Idiot question #3. Ports - continued

[Xover]

"Another question re the one port width rule of thumb, I am assuming that is side to side. Further assuming a front firing port, is there a rule of thumb re how much space is needed between the butt end of the tube and the back cabinet wall?"

I agree with Dr. Who on at least one port diameter from the butt end of the port but do not agree on the same rule for sides and bottom. Try it for yourself. I do agree that position of the port may change the length in final tuning but so long as the end of the port is not obstructed it will work fine. Consider ducted slot ports in this regard, they work fine.

Another consideration it is a good idea to put damping material on one of each opposing side of the enclosure. Do not put any damping material close ( a port diameter might be a good rule of thumb here too ) to the butt end of the port however you do want damping material directly behind the woofer.

[DrWho]

I agree with Dr. Who on at least one port diameter from the butt end of the port but do not agree on the same rule for sides and bottom. Try it for yourself. I do agree that position of the port may change the length in final tuning but so long as the end of the port is not obstructed it will work fine. Consider ducted slot ports in this regard, they work fine.

I totally agree...but wanted to point out that the port tuning calculations only work when you follow the port-diameter rule (because they were derived assuming those conditions). So whenever you choose to deviate you will need to implement some flexibility in the design. It's not a huge deal, but significant enough to point out.