Speaker design sounds easy, but is very, very complicated.
If you read some of the better, more complete books on speaker design, it will leave your head spinning.
What I am saying is look into thoroughly tested designs, and do not try to second guess the designers and substitute any parts!! unless they are accepted as ok by the designer!
Building a speaker can be very rewarding, if you do your homework.
Homework being: check out the designs, see what folks who built them have to say, how long has the company making the speaker kit been in business, do you have the skills needed to finish them. (Some cabinets are from scratch, some precut, some just need finishing)