The bell jar experiment is a common experiment to show that sound cannot travel through a vacuum

A bell jar’s shape is similar to that of a bell. A bell jar is placed on a base and connected to a vacuum pump as shown in the picture below. The air in the jar is varied by pumping the air out of it.

Now, we put an electrical bell in the bell jar. As the air is pumped, vacuum is being created inside the jar slowly and steadily and the sound from the bell jar fades. At a point when complete vacuum is maintained, no more sound is heard from the bell. Thus, the sound is not audible to our ears because of the vacuum inside the jar.