JPS57154998A - Electromagnetic speaker - Google Patents

Abstract

PURPOSE:To lower the two resonance frequencies of the connected two resonance systems, by setting a mobile iron bar as if it enclosed both the 1st and 2nd diaphragm bodies and having a contact between the outer circumference parts of the 1st and 2nd diaphragm bodies to fix these outer circumference parts to the step part of a resonator. CONSTITUTION:A magnetic circuit consists of a permanet magnet 24, a magnetic core body 23, a magnetic core 22 and a mobile iron bar 19. The bar 19 is excited by the constant magnetic force produced by a constant magnetic flux flowing to the magnetic circuit plus an alternating magnetic force generated by the signal applied to a coil 21 from outside. Thus the 1st diaphragm body 18 has coupled to the bar 19 has the vibration. The vibration of a diaphragm 32 is transmitted to the 2nd diaphragm body 30 via an air spring of an air chamber 14. Both bodies 18 and 30 are made of a plastic material with edges 29 and 16 provided at each circumference part respectively. Thus the internal loss increases within the edges 29 and 16, and the piston type vibration is obtained at the inner circumference parts of the edges 29 and 16. Then the internal spring constant is lowered for the edges 29 and 16 respectively. A resonance system comprising the diaphragm 32, the body 30 and the chamber 14 has a reduction owing to the lowering of the spring constant.