I have 4 Sundown Sa-8 V2s that I am thinking about putting in a 4th order box and I have a few questions about how to design it.

 

1. Do I use the manufacturer's specs for the sealed part?

 

2. What is the best ported to sealed ratio for a box that I would like to have an output of 20s+ hz?

 

3. Would tuning the ported area to 45 hz give me the best range in frequency response? (Maybe 20s-60s or so)

-Please refer to it as a single tuned bandpass  unless for some reason you need a 4th order mechanical filter

-There is no given ratio you can use

-The enclose will have to be designed as a whole , no rules of thumb, no using the sealed box recomendations

 

and have a good reason for wanting a single tuned bandpass enclosure for your woofers !

A 4th order enclosure is any alignment that has a high pass roll off that approximates a 4th order slope, which is 24db/oct. A standard ported enclosure is a 4th order enclosure. A passive radiator system is a 4th order enclosure as well. There is also the single tuned bandpass enclosure which I assume you are referring to, in which case you need to specify that.

Otherwise as Bassmaster said all of the questions you are asking are the wrong questions. There is no golden ratio to designing the enclosure and you can't ask about tuning without specifying more details of the enclosure....you can't single out design features like that. It has to be designed as a whole.

And why are you looking at a bandpass enclosure anyways? Given the bandwidth you want to cover a standard ported enclosure appears to be a more logical choice.