Port Depth/Area relation ?

[Dave Zan]

In a vented box tuned to a particular frequency the port becomes deeper as the area increases.
Intuitively I would expect that they would increase in proportion.
Double the area should require double the (end factor corrected) depth.
Is this correct?
I have box tune charts but not a formula.
The charts show the actual depth is not proportional to area but I can't tell what the corrected depth is to see if _that_ is proportional.
Any one here actually understand this ?
I don't want to just be a chart and/or CAD monkey.
But mainly I plan an enormous port and it's off the chart!

TIA

[4313B]

Enclosure Tuning: Lv = (Sv / (3.7E-4 * Vb * Fb^2)) - (0.83 * SQRT(Sv))
Vb enclosure volume in cubic feet
Fb enclosure tuning in Hertz
Sv port area in square inches
Lv duct length in inches

[Dave Zan]

Enclosure Tuning: Lv = (Sv / (3.7E-4 * Vb * Fb^2)) - (0.83 * SQRT(Sv))

Thank you. What's the reference for this particular formulation?

[4313B]

Good grief. I'll dig the binder out of a box later today and post the reference.

[Dave Zan]

Good grief. I'll dig the binder out of a box later today and post the reference.

No need for that much effort! Thanks.

[Datubie]

My problem is in reverse.

I already have plans that specify ports of a certain length and diameter. (Fb not known however) I know you can still maintain the current Fb by resizing the port by shortening the tube & increasing the vent size. I just need the math!!;)

[Dave Zan]

I already have plans that specify ports of a certain length and diameter. (Fb not known however) I know you can still maintain the current Fb by resizing the port by shortening the tube & increasing the vent size. I just need the math!!;)

Not correct. Shorter tube and DEcreased vent size.
Google "Helmholtz resonator" etc.