https://www.allaboutcircuits.com/technical-articles/introduction-audio-electronics-sound-microphones-speakers-amplifiers/
Photophone
Amplifier Kits
Piezo Cigar Box Ukelele Amplifier
Audio Filter Circuits
DIY Magnetic Pickup
DIY Speaker
Musical Bench
Laser Harp
Toy Organ
Fiberoptic Music
Musical Stairs
Copper Pipe Glockenspiel