bensimmo wrote:Stick a pickup microphone on it?
I'm looking for something more novel using a sensor directly attached to the wall rather than a decibel meter
No it's not a "decibel meter". It's a microphone, a sensor, it picks up the vibrations and converts it into an electrical waveform. You stick it on the wall.
Oddly designed to pick up vibrations
Though you'll need to be picking up low frequencies so check specs.
For novel (but not really novel) look at light pattern deflection of mirrors placed on on a wall, perhaps in a grid or not.
Or create an array of dots and use a camera to determine the vibrations as they move?
or a boring set of accelerometers.
Try them all, see what does/doesn't work.