I could have sworn that I read in Nick Collins book that DC motors and speakers oscillate at approximately the same rate or something, meaning that you could solder a DC motor's positive and negative leads to a 1/8" jack's associated wires and the motor would operate. I can't get it to work! Is there something else I'm not considering?
I'm using that well known radioshack amplifier (the white one) that Collins uses. It is a stereo jack, but I've tried it as one and both positive leads to no avail. Is the amplifier simply not powerful enough?
The best you can hope for is the motor operating as a very inferior motor. I don't know quite what you're trying to achieve, but I don't think it's what you would actually achieve.
Take the following scenario:
A 1KHz sine wave being fed into a speaker. The speaker cone moves in and out 1,000 times a second to move the air and produce the tone.
A 1KHz sine wave being fed into a motor. The motor starts to accelerate in one direction, then almost immediately is pulled in the opposite direction in which it then tries to accelerate. The result is a tiny amount of vibration of the spindle at 1KHz. You may just be able to hear a slight whine from it at 1KHz if you listen carefully.
Motors, compared to speakers, are very very slow. If you want to make the motor oscillate visibly then you will be limited to just a couple of Hz.
Majenjko: gotcha! I just re-read it and he recommends pager motors, so maybe thats why. Still, in that YouTube video, he's throwing back a decent sized motor. Maybe the signal is just wicked amplified?