Hi there
Simply put, position the sound and the listeners and reduce the sound volume if your world dimensions are too small for there to be a realistic effect. If the sound is close, the volume should be loud and the other way around too. But, in your case, your distances are too small. So, even staying further away from the sound (in your game) may make it still seem too loud. Have a look at this code. You'll need the attached sound too.
REM ************************************************************************************
REM 3D Sound
REM By: HWT Date: 5th May 2005
REM Simple program demonstrating 3d sound
REM ************************************************************************************
rem Make a cube object
make object cube 1,50
rem Load sound and position it at the cube, we set the volume too
load 3dsound "scream.wav",1
position sound 1,0,0,0
set sound volume 1,25
loop sound 1
rem Make a land and position it down
make matrix 1,2500,2500,15,15
position matrix 1,0,-15,0
sync on : do
rem Allow camera to move
if upkey()=1 then move camera 15
if downkey()=1 then move camera -15
if leftkey()=1 then turn camera left 6
if rightkey()=1 then turn camera right 6
rem Update listener's position and angle
position listener camera position x(),camera position y(),camera position z()
rotate listener camera angle x(),camera angle y(),camera angle z()
sync : loop
Ask if you don't understand

Hope this helps
HelloWorld Tommorrow