Beamed Voices interactive, Science Museum, London, 1992.

This exhibit uses no special equipment and your voice is not amplified: the effect is caused by the precise shape of the dishes which reflect and concentrate your voice so that it can be 'beamed' acros a crowded room and heard on the other side. The curve of the dishes is part of a shape called a parabola. A parabola reflects soundwaves - or any other waves - in a special way.