Effects of acoustic velocity and attenuation measurements during settling of 43-, 110- and 168-mu m glass beads in water are reported. Ultrasonic waves were generated at a frequency of 3.2 MHz. An abrupt increase in acoustic velocity and a sharp peak in the attenuation characterized the onset of settled bed. The observed attenuation peak at the transition between suspended and settled bed was attributed to dissipation caused by viscous absorption losses. The critical concentration at which increase in acoustic velocity and attenuation peak occurred was estimated for these particle sizes. (C) 2007 Elsevier B.V. All rights reserved.