I also have a Dayton Titanic 15" sub and a O audio 500 watt amp. When i put the data into WinIsd it gives a port length of 4 inches, is this right? I used the data from a link on this website. 12^3" with a 19hz tune. I will build a 24x24x36 box. On a side note: do any ported boxes need bracing? If there vented, how could there be internal pressure high enough to flex 3/4" mdf?:scratch: One more thing, I'm a little confused about port air speed. I read a turtorial and now I'm more confused. Thanks for the help.