Active control of sound transmission through a double-leaf partition by volume velocity cancellation

Abstract

The paper considers the active control of harmonic sound transmitted through a double-leaf partition by cancelling the volume velocity of the radiating panel. The double-leaf partition consists of a pair of small plates, 300×380 mm, separated by a 100-mm air-gap. The panel volume velocity can be sensed by a single shaped film of piezoelectric PVDF material attached to the plate. Cancellation of volume velocity using a single point force is compared with the result using a matched, distributed actuator which applies a uniform force to the plate and does not give rise to control spillover. Comparison with earlier work in which the volume velocity of a single plate was cancelled [Johnson and Elliott, J. Acoust. Soc. Am. 98, 2174–2186 (1995)] shows that substantial reductions in the transmitted sound power are only possible up to around 350 Hz, as opposed to 600 Hz in the single panel case. A radiation mode analysis of the panels shows that the double-leaf construction provides good passive attenuation of the first radiation mode at high frequencies, so that inefficiently radiating even modes of the radiating panel make a dominant contribution to the radiated sound power. Thus there is no advantage in controlling volume velocity in this frequency range.