Technical detailsIt is known that high-intensity modulated ultrasound radiates audible sound although ultrasonic frequency itself is inaudible. This effect and straight line propagation of ultrasound are utilized for a superdirective speaker that makes a beam of audible sound. This speaker drives many ultrasonic transducers with a single signal. Differently, we drive the transducers individually with different signals to make an ultrasonic focal point. Audible sound is generated only from the focal point. With this technology, we can place a point sound source freely in air. While a sound-beam speaker delivers sound to not only a target person but also other persons on the same straight line, our sound-point speaker can deliver sound to just the target person. This feature increases the freedom of sound environment design, for example, explanation in museums, paging in unquiet places, and digital signage in collaboration with smart phones.