[Ultralight]

Since Omegas are custom made, I see that it has been ported on the front, back and in the case of the Alnico XRS, bottom.

Curious why bottom.
And why not bottom for the others models?
And with bottom port, is it better to set on a hard surface rather than carpet?   I have seen at least one bottom ported Omega sitting on maple blocks for example.

Thanks,
UL
 

[Canada Rob]

The 3XRS has a ballast chamber, and the 7XRS has an empty chamber at the bottom so they can't have a bottom firing port, not to mention these designs work best in these configurations.  These aren't big towers, so they benefit from the rear port coupling with the backing wall to help bass.

The Alnico XRS has no chamber so it can have a bottom port.  The bottom port allows it to be out into a room or closer to a wall and carpet generally isn't a problem.  The Super 3 Desktop has a bottom port so it can sit on an outward (into the room) facing desk and still have a surface to couple to.  The 3i, 7, and Alnico Monitors are rear ported to couple with the backing wall to help with bass.

[JLM]

Is the port output insync with the driver (can't and not in perfect phase either)?  So I'd vote against any front mounting.

The theory is that boundaries close to port discharge effect performance (doesn't allow for free space function), so bottom mounting provides a known boundary distance that can be accounted for (but I've yet to see any math presented to justify a particular spacing).  Of course that bottom spacing can be awkward for stand mounting.

I know its popular to worry about effect from nearby boundaries on ports but I have a hard time imaging (or even trying to calculate) any effect from boundaries that are more than say an inch or so from the cabinet.  Would be interested to know if anyone has built front, back, and side ports of otherwise identical speakers to see if a difference can be measured (or double blind tested to be different).

A bigger effect of port location is the air flow route inside the cabinet.  Ported cabinets with driver at one end and port at the other will behave (whether intended or not) more like a pipe or transmission line than a simple ported enclosure.

[Canada Rob]

Generally speaking I've never cared for a front mounted port either, although there are always exceptions like the old Super 3.  I had a pair of front ported (hemp 4.5 driver) Omegas custom built to go on a mantle which sounded very nice, but they definitely needed a sub, which I didn't have.  I then put a pair of (hemp 4.5 driver, rear port) Super 3i in their place with only the binding posts to stop them from hitting the backing wall and the sound immediately improved in the bottom end and I don't recall the imaging suffering either.

Back in 1990 I got to hear the tiny (rear ported) Royd Eden on Royd stands right against the backing wall with no toe-in (they were designed to be set up that way) in two different venues on two different front ends.  The sound as I remember was electrifying with incredible imaging and no midbass boom that many small speakers are infamous for.

I currently run RS5 Super 3i on the desktop with the rear ports about 3" from the backing wall, and it's one of the best sounding desktop systems I've had. 
No sub needed IMO.

[FullRangeMan]

I would prefer a side/lateral port to help built central soundstage.
Lateral ports may have a prob I unaware as I never have see it.