Audio Systems: sub box ports, ported boxes, folded horn

Question
helo
thanks for reading my question
i've had minor experience in building vented sub boxes. i have made some ported boxes as specified in the owners manual, but i would like to make custum ported enclosures
questions
1. i would like to know if there is a formula for determining the diameter and lenght of the port
2. what kind of port is better round, slot, or just a square port
3.and if there are multiple ports how does it affect the formula
4.is a vented enclosure apropriate for SQ or what type of box do you recomend me

thanks for your time


Answer
You did not say if this was for car or home, I will presume it's for a vehicle.
In a nutshell, if you want a 'vented' design, I would use a folded horn if possiible since they are easier to solve the numbers for in most vehicles. The make and model of the car are paramount, also.
I do not use a sliderule when designing, you need a good PC application to really customise an enclosure.If you want a more consise answer, please resubmit this and use the 'private question' option.
I would use a sealed enclourse 95 out of 100 times if U had a choice for overall SQ and low bass.
Jerry Mael