Abstract
A minimized mechanical impedance is desirable in order that a phonograph pickup can trace a sound groove correctly. Current phonograph pickups, however, have resonance peaks in their frequency responses and mechanical impedance characteristics in the neighborhoods of their high frequency ends. This has introduced a great problem to sound groove tracing. Current pickups have high resonance frequencies beyond the hearing limit rather than damped resonances which can be achieved by lowering the equivalent mass of the vibrating system as shown in Fig. 2. But this method gives some problems such as degradations of sensitivities and fragilities. In this paper, as an effective method for damping out the high frequency resonance, a vibrating system with two degrees of freedom has been studied. As a result of the analysis, it has been made clear that the following method is useful. That is splitting the cantilever into two parts and connecting them with elastic material with small resistance, and damping the high frequency resonance by the resistance of the armature bearing. The split cantilever makes not only the high frequency flat but also the mechanical impedance characteristic in the high frequency range flat, as shown in Fig. 6, therefore the split cantilever is suitable for a high quality phonograph pickup. Experimental phonograph cartridges with split cantilevers (Fig. 7) have been made. Fig. 8, shows the frequency response and the mechanical impedance characteristic of the experimental cartridge. It's results agree well with the calculated results shown in Fig. 9.
