accurate distribution law, in consideration of a low frequency correction reported by him and by Bolt.
A rigorous derivation of angular distribution must utilize frequency-space instead of p-space as only in the former are the directions of characteristic points identical with space-directions of the corresponding modes. A detailed consideration of frequency space reveals, at low frequencies, a discontinuous angular distribution of the general form: N(θ) = N0 +  ∫ θ1θ2f(θ)dθ+N90, where N0 and N90 count the number of modes at exactly 0° and 90° (nearly 0° and 90° in actual practice), and f(θ) approximates a stepped curve between angles θ1 and θ2. Each of these quantities has been evaluated; the resulting formula closely fits several calculated plots of angular distribution in rectangular rooms. The “smooth” part, f(θ), agrees with Maa's Eq. 17, but the present form should possess advantages, especially for incorporating absorption at grazing incidence as reported by Hunt.
This result is applied to the average impedance of a material covering an entire wall of a room, giving an explicit equation: z̄/z0 = 12 + K1/ν + K2/ν2+… where ν is frequency (up to which all modes are counted), and K1, K2, etc. involve room geometry and placement of material. Diffraction effects have not been incorporated. An apparent inconsistency is noted in the usual definition of average absorption coefficient in terms of average impedance.
A Modern Concept of Acoustical Design
Authors: Potwin C. C. , Maxfield J. P. 
Published: September 2005

The modern view in architecture, as it relates to the functional and utilitarian concepts of planning, has recognized the importance of a fundamental approach to the solution of acoustical problems in buildings where auditory requirements constitute a vital element of their design. Incidentally, treating acoustics as an integral part of design, rather than as a corrective measure during the course of planning, has not only produced better acoustical conditions and more efficient structures, but has also contributed to pleasing architectural form and decoration as well.
The initially important and comprehensive work of Professor Wallace Sabine and the more recent contributions of other authorities have established a basis for this modern approach to acoustical design. The coordination and practical application of the basic principles set forth have led to the development of efficient methods of combining interior form with the selection and distribution of sound absorbing materials for enclosures of widely differing types.
One method is especially described in this paper, wherein the surfaces of an audition space are shaped and coordinated with the distribution of sound-absorbing material so as to disperse the first few sound reflections of discrete and multiple types and to retain partially and control other reflections which might be termed the “long-mean-free-path” or “around-the-room” type. Particular attention is directed to the advantages derived from acoustical forms coordinated with a more scattered distribution of material than has been common in previous design practice, and also to the fact that this method of design creates good acoustics in spaces of the most unconventional basic shape.
Photographs and measurements of several recent designs will be shown, including the interesting and unusual Voder Room of the A. T. & T. Exhibit at the New York World's Fair 1939.
Auditory Patterns. A Demonstration Lecture
Authors: Fletcher Harvey 
Published: September 2005

For many years physicists have been devising methods and apparatus for accurately measuring hearing, and it is now possible to describe the ear in physical terms much as other machines are described. In more recent years, auditory research has been directed more toward obtaining the relation between such a physical description and the character of the sensation evoked by a sound.
Sound waves entering the inner ear set into vibration a relatively long flexible membrane, which has distributed along its length the endings of the auditory nerve fibers. These endings are sensitive to the vibrations, and initiate a series of nerve impulses or tiny electrical currents, which travel along the nerve fibers to the brain. Such nerve messages contain the information that is used in forming the sensation of sound. By utilizing the discovery that human nerve fibers behave like busy telephone wires, relations have been obtained between the physical characteristics of a sound and the pattern of the nerve messages which it produces.
When a nerve fiber is busy carrying messages for one sound it is unable to carry messages for a second sound. In order to be heard, the intensity of the second sound must be increased until non-busy fibers can be found. From such busy tests, the fibers at different positions on the membrane that are excited by a given sound, can be charted. Such a chart is called an auditory pattern, and portrays to the eye the information that the brain must utilize in order to form sensation.
By choosing a sound which renders the fibers at different positions on the membrane uniformly busy, relations have been obtained between the pitch of a sound and the position of the excited fibers, the intensity of a sound and the rate at which messages are evoked and the changes in position and rate which accompany just noticeable changes in pitch and intensity, respectively.
In the demonstration lecture, this complicated process is vividly depicted by creating sounds and portraying the corresponding auditory patterns by means of animated charts. Deafness is artificially created and the audience sees and hears sound in the roles of both the normal hearing and the deafened.
Hearing Survey at the New York and San Francisco World's Fairs
Authors: Montgomery H. C. 
Published: September 2005

