Volume 58, Issue S1, November 1975
Index of content:
- PROGRAM OF THE 90TH MEETING OF THE ACOUSTICAL SOCIETY OF AMERICA
- Session B. Education in Acoustics: Diffusion of the Knowledge of Acoustics
- Invited Papers
58(1975); http://dx.doi.org/10.1121/1.2002051View Description Hide Description
A corrugated tube open at both ends, with air flowing through the tube, sings notes which depend on the flow velocity and the length of the tube. The notes it sings are the natural harmonics of the tube. A given note will sing when the flow velocity is such that the frequency at which the air bumps into the corrugations is close to the frequency of the note, provided that the flow velocity is sufficiently high to induce turbulent flow. Study of this phenomenon [F. Crawford, Am. J. Phys. 42, 278 (1974)] has led me to invent a new family of wind instruments I call Corrugahorns. The simplest of these is the Corrugahorn Bugle. It plays harmonics third to about tenth, plus additional notes obtained by tricks (finger flatting, whistle flatting, palm sharpening) that give it almost a complete chromatic scale. The most sophisticated is the Slide Corrugahorn, with a slide (like a trombone) that gives it a chromatic scale over its range. I will demonstrate various singing corrugated pipes, including corrugahorns and another instrument I call the Water Pipe.
58(1975); http://dx.doi.org/10.1121/1.2002052View Description Hide Description
Some of the author's experiences during 18 years of teaching acoustics courses of a non‐technical nature are described. Laboratory instruction is considered to be a most desirable feature of such courses. Some favorite laboratory and demonstration experiments are described, as well as course materials.
58(1975); http://dx.doi.org/10.1121/1.2002053View Description Hide Description
A partially unwrapped string on a guitar provides a simple demonstration of overtones which are not harmonics of a fundamental. The modes of vibration can be predicted from solving the wave equation, but a simpler solution may be obtained by the application of transmission‐line theory. The measured frequencies are found to agree closely with the predicted ones. This constitutes a novel and instructive experiment for an intermediate laboratory in acoustics.
58(1975); http://dx.doi.org/10.1121/1.2002054View Description Hide Description
We have used Stevens' method of magnitude estimation in a number of classes and with individual observers to obtain estimates of the loudness of pure tones. These unpracticed observers give results that mimic the tone scale: They agree that approximately a 10‐dB change in sound pressure corresponds to a twofold change in loudness. Such results convince the student of the distinction between loudness, a subjective magnitude, and intensity, a stimulus magnitude. Moreover, the consistency across groups of listeners means that untrained people are able to judge loudness ratios directly. It would then be appropriate and more informative to tell consumers about the loudness or noisiness of products by giving the relative positions of products on a true number scale of loudness, rather than by giving the positions of products on a logarithmic scale of acoustical output.
58(1975); http://dx.doi.org/10.1121/1.2002055View Description Hide Description
From everyday contact with the architectural profession, we see clearly that few practicing architects really understand enough about acoustics to apply it effectively in architectural and urban design. This shortcoming can be attributed largely to the lack of acoustics training in architecture schools. Some schools have fortunately progressed beyond the physics survey course to well‐taught, practically oriented acoustics courses; but these are few in number, and there is room for much wider extension of acoustics training. This paper presents a brief outline of the information that a student could acquire in a basic acoustics course and should know before graduation.
58(1975); http://dx.doi.org/10.1121/1.2002107View Description Hide Description
In teaching scientific material to nonscience majors, three basic problems are encountered. One is that the students' fear of failure in dealing with totally unfamiliar material is heightened and grade‐consciousness reaches a very high level. A second is an increased need to convince the students of the relevance of the course material in their preprofessional (or academic) training. A third problem is that of compensating for the students' lack of technical knowledge while trying to impart technical concepts. Instructors in a course in general acoustics at Penn State attempted to deal with the above‐mentioned difficulties through a variety of approaches which included using the contract system for grades, tailoring the material for application in a particular discipline (in this case SpeechPathology and Audiology), and substituting highly visual and auditory demonstrations for technical lectures. This paper discusses the various approaches and reports the degree of their success in facilitating the learning of basic acoustics for nonscience majors.
58(1975); http://dx.doi.org/10.1121/1.2002108View Description Hide Description
There is presently a need for courses and research at the undergraduate level in acoustics and noise control. Several projects which have utilized undergraduate engineering and technology students in the areas of transportation and industrial noise research are presented. It has been found that students profit greatly from the confidence and experience gained by attacking and solving real problems.
58(1975); http://dx.doi.org/10.1121/1.2002109View Description Hide Description
It is suggested that the formal syllabus for graduate study in acoustics, not unlike those for other disciplines, may be remiss in providing certain background that may be found essential for the successful postgraduate career. Of the many endeavors that will subsequently be considered and/or attempted by the acoustician, funded research offers unique opportunities for personal development and contribution to the field. As they have been found to exist in the academic setting, the processes involved in being successful in obtaining funding for acoustical research from either the public, private, or foundational support sectors are addressed. It is suggested that ample opportunity exists during the education experience to become exposed to these processes and that the student be encouraged to do so. Such encouragement might well be formalized along with other aspects of professional activity considered to comprise the essentials for a successful career in acoustics.
