Noise Control Research Research Articles

Historical developments in the control of noise generated by small air-moving devices

The scaling laws for air-moving device noise developed by R. D. Madison form a useful starting point in the development of techniques for the control of air-moving device noise. The commercial building boom after World War II provided the impetus for research into air-moving device noise, and the increase in the use of home air-conditioning systems provided the motivation for further research. Beginning in the 1960s, noise generated by computing machinery became important, and the development of air-cooled computing equipment provided a further stimulus to noise control research. Developments in the control of air-moving device noise are reviewed with emphasis on scaling laws, dimensional analysis techniques, mechanisms of noise generation, noise emission measurements, noise reduction techniques, design guidelines, and system effects. Some suggestions for future research on air-moving device noise are given.

Active control of extended acoustic sources in a half-space

Many noise sources, such as an electronic transformer, are located on or near an acoustically rigid planar surface, such as a concrete floor. Thus far, however, most of the active noise control research has been based on the free-field assumption. The work presented here investigates the effect the presence of a rigid plane has on the active noise control of an acoustic source with characteristic dimensions comparable to the acoustic wavelength at the frequency of interest. It is shown that when the source is located a distance of one wavelength or more from the plane, the presence of the plane may be neglected. However, the minimum radiated power computed using a free space active analysis can be significantly greater than that predicted using a half space active analysis for distances less than one wavelength. As a result, using the simpler free space analysis techniques leads to less effective control for distances less than one wavelength.

The graduate acoustics education program in the School of Mechanical Engineering at Purdue University

The Acoustics and Noise Control Research Program of the School of Mechanical Engineering at Purdue offers educational and research opportunities at both the undergraduate and graduate level. In addition to undergraduate elective courses in noise control and vibration measurement and control, two graduate engineering acoustics classes are offered within the school. In addition, complementary graduate courses are offered in the areas of digital signal processing, using mechanical vibrations of discretized systems, vibrations of plates and shells, intermediate fluid mechanics, theory and design of control systems, digital control, numerical methods in mechanical engineering, and finite and boundary element methods. Graduate students also have access to a broad spectrum of courses taught in the School of Electrical Engineering and the Department of Physics. Eight faculty members and approximately 20 graduate students participate in the Acoustics and Noise Control Research Program. Most of the research is conducted at the Ray W. Herrick Laboratories. The facilities of the laboratories include an anechoic chamber with a useful working volume of 50 m3, a reverberation room with a volume of 200 m3, and a semi-anechoic chamber with a useful volume of 550 m3. Current research investigations consider: active noise control, active vibration control, structure-borne noise, nonlinear system modeling, numerical noise control design methods, acoustical imaging, modeling of acoustical foams, signature analysis and machinery monitoring, noise source identification, and application of noise control techniques to automotive powertrains and large refrigerant compressors.

Review of recent research on interior noise of propeller aircraft

Publications on the topics of propeller source noise, airborne noise transmission, and passenger comfort response to noise and vibration are reviewed. Of the 187 publications referenced, 140 have appeared since 1978. Examples of research accomplishments are presented to illustrate the state of the art. Emphasis is on comparisons of theoretical and measured results, but the description of the theories is left to the references. This review shows that substantial progress has been made in understanding the characteristics of propeller noise, airborne noise, and passenger response, and in the development of prediction methods. Application of the technology to cabin noise control and possible future research directions are discussed.

Unified acoustic theory and its application

The role of acoustics theory in Noise Control Research is reviewed. The classical sound theory of ∂2ρ/∂t2 − c2 ∂2ρ/∂xi2 = 0 which deals only with the wave propagation problem is compared with the unified acoustic theory derived by Lighthill, ∂2ρ/∂t2 − c2 ∂2ρ/∂xi2 = ∂Q/∂t − ∂Fi/∂xi + ∂2Tij/∂xi ∂xj, which deals with the sound propagation problems as well as the sound generation problems. With this unified theory, the problems of fan noise, axial compressor noise, jet noise, flow noise, and turbulent noise all become apparent. The unified theory clearly illustrates the limitation of the nearfield and farfield sound measurement that can be confidently performed. Examples of various types of noise sources and their radiation directivity will be discussed.