To expand on the title, I'm building a pair of 3 way speakers and, to make them more compact, I'm planning on facing the sub woofer to the sides or rear. I'd expect to use them in small venues (pubs, clubs). I know it's an ambiguous question and it will depend on the room, but will the direction of the sub woofer have any impact at all, and would there be any real draw back in pointing the sub woofer to the sides or rear compared to front facing? Should I point the ports in the same direction as the sub woofer? If the majority of answers revolve about the unknown conditions, I'll give it a go and see how they turn out.
It's somewhat dependent on what the speakers are for. One assumes p.a., for vocals. That will mean there's no great need, in smaller venues, for sub-woofers anyway. If it's for the whole band, a disco or suchlike, then sub-woofers are generally a separate entity in my experience in small venues. Mounting them in the same cabinets as other speakers makes the cabs heavier. And more bulky. In smaller venues one sub will be sufficient anyway, and since it's not directional, it could go centre stage.
As far as ports go, face them the same way as the speaker itself, and face the whole lot forward, so the sound from it goes out the same as the rest of the p.a., rather than be reflected from side or back of stage. Right now, we have no clue as to the size of drivers intended. 12", 15", maybe 18" will make the cab pretty big anyway, with all the other stuff. Possible re-think?
If you’re making a single enclosure, all the drivers should face the same direction for time alignment purposes. Below certain frequencies, it matters a lot less, but you’ll get the tightest bass response by having everything facing the same way.
Generally space isn’t a problem because you’ll want a large enough cabinet to make the drivers efficient. If you haven’t calculated advantageous cabinet dimensions using the Thiel-Small parameters of your woofer, then that should probably be your next step.
I would say you need to be more specific about what you mean by "subwoofer" to get a proper answer here. Are we talking about a 10" speaker? A 12" speaker? 15"? 18"? Below a certain frequency, sounds are unidirectional. There's a Wikipedia article on directional sound. There's also a reddit asking 'At what frequency does sound become too directional for a sub?'. Various forums including Ars Technica also address this issue.
Generally speaking, high frequences are more directional and easily absorbed by walls, fabric, human bodies, etc. Low frequencies penetrate cloud, shadow, earth and flesh.
The intensity of your low-frequency sounds from your speakers is more likely to be affected by your 3 sound sources being out of phase and possibly the proximity of your bass source to a wall. Speakers tend to give off a stronger bass signal when they are placed right up against the wall because you don't have wave reflections bouncing back at your speakers to cause phase cancellation. My Mackie 824 speakers have a switch on the back for bass roll off depending on their placement relative to their enclosing space. A diagram printed on the back to help elucidate how to set the switch.
It's worth noting that some subwoofers are down-firing -- meaning the speaker just aims at the floor. Here's an article about down-firing vs front-firing that you may find useful.
Generally speaking, you want all your three sound sources as close to each other as possible and firing in the same direction to reduce phase cancellation as much as possible. Obviously, they should also be wired in-phase. This might be tricker than you think and you may want to experiment with the polarity of your wiring to make sure they aren't working against each other.
If it was me, I'd say you should try and get them all pointing the same direction, but if the subwoofer is limited to sounds below 100Hz or so, you can probably worry about it less.
EDIT: I just remembered I used to have a book on Building Speaker Enclosures from radio shack. You could pick up a copy super cheap.