Abstract: A loudspeaker comprising at least one magnet 27, a yoke 24 fixed to a bottom surface of the magnet, a flat plate 26 fixed on an upper surface of the magnet, a magnetic circuit 29 having a magnetic gap 28 formed between the plate and the yoke, and a flat diaphragm 23 provided with a coil 21 disposed above the magnetic gap. The magnet has a width greater than that of the plate, and at least a part of the upper surface of the magnet is exposed so that it directly faces the diaphragm. According to the structure of the present invention, a larger volume magnet can be used without increasing the size of the magnetic circuit. Furthermore, as magnetic flux can be concentrated in an upper region of the magnetic gap, the magnetic circuit becomes efficient and compact. Thus a compact and high-efficiency loudspeaker for high frequency sound reproduction can be provided.

Abstract: A loudspeaker comprising at least one magnet 27, yoke 24 fixed to a bottom surface of the magnet, flat plate 26 fixed on an upper surface of the magnet, magnetic circuit 29 having magnetic gap 28 formed between the plate and the yoke, and flat diaphragm 23 provided with coil 21 disposed above the magnetic gap. The magnet has a width greater than that of the plate, and at least a part of the upper surface of magnet is exposed so that it faces directly to the diaphragm. According to the structure of the present invention, a larger volume magnet can be used without increasing a size of the magnetic circuit. Furthermore, as magnetic flux can be concentrated to an upper region of the magnetic gap, the magnetic circuit becomes efficient and compact. Thus a compact and high-efficiency loudspeaker for high frequency sounds reproduction can be provided.

Abstract: A highly stiff end mill comprising a shank, a plurality of helix cutting edges on the periphery of the end mill, the end mill being characterized in that a radial rake angle of the helix cutting edges in a cross section perpendicular to the longitudinal axis of the end mill is set in the range of -29.degree. to 0.degree. and a core diameter of the end mill is set in the range of 70 to 90% of the outside diameter of the end mill.By selectively determining the negative rake angle in the range described above, this end mill is applicable to hard materials and has general-purpose properties. The improper factors of the end mill, such as increased cutting resistance, can be compensated for by setting the core diameter thereof to the range described above. This end mill is also structured to be able to cut materials with less hardness values as well as hard materials, thereby covering a wide range of applications.