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Use a speaker cone as a linear oscillator?

post #1 of 9
10/29/09 at 2:46pm
Thread Starter 
Ok, so I have a bit of an unorthodox question, and was hoping someone more experienced with speakers (or mechanical engineering in general) could help.

I need a variable-amplitude variable-frequency vertically vibrating device for a project I am working on. The desired amplitude is in the range of 0.2mm and frequency at 40Hz and above. The object vibrated will be a very small petri dish. The budget for the project is quite small.

Now, before thinking of using a speaker cone I considered various setups, inlcuding a spring-loaded electromagnetic oscillator, a piston motor, a variable-radius camshaft, etc. All of these have limitations, not the least of which is availability. A speaker cone is very easy to get, but I have extremely limited experience with speakers and such. I assume I'd need a powered amplifier (which would double as an amplitude (volume) control) and also a frequency generator (probably a PC), as well as a way to actually measure the output amplitude and frequency (possibly running a DC voltage for a short time at a particular volume to measure the amplitude).

Can anyone think of any reason for why this wouldn't work? I'm sure there are several problems with this setup that I'm just not experienced enough to see. Maybe I'm not thinking hard enough.

Anything helps, guys. TiA.
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post #2 of 9
10/29/09 at 2:52pm
The frequency would be easy enough to measure. Use a mic and record it into some software. Do a spectrum view and you should see a spike at 40hz. Conception ally it sounds good to me. I have seen videos of those liquids that can become solid with the proper stimulation. You can "see" the waves ripple across it. I presume they used a speaker at a specific frequency to trigger it.
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post #3 of 9
10/30/09 at 12:32am
Freq. should be the easy part. There are many tone generator programs. Here's one for windows. Some math may be involved to get the proper excursion distance.

The petri dish may make it slightly more difficult depending on the required accuracy in the freq. due to it's weight on a driver. You should use the method flashnolan posted above to be sure of the effect on the freq.

And why do you ask the Member's lounge? Sound Science is a much better place to ask in my opinion.
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post #4 of 9
10/30/09 at 1:48am
Thread Starter 
Quote:
Originally Posted by flashnolan View Post
The frequency would be easy enough to measure. Use a mic and record it into some software. Do a spectrum view and you should see a spike at 40hz. Conception ally it sounds good to me. I have seen videos of those liquids that can become solid with the proper stimulation. You can "see" the waves ripple across it. I presume they used a speaker at a specific frequency to trigger it.
Thanks, that's what I had in mind for a frequency feedback circuit since I figured the petri dish would cause it to deviate from input.

Quote:
Originally Posted by notmuchcash View Post
Freq. should be the easy part. There are many tone generator programs. Here's one for windows. Some math may be involved to get the proper excursion distance.
Thanks for the link. I have another generator but yours seems nice and simple .

Quote:
Originally Posted by notmuchcash View Post
And why do you ask the Member's lounge? Sound Science is a much better place to ask in my opinion.
Lounge gets a lot more traffic. Plus I wasn't sure it was science as much as a practical application... and not really of sound per se.

Thanks for the responses, guys.
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post #5 of 9
10/30/09 at 10:03am
I think it would work. After all, a hard drive's read/write heads are moved by dynamic transducers.
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post #6 of 9
10/30/09 at 1:31pm
It would work but the added mass would mean extra power. You can calculate how much you'd need using some fairly simple electromag and forced harmonic oscillator equations - I was going to do it but I'm pretty lazy. I might later. With a bit of luck it should express how much power you need as a function of the mass.
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post #7 of 9
10/30/09 at 9:42pm
Thread Starter 
Quote:
Originally Posted by DanielCox View Post
It would work but the added mass would mean extra power. You can calculate how much you'd need using some fairly simple electromag and forced harmonic oscillator equations - I was going to do it but I'm pretty lazy. I might later. With a bit of luck it should express how much power you need as a function of the mass.
I intend to vary the power anyway, so I'd need to figure out how much amplitude I'm actually getting at each volume level.

Also, I'm guessing that I need something like a guitar amp for this? My netbook is going to be the function generator, feeding into a DAC.
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post #8 of 9
10/30/09 at 9:46pm
Probably. I wouldn't know much about the practical side of things.
As for amplitude - you could use a sound meter or a cheap accelerometer to get that - or try calculating it.
How critical is this project.
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post #9 of 9
10/30/09 at 11:45pm
Thread Starter 
Quote:
Originally Posted by DanielCox View Post
Probably. I wouldn't know much about the practical side of things.
As for amplitude - you could use a sound meter or a cheap accelerometer to get that - or try calculating it.
How critical is this project.
Well, maximum attainable precision would be nice. Hoping to get some quantitative results out of it. A soundmeter might work. I should be able to get amplitude from that.
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