One of the problems with a lot of the “audio through laser” circuits is that the audio input is from a weak source, like an iphone or mp3 player. I teach in a loud classroom and this is just impossible for my students to get hooked on if they can’t hear it.
This means you normally need to heavily amplify your audio or amplify your input source or both depending on the ambient brightness of the room or condition of your laser. I solved HALF of the problem by building an input amplifier that boosts the audio signal (and therefore the brightness). now all you have to worry about is amplifying (or not) the receiver end. This is based on the common LM386 chip.
TRANSMITTER: If you want to make my amplified version, please watch this video for the results and the schematic is below.
RECEIVER: all you need to do is rig a solar cell’s + and – leads to a 1/8 inch audio cable and then plug that into an amplified speaker like your computer desk speakers or the little portable ones. You can sub a solar cell for a photoresistor as well.