I want to directly control the movement of a speaker cone with Arduino, so to push it in and out by sending a signal from an arduino board. Is it correct to assume this a case of just sending a pwm signal at 0% (cone out), then 100% (cone in), 50% (cone half way)?
Please note: I don't want to generate tones, sounds, just control the movement of the speaker cone relatively slowly.
Welcome to the forum.
Can you tell more about your project ? What is it for ?
For a movement, perhaps a solenoid can be used or a servo motor. A speaker is designed to make air pressure waves. It is certainly not designed for a static position !
Maybe a 100W subwoofer can do this. If you look for a used one, it could cost only 20 euros/dollars or less.
You need more current than the Arduino can give, so you need some kind of "driver module" or amplifier. A simple driver module with a H-bridge should be good. However, if you use 5V for a 8Ω speaker then the speaker coil will melt.
The PWM of a Arduino Uno is about 500Hz, that will be a very loud noise.
Some Arduino boards have a analog output. That is better.
Half-way is the same as applying no current. Most "driver modules" or amplifier have an "Enable" pin to turn it off.
You are assuming PWM will be linear with cone movement. You should probably check that. Easy enough to compensate for it not.
How much power does it take to push this cone? An arduino pin can only source about 20-30 mA. If that isn't enough, you will need a transistor to control the cone and the arduino pin to control the gate of the transistor.
You'll have to increase the PWM frequency because the speaker can obviously move at ~500Hz to reproduce sound. You'll have to research how to do that. I know it can be done but I've never tried it.
It would also help if you can somehow add mass to the speaker cone so it can't move as fast... Maybe glue a weight to it.
And you'll need a driver circuit because an 8-Ohm speaker will draw too much current if connected directly to the Arduino. You might burn-up the Arduino and you won't get the "expected" 5V.
Most speakers won't "melt" with 5V. That's a little more than 3W. (Power = Voltage squared / Resistance)
The speaker should probably be rated for about 10W because a 3W speaker is designed for 3W on the peaks. Regular audio is constantly changing so if you're hitting 3W on the peaks the average is a lot less.
At lower PWM values you'll be dissipating less power.
You are dealing with magnetism from direct current going through the speaker coil. Since you are ONLY using direct current, that will only move the cone one way. The spriginess of the speaker will return it to it's resting place. It will NOT move the cone in the opposite direction past the resting position.
Is this what you want?
Paul
I'll bet, you want a cheap galvanometer mechanism? It can work but the cone excursion is tiny, and frequency dependent. A woofer outside of its enclosure would be the best choice for that. As mentioned, you will really need some kind of power driver.
Have you ever "smoked" a speaker? I have, many year ago, using DC.
Paul
The DC impedance of a speaker is much lower than the AC impedance. Or you could say the impedance rises as a function of frequency. That means for example, a 100W rated speaker can not withstand 100W of DC, not even close. Cone or coil destruction will result.
I'm trying to think if I've done it, I guess I must have at some point but I can't remember. Here's one - when I was a teen I babysat for pocket money. Client had a home made set of electrostatic speakers. Wow, and they were incredible! But he warned me a few times not to turn it up, or the bass too much. Well, guess what, music sounds great but needs a little volume, and "sizzle, crackle". I look over, there are plumes of smoke emanating. I killed everything and tested it gently after that, it sounded fine. 
This looks like an X-Y Problem
Hi,
yes, sounds like these;
Tom... 
hi everyone thank you for all the replies, that instructables link helps me to understand. I want to make something similar but with smaller speakers.
The smaller the speaker, the worse it will perform as a galvanometer.
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