Abstract: A speaker which is thin but which is capable of providing high-fidelity reproduction and ensuring a suitable level of sound pressure even when it is brought close to a wall. A closed chamber is formed behind one part of a diaphragm mounted in an enclosure, and an open chamber is formed behind another part of the diaphragm. At least one voice coil drive unit is connected to the diaphragm. The phase difference between sounds radiated from the front and rear surfaces of the diaphragm is increased as large as possible by using an acoustic duct for the sound radiated through the open chamber, thereby minimizing cancellation of sounds and improving the sound pressure level.

Abstract: A microwave heating apparatus for heating an object for cooking which is placed on a turntable in a heating chamber. The microwave heating apparatus is arranged so as to automatically determining an appropriate heating condition of the object on the basis of a distinctive feature such as configuration and density of the object. The distinctive feature of the object is obtained by successively measuring a distance between the center of the turntable and a surface of the object. The measurement of the distance therebetween is performed by means of an ultrasonic transducer which is provided on a wall of the heating chamber so as to transmit an ultrasonic wave to the object and receive an echo wave from the object, the distance therebetween being obtained on the basis of the time between the transmission of the ultrasonic wave and the reception of the echo wave.

Abstract: A digital signal represents a desired amplitude frequency characteristic. A desired transmission characteristic is derived from the desired amplitude frequency characteristic. A sound signal is processed in accordance with the desired transmission characteristic. The processed sound signal is converted by a speaker into corresponding sound. The process of the sound signal corrects and compensates for the original sound pressure frequency characteristic of the speaker and thereby actualizes the desired amplitude frequency characteristic.