Electro-acoustic converter

#The present invention relates generally to loud speakers and like devices for converting variations of electrical energy into corresponding variations of acoustic energy, such as, sound. The present invention is suitable for use both in specialized loud speakers forming part of hi-fidelity sound reproduction systems, and as a loud speaker for general applications in televisions, radio and other consumer markets, and it will be convenient to describe the invention in relation to such an exemplary, non limiting applications.

#The basic operation of loud speakers and like electro-acoustic converters is well known. In such devices, an electrically driven vibration inducing member, such as a moving coil or piezo-electric crystal, is attached to one end of a diaphragm. Variations in the electrical signal applied to the vibration inducing member are converted into mechanical vibrations which are amplified by the diaphragm and result in the production of sound waves in the air.

#In dynamic or moving-coil loud speakers the vibration inducing member includes a moving coil, attached to the diaphragm, which oscillates in an annular cavity of either a specially shaped permanent magnet or an electro magnet. The efficiency of such a loud speaker in converting electrical energy into sound energy is governed by three main factors, namely, the product of the active links of the moving coil and the magnetic field strength, the effective area of the diaphragm, and the total moving mass of the diaphragm, moving coil assembly and the acoustic air load. An increase in the first two parameters, either singly or together will result in an increase in the efficiency of the loud speaker. However, an increase in the mass will result in a reduction in the loud speaker efficiency.

#These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying figures where:

#FIG. 1 is a cross sectional view of one embodiment of an electro-acoustic converter according to the present invention;

#FIG. 2 is a schematic diagram illustrating the movement of the diaphragm of the electro-acoustic converter of FIG. 1;

#The following description refers in more detail to the various features of the electro-acoustic converter of the present invention. To facilitate an understanding of the invention, reference is made in the description to the accompanying drawings where the electro-acoustic converter is illustrated in a preferred embodiment. It is to be understood that the electro-acoustic converter of the present invention is not limited to the preferred embodiment illustrated in the drawings.

#Referring now to FIG. 1, there is shown generally an electro-acoustic converter 1 comprising a diaphragm 2 having a barrel shaped body formed about a longitudinal axis 3 between a first annular end 4 and a second opposed annular end 5. As can be seen from this Figure, the barrel shaped diaphragm 2 is curved so that the diameter of the diaphragm at the two opposed annular ends 4, 5 is less than the diameter of the diaphragm at a point intermediate these two ends. Typically, the diaphragm may be formed from a textile or like material, but other materials known to persons skilled in the sound reproduction field may also be used.

#In this embodiment, a first moving coil 6 is attached around the first annular end 4 of the diaphragm 2. The moving coil 6 is located within the electro-acoustic converter 1 in an annular cavity 7 within a permanent upper magnet assembly 8. Electrical oscillations in the current flowing through the moving coil 6 in the presence of the magnet field generated by the permanent magnet 8 cause the moving coil 6, and the first annular end 4 of the diaphragm 2 to oscillate in the annular cavity 7.