Port Placement

Kornbread

In relation to location inside the box and the floor, what does what? 

jr@mac

Boundary proximity can change tuning somewhat, makes it a bit lower. It has to be a pretty close relationship, though - less than an inch or two. If your port is going to be close to an interior panel, keep that in mind. You may need to lop off an inch of the port. On one build, I deliberately installed the ports as close to two interior panels as possible to take advantage of that. 

Kornbread

Is there a way to model port position in relation to floor and box interior?    

jr@mac

I'm honestly not sure. If memory serves, some of the software can make some assumptions, though.

dcibel

There is some port end correction factor that can be used to compensate for things like port flares, as well as boundaries. I had suggested to Jeff B some years back that allowing adjustment to the port end correction factor would be a good addition to his WBCD spreadsheet, but he didn't appear that interested.

IIRC WinISD does allow for adjustment of the end correction. The image below provides some values to work with based on the port location in the cabinet. In general you will find most software is using the 0.732 value for calculation of a straight port, which is why you might find that in most installations the port tuning works out at 10-15% shorter than what the software calculated for you, since the port is often near a boundary.

dcibel

The above image shows k factors for various cabinet arrangements, with a straight port assumed in all cases.

Here's a link that provides the port tuning calculations, if you want to do the math by hand.

http://www.mh-audio.nl/Calculators/WVC.html

For flared ports, a note at the bottom of that link provides some info:

Both ends flanged: k = 0.850
One end flanged, one end free: k = 0.732
Both ends free: k = 0.614

Normally, k = 0.732 is assumed