[Openal] Howto use sound obstruction

[Stefan Burghardt]

Hello members of the mailing list,

what do I need to add an obstacle (like a wall) between the listener and 
a sound source into a scene. As far as i see efx should provide 
everything or do I even need creativs EFX? Does somebody have sample 
code for that (I wasn't able to find any tutorial for that)?

I want to implement a simple scene like on page 136 of the OpenAL 
Extension Guide.

Thx in advance,
Stefan