58(1975); http://dx.doi.org/10.1121/1.2002110View Description Hide Description
Practical suggestions are given for preparing short technical talks that are designed for maximum information exchange. The coordinated use of figures to complement the text is discussed, and rules for numbers and types of figures are proposed. The needs of the listener are stressed and examples are given of preferred combinations of text and figures, particularly from the listener's point of view. The problem of timing is emphasized and rules are proposed for estimating the presentation time of a given amount of material or conversely for fitting material into a given time slot. Suggestions for improving clarity and efficiency of effort are briefly reviewed.
58(1975); http://dx.doi.org/10.1121/1.2002111View Description Hide Description
The Acoustical Society of America has sponsored studies which addressed relevant purposes and means for carrying out its Charter, i.e., “…diffuse the knowledge of acoustics….” A summary of findings due to such studies is presented. Primary audiences served by knowledge of or about acoustics can be classified as technical societies (professional and scientific); scholars (students, teachers, and researchers); governing bodies (private and public); and society (the public at large). The sequel means for communication to each of these audiences are normally publications; educational institutions; written reports; and mass media; respectively. There are exceptions to these generalizations, however, such categorization assists in the consideration of a rather complex subject.
- Session C. Architectural Acoustics I
58(1975); http://dx.doi.org/10.1121/1.2002162View Description Hide Description
Too many large, music performance facilities around the country have acoustical characteristics which are not suitable for concert tours, particularly when electronic sound amplification is required. This paper concentrates on the acoustical problems affecting the musician and his performance. The various problems encountered and corrective procedures utilized by The Grateful Dead are discussed and include electronic instrumentation and measurement techniques, sound system applications, and room treatments.
- Contributed Papers
58(1975); http://dx.doi.org/10.1121/1.2002163View Description Hide Description
Even for the small number of building projects in which they are involved, acoustics consultants may have little or no influence upon the matters that ultimately determine the success or failure of the design. Often important design decisions are made on the basis of any one of a dozen criteria without any consideration—or understanding—of their effect upon acoustics. During construction, the problems are compounded further by unknowing workmen. This paper reviews some of the prevalent situations that lead to acoustics problems. They can be broadly grouped into three categories: difficulties of interpretation, changes in materials and techniques, and getting things built as specified.
58(1975); http://dx.doi.org/10.1121/1.2002164View Description Hide Description
The business of devising a rating for airborne sound attenuation of building elements that closely corresponds to people's subjective evaluation of the acoustical performance, and of devising test methods for demonstrating satisfactory acoustical performance in a finished building, is very complicated indeed. Until recently, the tendency has been toward increasing complication of the test and rating procedure, in an attempt to make the single procedure account in near‐complete detail for the complexities of human response to noise. The result has been a test procedure that is too complicated for routine use in evaluating finished buildings. An alternative approach would be to divide the complicated task into a number of simpler tasks, each of which can be handled by relatively untrained staff, and to assure by regulation that all of the simpler tasks will be done for each evaluation. This paper proposes an example of the latter approach.
58(1975); http://dx.doi.org/10.1121/1.2002165View Description Hide Description
The current national (ASTM E‐492) and international (ISO‐R140/R717) impact method involves the use of a standard hammer machine for evaluating the impactnoise isolation of floor/ceiling structure. The method has been severely criticized on the ground that ratings based on the test data correlate poorly with the subjective judgments of people listening to real‐life impacts on the same floors. An alternative test method is proposed that uses a modified hammer machine whose internal impedance, intensity of impact and striking frequency simulate those of real footfalls; the new method involves reading the "peak" (i.e., short‐term rms) impactsound pressure levels in the receiving room, replacing the current practice of reading long‐term rms levels. No normalization for the sound absorption of the receiving room is required. Since the peak impact levels, particularly for floors with good impact isolation, are much higher than the long‐term rms levels usually measured, the interference of background noise is much less for the new method. These proposed changes, based on recent studies, are expected to lead to better correlation between the test data and subjective judgments of floors. On an experimental basis, it is proposed that the range of measurement be extended down to 40 Hz, because of the certainty that low‐frequency components are significant in the subjective evaluation of wood joist floors and the probability that peak levels are less susceptible to the problems of standing waves and lack of diffuseness than rms levels.
