So, I am aware that on the back of a speaker strobe there are generally four terminals: two for the speaker and two for the strobe. But how does the speaker receive both power for the speaker and an audio signal through the same wires connected to the speaker terminals? In other words, how does a voice evac panel output both speaker power and an audio signal through the same connection?
An audio signal is essentially just a modulated voltage (around 5V for headphones and RCA cables), so the audio signal is the speaker power (which is either 25V or 70.1V for fire alarm).
@HenBasket is right. A speaker signal/ power is really just AC voltage where the frequency goes up and down to determine the frequency of sound that you hear. For example, if you give a speaker around 3v AC at 60 Hz, you will hear a 120hz sound because the speaker is vibrating in and out. This causes the frequency that you hear to be double the frequency that is going to the speaker.
A speaker is really just an electromagnet that makes a surface (usually a paper cone) vibrate to create sound. If you apply DC power to a speaker, it will either pull in or push out. If you reverse the polarity, it will do the opposite.
So yes, the power is the signal because it is really just AC power where the frequency changes to affect the frequency of the sound. A speaker “power supply” is really just an amplifier which takes the extremely low voltage from the sound source (the panel) and converts it into the power that speakers need.
With speakers, the power and signal is given to the amplifier which gives power to the speakers with fluctuating frequency to create sound. With horns, the panel or power supply provided DC power to power the small amplifier in each horn. Every horn, in a sense, just has a built in speaker and amplifier that plays a specific sound when given power.
Sorry that this was a long explanation. Here is a video to help:
