I wish to measure vibrations that come from sound. The sound is likely well under 100 hz since it can never be heard. It is only felt as a mild pressure sensation. I may refer to it as "sound", perhaps it is better to call it something else.
My goal is not necessarily to get an extremely accurate level of whatever unit, rather to get a somewhat accurate - AND consistent reading - if the 'sound' remains the same each time it is measured.
I had used a Vibrometer app on my smart phone (a Samsung Galaxy S4). I was clearly able to see that 'ordinary' events within a building where it was used resulted in a relatively low reading, then the 'sound' - which I knew was present due to the feeling it produces, produced a much higher reading.
So, I saw it work. Over time the characteristics of the 'sound' changed, and
although I could still feel it, the reading on the phone app was noticeably lower. I suspect that the frequency was lowered rather then its power or amplitude.
So, I am looking for a better way to measure the sound. I've been told that it is best not to view this as measuring 'sound', since to most that implies 'audio' frequencies over 200 hz, and also that the equipment available for that purpose is not suited to very low frequencies.
Ideally, I'd like to be able to measure the sound, and get that in the form of a digital output that I can record with my computer - my strong preference is RS232. I would rather not play with any sort of analog output as that would be of little use to me. I'd need to convert that, and I do not want to go through the hassle.
I looked at devices like this on eBay
http://www.ebay.com/itm/VM-6360-Digital-Vibration-Tester-Meter-Vibrometer-w-Software-/320989123440?pt=LH_DefaultDomain_0&hash=item4abc715370
("VM-6360 Digital Vibration Tester Meter Vibrometer")
but had some questions I didn't know how to answer. First, I wanted to get an idea of how well my phone app could perform at the lower frequencies compared to devices like this. For example, if my phone app handle frequencies down to 5 hz, then perhaps a gadget like this would not be useful. If my phone app only handled frequencies down to 80 hz, then perhaps a device like this would be useful to me, or perhaps one made by Campbell.
Secondly, I am not at all sure if this sort of device would be able to measure vibrations in the air. I suspect these devices were meant to be bolted to some machinery that is being evaluated. I know the phone app does NOT use the microphone - but rather other sensors within the phone. So, I guess that is essentially what these devices do.
I'd appreciate any insight.
Hi cavibs,
I'm no expert, so don't spend your money based on what I say, but:
I think you might be requiring a microphone that can read those frequencies.
There are fully integrated system you can buy, but I expect that there are microphones you can buy that would work well with a CR6 etc.
Steve
Cavibs,
I've actually done this very thing with a cr6 using a regular subwoofer, a microphone, and also tried with a geophone to measure low frequency shocks. It actually works quite well. I used a burstmode voltdiff command and was recording at 4k Hz. I was even able to convert the data to a wav file and play it back. Quite impressed with the results.