Help with filter!

I am new to all the his but I am planning to build some Cubo 15’s to add to my PA system. My question is what filters would I need to buy so that there is only low frequencies going to to sub?

Something like this (called a crossover): dbxpro.com/en/products/223xs

Hello, not sure if this answer your question for your set up but I've been running a sound with 4 12" Cubo + 2 12" cubo kicks + mids and highs and been using a Behringer DCX2496 where you can select and adjust xovers, eq, gain, limiters etc..
I like to have the chance of adjusting the parameters to get the sound how we like it. With passive xovers you have to go with what you decided to set them up in the circuit. Which can be fine for me on my house speakers but with PA I'd prefer more flexibility.