George C. Maling

Effect of a Plane on the Power Output of a Monopole

The presence of a plane boundary is known to affect the power output of a sound source, and the effect is most conveniently expressed as a “power amplification factor (W/W0)” which will in general depend on type of sound source, distance from plane, and boundary admittance. For a constant strength monopole near a plane with specified normal admittance (real), the power amplification factor can be calculated rigorously in terms of tabulated functions using existing theory on the reflection of a spherical wave from an infinite plane specified by impedance boundary conditions [U. Ingard, J. Acoust. Soc. Am. 23, 329 (1951)]. Plots of W/W0 as a function of source height are presented for several values of normal admittance including β = 1. [.This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Air Research and Development Command), and the U. S. Navy (Office of Naval Research).]

Leo Beranek's contributions to noise control

Leo Beranek has made contributions to noise control for many years, beginning with projects during World War II when he was a Harvard University. Later, at MIT, he taught a course (6.35) which included noise control, and ran MIT summer courses on the subject. His book, Noise Reduction, was published during that time. Additional books followed. Noise control became an important part of the consulting work at Bolt Beranek and Newman. Two projects are of particular interest: The efforts to silence a wind tunnel in Cleveland, Ohio, and the differences in noise emissions and perception as the country entered the jet age. Leo was one of the founders of the Institute of Noise Control Engineering, and served as its charter president. Much of the success of the Institute is due to his early leadership. He has also played an important role in noise policy, beginning in the late 1960s and, in particular, with the passage of the Noise Control Act of 1972. This work continued into the 1990s with the formation of the “...

Kenneth McKechnie Eldred—A distinguished noise control engineer II

Kens accomplishments in noise control engineering cover the spectrum from basic engineering research to recommendations for noise control in six areas: measurement of industrial noise; measurement and reduction of structural vibration in space vehicles; noise radiation from jet flow; noise reduction of jets by multiple nozzles and turbofans; vibroacoustic environmental simulation for aerospace vehicles; and community and transportation noise control. Some of these areas are discussed in consulting reports, and others in papers published in the open literature. He was a consultant at Bolt Beranek and Newman from 1973 until 1982 when he formed Ken Eldred Engineering. His publications appeared in the journal NOISE Control, several NOISE-CON and INTER-NOISE Proceedings, Noise Control Engineering Journal, and the Journal of the Acoustical Society of America. Representative samples of his accomplishments taken from the above sources will be presented.

Maa Dah-You and the design of reverberant rooms for determination of sound power

Reverberation rooms are useful tools for the determination of sound power emitted by machines and other sound sources. One critical factor in the design of such rooms is the mode spacing at low frequencies. A seminal contribution to our understanding of mode spacing was made by Maa in 1939, and his paper was published in the Journal of the Acoustical Society of America. Richard Bolt also made a contribution at about the same time. In this paper, we begin with Maa’s work and trace the development of mode spacing statistics through the work of Richard H. Bolt and Ludwig Sepmeyer. A computer study by the author of mode spacing statistics in 200 cubic meter rooms is described. This work led to recommendations for room dimensions to be included in an international standard on determination of sound power in reverberation rooms.

Increasing the Acoustical Society’s role in noise control and noise effects

At the meeting of the Technical Committee on Noise at the fall 1991 meeting of ASA in Houston, a discussion was held on how, or if, the Acoustical Society should develop more concrete policies or action concerning noise control and noise effects. As a result of that discussion, a Noise Task Group was formed by the authors at the direction of the Chair of the Technical Committee to explore the issues involved. Since that time, several special sessions have been held to help establish a direction for this activity. This talk will briefly review some of the more important elements of that activity which, properly, are beginning to involve members of other technical committees within the Society in such areas as hearing screening tests at ASA meetings, development of lecture materials for use in presenting talks to youth on acoustics and noise, and potential development of room noise criteria and/or rating schemes for meeting spaces. Other such action areas that have evolved from these special sessions will b...

Noise Generation by Interacting Air Jets

At a previous meeting of the Acoustical Society measurements of the noise produced as a result of the interaction of two air jets at angles of intersection between 0° and 180° were reported. The acoustic power from the jets was found to increase with the angle of intersection and reach a maximum when the angle is about 90°. In the present case (jet diameter 2 cm, Mach number M≅0.5) the maximum value of the interaction noise power is about 12 db larger than the power from the two jets separately. As an extension of this work measurements have been made as a function of the vertical separation of the jets, keeping the angle of intersection constant, equal to 90°. An attempt is made to explain the results from these experiments in terms of the effect of the mean gradients in the flow, which leads to a radiated sound power proportional to the integral of u′6|grad U|2 [Lighthill, 1952] where u′ and U are the local fluctuating and mean velocities of the jets, respectively. The experimental results can be satisf...