I'm in the process of doing my first build and have gone with the front firing ports for the reasons above. I'm no expert on design but am working on the theory that having the ports on the front will reduce the proximity effect when placed close to walls.
They look like some nice cab's. What timber have you used for the baffle?
Very nice. YOu of course need to give more details.. like drivers used, goal designs etc.
I thought of soemthing else to add in the front or back firing port -- I just finished a new speaker design where the port fires to the side. The side firing port came about because:
We wanted the low end extension
The ultimate owner of the box wanted a shallow box
Probably because it's going to be set up against the wall.
So I couldn't put in it the back because it was giong to be too close to the wall. I couldn't put it in the front because the cabinent was too shallow, so we put it in the side. I was told by people smarter than I that it was non-issue.
great to know! yeah these speakers are being setup with limited room as well, pretty much in the corners with one about 6 inches lower than the other and about 15 feet apart so thinking about a center channel. but these where put together with extra wood and speakers any way. they are ment for car audio. passive crossovers and such but it sounds good for what it is and my friend is happy. we watched the muse dvd a while ago, was killer!
Relative phase between the driver and the port is definitely an issue too. The T/S model is assuming zero relative delay between driver and port. Hornresp will actually let you model the effects of moving the port further away.
Although port chuffing might be less audible with rear firing ports, the corresponding power compression is very real. You also get some extra attenuation from the further distance the sound from the port needs to travel...could easily be a couple dB depending on the cabinet.
I think the biggest advantage to rear firing is the natural attenuation of all the higher frequency content happening inside the speaker enclosure. If you make the port big enough to avoid power compression you almost always invariably end up with excess midband energy coming out of the ports. Also, rear loading helps attenuate the port resonance as well...which is a much bigger issue for wide bandwidth designs. Port resonance moves lower as you make the port bigger, but you need a bigger port for less compression...there's definitely a balance to be achieved.