Volume 35, Issue 5, May 1963
Index of content:
- PROGRAM OF THE SIXTY‐FIFTH MEETING OF THE ACOUSTICAL SOCIETY OF AMERICA
- Session A. Musical Acoustics
- Contributed Papers
35(1963); http://dx.doi.org/10.1121/1.1918612View Description Hide Description
A fruitful method of studying the action of the violin is to consider it as a system of generators (the strings) and resonators (the body). The body has many resonances, some being caused by the air inside, others being caused by the wood. These two sets of resonances were separated. A tiny microphone was placed inside a violin, which was then buried in sand to dampen the wood resonances. The F holes were kept clear. The violin was placed in a swept‐frequency sound field. This gave the air resonances alone. In addition to the main Helmholtz resonance, others were found, together with notches in response due to standing waves. Next, a magnetic driver and a pickup were attached to the violin, which was placed in a vacuum system. This yielded the wood resonances alone. The peaks became more prominent in the absence of radiation resistance. Finally, the total response of the violin was obtained in air, using the magnetic driver and both the microphone and the magnetic pickup. Since the pickup does not respond to the main air resonance, interactions between the two sets of resonances are weak.
35(1963); http://dx.doi.org/10.1121/1.2142342View Description Hide Description
An analysis has been made of the sounds of a Highland bagpipe played by a professional piper. This instrument consists of a leather bag fitted with five pipes: the blowpipe, through which the player fills the bag with air; the chanter, which has eight open holes on which the melody is played; and the outer tenor drone, middle tenor drone, and bass drone, which produce harmonious steady tones. Spectral analyses were made of each of the drones and the chanter by sounding separately, in various combinations, and under normal playing conditions. The harmonic structure of these sounds was investigated as a function of a number of parameters, including blowing pressure, length of drone, and type of reed. Transient, as well as steady‐state, conditions were investigated. These results are presented, together with a live demonstration of sounds of the bagpipe.
35(1963); http://dx.doi.org/10.1121/1.2142343View Description Hide Description
The acoustical characteristics of musical instruments depend greatly on the material from which they are constructed. In wood, damping for transverse vibrations is relatively low at low frequencies and increases relatively rapidly at the higher frequencies. As a consequence, wooden instruments have relatively pronounced low‐frequency transients and are low in high‐overtone content. Because of their pronounced transients. they can be easily located in the orchestra; their sound is soft and agreeable because of the damped high overtones. Old wood has particularly low damping at low frequencies, and more damping than recent wood at higher frequencies. Because of the low damping at low frequencies, old violins usually have much better carrying power than new violins. Varnishing increases the damping at high frequencies and may render new instruments soft and agreeable, but it cannot make up for the greater carrying power of the older instruments. Since the main feature of a good violin is its carrying power in the orchestra, judgment of individual violins in solo leads necessarily to wrong conclusions. It is not accidental that bell metal has absorption characteristics similar to those of wood. Interesting experiences with musical instruments are discussed in this paper.
35(1963); http://dx.doi.org/10.1121/1.2142344View Description Hide Description
The theory outlined in the previous paper [J. Acoust. Sec. Am. 34, 1991 (1962)] develops an expression for the shift in playing frequency of the clarinet as a function of reed phase shifts, reed opening, and clarinetQ, when the instrument is played softly. This theory has now been extended to cover the frequency shift for loud tones. Use is made of the experimental observation that for loud tones the reed is in contact with the mouthpiece for very nearly one half‐cycle, and that the maximum displacement of the reed from the mouthpiece during the other half‐cycle is always less than the displacement with blowing pressure removed. The fundamental component of the air flow through the pulsating reed opening is obtained and evaluated to give a standing wave inside the clarinet, which in turn produces the assumed reed motion. The result is an expression for frequency shift for loud tones, which resembles closely the previously obtained expression for soft tones. [This work was supported by a grant from the National Science Fonndation.]
35(1963); http://dx.doi.org/10.1121/1.2142345View Description Hide Description
An interesting transient effect occurs in a flute, or other wind musical instrument, when it plays in sequence two tones that are more than a semitone apart in pitch. If the pitch change is made abruptly (1) tone generation decreases and may stop momentarily even if air supply is held constant at the mouthpiece—that is, oscillation decays at the old frequency and then builds up again at the new; (2) the ear does not perceive that oscillation is interrupted; (3) if the pitch change were made without the interruption—that is, at constant amplitude—a click would be heard accompanying the pitch change. These statements are demonstrated by means of an electronic device. The transient behavior of the wind instruments is analyzed by use of equivalent circuits in which the mouthpiece is represented as a negative resistance. [This work was supported by the John Simon Guggenheim Memorial Foundation and the U. S. Office of Naval Research.]
