The point of my reply was to debunk what you said. I've not read that text and I am no expert. I can only speculate.

If you know that sound is caused by something vibrating, as was known, and you also know that when something moves through air it pushes the air away, you can reasonably conclude that sound is a vibration in the air caused by a vibration in an object.

But I don't know how he came to that conclusion, or what, of any he ran experiments he ran to show it.

My point is that anyone saying you need a microphone to learn about acoustics are talking nonsense. You have to already understand acoustics to even build the first microphone.

At that time it was a hypothesis. But the motion of snares was one of his inspirations.

In any case, it's impossible to "proof" anything in physics, you can only disprove things. If enough people fail to disprove a hypothesis, for a long enough time, a hypothesis is generally accepted as true.

An early experiment that supports the hypothesis, was in the 17th century, when experiments in vacuum became possible. Robert Boyle put a mechanical bell inside a vacuum chamber and, as the bell rang, no sound was transmitted. Highly suggesting that the presence of a medium to transfer the motion is important. (1)

Changing the type or amount of gas changes the pitch, again suggesting the medium is important.