Silent floor/lifts

In Back to Saturn X E1M25, there is a lowering floor that doesn't make any sound, anybody knows how to make this trick? No matter how many times I look at the map on Doom Builder, I can't figure out how to do it.

In the vanilla engine / engines that respect the way the vanilla engine works, sector sounds work thusly: imagine drawing a rectangular bounding box around the outside of a sector. The sector moving sounds will originate from the center of that box.

So if you want a "silent" sector, you make a control-sector piece of it thousands of units away. This makes the bounding box for the sector huge, and the sound will originate from a place far away from the player.

Thanks, it worked well on prboom, however I have another question: I know zdoom is miles away from being close to the vanilla behavior, but the silent floor on BTSX works well on that port too, did they made anything else to make it work?

It has a compatibility flag, that probably makes it work or not:
http://zdoom.org/wiki/CVARs:Configuration#compat_sectorsounds