A case in which electric parts are housed is provided with an electric cord outlet out of which various electric cords including a power supply cord and a signal cord are drawn. Normally, a cord bush is attached to the electric cord outlet to protect the part out of which the electric cords are drawn (see, for example, Japanese Utility Model Application Publication No. 3027420).
Tie pin or headset microphones are often used if users, for example, TV announcers and aerobics instructors, need to speak with their hands free. Such microphones are located at the user's mouth so that the user can use his or her hands freely.
In the tie pin or headset microphone, a microphone unit is separated from a control box including a power module and a transmitter. The microphone unit and the control box are electrically connected together via a microphone cord. A two-core shield coated wire is normally used as the microphone cord.
FIG. 2 is a diagram illustrating the relationship between the conventional control box and microphone cord. As shown in FIG. 2, the control box 1 comprises a box-like case 2 in which a power module including a driving circuit and batteries as well as a transmitter for a wireless microphone (neither of the components is shown) are housed. The control box 1 is installed on a pelvic belt or the like.
The case 2 is provided with an outlet 3 through which the microphone cord 6 is drawn out of the case 2. A cord bush 4 is attached to the outlet 3 so as to surround the periphery of the microphone cord 6 to protect the cord 6. The microphone cord 6 is drawn out through a guide hole 5 formed in the cord bush 4. A microphone unit (not shown) is connected to the other end (in FIG. 2, the upper end) of the microphone cord 6.
In general, in the microphone cord 6 of this kind, the cord length between the control box 1 and the microphone unit can be freely adjusted depending on the user's physique.
Thus, in the microphone control box 4, shown in FIG. 2, a gap, which is very small, is created between the cord bush 4 and the microphone cord 6 to enable the length of the microphone cord 6 to be adjusted.
Accordingly, when an aerobic instructor wears the control box 1 on his or her pelvis, sweat may run along the microphone cord 6 and enter the case 2 through the gap between the microphone cord 6 and the cord bush 4. The sweat may thus corrode any of the internal electric circuits or batteries to cause it to malfunction.
To avoid such an inconvenience, a waterproof treatment may be carried out by using an adhesive such as a sealant material to seal the cord bush 4 and microphone cord 6. However, this may preclude the adjustment of the length of the microphone cord.
In view of these problems of the prior art, it is thus an object of the present invention to provide a cord bush and a microphone control box which enable the free adjustment of the length of an electric cord and which can reliably prevent a liquid from infiltrating into the control box along the electric cord.