58(1975); http://dx.doi.org/10.1121/1.2002166View Description Hide Description
The paper describes Assisted Resonance installations designed to provide variable reverberation time in two different types of situation. The first, in Concord, California, consists of a 3500‐seat pavilion with a backstage wall, but with the other sides open. The acoustic consultant has designed this space to provide ideal acoustic conditions for a full range of activity from drama through to symphonic presentations. The second, in Scottsdale, Arizona, is a smaller enclosed space but once again it is designed to accomodate a wide range of presentations. At the time of writing the abstract, the Concord installation is completed and believed to be successful but the Scottsdale installation is still under way and the outcome will not be clear until the paper is presented. The paper does not discuss the overall acoustic design, but is restricted to the role of Assisted Resonance, which deals with only one parameter, and the potential and limitations of the technique will be discussed.
58(1975); http://dx.doi.org/10.1121/1.2002215View Description Hide Description
Due to the complex nature of weave room equipment and materials,absorption coefficients of the various surfaces are difficult to calculate. Knowledge of this information could provide a basis for determining noise reduction due to architectural treatment as well as weave room noise level predictions. A typical weave room consists of masonry walls, wood ceilings, and either wood or concrete floors. Volumes are on the order of 400 000 to 900 000 cubic feet, and surface areas 60 000 to 140 000 square feet. Temperatures of 70° to 80° Fahrenheit, and relative humidities approaching 70% are not uncommon. Because of the unusual room proportions, for acoustic calculation purposes, a weave room is essentially two horizontal parallel planes. Reverberation time (decay rate) measurements were made in several weave rooms, and absorption coefficients calculated. Assuming known absorption coefficients of walls and ceiling, and accounting for high‐frequency attenuation due to relative high temperature and humidity, floor‐machine absorption coefficients have been calculated. Additional tests were conducted to determine decay with distance effects. A single source (fly shuttle loom) noise level was measured at various distances both along and across the weavers alley. This was done in two weave rooms, one with concrete floors and the other with wood.
58(1975); http://dx.doi.org/10.1121/1.2002216View Description Hide Description
ASTM E‐33.04C Subcommittee on Environmental Acoustics, Applications Subcommittee Task Force on Open Office Acoustics has prepared a publication titled, “Acoustical Environment in Open Plan Office—The State of the Art.” The purpose is to “assemble and explain responsible references to the state of the art.” Principles gathered to prepare this paper will be used to develop “applicable ASTM Standards and Recommended Practices.” The paper deals with the “acoustics of an open plane office in a manner that will clarify the basic acoustical principles and help designers and architects to achieve an acceptable and flexible environment.” Items covered include the nature of the sound field,speech communication versus privacy, attainment of privacy, ceiling screen and masking sound effectiveness, testing, and design parameters. A summary of the paper will be presented.
58(1975); http://dx.doi.org/10.1121/1.2002217View Description Hide Description
Achieving speech privacy in the remodeled or renovated open plan office space is usually complicated by the need to retain ceiling assembly fire resistant properties. The designer has few alternatives from which to choose. He may either install ceiling baffles beneath the existing fire‐rated assembly or remove the entire ceiling, lights, air terminals, and board, and install a new one. A sprinkler system may also be required. The expense and disruption of the latter solution poses a monumental obstacle. Acoustical properties of ceiling baffles have been evaluated by both objective and subjective tests. Although the baffles are not as efficient as recently developed open plan office ceiling systems, they can satisfy minimal speech privacy criteria. Design of both the baffle and their array is critical. To support these conclusions, test data and evaluation techniques will be presented.
58(1975); http://dx.doi.org/10.1121/1.2002218View Description Hide Description
The open plan school has been with us now for over ten years, and the number of these schools being built per year is still on the increase. However, the acoustical environment of these spaces has received criticism with regard to high noise levels which result in annoyance, distraction, and speech interference. Even though the usage of open plan school spaces is quite different from that of open plan offices, the acoustical design recommendations for schools have generally been based on requirements for open plan offices. It appears that other considerations should be investigated for defining an acoustical environment acceptable for educational purposes. Our work has concentrated primarily on noise levels and annoyance in open plan classrooms. Direct relationships between noise levels, class size, student age level, and room finish treatments have been developed from extensive measured data. The subjective factor of annoyance has also been investigated and is related to background noise level and peak level fluctuations. Further investigations on the effects of room shaping are discussed as are statistical distributions of class noise.
- Session D. Engineering Acoustics I: Propagation and Attenuation of Sound in Ducts and Tubes
Adjointness properties for differential systems with eigenvalue‐dependent boundary conditions, with application to flow duct acoustics58(1975); http://dx.doi.org/10.1121/1.2002261View Description Hide Description
When the boundary conditions at the two endpoints of a second order differential system depend explicitly upon the eigenvalues such that the system becomes non‐self‐adjoint, a generalized condition of orthogonality which includes endpoint terms can be developed. The generalized orthogonality condition is used to determine modal coefficients for the expansion of arbitrary functions in series of eigenfunctions. The method is applied to the particular ease of acoustic wave propagation in a rectangular duct with a uniform mean flow profile and walls with finite acoustic impedance. The ability of the eigenfunction expansion to converge to a plane‐wave acoustic pressure profile is demonstrated under a variety of flow, frequency, and wall impedance conditions.