A statistical study of hearing is being made from hearing tests at the New York and San Francisco Fairs. An acuity test for pure tones and one for spoken words were offered as part of The Bell System exhibits, and over half a million visitors permitted a photographic record to be made of their test blanks. The results of a preliminary study of these records will be presented.
About one person in seven showed a hearing loss of 25 db or more at 7040 cycles, and about one in twenty-five showed sufficient impairment at the lower frequencies to indicate a handicap in understanding speech in a public auditorium. The age and sex trends observed agree in general with those found in earlier surveys. Thresholds for certain representative groups will be gives in terms of ear canal pressure.
The results were consistent at different times of the day and from day to day. Comparison of data from New York and San Francisco indicates little difference between the groups. Certain other geographical comparisons will also be presented.
Applications of the Buchmann-Meyer Effect in the Calibration of Phonograph Recording and Reproducing Equipment
Authors: Cowan Milton , Griffith Paul 
Published: September 2005

Buchmann and Meyer have shown that the optical patterns reflected from a modulated phonograph record can be evaluated quantitatively in terms of the stylus-point velocity at the time of recording. If a record is illuminated with parallel rays of light, the width of the luminous band is directly proportional to the lateral velocity. Thus, the over-all frequency-response characteristic of a recording mechanism may be readily and quickly determined. Also, the characteristic of a reproducing system may be determined from a record of known lateral velocities at various frequencies. The effect may also be used to determine the magnitude of recording turntable speed fluctuations, surface noise level of a record, and the state of the division of the particles constituting the surface of a record.
The paper develops the theory of the effect, and its practical applications will be demonstrated in the University recording laboratories.
Sound in the Theater
Authors: Burris-Meyer Harold 
Published: September 2005

The showman has two principal avenues of approach to the emotions and, in rare cases, to the reason of his audience: sight and hearing. The visual component of the show depends ultimately upon the light reflected to the audience from actors, scenery, etc. Lighting instruments and control devices make it possible for the showman to employ the complete color spectrum, and to vary intensity from a level which gives only partial visibility to one which is unpleasantly bright.
Until recently the auditory component of the production has been limited in its characteristics by the limitations inherent in the source of the sound and the acoustic properties of the theater. By introducing thermionic means of sound control, it is possible to employ for dramatic purposes the whole frequency and intensity ranges to which the ear responds, and thereby give the auditory component of the show the same flexibility and susceptibility to artistry that are possessed by the visual component.
It is no longer necessary to hamper the actor by forcing him, in addition to interpreting his part, to compensate for the acoustic deficiencies of the theater, for the orchestra to misinterpret a piece to avoid drowning out the singer, or for the playwright to depend upon eleventh-century prop sound effect devices for the sound which he uses to establish locale, atmosphere and mood. It is possible to achieve with sound numerous dramatic values usually assigned to scenery, light, movement, etc. It is possible to use sound as an arbitrary independent means for stimulating predictable involuntary audience reaction; to engender by auditory means that emotional flux which will make it easy for the audience to suspend disbelief, to laugh at, weep for, or believe in something which would have seemed absurd when first the curtain went up.
The effort to devise a technique for subjecting all sound in the theater to control has been pursued for ten years. Results of that effort have already brought about some innovations in radio and legitimate production, and have made possible the development of at least one new dramatic idiom. The control of sound in the theater is now the subject of a research project underwritten by the Rockefeller Foundation. Producing organizations in the fields of motion pictures and radio as well as legitimate drama are aiding the enterprise, as are also research organizations and equipment manufacturers. Experiments in the application of the technique to a wide variety of productions will be cited. Results of experiments since the report on the subject made to the Acoustical Society (April 29, 1935) will be summarized.
Pitch as a Function of the Amount and Rate of Frequency Modulation
Authors: Pepinsky Abe 
Published: September 2005

