I am hacking an existing MP3 player. It reads tracks from a USB stick and plays it in to an earphone socket connected to a small speaker.
At the moment I have a mechanical switch that disconnects the two signal lines to the earphone socket and connects them to a bigger speaker that has a built-in amplifier.
I want to replace my mechanical switch with something controlled by the Arduino. I have considered using a relay but they seem big and expensive. All the ones I have looked at are about power switching. All I want to do is change where a signal line goes...
If it helps in your application you can get a [u]"closed circuit" headphone jack[/u] with a built-in switch to turn-off the speakers when headphones are plugged-in.
Otherwise, a relay (or switch) is usually the easiest/best way to switch a low-impedance connection like speakers/headphones. Even with "regular" audio signals there are advantages to using relays/switches.