# Vibration Sensor

I would like to make a vibration sensor but the surface is moving around a lot and the sensor might be displaced due to said movement, friction etc.

One way to do this is using a microphone over a membrane, separated by capsule so the sound can travel through.

Accelerometers are one way but I want to do it using a microphone.

I need an MEMS Analog Microphone with Frequency range from 0Hz to, at least, 1000Hz.

I can only find microphones with low cutoff point at 20Hz, 60Hz and 100Hz.

Any suggestions? Thank you for your time.

• Specific product recommendations are off-topic but maybe you could describe your application and ask what kind of sensors might be used for it. It sounds a bit like you might really want an accelerometer. Feb 5, 2014 at 8:40
• Whilst the stated cut-off might be 20Hz for example. You might find that this is the 3db point. It might still have useful detection below this, just not as sensitive. You need to look at the plots of signal v frequency to determine this. The sensor designed for around 0Hz is, as PeterJ says, an accelerometer. Feb 5, 2014 at 9:06
• If you REALLY need to measure down to DC you will need to use a microphone down to 20Hz or so, then cross over to an atmospheric pressure sensor for frequencies lower than that. [1]: sengpielaudio.com/calculator-soundlevel.htm [2]: xcweather.co.uk/forecast/PA23_7QL
– user16324
Feb 5, 2014 at 11:52
• Given your revised quesiton, how do you distinguish between "vibration" and "moving around a lot"? Do you want to collect data on all of the motions of the surface, or only some of them? Feb 5, 2014 at 14:52
• As much data as possible from the surface with the least possible movement artifacts. Feb 5, 2014 at 18:42

I doubt that you will find a microphone with a flat response to DC. Simple logic will tell you this :

• Standard atmospheric pressure is 101,325 pascals
• 94dBa (loud!) = 1 Pa
• My local weather forecast is for an air pressure of 950mb (95% of standard pressure) this coming Saturday night (apologies to later readers, weather does vary!)
• That is an amplitude of 101,325 * 0.05 = 5066 Pa
• or a peak SPL of 168 dBa if you measure sound pressure down to DC.

Such a sound pressure level would damage any reasonably sensitive microphone : in practice there is a "leak" to the cavity behind the diaphragm to prevent such damage, and this necessarily limits the LF response.

If you REALLY need to measure down to DC, you will need to use a microphone down to 20Hz or so, then cross over to an atmospheric pressure sensor for frequencies lower than that.

But the revised question suggests that your application is probably better served by an accelerometer; you are looking to measure vibration (movement) rather than air pressure.

• Do you know what range of frequencies and at what resolution could a normal SMD atmospheric pressure sensor detect? Feb 5, 2014 at 18:44
• Unfortunately no.
– user16324
Feb 5, 2014 at 20:04
• I don't understand why a atm. pressure sensor would work for low frequency vibration. (Nor do I understand what a DC vibration is, but that's a slightly different story). Feb 5, 2014 at 21:32
• @Scott Seidman : Prior to editing, the question was about microphones, not vibration sensors.
– user16324
Feb 5, 2014 at 21:38