Pitch variation arising from frequency modulation was first studied by Lewis, Cowan and Fairbanks. Their stimuli consisted of short sound-pulses whose frequencies were continuously and rapidly raised or lowered. Results of their study led to the present elaboration and subsequent reinterpretation of prevalent concepts of the ear's response to modulated sounds.
Thresholds of perceived pitch change were found to vary as a function of the amount and rate of modulation. Perceived extent of pitch change was shown to depend upon the amount, rate and form of modulation. Correspondence between physical and perceived extents was much greater than expected.
It is believed that the data have an important bearing upon problems relating to the perception of the pitch element in speech.
Comments on Paper by Professor F. V. Hunt Presented at the Meeting of the Acoustical Society of America at Iowa State University
Authors: Hasbrouck H. J. 
Published: September 2005

The high frequency translation losses in record reproduction which Professor Hunt has quoted from a former paper of mine apply only to soft plastic-coated recording disks such as are used for instantaneous play-back recording. They do not hold and are very much less on the relatively hard material of which commercial transcription records are pressed. The RCA reproducer was designed and primarily intended for use with these hard commercial pressings.
With reference to the frequency characteristic which is to be adopted and which is being used for the new Orthocoustic broadcast transcription records and which Professor Hunt contends represents too much high frequency pre-emphasis, let me say that this program was started solely with the idea of producing ultra-high quality disks. It seems inconsistent that such a characteristic would be used if it resulted in objectionable distortion. The direct purpose in accenting the high frequency range in recording and attenuating it in reproduction is of course to reduce surface noise. Our object in demonstrating such a record at this meeting was not only to show how far the surface or background noise can be reduced but also to direct attention to the absence of distortion.
As Mr. Robert Morris, of the National Broadcasting Company, indicated, the requirements for low surface noise on broadcast records are rather severe. Low distortion is not alone of paramount interest. The noise level too must be below a commercially acceptable value. This level is far below that which would be tolerated in home record reproduction. Assuming that it were possible to make a record totally free from wave form distortion the broadcasters would immediately insist on raising the recording level until the distortion was brought up to but not beyond the acceptable amount just mentioned. Thus the signal to noise ratio would be improved and no harm done.
I cannot argue with Professor Hunt's calculations on distortion but think perhaps he based them upon a higher recorded level than we propose to use in Orthocoustic disks. It is intended of course that the distortion will be objectionable to no one, and for all practical considerations not audible. By this method of recording it has been found possible to make ultra-high quality lateral transcription records which, in side-by-side comparison with the output from a high quality monitoring loudspeaker operating on “live” programs, defy detection, from the standpoints of frequency range, background noise and low distortion. That is all we can expect from any recording system.
The Musical Scale of Just Intonation
Authors: Urquhart Noel 
Published: September 2005

