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Wideband Acoustical Holography (WBH), which is a monopole-based, equivalent source procedure (J. Hald, “Wideband Acoustical Holography,” INTER-NOISE 2014), has proven to offer accurate noise source visualization results in experiments with a simple noise source: e.g., a loudspeaker (T. Shi, Y. Liu, J.S. Bolton, “The Use of Wideband Holography for Noise Source Visualization”, NOISE-CON 2016). From a previous study, it was found that the advantage of this procedure is the ability to optimize the solution in the case of an under-determined system: i.e., when the number of measurements is much smaller than the number of parameters that must be estimated in the model. In the present work, a diesel engine noise source was measured by using one set of measurements from a thirty-five channel combo-array placed in front of the engine.

A project is described where spherical beam-forming was used to perform real time evaluation and development of an automotive dash silencer assembly. By eliminating the iterative laboratory sound transmission loss testing, significant advantages were achieved in part development. These advantages include a reduction in development cost and time, reduced part cost, and lower part mass. Reducing the time to develop lighter and less expensive sound package parts was the most obvious benefit of the project, but the process also: 1) eliminated the time and cost to procure competitive parts; 2) allowed the evaluation of the parts in-vehicle rather than on a laboratory buck; and 3) reduced the time required with the development vehicle.

This paper describes the successful development of an active muffler system for the Detroit Diesel 6V-92TA industrial diesel engine used in a generator set application. The active muffler analyzes the structure of the exhaust sound and generates ‘anti-noise’ through loudspeakers. The ‘anti-noise’ is equal in magnitude and 180 degrees out of phase with the exhaust sound. The exhaust sound and ‘anti-noise’ cancel each other at the exhaust outlet. Adaptive filter techniques are used to update the ‘anti-noise’ signal in response to changes in engine operating conditions. This technique is effective at frequencies less than 500 Hz, where a significant portion of the exhaust sound is concentrated. Combined with a low flow restriction passive silencer to attenuate primarily high frequency sound, exhaust noise is reduced well below levels emitted by conventional passive mufflers.