For example, as described in Japanese Patent Application Publication No. 2006-33216, in a gooseneck condenser microphone, a microphone unit is attached to the distal end of a support pipe in which a flexible pipe is used partially, and a connector terminal incorporating a power module for the microphone unit is provided on the rear end side of the support pipe.
This gooseneck microphone is configured so that the direction of the microphone unit can be changed freely by flexing the flexible pipe. Also, because of its small size and good appearance, the gooseneck microphone has come into wide use mainly as conference equipment.
Usually, in the condenser microphone, a field effect transistor (FET) serving as an impedance converter is incorporated, and the condenser microphone unit and an output module are connected to each other via a microphone cable.
As the microphone cable, there has been used a two-core shielding covered cable having a power line for supplying power, a signal line for sending signals to the output module, a shielding wire for electrostatically shielding these lines, and an external sheath (skin) for covering the shielding wire.
Since sound signals are sent imbalancedly in the portion of microphone cable, the microphone cable is vulnerable to extraneous noise (electromagnetic waves). That is, if strong electromagnetic waves are applied to the microphone cable, a high-frequency current intrudes into the unit part and the power module part, and noise is generated. In particular, with the recent widespread use of cellular phones, such a trouble occurs often when a cellular phone is used in the vicinity of the microphone, which poses a big problem.
To solve this problem, in the condenser microphone disclosed in Japanese Patent Application Publication No. 2006-33216, the microphone cable is inserted in the support pipe in the state in which the external sheath is not provided and the shielding wire is exposed. According to this configuration, the shielding wire and the inner peripheral surface of support pipe are connected electrically to each other at multiple contact points, so that the resistance value of support pipe decreases extremely, and the shieldability against electromagnetic waves is improved significantly.
Unfortunately, the condenser microphone disclosed in Japanese Patent Application Publication No. 2006-33216 has problems described below. Since the flexible pipe is capable of being flexed, both of the position and the number of contact points between the support pipe and the shielding wire are unspecified, so that differences in shieldability among individual microphone cables are liable to occur.
Also, when the gooseneck portion is flexed repeatedly, metal powder is produced by intermetallic friction between the support pipe and the shielding wire. The metal powder drops into the power module part, which may cause a short-circuit accident.
Further, since the flexible pipe consists of a combination of steel wires and copper wires, rusting takes place due to a potential difference between dissimilar metals, and the rust may exert an influence on the shieldability.
Besides, since the interior of the support pipe is a cavity, sounds pass through the interior of the support pipe and intrude into the microphone unit, so that noise due to cavity resonance may be generated.
The present invention has been made to solve the above problems, and accordingly an object thereof is to provide a gooseneck condenser microphone that is further strengthened the shield structure of a support pipe and is less prone to causing a trouble.