Use of scale model to design vehicle pass-by noise test facility enclosure

Abstract

Inclement weather can cause up to 50% downtime for a vehicle pass-by noise measurement facility. One way to increase the facility efficiency is to shelter the test pad by an enclosure. Such an enclosure must be designed acoustically to minimize the effect that the enclosure structure has on altering the hemispherical sound field of the pass-by facility. This acoustic design is developed accurately and relatively inexpensively by tests on a scale model of the enclosure. The model structure is a replica of the proposed enclosure. The vehicle is modelled by a point noise source fixed at positions to simulate the source-receiver orientations of the major noise sources of a vehicle during drive-by. Each acoustic design is evaluated by comparison of sound pressure level spectra measured within the structure to spectra gathered in the semifree acoustic field. The spectra of the final acoustic design generally agree with the semifree field spectra to within ±1 − 12 dB. A properly designed enclosure could double the usable time of a vehicle pass-by noise measurement facility. By tests on a scale model, a feasible design has been developed.