Speakers are Changing with Fewer Wires

It once was that you needed a bulky amplifier for quality PC speakers, with power(1), amplifier input(2), and output(3) wires. 

Then, speakers came out with builtin amplification, but they still needed power and output wires.

Now USB speakers are more and more USB self-powered, and even the cheapest are often excellent.   Just combined power/output via USB.