Confused by OpenAL AL_REFERENCE_DISTANCE

[napier]

Does anybody know how to use the AL_REFERENCE_DISTANCE setting in OpenAL?  

I'm configuring sound for a large scene, meant to be hundreds of meters across.  I set the reference distance on the sound source to 100 so the sounds carry proportionally to the size of the scene.  

AL10.alSourcef( soundSourceHandle, AL10.AL_REFERENCE_DISTANCE,  100f);

The setting works, but I'm wondering what exactly this is supposed to be (I just pulled 100 out of a hat).  The value doesn't seem to be a limiting factor (I can hear sounds further than 100 units away).  I looked at the docs at openal.org but didn't get much clarity from them.  

Any clues are appreciated.