Box help please?

[JohnBlayz142 10+ year member]

I am about to begin constructing a box for my RE SX15. I've built many boxes over the last couple years, all ported, but this one is my first attempt at a "CRX" style box with Precision Ports rather than a slot port. The box will be +/- 4cf, with +/- 35hz tuning with 3 17" long, 4" round ports.

What I want to know is, just how big do I have to build the box to keep tuning right around 35hz? Also, I may plug one of the ports if I feel the desire for a lower tune while driving around.

The only reason I am asking is because I hear there may be a discrepancy in WinISD with round ports, or something like that, so I'd just like to make sure.

According to my calculations, 3 17" long, 4" round ports will require me to build the box about 4.1cf after all displacements. Is this right? Thanks!

John

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[VereChronicus 10+ year member]

After doing some "scientific experimentation" with 4" aeroports, we found that they operate and tune more like a 4.5" ID cylinder of the same length. With your application, the math then came out to a 5 net cubic feet enclosure with the 3) 4" x 17" aeroports for a tuning "roughly to 35Hz+/-." If you plug one of the ports, you should tune from 5-8Hz lower than all three open. I hope this helps you out some John.

 

[JohnBlayz142 10+ year member]

After doing some "scientific experimentation" with 4" aeroports, we found that they operate and tune more like a 4.5" ID cylinder of the same length. With your application, the math then came out to a 5 net cubic feet enclosure with the 3) 4" x 17" aeroports for a tuning "roughly to 35Hz+/-." If you plug one of the ports, you should tune from 5-8Hz lower than all three open. I hope this helps you out some John.

I appreciate your help. What tuning would I be at at 4 cubes?
When you say net, does that mean before sub and port displacement?

Thanks.

 

[JohnBlayz142 10+ year member]

After playing around with WinISD a bit more, I think I will go with 2 of the ports, and possibly add the third if I wish to start competing, which is very likely in the near future.

If they operate more like 4.5" dia ports, the port area will act like over 30sq in, which is right around what I need.

So, 2 for daily, 3 for spl.

 

[VereChronicus 10+ year member]

Net is the term for AFTER all displacements being taken into account. Gross is a term you'll read about that means BEFORE all displacements such as driver, bracing and port. I'd recommend that you build it with 4 aeroports in place. You can always tune it to your daily driving frequency by plugging two of them. The 4 would give you alot of tunability and possibility of maybe a higher SPL than the 3 you were thinking about. With 4, you would have around 4.8 cubes and roughly 63 square inches worth of port. That should tune you to about 41-42Hz. Still a little low for burping in competitions where you'll be ultimately paired up with a CRX or something, tuned to 55Hz+.

 

[JohnBlayz142 10+ year member]

Net is the term for AFTER all displacements being taken into account. Gross is a term you'll read about that means BEFORE all displacements such as driver, bracing and port. I'd recommend that you build it with 4 aeroports in place. You can always tune it to your daily driving frequency by plugging two of them. The 4 would give you alot of tunability and possibility of maybe a higher SPL than the 3 you were thinking about. With 4, you would have around 4.8 cubes and roughly 63 square inches worth of port. That should tune you to about 41-42Hz. Still a little low for burping in competitions where you'll be ultimately paired up with a CRX or something, tuned to 55Hz+.

I'm sorry I did not get back to you after posting this. Thanks a lot for the suggestions. My ports just arrived today, however, and I will only be using three, as tomorrow is the day I have reserved to build the box.

Is 5 cubes alright for a daily box for an SX15? I tend to listen to it conservatively, although sometimes I bump for awhile.....thanks again.

Last but not least, how much does one 4" precision port, 17" long, take up airspace wise?

Thanks!

 

[VereChronicus 10+ year member]

.16 per aeroport of those dimensions. If you are off a tenth or 4 in a 5 cubic foot box, you won't be hearing the difference in a street beat situation. Don't sweat the small stuff. That box will work great with that sub.