The measurement of frame motion in flexible porous materials

This paper describes a method for measuring the vibrational velocity of the solid skeleton of a flexible porous sound-absorbing material. The method i s based on a simple electromagnetic principle, involving a thin conductor t hat is structurally connected to the frame of the absorbent and placed in a magnetic field. The sample test results that are presented here demonstrat e that links may be established between acoustic data and frame velocity me asurements, In the presence of a high-amplitude sound held, measurements sh owed that the velocity of the frame exhibits very nonlinear properties, whi ch cannot be explained by nonlinearities in the airborne sound wave. (C) 19 99 Acoustical Society of` America. [S0001-4966(99)04001-1].