For my speakers you suggested a port of 4" diameter by 4" length. I found the Parts Express 260-403, a very nice 4" by 4" flared port.

Problem is, the 4" diameter part of the port is really only 3.5" long and then the flare starts and continues for the remaining 0.5".

So is this really a 4" diam by 3.5" long port, a 4" x 4" port or something in between?

Thanks,
Jeff