[Openal] problem in moving 1 source on 4 speakers

[Luca Brayda]

Hello.
I'm a newbie of the list.
My issue is that I cant' move a single sound source around me when  
using 4 speakers around me, i.e in the XZ plane according to OpenAL  
specs.
I have MacOSX Leopard and use AudioMidi Setup under MacOSX to  
configure the speaker setup first, then I launch my executable, which  
uses the dynamic libraries downloaded from the macport version of  
OpenAL 1.0.0

I do succeed in moving the source left to right and viceversa when  
only stereo is set up. In order to move the source, I play the sound  
first and then just overwrite the  SourcePos vector and call:

	alSourcefv(Source, AL_POSITION, SourcePos);

But when I change the speaker configuration to four speakers (through  
AudioMidi Setup) and restart the executable, the first two channels  
are correctly rendered (front left and front right, as it were  
stereo), while the back channels sound very weak and the sound  
amplitude seems uncorrelated with the position I give in input. What  
could be the issue? Did I forget to speacify somewhere the speaker  
configuration or everything should be done by the AudioMidiSetup?

I add that my soundcard normally works fine on my system using Ardour  
per Mac while playing multichannel audio, i.e. the 4 channels are  
correctly addressed, so a priori it may not be a harware or mixer  
problem.

Thanks so much.

--

Luca