This is a newbie question so I'm really looking for a nice "101" intro information source I guess... but here's what I did: A while back I bought a 2-way custom built cabinet that has a 12" driver and a small bullet tweeter. It had a crossover in it that has a 2nd order circuit with a 3.5kHz crossover point. The maker of this cab now does a 3-way design with the same driver & tweeter and has added a 6.5" midrange driver. His website says the midrange is 800Hz to 3.5kHz so I got a 3-way crossover that has those crossover frequencies. The baffle of the box I bought had plenty of room for the 6.5" and the internal volume allowed me to build a box-in-a-box with the correct volume sealed off beind the 6.5" driver. Well, it's all wired up and sounds really good, which I recognize is due largely to luck. But it got me thinking about why crossover at 800Hz? If the 12" can handle up to 4kHz with reltavily flat response curve and the 6.5" specs claim it's fairly flat down to around 120-150Hz, how was that 800Hz frequency determined? I ordered a book online by David Weems on speaker building but would love to find some online info on how one goes about determining crossover points for bass guitar cabs. Any thoughts or guidance would be most appreciated. Cheers.