[mike1127]

Good to meet all of you DIY speaker builders. I built speakers in college. It was fun.

Currently I'm not building speakers but instead playing around with the mounting and isolation of electronics... that is, a DIY equipment rack. And I'm doing experiments like putting the equipment directly on the ground to see if it sounds better. Basically I'm (1) trying to learn something, (2) might get a better rack out of it, or might not.

So I have gotten interested in measuring the resonant modes of my DIY rack (made of wood), and seeing how it responds to vibration in the floor (for example, creating an impulse in the floor by dropping a bowling ball onto it). Therefore I need an accelerometer, and it would be cool if I didn't have to pay a lot.

I know I will need to purchase the acceleromter itself. I will need some kind of preamp, but I'm wondering if I can use the microphone preamps I already own. And then I need a way of digitizing the signal, which could be the soundcard on my computer. Finally I need software to analyze an impulse. (I know that Audacity has a spectrum analyzer but not sure if it is suited to the job.)

Note: in this application I think I need to physically induce an impulse... there is no way to use something like MLSSA because there is no speaker to play a signal out of.

So I'm wondering what other people have used.

 

[Deephaven]

Measuring modes takes a bit more than just measuring vibration. If you want to know the true damping you are going to have to measure the input force as well. On top of that it isn't trivial to do "modal analysis" by hand. Vibrant Technologies ME'Scope is one of the cheaper softwares to do it and it is well over $5k alone, $20k with FE correlation options and such.

As for what is super cheap in an accel you need something that measures rather low in frequency, but also need to find some OEM style solution for it to be low cost. (ie like an airbag sensor) Otherwise a fairly low cost accel will be strain gage based and still over a hundred bucks plus you'll need a stable source to excite the bridge.

Probably easier to overbuild.

If you are really just curious you could look for some strobe light that takes a sine wave input and synchronize it with a loud acoustic source and just watch for the rack to move around. If you don't get in enough energy that way you could use stick the driver to the rack itself and add some mass to the cone to make it input more energy into the structure. Your eyes aren't exactly the most sensitive accel made, but if you have a modal problem you could probably find it this way.

 

[Dennis H]

I'm late to this thread so I don't know if the OP will see this. You can get a nice one with 2Hz-20kHz response, from Digikey for $45.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MSP1001-ND

It will work with a sound card mic input with 5V phantom power if you wire it to a plug like in this article. The 48V phantom power of a pro mic preamp is too high.

http://www.libinst.com/accel.htm

 

[Deephaven]

If the specs on that are real it is a steal. I'd expect a piezo accel to cost at least 10x that.