Abstract: The present invention provides monitoring a sounding state of a speaker even in a case where any given sound is broadcast. In detecting the sounding state of the speaker with the microphone for sound detection, noises around the speaker are also collected by the microphone for sound detection. Therefore, in a case where there are ambient noises, it is difficult to monitor the sounding state of the speaker.

Abstract: The present invention provides monitoring a sounding state of a speaker even in a case where any given sound is broadcast. In detecting the sounding state of the speaker with the microphone for sound detection, noises around the speaker are also collected by the microphone for sound detection. Therefore, in a case where there are ambient noises, it is difficult to monitor the sounding state of the speaker.

Abstract: A system for automatically feeding a chemical liquid to a cooling tower includes a water reservoir for storing water circulating through the cooling tower, a water feeding pipe extending into said water reservoir, a float valve provided in a passage of said water-feeding pipe, which is actuated in response to a variation in a water level in said water reservoir to open or close said passage, a means for increasing the flow rate of water flowing through said passage to inject water from a discharge port at the time when said float valve opens, a negative pressure generating chamber located in said passage and defined by said injection of water and a chemical liquid pipe in communication with said negative pressure generating chamber. A chemical liquid in the chemical liquid pipe is injected with water from the discharge port through the negative pressure generating chamber under the action of a negative pressure generated therein.