ruby-fmod wraps the excellent FMOD C/C++ libraries using the equally excellent FFI.
It is far from finished, but all the basic techniques for interfacing Ruby with the FMOD library are outlined. If you want to contribute to this project, please get in touch.
"FMOD is a programming library and toolkit for the creation and playback of interactive audio. It supports all leading operating systems and game platforms." And now Ruby too. FMOD supports all sorts of audio file playback, surround sound and multichannel, as well as effects, VST plugins, 3D sound, and wavetable synthesis.
FMOD is not free, nor is it open source, but it does have a very liberal license. While commercial use is quite expensive, it is free to use in your non-commercial projects.
To use this Ruby library, you must have the FMOD on you machine. Go get it. At the moment, only Mac OS X is supported, but adding Linux or Windows is likely as easy as pointing to the library locations.
That being said:
gem install ruby-fmod
FMOD.init sound = FMOD::Sound.new(file) sound.play