hispls
5,000+ posts
CarAudio.com Veteran
Where did you read that, on faceberg?Hey guys, I just read something about if a port is too big it could cause sub unloading?
You should probably listen to actual engineers and professionals who understand how these things work.
http://jahonen.kapsi.fi/Audio/Papers/AES_PortPaper.pdf
In fact too small port will tend to unload at high power (if you are trying to displace more air than the volume of the port) then the box behaves as a "leaky sealed box". For practical purposes, in a car you'll probably never hit the point where you have so much port area that it stops gaining efficiency.
That said there's other problems that may come up with the port not behaving as intended because you're crowding it somewhere so really depending how the box is laid out smaller may work better. In any event assuming you mean 5 cube box (net or gross), 80 square inches of port area is fine provided it's placed in a way it can function correctly.
IMO the bigger issue I see is that seems like an awful small box for a pair of 15s and I suspect you may be compromising somewhere to cram that much port in such a small box. I'd probably consider 8" round port on a 5 cube box because 10 will invariably be too close to something and likely won't perform as expected.
