Originally Posted by Vmax911
Thanks again for the info. Looks like I need to add with some numbers now.
Lastly (hopefully), does it matter where the port openings are located?
It can. The concept is referred to as "end correction". Ports rely on a very specific amount of air that is contained within the boundary of the port volume. Imagine a square port that goes through the middle of the enclosure wall and the inside port opening (terminus) isn't near a corner or nearby wall. The volume of air in the port will be consistent with the port dimensions. If the same sized port is moved over so that it is against one of the enclosure walls, the enclosure wall acts like a port extension on one side. In the attached drawing you can see a "normal" port on the left. The green lines represent the walls of the port and the yellow area is the volume of the port. The picture on the right represents the same port width and depth but you can see that the enclosure wall on the right acts like a really long port wall. The yellow area of the port volume is extended out a bit and becomes larger due to that longer wall. The longer the port the lower the tuning, so as you can see the port of the right will be tuned lower than the port on the left even though the port length is exactly the same.
This is called "slot loading", which you will probably see listed in most online port tuning calculators.
Also note that anything which is around or next to the port opening on the inside or the outside of the enclosure can result in a lower tuning. Pushing a ported enclosure up next to the side wall of your trunk so that the port fires off of the side of the trunk will cause effective tuning to lower because of the same concept; the calculated volume of the port will "couple" to some additional air volume that is squeezed in next to the port due to the close proximity of a loading surface near the port terminus.
Note that the larger the enclosure (and/or port) the bigger the role this concept plays. For averaged sized ports the enc correction might only account for a couple hertz difference in effective tuning, but for large enclosures with short port lengths there could be a difference of 10 or more hertz between the calculated tuning and the effective tuning after accounting for end correction.