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A new laboratory method has been developed to evaluate the acoustical properties of expandable and other automotive sealants. These materials are used to reduce wind, road, and powertrain noise transmission into passenger compartments. In the new method, ASTM E 1050 absorption measurement equipment is used along with a new sample holder, a downstream microphone holder (providing two additional microphone locations) and an anechoic termination. These additions permit measurement of normal incidence transmission loss as well as absorption. It is intended to encourage adoption of this method as a standard way of quantifying the acoustical performance of sealants and sealing composites in automotive noise control applications.

A hemi-anechoic room and roadwheel facility, for the study of noise from small automobile tires, has been constructed at Stanford University. Fundamental research on sound generation mechanisms and superposition of simple tread elements has been conducted. Through use of the signal average, (roadwheel) tire noise may be separated into tire-rotation correlated and roadwheel-rotatlon correlated components which account for essentially all of the sound. Level and spectral characteristics of these components are examined for three tires with very simple tread patterns and one commercial type tire. Results suggest that several distinct excitation mechanisms are responsible for “tire vibration” noise. The “groove pipe resonance” is discussed. Problems in coastby-roadwheel noise measurement correlation are examined. Published coastby data are contrasted with component separated roadwheel data. Legislative implications are also suggested.