Identifying resonant frequencies in various objects

[Fred Austere]

Hi

I was wondering if someone would be kind enough to help me with a project I have at the moment.

Here is the scenario;

I am playing various tones through a speaker system at a fridge and I need to be able to detect which of the tones make the fridge resonate.

I have been using a flat microphone taped to the fridge but that seems to be showing me nothing more than its own best frequency response.

What would be a more sensitive/suitable way to measure the vibrations in the fridge.

I would like to display the measurement signal on an oscilloscope

Thanks in advance to anyone who can help.

James

 

[nasu]

An accelerometer attached to the fridge will pick-up the vibrations while being quite insensitive to the sound waves coming though the air.

 

[Fred Austere]

Thank you, that sounds good.

Any particular one you think would be good? Can they be outputted to an oscilloscope.

James

 

[AJ Bentley]

When I was a teenager, I built an incredibly sensitive microphone that picked up vibrations from a surface without being affected by sound in the air. (It was really good at picking up conversations in the next room!)

All it was, was a piece of graphite rod extracted from a dry cell balanced on a pivot slightly off centre so that one end rested on another piece of graphite rod.

Very slight movements of the rods caused pressure changes at the contact points giving a change in conduction. A simple battery supply and a pair of headphones (no amplification) were all it took to make it work.