Need help with a 4th order bandpass box

[rgarrett]

Hello everyone, I am in the process of designing a 4th order bandpass box for my 2 Sundown Zv3 12s. This build will be mostly for SPL numbers but would still like to be able to play some music with it. I talked to Sundown and they said to use 1 cuft per sub for the sealed portion with a 3:1 ratio. So I have a box design with a sealed portion of 2 cuft and a ported portion of 6 cuft (all after displacement). The subs will be inverted firing into the sealed portion with the motor in the ported portion. The ported side will be 41" w x 20" d x 17" h (outside dimension). My question is about tunning. What should I tune the ported side to? Should I use a large rectangle port or round ports or aero ports? What port area per foot should I use? This is going in the trunk of my 2007 Ford Focus. The car peaks around 48hz. Any and all help will be greatly appriciated. Thanks.

[Sanitarium]

if you're going for spl, we can't tell you port tuning, only a termlab can. start at 45 hz and change it up from there. go for 13-16 square inches of port area per ported cube.

[Tarball]

remember your port is going to subtract from your ported enclosure volume unless its going to be external.

[rgarrett]

if you're going for spl, we can't tell you port tuning, only a termlab can. start at 45 hz and change it up from there. go for 13-16 square inches of port area per ported cube.

Very true, but how does the tuning in a bandpass work. For straight ported boxes you tune below your frequency. It is the same for bandpass? I have heard the tuning should be higher like 50+. Thanks for the help

[Real96SS]

I just built a 4h order and its best to do a removable port so you can play around with the tuning until you find the right tuning for what you are trying to achieve. I thought tuning the ported side higher would result in a higher SPL score but it doesn't. So I would suggest you start out around 45-50hz tuning and go from there. From my testing so far I gained 3db going from a 60hz tuned port(No port plug) to 49hz tuning with the plug in. Now I'm going to try a port tuned around 43hz and see if I still increase. Be patient and do alot of testing to see when and where you gain. My 2 cents

[rgarrett]

I just built a 4h order and its best to do a removable port so you can play around with the tuning until you find the right tuning for what you are trying to achieve. I thought tuning the ported side higher would result in a higher SPL score but it doesn't. So I would suggest you start out around 45-50hz tuning and go from there. From my testing so far I gained 3db going from a 60hz tuned port(No port plug) to 49hz tuning with the plug in. Now I'm going to try a port tuned around 43hz and see if I still increase. Be patient and do alot of testing to see when and where you gain. My 2 cents

Thanks for the advice. I am definitely going to do the removable port. Would you go with a rectangle port or multiple round/aero ports? Also I will be using about 4k watts, is there anything I need to look out for or be aware of with that much power in a bandpass?

[Real96SS]

I just built a 4h order and its best to do a removable port so you can play around with the tuning until you find the right tuning for what you are trying to achieve. I thought tuning the ported side higher would result in a higher SPL score but it doesn't. So I would suggest you start out around 45-50hz tuning and go from there. From my testing so far I gained 3db going from a 60hz tuned port(No port plug) to 49hz tuning with the plug in. Now I'm going to try a port tuned around 43hz and see if I still increase. Be patient and do alot of testing to see when and where you gain. My 2 cents

Thanks for the advice. I am definitely going to do the removable port. Would you go with a rectangle port or multiple round/aero ports? Also I will be using about 4k watts, is there anything I need to look out for or be aware of with that much power in a bandpass?

The type of port you use really is your preference. I have no experience with aero ports so I couldn't tell you the upside of using them. As for the power, it's just like with a normal ported box. The more power you run over RMS the smaller you want the enclosure for power handling. I'm running a DC 9K on 2 PSI P3 18's and I have no problems with my 2:1 ratio. Again I'm not the expert and every setup is different. So the only way to know what works is to try it and try it again.