2) Why does this speaker have 4 wires? (Shouldn't it just be 2?)
Absolute Max from an IO pin is 40mA, and the pin will not have a long life if driving it that hard.Using Ohms Law, V=IR, if you have 5V and 40mA, then you must have 5/.04 = 125 ohm of resistance for a load.So take your 4 ohm speaker and put a big resistor in series with it.Above 20mA, the pin will drop to 4.2V and lower as the current goes up.Power P = I*V, so .04 x 5V = 200mW max volume, so not very loud.If you want 5W, you're going to need an amplifier.
Do you have a multimeter and can measure the resistance of the two speaker connections?Most likely it is a two-in-one speaker which is actually consisting of two speakers:- a tweeter speaker for playing high pitch tones- a woofer speaker for paying bass tones
I have a multimeter and will try to measure the resistance.
Just bear in mind that just because a speaker is rated as 4 ohm doesn't mean that that is what you'lle measure with a meter.The rated impedance is usually quoted as the lowest impedance measured at any frequency above the resonant frequency. If you measure at dc as with a multimeter you will usually get a resistance of about half the rated impedance.Russell.