Dukk, I disagree with you, I can't stand my comp setting for daily. For comps (IASCA) the listening level is set at 90db, you want to have a port size that will get the max for that level. That's parked with no engine running, now add road and engine noise and with the same 90db you will say where the hell is my bass. You need to crank volume and the subbass level, but by doing this you get more air moving and your SQ port will probably be to small. That's where come an interchangeable port. Not sure if i explain myself properly, but tell me if my theory is flawed.

You run sealed - I can understand why you can't stand it :D lol, j/k

A smaller size vent does not get you more output. I see no point in changing the tuning of the enclosure. Yes you may want more or less gain on the box depending on the situation and the music (I find that IASCA wants no real bass output but lots of extension) but a remote gain on the sub amp accomplishes that.

lol,

well i'm not talking about the port tuning but the port size(opening), if you have a port of 6" in diameter for a 15, at IASCA level the port will probably only act as a hole in the box, but for daily at higher level it might work perfect. Port velocity is still a concept i try to understand as you can see.

That's alright. Of all the professional installers and hardcore enthusiasts I know, and have known, it is surprising how few are really solid on box theory.

Within reason, the vent tunes the enclosure to XX frequency regardless of the energy put into the system. 150watts or 1500 watts, same same.

Now a 15 with a 1.5" port or an 8 with a 12" port, maybe not, but within reason..

Too small a port is like a leaky sealed box with mingling responses of ported and sealed. Is that correct? Is that not like a 4th order? You're just separating the ported and sealed portions so that one doesn't equal the other. Even if you tap on a sub it's going to react as the port makes it.

4th order? As in a sealed bandpass? The response of a sealed bandpass is different again from a vented or sealed box.

Bottom line, Yes 15" subs can indeed be utilized for "True" SQ vehicles.