i was talking with my boss the other day, and its now bugging me. can some body post the formula for porting a box when the port is out of phase with the sub. (port on side or back w/ sub mounted on front) i have built many of ported boxes can do it with realative ease. i just can't remember the formula to bring the port back in phase. and i love using slot ports. anybody have any info for doing this port or even pvc style when out of phase with the sub.
There's no such thing. Port through the back if you wish with no changes to port formulas. The phase shifts at the Fb regardless of port direction and there is inherently a greater group delay centered at the box freq with any vented design; doesn't matter whether it fires forward or from rear. What you hear at your listening location is the effect of the total sound, which includes interaction with the vehicle itself.
Your concern in this design should be about how well this interaction of driver / port / vehicle sounds to your listening position. It may even sound better than a front-firing vent...you'd never know unless you tried it both ways. And since that is always the case, build the enclosure so that you allow maximum amount of airspace per recommendation (or model) and shape it so that it fits the vehicle in the best way for your needs. Allow several inches of space at the port end outside (as well as inside) the box.
-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
alright thanks. maybe i was thinking of something else. hummmm???? that works out well if i don't have to do anything special for the port. i will build some different boxes with different port locations and play around a bit. i know vehicle has a big effect on sound. i was just thinking (for some reason?) that if i were to put a port out the side of the box, that it would be out of phase with the subs and make a drastic sound change, like a set of speakers wire out of phase. but if thats not the case other than a phase shift using a port in the first place, then all is well and i will do some building when im boared. thank you for your response.