The musical scale of Just Intonation in one tonality (key) as evolved since early Greek times, may be defined as consisting of four tonal notes: subdominant, tonic, dominant and supertonic at intervals of fifths (3/2) apart with four major notes, each an interval of the major third (5/4) above these tonal notes and with four minor notes, each an interval of the major third (5/4) below these tonal notes, all brought within the limits of an octave (2/1). Assuming the frequency of the keynote of C equals 260.74 cycles per second, we obtain the following scale of frequencies:
Frequency Frequency
Note Name of Interval Ratio to Prime Cycles/Second
C Prime (Tonic) 1/1 1.0000 260.74
D♭ Subdominant Minor Sixth 16/15 1.0667 278.13
D Second (Supertonic) 9/8 1.1250 293.33
E♭ Minor Third 6/5 1.2000 312.89
E Major Third 5/4 1.2500 325.93
F Fourth (Subdominant) 4/3 1.3333 347.65
F♯ Dominant Major Seventh 45/32 1.4063 366.69
G Fifth (Dominant) 3/2 1.5000 391.11
A♭ Minor Sixth 8/5 1.6000 417.18
A Major Sixth 5/3 1.6667 434.57
B♭ Minor Seventh 9/5 1.8000 469.33
B Major Seventh 15/8 1.8750 488.89
C Octave (Tonic) 2/1 2.0000 521.48
In connection with research and experimental work on an electronic type piano, the writer devised the Electronichord as described in the American Physics Teacher, February, 1934. Using two Electronichords, it was possible to study the relations that exist between the harmonic overtones of two string tones tuned any harmonic or tempered interval apart. These experiments, among other things, audibly demonstrated the importance of the harmonic intervals to satisfy the discriminating musical ear. The purpose of this paper is to offer a mathematical approach in demonstrating that the musical scale of just intonation is a fundamental acoustical measurement.
Effects of Differentiation, Integration, and Infinite Peak Clipping upon the Intelligibility of Speech
Authors: Licklider J. C. R. , Pollack Irwin 
Published: September 2005

Previous experiments on the effects of distortion in voice communication circuits have shown that intelligibility is impaired surprisingly little by the type of amplitude distortion known as peak clipping. It has been found, in fact, that conversation is possible even over a system that introduces “infinite” peak clipping, i.e., that reduces speech to a succession of rectangular waves in which the discontinuities correspond to the crossings of the time axis in the original speech signal.
The intelligibility of the rectangular speech waves depends critically upon the frequency-response characteristics of the speech transmission circuits used in conjunction with the “infinite clipper.” In the present experiments, resistance-capacitance circuits with sloping frequency-response characteristics (tilting circuits) were introduced into the system at points preceding and/or following the clipping circuit. The interactions of the nonuniform frequency characteristics of the resistance-capacitance circuits with the nonlinear amplitude characteristic of the clipping circuit were studied by means of articulation tests. That there was strong interaction is evidenced by the fact that word articulation scores of 97 and 15 percent were obtained with two systems consisting of the same components in different orders. The components were (1) a tilter with a frequency-response characteristic rising 6 db per octave (a “differentiating” circuit), (2) an infinite peak clipper, and (3) a tilter with a frequency-response characteristic falling 6 db per octave (an “integrating” circuit). When these distorters were cascaded in the sequence 1-2-3 the speech output consisted of triangularly shaped waves which sounded very much like normal speech and which were highly intelligible (97 percent). When the reverse sequence (3-2-1) was used, the speech output consisted of sharp pulses giving rise to extremely poor quality and very low intelligibility (15 percent).
Tests with single distorters and with pairs of distorters indicated that: (1) In the absence of frequency distortion, infinitely clipped speech is of poor quality but moderate intelligibility (50 to 90 percent depending on the listeners skill and familiarity with the test words). (2) A differentiator or an integrator preceding the clipper determines the degree to which intelligibility is impaired by infinite clipping. (3) A differentiator or an integrator following the clipper (or used alone in a linear system) affects the quality but not the intelligibility of the speech transmitted by the system.
The Atonal Interval
Authors: Pollack Irwin 
Published: September 2005

Thresholds for the detection of the presence of a sinusoidal signal (thresholds of audibility) and thresholds for the perception of the tonal character of the signal (thresholds of tonality) were determined by three listeners over a wide range of audible frequencies. At each of the frequencies tested, the threshold of audibility was found to be significantly lower than the threshold of tonality. The difference between the two thresholds—the atonal interval—ranged from about 2.5 db at 500 c.p.s. to about 6.5 db at 4000 c.p.s. Little difference was found between the variabilities of the two thresholds.
Preliminary measurements indicated that acuity of frequency discrimination changes quite abruptly at the threshold of tonality. Below the threshold of tonality, frequency discrimination is very poor; above the threshold of tonality, frequency discrimination is markedly more acute.