Abstract: A speaker has a vibration device disposed under a floor approximately in the shape of a board, which can vibrate in the direction of thickness. The floor can vibrate at least around the vibration device. Since the vibration device vibrates the floor, sound is emitted from a floor surface, and hence the sound is transmitted to a wide area above the floor surface.

Abstract: A resistive temperature sensor is constituted by an insulating body mainly composed of alumina; and a temperature sensing resistor mainly composed of a conductive material containing a metal silicide. The insulating body and the temperature sensing resistor are laminated and sintered to form a lamination sintered body in which a resistance circuit is formed.

Abstract: A PTC thermistor capable of ensuring ohmic contact between a PTC thermistor body and an electrode and preventing deterioration in appearance of the thermistor to increase the yields. The PTC thermistor includes a PTC thermistor body, a first electrode formed of plated Ni of 0.2 to 0.7 .mu.m in thickness and a second electrode arranged on the first electrode and mainly formed of metal of low contact resistance. Moisture or water such as a Ni plating solution enters into the PTC thermistor body during formation of the first electrode on the body. The water then bursts due to expansion during baking of the second electrode formed on the first electrode, to produce craters on a surface of the second electrode. A decrease in thickness of the first electrode to a level as small as 0.2 to 0.7 .mu.m facilitates outward discharge of the water to reduce occurrence of the craters.