When you build a box with a swapable port, how to you determine internal box volume, as in, what it needs to be once the port is in?

I'm going to build a box for the BTL that's 7.5 cubes and want three different ports, 26hz, 34hz, and one for whatever my peak frequency in the vehicle with be. I'm not sure, but wouldn't the different port sizes also affect tuning by changing box volume? I feel like this is really simple and i'm just punching myself in the face here. 

What am I missing?
 

Build the removable part of the port with the varying lengths outside the enclosure.  Say you know you need 10" of length to get the peak frequency of 43hz for example.  For the 34hz and 26hz tunes the part of the port that goes into the enclosure is still 10" long BUT the extra length to get the lower tunes is sticking outside.

Yes^^

 

Or just have them inside the box and calculate accordingly.  You'll have to adjust your volume accordingly, but  that, and your efficiency are only going to go up with the higher tuning (shorter) port.  

 

Use easy round numbers like 7.25 cubic feet tuned to 32Hz.  Nobody builds a box that is 7.2466756 cubic feet tuned to 32.564729487Hz.  That is what I call mental masturbation, and gets you nowhere.  Just think it through and keep it simple.

Yes^^

Or just have them inside the box and calculate accordingly. You'll have to adjust your volume accordingly, but that, and your efficiency are only going to go up with the higher tuning (shorter) port.

Use easy round numbers like 7.25 cubic feet tuned to 32Hz. Nobody builds a box that is 7.2466756 cubic feet tuned to 32.564729487Hz. That is what I call mental masturbation, and gets you nowhere. Just think it through and keep it simple.

Thanks, both of ya

Any tips on how to make the external port length look not so funky?

Yeah, make it internal...  Seriously, you don't need to make it stick out.  It doesn't make designing any easier...

Math is the same either way. X volume minus y volume.

It makes a lot more sense when 7.5 doesn't have to be the constant, I'm not sure why I got hung up on that.