\”sound level meter\”的運作是點???

It is called a sound intensity level meter (or sound-level meter).





圖片參考：http://physics.ucsd.edu/was-sdphul/labs/demos/pics/dB_meter.gif

It is a device for measuring the intensity of noise, music, and other sounds. A typical meter consists of a microphone (q.v.) for picking up the sound and converting it into an electrical signal, followed by electronic circuitry for operating on this signal so that the desired characteristics can be measured. The indicating device is usually a meter calibrated to read the sound level in decibels (dB), a logarithmic unit used to measure the sound intensity (q.v.). Threshold of hearing is about zero decibels for the average young listener, and threshold of pain (extremely loud sounds) is around 120 decibels, representing a power 1,000,000,000,000 (or 1012) times greater than zero decibels.


The electronic circuitry can be adjusted, usually by an external switch, to register the integrated level of all frequencies in the sound being measured or the intensity of selected bands of frequencies. A time lag is usually incorporated to slow down meter response and thus permit rapidly varying sounds to be averaged. The amount of time lag may vary somewhat among instruments, depending on the purpose for which the instrument was designed. (from http://www.britannica.com/eb/article-9068801 )

感應聲音在空氣傳播的壓力, 然後折算為 dB 單位, 用指針或跳字顯示結果