Help with modifications to speaker plans - Sub design

Hi all,

First time posting so just want to say a big thankyou to everyone on here - it's an absolute wealth of knowledge that's been super useful in helping me get to grips with some of the basic concepts of speaker design.

I'm trying to design a sub to support an altec 816 cab, I've been thinking about trying to build the C-Sub from speaker plans, link below, but make some modifications to the width and depth of the box such that the altec will sit nicely on top - in its current state the altec would overhang on all sides.

I'm quite happy with modelling how the volume changes affect the tuning of the rear chamber of the box using Win ISD, that's fine. What I'm unsure about is how these same changes will affect the top chamber?
Could anyone please explain how I'd go about this - would it be a valid option to just keep the volumes of each of the chambers the same whilst messing with the width/depth or will I need to also think about changing the top vent size.

Also open to any suggestions of sub designs which would better suit this altec cab (slightly modified, and to be fitted with faital pro 15PR400).

Many thanks!
Hi GM,

Thanks for coming back to me - if I understand correctly you’re referring to the Faital driver and how I should look to bring to down the driver Qts the original alter driver at .25 ? Thanks that’s helpful information that I was not aware of. I shall try to implement that in my build.

However my question is more about modifications to the top chamber of the C Sub (linked above), and what changes need to be applied to the shelf/vent if I change some of the other dimensions of the top chamber - are you also able to provide some insight on this?

Appreciate the response - cheers!