1. Technical Field of the Invention
The present invention relates generally to a sound collecting device designed to minimize electric noises caused by dust, frozen foreign substances lying on an electroacoustic transducer exposed to the air, or electromagnetic noises inputted directly to the transducer.
2. Background Art
FIG. 8 shows a conventional sound collecting device which consists of a horn 1 designed so as to increase in sectional area in a lengthwise direction for ease of collecting the sound wave, an electroacoustic transducer 2 (i.e., a microphone) installed in a base of the horn 1, and a preamplifier 3 connecting electrically with the transducer 2. An audio signal outputted from the transducer 2 is, as clearly shown in FIG. 9, amplified by the preamplifier 3 and outputted to an external device.
The transducer 2 is usually exposed to the air for catching sound waves and thus has the problems in that dust is gathered on a diaphragm of the transducer 2 with time or when the device is used in winter, it may cause the moisture in the air to be frozen solid on the diaphragm, which affects on an operation of the transducer 2, and in that since the transducer 2 needs to be exposed directly to the air, it is difficult to use a shield for protecting the transducer 2 from electromagnetic waves originating from high-voltage cables or transmission antennas, so that the electromagnetic noises are inputted directly to the transducer 2.