Acoustic Parameters of Violin Design Applied to the Development of a Graduated Series of Violin‐Type Instruments35(1963); http://dx.doi.org/10.1121/1.2142346View Description Hide Description
The static situation among the strings since Bach's time has fostered a great musical literature. Information is now available for a reconsideration of the possibilities of string instruments, both in relation to a practically unheard body of early music and to music of the future. Findings in present violin research are discussed in relation to the development of a self‐consistent choir of eight violin‐type instruments covering approximately piano range; placement and relationship of main wood and air resonances in the violin itself; “tap tone” relationships in free top and backplates to produce desired tone quality in a finished instrument; methods of putting resonances at desired frequencies for a given instrmnent; dimensional scaling based on the violin; clues to characteristic tone production as found in German and Italian methods of violin making.
35(1963); http://dx.doi.org/10.1121/1.2142347View Description Hide Description
Musicians selected their preferred tunings for specific melodies, using an instrument that allows choice of intonation. In this critical listening situation, their choices were found to represent a number of variations on a principle of organization by simple whole‐number ratios to tonal centers. Even without modulation, these melodic choices shift away from direct relation to the tonic to relation to other tonal centers. These acting tonal centers stand in small‐whole‐number ratios to other centers, which in turn have the same class of relation to the tonic. The instances presented do not match any known scale; they indicate structural importance for variant tunings of the same note, and for what is here called “extended reference,” a tendency to avoid direct relationship to the tonic until resolution is desired. Thus, they indicate that tuning preferences are the result of the operation of structural principles embodied in a melody rather than in a scale.
35(1963); http://dx.doi.org/10.1121/1.2142349View Description Hide Description
Composers of synthetic music, although no longer bound by the constraints of fixed‐tuned instruments, must still reckon with the reference structures that listeners impose on musical tones. Indeed, acoustically identical intervals will be perceived differently when these structures are altered by variations either in interval size or in timbre. Existing musical scales appear to be characterized by minimum redundancy, in the sense that few tones can be predicted from a knowledge of those already present, and by maximum stability, in the sense that acoustically equivalent intervals tend to possess equal numbers of interpolatedtones. A mathematical model is proposed to measure the redundancy and stability of any scale, and a computer program has been written to implement it. The input consists of a set of integers describing the acoustic distances between consecutive tones within an octave from which the program creates a combinatorial matrix. Redundancy is calculated from the occurrence of unique combinations and stability from a count of the different contexts in which each interval occurs. When applied to existing scales, the model accounts for many of the historical rules of composition. It also permits one to evaluate new scales and predict their perceptual properties.
35(1963); http://dx.doi.org/10.1121/1.2142350View Description Hide Description
It is usually claimed by students of musical temperament that equal temperament is the only feasible one with a fixed 12‐note system. Artist musicians, however, not infrequently insist from an empirical viewpoint that equal temperament is inferior, implying that they use some sort of superior artistic scale in their performance. This study is undertaken to determine, by the repeated measurements of musical intervals in differing contexts, just what the preferences and tendencies of professional musicians are, and what relationship they have to equal temperament or any other scale context. The first study in this series will attempt to measure the use of the major third, which is, of course, the most important and strategic color interval in our musical system. Repeated renditions of this interval will be measured against a standard tempered major third in an effort to form conclusions as to musicians' preferences under varying musical situations.
- Session B. Physical Acoustics I: Combustion and Other Topics
- Invited Papers
35(1963); http://dx.doi.org/10.1121/1.2142351View Description Hide Description
Combustion systems are discussed in terms of their properties as acoustic cavities. Particular attention is paid to those characteristic features that distinguish them from more‐conventional acoustic cavities. Special reference is made to solid‐fuel rockets as a particular example to illustrate some of the factors in a more quantitative way.
35(1963); http://dx.doi.org/10.1121/1.2142352View Description Hide Description
Measurements of the perturbations in pressure as recorded by flush‐mounted transducers during the combustion of mixtures of air and natural gas in a cooled copper tube at atmospheric pressure are reported for a range of mixture ratios. Also presented are the residual quantities of the oxides of nitrogen, as well as the principal components of the products of reaction. The results indicate two stable modes of oscillation. One was found predominantly at mixture ratios above stoichiometric. There was a region near stoichiometric where both modes existed. The quantities of the residual oxides of nitrogen were from 10–30 times as large during oscillatory combustion as during relatively steady combustion. In addition, measurements in a smaller, cooled, copper combustor at pressures up to 50 lb/sq in. absolute are recorded. Again, two stable modes of oscillation were encountered, and the double amplitude of the oscillation for the mode near stoichiometric was nearly five times as great as that away from stoichiometric. The influence of mixture ratio and rates of flow was explored. The quantities of the oxides of nitrogen were determined after quenching the products of reaction at rates of approximately 5° per μsec. Again, the presence of oscillatory combustion appeared to exert a pronounced influence on the presence of oxides of nitrogen. In the case of the high‐pressure combustor, the premixed fuel and oxidant were introduced through a supersonic converging‐diverging nozzle to avoid coupling between the feed system and the combustor.
