A variety of different frequency motors

Hello everyone, I am planning a prototype project and could really use a little help with the feasibility. The idea is to use haptic feedback to communicate a variety of frequencies through materials so that audience members can "hear" them with their hands. If I wanted to excite several different metal plate or tube at various fixed frequencies without any audible sound, what would be the best way to do it? I have found this: http://www.precisionmicrodrives.com/new-vibration-motors/310-101-10mm-coin-vibrator-motor but it only vibrates at 183hz, I'll need a broader range of frequencies to make my project effective. It would also be desirable to effect the amplitude of the resulting vibrations. Do you think this is feasible? Many thanks in advance.

If I wanted to excite a metal plate or tube at a variety of different frequencies without any audible sound, what would be the best way to do it

Use a def audience. Any vibrating plate is going to produce sound, that is how speakers work. All you can do is to minimise the vibration and hence the sound. Vibrating motors are just motors will offset loads. Change the speed of the motor and you change the vibration frequency.

The only problem with changing motor speed is there is also a rapid change in amplitude, ie at lower speed there will be a gross reduction in amplitude and at higher speed a gross increase since the vibration is induced by an out-of-balance spinning mass.

One alternative is to use the natural frequency of a vibrating strip of metal. Differing frequency of vibration gives you the required haptic feedback. Use a coil to excite the strip. Alter the natural frequency by driving a damper finger along the strip by use of a small servo motor.

Yes that arrangement is called a buzzer, it still makes a noise.

Thanks very much for the replies. I know that this is how speakers work, however they, like guitars and many other instruments, rely on a resonant chamber to amplify this vibration. This will be absent in my set up and whilst I know this won't render it silent it will still retain a profound physical sensation of the sound when touched. Its a bit like suspending a taught string in mid air and twanging it, without a resonant chamber its pretty inaudible, in fact the residual noise will also prove interesting, this is after all a sonic art installation!

Just to amend this slightly, I think this project will work better if there are a variety of different motors, each operating at different fixed frequencies i.e motors at 500hz, 550hz, 600hz, 650hz and so on. I then only really need to vary the amplitudes. What do you think would be the best way to achieve this array of different frequencies? Do you think its feasible getting up to 10000hz with this? Many, many thanks.

I would actually agree with jackrae- I would just make an electromagnet (obviously wouldn’t work with a non-ferroud material, though :confused: ) and use the natural resonance frequency of the materials. You could do this as well using fixed-frequency motors, powering them through PWM to modify their speed and resonating frequency.

Its a bit like suspending a taught string in mid air and twanging it, without a resonant chamber its pretty inaudible, in fact the residual noise will also prove interesting, this is after all a sonic art installation!

Depends on how well it was taught, and on how taut the string is.

This is really bouncing concepts off the wall. How about stripping out a musical box to salvage the reed assembly. These are made of high tensile steel and are therefore magnetic. Now, if you place a wound ferro magnetic coil adjacent to the reeds and excite this at various frequencies, only the reed which matches the excitation frequency will vibrate. jack

Now, if you place a wound ferro magnetic coil adjacent to the reeds and excite this at various frequencies, only the reed which matches the excitation frequency will vibrate

OT - this is pretty much how multi-channel R/C operated, before the advent of digital electronics!

http://www.healthandcare.co.uk/oscillations/vibration-generator.html booooom!