A microphone unit includes a vibrating part having a diaphragm capable of vibrating with respect to a microphone case and a fixed part including a magnetism generating circuit or a backplate supported directly on the microphone case.
Of various types of microphones, a hand-held microphone frequently presents a problem of vibration noise generated, for example, when the microphone case is rubbed with a finger. The vibration noise of this kind is generated by an inertial force such that the effective mass of the vibrating part of microphone unit tends to stay in the original state when vibrations are applied to the microphone case.
Generally, for a microphone provided with a diaphragm having the same area density, vibration noise of a low frequency component increases in the order of non-directional, unidirectional, and bidirectional. Also, comparing with a condenser microphone and a ribbon microphone, a dynamic (electrodynamic) microphone is liable to generate vibration noise because its diaphragm is heavy.
Therefore, for a hand-held unidirectional dynamic microphone especially used for vocals, conventionally, handling noise generated by the rubbing of microphone case with a finger has caused a problem.
As one method for reducing such handling noise, there is available a so-called shock mount method in which vibrations are insulated by using an elastic body such as rubber when the microphone unit is supported on the microphone case (for example, Japanese Patent Application Publication No. H01-197000).
However, the shock mount method has problems described below. The vibration insulating effect of the shock mount method depends on the resonance frequency and resonance sharpness of a vibration system. Therefore, the vibration noise reducing effect can be anticipated only on a frequency band on which frequencies are higher than or equal to the frequency correlated with the resonance frequency. Also, when solid-borne noise is loud, the vibration insulating effect cannot be achieved for the high frequency component thereof.
Accordingly, the applicant of the present invention has proposed a method for canceling handling noise by providing a vibration detecting unit having almost the same configuration as that of the microphone unit in the microphone case and by adding an output signal from the vibration detecting unit to an output signal from the microphone unit as a negative phase (Japanese Patent Application Publication No. H11-196489).
With this method, if vibrations are applied to a microphone case, not shown, whereas, for example, an output signal of positive phase is delivered from a microphone unit 1, an output signal of negative phase is delivered from a vibration detecting unit 2. Therefore, after, for example, the magnetization direction of a permanent magnet has been reversed or the winding method of a voice coil has been reversed, the microphone unit 1 and the vibration detecting unit 2 are connected to each other in series as shown in FIG. 3. Thereby, handling noise can be reduced satisfactorily over a relatively wide frequency range.
However, since the microphone unit and the vibration detecting unit are connected to each other in series, if the impedance of each unit is the same, the output impedance of microphone doubles.
As the output impedance of microphone decreases, the noise caused by electrostatic coupling or magnetic coupling from the outside is more difficult to be brought in. Therefore, the rise in output impedance of microphone is unfavorable in this respect.
Also, a main cause for failure of dynamic microphone is wire breaking. Wire breaking takes place mainly at a soldering location in the end part of voice coil. In the case where the voice coils of the microphone unit and the vibration detecting unit are connected to each other in series, if the wire breaks even at only one place, no sound is produced, so that the failure rate doubles as compared with the ordinary dynamic microphone having no vibration detecting unit.
Accordingly, an object of the present invention is to provide a dynamic microphone in which the output impedance does not increase and also the failure rate does not increase while handling noise is reduced by using a microphone unit and a vibration detecting unit.