| 摘要 |
PURPOSE:To nicely and conveniently hear the sound from a speaker even when circumstance is changed to be noisy from silent by providing an automatic sound volume adjustment means which reversibly increases the sound volume of the speaker when the sound volume of the noise in surroundings increases. CONSTITUTION:An amplifier 2 which amplifies a sound signal voltage according to the output voltage from a sound volume adjustment volume 1 which is manually operated and the speaker 3 which works according to the output voltage from the amplifier 2 are provided. The automatic sound volume adjustment means 4 which automatically adjusts the sound volume of the speaker 3 in proportion to the sound volume of the surrounding noise is equipped. The sound volume automatic adjustment means 4 is composed of a sound collecting microphone 4A which collects the surrounding sound, a noise sound volume detection circuit 4B which outputs the difference of the output voltage of the sound collecting microphone 4A and the output voltage for the speaker 3 and a sound volume adjustment amplifier 4C which adjusts the output voltage for the speaker 3 based on the output from the noise sound volume detection circuit 4B. |