35(1963); http://dx.doi.org/10.1121/1.2142353View Description Hide Description
Oscillatory burning is a complicated phenomenon. The most fruitful and stimulating contribution to its understanding has been the acoustic theory of F. T. McClure, R. W. Hart, and their associates. The most important single concept of the theory is the recognition of the acoustic admittance as the key property of the combustion process. Of the several streams of research aimed at determining the acoustic admittance of burning surfaces, the most productive has been that employing the device known as the side‐vented endburner. Work with this tool is proceeding in at least seven laboratories, the three that have been in the business longest being at the University of Utah (UU), at the Naval Ordnance Test Station (NOTS), and at the Ballistics Research Laboratory (BRL). This paper summarizes related aspects of the work at these three laboratories. Despite variations in burner design, experimental procedures, kinds of data, and data‐processing methods, the three laboratories report acoustic admittances in good agreement. In addition to their common work, the three laboratories have branched into other aspects of the oscillatory‐burning problem. Some of these aspects are investigation of burner characteristics (BRL), the quantitative influence of oscillatory‐burning suppressants (NOTS), and the participation of the solid phase in acoustic oscillations (UU).
- Contributed Papers
35(1963); http://dx.doi.org/10.1121/1.2142354View Description Hide Description
The possible applications of combustion‐driven oscillations fall into two categories. The first category includes applications that are related to the combustion process itself, such as those concerned with the possibility of alterlog space heat‐release rate, combustion efficiency, heat transfer to surfaces, and agglomeration of solid or liquid products of combustion. A consideration of available experimental and theoreticalinformation indicates that none of these applications are too promising when compared with alternative methods of performing the same functions. The second category includes applications that use pulsatory phenomena to do a particular iob. Examples are the application of valveless pulse jets to (a) the propulsion of drones, (b) helicopter blade‐tip propulsion, (c) cutting of Arctic ice, and (d) inducing pressure rises in through‐flow combustion systems. For one reason or another, most of these ideas have been dropped. However, the use of the pulsating‐combustion process to supply both the air at a high flow velocity to a combustor and the products of combustion at a high velocity to a heat exchanger, thereby making possible a compact self‐contained unit, appears to have great promise. One such unit of residential boiler size is already available. Although this unit is valved as was the V‐1, conversion to a valveless unit appears possible. The development of industrial‐sized units appears equally feasible. Apparently the development of such units is contingent upon (a) adequate understanding of how to design effective aerodynamic valves, and (b) the collaboration of an inventor, experimentalist, analyst, and financier on a specific program.
35(1963); http://dx.doi.org/10.1121/1.2142355View Description Hide Description
Solid‐propellant combustion‐instability studies at the Ballistic Research Laboratories have been concerned with three main areas: namely, (1) a photographic investigation of aluminum‐additive burning phenomena, (2) acoustic admittance measurements of the burning surface, and (3) measurement of acoustic erosivity effects on the burning rate. The first program, which was recently completed, was a photographic study of possible aluminum‐additive contributions to low‐frequency instability. In this investigation, propellant slabs were burned in a windowed and vented chamber. A rotating slotted wheel was pulled over the vent in some instances to provide pressure waves normal to the burning surface. A short film is shown of some of the test runs. The second program is concerned with the measurement of the acoustic admittance of a burning‐propellant surface, using a resonant‐tube technique. This work closely parallels that at the Naval Ordnance Test Station and the University of Utah. Recent studies have been aimed at evaluating experimentally some of the sources of acoustic losses in this system. The third program is a study of the dependence of the burning rate of a propellant on the frequency and magnitude of the fluctuating gas velocity parallel to the transpiring surface. A description of the apparatus and a summary of recent results are given.
35(1963); http://dx.doi.org/10.1121/1.2142356View Description Hide Description
The presence of a mean‐flow field, steady‐state temperature gradients, and an exhaust port give the rocket‐engine cavity somewhat different acoustic properties from the cavities usually encountered by acousticians. As a result, the gain‐loss balance of acoustic energy in the cavity can be significantly changed from the usual case. For example, the cavity walls are often much cooler than the main body of gas, so that the wall losses must not be calculated in the usual way. We discuss some of the factors that affect the theoretical calculation of acoustic losses. [Work supported by Bureau of Naval Weapons, U. S. Department of the Navy, under NOw 62‐0604‐c.]
