As a low frequency standard a tuning fork offers certain advantages because of its high Q value. Analysis was conducted with the view of finding the characteristics of added-mass cantilever structure for miniaturizing the tuning fork. Thus a tuning fork of added-mass type with dimension 26. 5×6. 0×2. 0 mm and frequency of about 300 cps was designed. In maintaining the vibration by piezoelectric means, the cementing of piezoelectric elements to the tuning fork is one of the most important factors which effect the values of Q. The relation between the values of Q and the place of attachment of the piezoelectric elements was investigated, and a piezoelectric tuning fork with high Q at about 3000 was obtained. Several further characteristics of this piezoelectric tuning fork were investigated and discussed. The equivalent circuit of this tuning fork was obtained, and several constants of this equivalent circuit were measured.
When magnetic or dielectric circuits exist in the electromechanical energy conversion of reciprocal electroacoustic transducers, the mechanical impedance z in the transducer equation for the system includes a negative stiffness. In this paper, it is pointed out that the vector power consumed as negative stiffness constitutes a part of magnetically consumed vector power. Then, in the calculation of electromagnetic and electrostatic transducers, the mechanically consumed vector power should be given by the power consumed by purely mechanical impedance which is obtained by subtraction of negative stiffness from the impedance z. In the electrodynamic transducer, there is no change in the polarizing magnetic field, because driving current and/or mechanical vibrations of the diaphragm have no effect on the field. The negative stiffness in this system become zero, and z in the equation equal to the pure mechanical impedance z_m. As a result of this consideration, the relation of the vector powers in the reciprocal transducers are shown as follows : EI^^^-+Fv^^^-=Z_eI^2+E^<'2>/(Z^^^-_r)+z_mv^2 for electromagnetic transducers, EI^^^-+F^^^-v=Y^^^-_eE^2+I^<'2>/(Y_r)+z^^^-_mv^2 for electrostatic transducers; EI^^^-+F^^^-v=Z_eI^2+0+z^^^-_mv^2 for electrodynamic transducers, where the first term of the right side denotes electrically consumed vector power, the second term magnetical one, and the third mechanical one respectively. It is also stated that the expression of mechanical vector power depends on the type of transducers and from this point of view a new classification of transducers is proposed in Fig. 11.