If an audio signal is AC, then how does my crystal set work?

I drove my friend crazy because i didnt understand how a speaker worked.

So he showed me how to make a microphone from scratch with a magnet and a coil of wire. He explained lenzs law and faradays law. He even hooked the leads from the osciliscope up to the mic so i could see the voltage fluctuations as i spoke into my crude microphone.

If i were to wire a diode in series after the microphone, itd cut the signal and id only get half! Wouldnt that mean id only get half the signal? Wouldnt that sound funny?

From my understanding, speakers run on ac. How is the cone moving back and forth on dc from my crystal set? I assume the suspension of the speaker is "pulling" the speaker cone back at rest? ....ie not a changing signal ...which depending upon the flow of current and the orientation of the speaker would push or pull the cone of the loudspeaker via magnetic field

I can't explain too thorough, but if you modulate a squarewave somehow, (turning it on and off) the speaker will give you sounds with the frequency you modulate your signal width. So it doesn't have to be AC, it just has to change enough to make your speaker move. It has a permanent magnet with a narrow circle cut into it, that is where the coil (which is glued to the cone) goes. Change the voltage across the terminals, and the cone will move - the permanent magnet is fixed, the cone is partially fixed with a membrane. I hope this helps

pityu

DC blocking capacitor

Your crystal radio is an AM radio. AM means Amplitude Modulated. The amplitude (the level) of the radio signal is varied up and down with audio.
The "crystal" in your radio is a diode which passes only half of the amplitude modulated radio signal and a capacitor filters out the radio signal leaving the DC voltage fluctuating with the audio modulation.