35(1963); http://dx.doi.org/10.1121/1.2142357View Description Hide Description
Extensive study of the sound field in the region surrounding a rigid obstacle has led to the development of a three‐dimensional representation of the pressure field. The obstacle under investigation was placed in an anechoic chamber in the path of a plane acoustic wave. The sound field in a selected horizontal plane surrounding the obstacle was studied by automatically moving a small probe microphone through the region at a speed of 4 mm/sec. The signal from the probe microphone was fed to an audiofrequency spectrometer and recorded by means of a graphic level recorder. The data tapes were coordinated to construct a three‐dimensional model showing the pressure amplitude as a function of two position coordinates (x and y). Models have been constructed for the sound field in the region surrounding a sphere and a cube at different frequencies. [This work was supported by a Research Grant from Temple University.]
35(1963); http://dx.doi.org/10.1121/1.2142358View Description Hide Description
The reflection and refraction of plane magnetohydrodynamic waves at an interface separating two different media are studied for various orientations of the external magnetic field. It is pointed out that, by making use of trace velocity plots, it is a simple matter to determine the nature and disposition of the reflected and refracted waves that are generated by an incident wave of any given species.
35(1963); http://dx.doi.org/10.1121/1.2142359View Description Hide Description
An asymptotic solution, valid for long times after the explosion, is derived; it expresses the response in terms of characteristic vibrations of the medium. Special emphasis is placed on the description of sustained reverberations (singing). This phenomenon is described in terms of complex modes [J. H. Rosenbaum, J. Geophys. Res. 65, 1577 (1960)], where some energy travels back radially toward the source; at long times, this leads to standing waves of nonvanishing horizontal wavenumber. Singing is closely connected with trapped waves of high horizontal phase velocity, which are decoupled from the liquid half‐space below the plate [M. A. Biot and J. H. Rosenbaum, J. Acoust. Soc Am. 33, 27 (1961)]. At very long times, however, the strongest signal is associated with an almost completely decoupled shear motion of the plate, and the horizontal wavenumber approaches zero. Total transmission curves of plane harmonic sound waves through a submerged plate are used to show qualitatively why singing often may not be observed in connection with the trapped waves mentioned earlier.
- Session C. Electroacoustics I
35(1963); http://dx.doi.org/10.1121/1.2142360View Description Hide Description
A simplified technique of performing a closed‐coupler (cylindrical cavity) reciprocity calibration of microphones is discussed All three transducers needed in the calibration procedure remain as parts of the coupler throughout the measurement. A multiple‐function switch is used to connect the circuits for the required operations in sequence, without physically interchanging transducers. The same switch operates an analog computer, which uses a logarithmic potentiometer to solve the necessary calculations. The auxiliary transducer is a piezoelectricceramic ring, which makes up the cylindrical wall of the cavity; thus, difficulties associated with having all three transducers in the coupler at the same time are avoided. Considerations involved in using this piezoelectric ring are discussed. Additional features of the calibration technique are (1) use of a capacitor in the measurement of the driving current of the reciprocal transducer, and (2) use of a resistive‐attenuator‐insert technique in the measurement of open‐circuit voltage ratios. The calibrator is designed for calibration of a front‐damped piezoelectric‐ceramic microphone, and the problems resulting from the front‐damping are discussed.
35(1963); http://dx.doi.org/10.1121/1.2142361View Description Hide Description
A versatile instrument for measuring and recording complex impedance and admittance has been constrncted. A variable‐frequency two‐phase oscillator supplies a reference signal to the unknown immittance and reference and quadrature signals to a two‐channel synchronous detector. For the measurement of impedance, a constant current is supplied to the variable load, and the voltage across the unknown is applied to each channel of the synchronous‐detector. The two filtered dc‐output voltages are then proportional to the real and imaginary parts of the unknown impedance. For the measurement of admittance, a constant voltage is supplied to varying loads, and the current through the unknown becomes the input signal to the synchronous detector. The present model of the Z‐Y plotter (ZYP) was constructed for the measurement of driving‐point immittance of electroacoustic transducers. For unknowns whose impedance magnitude ranges from 100 Ω–100 kΩ, either impedance or admittance can be measured and plotted as a function of frequency between 30 and 30 000 cps. Full‐scale deflection on any range was made to correspond to 10 μW power dissipated in a resistive unknown, but operation at other power, voltage, or current levels could be achieved. ZYP can also be adapted to measure complex transfer functions. [This research was supported in part by funds made available under a contract with the U. S. Office of Naval Research.]