DIY acoustic to mechanical energy conversion

I need to make a high speed vibrating platform for work and I'm looking for some design ideas. The device will be a small platform that will be used to vibrate samples of wet ink to look at the flow leveling characteristics under sheer (from the vibration). This is similar in practice to the mechanical vibrators used to speed the leveling and curing of wet concrete. A typical mechanical vibrator is probably out of the question, because the ink in question has a very fast recovery time, and it will re-build viscosity quicker than the vibrator can shake it. I've thought about using one of those "subwoofer" shakers that attach to chairs to simulate LF from speakers, but if they reproduce frequencies as high as 120 Hz that still won't be enough. 120Hz = 8 milliseconds. The recovery time of the ink is believed to be about 1 ms, so I will need to shake it faster than 1kHz. A typical mechanical industrial vibrator lies in the 60-300 Hz range.

I've though about laying a speaker on it's side and running a 1K sine wave through it at high volumes, but the efficiency would be very poor, and the neighbors in our industrial park would likely visit our suite with lit torches. A couple of ideas that come to mind are piezos glued on to a board, or a sealed box subdivided with a baffle containing a speaker. Do these sound like viable options? I don't need a high energy output, just relatively efficient energy transfer to minimize acoustic dB.

This is a proof-of-concept experiment, so the budget is almost nothing. Any suggestions employing "junkyard wars" methods would be much appreciated.

Thanks,
Chris

Torn-cone speakers.

Whaddayaneed a cone for, anyway?

Link the paper/surface it to the coils and let em rip. Almost noiseless by comparison, and I'm sure 10Watts continuous should be enough, unless you're talking about a high-mass load... -right?

Or am I picturing something wrongly?

Keith

Hmm, so if I glue a small piece of card stock to the voice coil, that basically gives me a table which acts like a piston moving up and down at the input frequency. My audio amplifier power will then control the amplitude of the piston extension. That should work.

So how about the impedance of the coneless speaker? Any risk of damaging the audio amplifier driving it by having not enough load? I'd imagine that impedance would also be a function of the weight of the cardboard "table" that is attached to it.

Just so happens that I have a couple of blown speakers lying around... :green:

Thanks,
Chris

Yes, basically... though I for some reason was envisioning this whole thing rotated through 90°, so that the LS motor was "pulling the tablecloth from under the dishes", and then "pushing" the opposite way on the return part of the cycle... Now I see what you're getting at a little better, but either way, you'll be okay.

The speaker will be much quieter if it ISN'T in a box... acoustic self-cancellation. Also, easier to quieten leakage from a room if the frequency is higher, but the reciprocating energygets higher proportionally to the frequency, so there are tradeoffs of course...

Keith

Chicken debeaker! Some evil apparatus is coming to mind...

The offset weight is what many of the mechanical vibrators use. 3600 RPM is pretty fast to be spinning an offset weight, and that only translates into 60 Hz. 10K RPM is crazy fast, and that translates into 167 Hz, and I'd be afraid that someone would get killed by a flying flywheel because I forgot to tighten the set screw . :green:

-Chris

Head mover from Winchester hard drive.

Or a "coneless speaker" - like the ones used in DIY plate reverbs

http://www.prosoundweb.com/recording/tapeop/plate/plate3.shtml

Jakob E.

Thanks Jakob. That link also brought this item to mind:

https://amptechtools.powweb.com/truload.htm

$30 is quite a nice price too. I have some reservations about the voice coil on a normal speaker getting bound up if I cut away the driver (which normally helps keep the coil centered in the magnet's gap). I'm not so sure if the spider will keep it in alignment well enough, especially if the "table" that I am attaching to it imparts any torque.

-Chris

[quote author="Emperor-TK"]I have some reservations about the voice coil on a normal speaker getting bound up if I cut away the driver (which normally helps keep the coil centered in the magnet's gap).[/quote]
Just cut four large quadrants out of the cone, leaving four paper "spokes" to keep the cone 'steered' correctly. Tha back spider will keep it centered in the gap. That'll be enough to largely silence the speaker.

Keith

[quote author="Emperor-TK"] The recovery time of the ink is believed to be about 1 ms, so I will need to shake it faster than 1kHz. A typical mechanical industrial vibrator lies in the 60-300 Hz range.

Thanks,
Chris[/quote]

Piezo stacks sound like the way to go at those frequencies, if you don't need large displacements. The load is mostly capacitative and requires a fairly specialized high voltage amplifier to drive.

[quote author="bcarso"]The load is mostly capacitative and requires a fairly specialized high voltage amplifier to drive.[/quote]
...can anyone say:
"LA-2a sidechain driver"

:green:

Keef

apart from what Jakob and Chris linked too
... how about seat shakers ?

as used in E-Drums
and suround sound chairs

I think Jaycar had one ... once

piezo buzzer transducer. they are usually flat and usually resonate at a specified freq that should allow you to power it without a signal source.

I used to agitate my Ferric chloride etchant in a tray resting on the basket of a 12 inch speaker on the bench. I would vary the frequency until I would get nice ripples in the solution, probably some resonant frequency. Perhaps you could use the same technique using a high frequency driver.

[quote author="BYacey"]I used to agitate my Ferric chloride etchant in a tray resting on the basket of a 12 inch speaker on the bench. I would vary the frequency until I would get nice ripples in the solution, probably some resonant frequency. Perhaps you could use the same technique using a high frequency driver.[/quote]

May be some John Robert's drum related tricks may help to find that resonant frequency for better etching? :grin:

[quote author="Wavebourn"]

May be some John Robert's drum related tricks may help to find that resonant frequency for better etching? :grin:[/quote]

We used to put the ferric chloride solution in a pyrex(?) tray on an electric heating element.... It etched must faster when hot, at least until that one time when the glass bowl broke. Luckily nobody was in the room at the time as the ferric chloride cloud that engulfed the room immediately turned every bit of exposed metal to instant rust. A nice drill press got trashed, but better that than somebody's lungs, really nasty stuff. :roll:

JR

[quote author="SSLtech"]
...can anyone say:
"LA-2a sidechain driver"

:green:

Keef[/quote]

Also these folks: http://www.electronicproducts.com/Showpage.asp?Filename=poycn02.jan2006.HTML

[quote author="JohnRoberts"][quote author="Wavebourn"]

May be some John Robert's drum related tricks may help to find that resonant frequency for better etching? :grin:[/quote]

We used to put the ferric chloride solution in a pyrex(?) tray on an electric heating element.... It etched must faster when hot, at least until that one time when the glass bowl broke. Luckily nobody was in the room at the time as the ferric chloride cloud that engulfed the room immediately turned every bit of exposed metal to instant rust. A nice drill press got trashed, but better that than somebody's lungs, really nasty stuff. :roll:

JR[/quote]

Copper lungs? :shock:

In a laboratory of equipment testing we baked potato in muffin stove and kept a beer in Peltier stabilized camera. However, we did not think of etching PCBs on a vibrostand though...

teeth on a gear...like a hammond tonewheel