Just a little Help Please...

[chevydudesixty9]

I have a Port thats 15" Wide, 3" Tall and X Inches Deep... How would I lower the Frequency of my box? Make the Port Longer?

[TheOtherSide]

Yes.

But remember by lengthening the port, you are making the box smaller too. They are proportional in some way. For instance, if everything (including box size) is constant, let's say 3 ft^3, a 15"x3"x27" port would be tuned to about 34 hz while a 15"x3"x45" port would be tuned to about 28 Hz.

[chevydudesixty9]

Box is 3 Cubes without port... So, I need to make it that much longer to bring it down from 39 to lets say 30?

[TheOtherSide]

Yeah, the lower you go tuning, the longer your port has to be. For a 3 ft^3 box, with slot port, these are the port lengths and extra length needed to lower tuning:
Port Length Increase By
39 21.044195
38 22.461635 1.41744
37 23.995555 1.53392
36 25.659065 1.66351
35 27.467185 1.80812
34 29.437185 1.97
33 31.588975 2.15179
32 33.945635 2.35666
31 36.534015 2.58838
30 39.385525 2.85151
29 42.537085 3.15156
28 46.032295 3.49521