End correction factor question

[Newbomb]

I have a sub plan finalized, but the ECF for the port is a bit of a question. Construction is to be 11/16" plywood.

This sub is only 7.25 inches high (42" d x 34" w). The vent is square, internal on one side, and 33 1/8" long - along the 42" side.
One side of the vent is the long (42") edge of the enclosure, the top and bottom of the vent have a single extra 11/16" piece of plywood (to reduce vent volume).

So, internal vent dimensions are 5 3/8"w x 4 1/2" h X 33 1/8 l. Logic says I should approximate by adding 1/2 the width (5 3/8"), but the height only has an extra 11/16" of room due to the one extra layer of plywood. Should I compensate for this?

If someone has time on their hands, what would be the tuning frequency of this enclosure be if the volume were 100 liters. This, after driver (Dayton rss265hf) and bracing and vent are accounted for. I am aiming for 21 Hz, and my calculations come to about 21.3 Hz.

Finally, this is important, as a 1 Hz error could give me a bump of ~ 1 dB right near a room mode.

[Svante]

Calculating the port length of this port exactly is hard. I'd do a bit of simple calculations just as you have done, build it and measure the result. If the Helmholtz frequency is not close enough to what you wanted, the make some adjustments.

[Wayne Parham]

I would suggest doing impedance measurements at various power levels. This will confirm not only your Helmholtz frequency but also the amount of electro-mechanical parameter shift and how that affects overall performance.

I am concerned about any application that requires electro-mechanical parameters to stay put. The problem is they don't. It's always good to do things that reduce parameter shift, but you can't completely remove it. If you can make your system be tolerant of changes, it will be more robust and will sound better as a result.