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.

 

[pmacias]

Hello James,

Thank you for reaching out and seeking advice on your project. Identifying resonant frequencies in various objects can be a challenging task, but there are different methods and equipment that can help you achieve accurate results.

One option could be to use a contact microphone instead of a flat microphone taped to the fridge. This type of microphone is designed to capture vibrations from solid surfaces and can provide more sensitive and accurate measurements. You can attach the contact microphone to the fridge using a small piece of putty or adhesive.

Another option could be to use a laser vibrometer, which is a non-contact device that measures vibrations by detecting changes in the laser beam reflected off the object. This can also provide precise measurements of resonant frequencies.

In terms of displaying the measurement signal on an oscilloscope, you can connect the output of the microphone or vibrometer to the oscilloscope and adjust the settings to display the vibrations as a waveform. This will allow you to visualize the resonant frequencies and their amplitudes.

I hope this helps and good luck with your project!

Best,