Piezo or vibration sensors?
Piezo is very good for detecting vibrations, bias it to a non-zero voltage would also make it suitable for vibration in both ways. You can check this post, where a few people helped me with a good circuit diagram.

Piezo into 0-5v ADC, with offset center voltage?

note : to protect the input of the opamps, use a 10k in series into the opamp input.

note2 : with a bouncy material (like wood and rubber), it would have a lot of a small vibrations after the initial knocking, you would need to work it in the code to isolated the 1st knock to avoid multi triggers in a very short times.