Flat speakers get smaller

The new DMAs from NXT plc, Huntingdon, U.K. (www.nxtsound.com/general/home.php), measure 22 7 3.5 mm and rely on piezoelectric polycrystalline ceramics. Applying a voltage changes the ceramic actuator, which generates sound when the actuator is connected to an acoustic lens. In a portable phone, for example, the DMA, which contains two ceramic actuators, attaches to the display screen, which vibrates to create sound. DMAs are typically 1.5-mm thick, weigh about 2 gm, and cost less than $2.00.