I'm just about to embark on making a cabinet for two 12" speakers (and possibly bullet) for use with guitar.
Some cabs are totally enclosed, some have open backs, and I've built some with a port at the front. Albeit not with a pair of Celestion 12" speakers, which may/not have a bearing.
Not sure what the actual sonic differences are - which would suit a decent sized amp for the purposes of gigging, for what reasons?
Open back actually sounds more open. They fill a small stage, so you and the band can hear what's going on without need for on-stage monitoring so much.
Downside, front of house can have more trouble capturing that sound & sending it to the audience. You can get spill in other stage mics. They have less low end & 'punch' in the mids.
Closed back - you got it, more closed - a tighter sound, and more directional. They project forwards, with far less spill. Consequently, if you're not directly in line with it, you don't hear the top so well. Walking round the stage your perception of your own sound will change. Cab designers describe it as 'laser-like'. Front of house will like it too, it spills less.
Overall, sonically, it has more low & more mid 'punch'. You could consider it more 'contained' in all senses of the word.
Some cab manufacturers who seem to agree -
Roland - Open Back Vs Closed Back Guitar Speaker Cabinets – What’s The Difference?
Laney - Open Back vs Closed Back Cabinets – Do Cabs Make A Difference?
Celestion - Open Back or Closed Back Cabinet – Which is for Me?
Fender - What's The Difference Between Open-Back And Closed-Back Speaker Enclosures?
More opinion than researched fact…
Bullets are highly directional anyway. I don't think the cabinet design has much influence at all.
Ports, on the other hand, are complete voodoo.
I've never used a guitar amp/cab with a port. My home theatre rig has one… makes the walls shake whilst not being able to hear much from the centre of the room.
My old gig rig bass amp was ported - in fact it was a 5ft tall reverse folded twin-port single 15". Perhaps not the wisest move in retrospect, but I was young. On-stage it sounded fine, got just the sound I & the band wanted. In a small gig, however, the very low end barely had chance to form. In a large venue, it nearly pushed the back 6 rows of the audience into the rear wall. It was a beast… an uncontrollable beast.
My current bass rig doesn't so much have a tuned port as a 'slot at the bottom'. There is no actual shaped porting, just a letter-box hole. It does, however have a DI out that you send to the desk, so it really doesn't matter at all that the sound nearfield is a bit 'loose'.
Long & short; I'd avoid ports on DIY-designed cabinets, as even the pros struggle to tune them to all eventualities.
Just for fun, here are pics of that reverse-folded design, as supplied, & with the front grill & panel removed to see how it was loaded. All port, no forward-facing component at all.
…and my current rig, a pic showing off that 'hole' in the bottom. (This is off the interwebz, mine is in much better condition that this;)
You need a port for somewhere for the air to go. When the low frequency speaker (woofer) moves you want to avoid compressing the air as this like loading the woofer with a spring. If the cabinet is ported - there is a path for this air.
The air at the back of the woofer is moving in the opposite direction to the air in front of the woofer - it wants to be going in the same direction (phase). A port in the front usually has a extra path to reverse the direction, out the back relies on the depth of the cabinet.
Directionality depends on the "effective aperture" of the woofer/cabinet combination and a wider "effective aperture" produces a more directional sound.
