We know that the sound-producing part of a #speaker is a speaker, but why use a #speaker instead of directly listening to the #speaker? The purpose of the #speaker is to prevent the sound wave signal from the front and back of the #speaker diaphragm. A loop is formed, so that only high-frequency and intermediate-frequency sounds with a small wavelength can be transmitted, and other sound signals are superimposed and cancelled out. The physical model of the #speaker is to open a hole in an infinite rigid baffle to install the #speaker, so as to ensure that the sound signal on the front and back of the #speaker will not form a loop, resulting in a sound wave loop. However, in actual use, the #speaker cannot be made infinite. Therefore, people use a baffle behind the #speaker to form a closed space to ensure the frontal transmission of sound waves.