Building Passive Crossovers!

For the last couple of days I have been reading up on how to build passive crossovers so that I can build one for the X15 Cabs that I have built.

But still some questions remain, I am experienced with basic electronics and soldering so shouldn't have a problem making th circuit up and now understand how the circuits are working I think.

Anyway here are my questions:

1) How do you pick the crossover points, i.e for the X15's the woofer is rated at - 45Hz to 3500Hz and the horn at - 1Khz to 20Khz, Everyone on the forums has different ideas for these cabs!! It almost seams to be just a matter of opinion. The manufacturer of the horn says 1.5Khz crossover? Should you always go by the manufacturers guide for the horn but surly it matters which woofer your using?
Or should you just go in the middle i.e. an equal amouont from the end of the frequency range for each driver so that would be 1.75khz!

2) Should the cutoff always be the same for each driver or can you do a overlap i.e. bass cutoff at say 2khz and high cut at 1.5khz so between 1.5 and 2 they are both working?

3) So we're cutting the top freq off for the bass and bottom off high but should we cut the other end as well i.e. use a high pass filter to cut off everything below say 45khz for the bass so that it isn't driven below its range and the same for the high so cut off everything above 20khz with a low pass filter for the high or this all not needed. Does it not affect the horn given too high and what about the woofer is that affected too much been given too low? I think the bass is affected more?

Many thanks, sorry for the long questions, I was just trying to explain!

Usually I get hold of an active crossover (analog or digital) and play with crossover slopes/gains until I like what I hear. Then I try to transfer the design over to a passive crossover. Cuts out a lot of guesswork.

As long as you factor in the impedance of your drivers at the crossover frequency when designing the passive circuit then you should end up pretty close to the original spec.

Hi thanks, for the replies,

and to Cravings the drivers are - P-Audio 15BM-300B and the P-Audio BM2-D450,

Cheers - Simon.

One thing I would add is you should add a high-frequency bypass around the L-pad for the tweeter, as the BM2-D450 has a falling response above 8k, and requires power shaping to get a flat response.

Have a read through  this book Simon.

reessi wrote: Thats interesting about getting a flat response, I haven't seen any websites describing how to do this, so really all passive cross-overs should be tailered to the tweeter! I'll definitly try that out, cheers. Did you read my previous question just above your post about whether I should be cutting off the bottom for the woofer? What are your thoughts on that and at what value it should be cut off? Cheers - Reesy.

This is why a play with an LMS such as the DCX2496 and bi-amping to start  with (if you can get hold of one) is a great idea - you can try out all sorts of filter slopes and EQs on the cabs to decide what you like before you even start designing a passive circuit. It's much harder to try a spurious idea such as a HF rising boost  in component world. It also lets you implement baffle step correction as well which depending on the size of your cab and design can make a big difference in the bass:mid ratio.

Agreed on not bothering with a  45Hz high pass too, for full range low level listening then excursion under a cut off isn't usually a big deal, and if it was then I'd handle it in low level line circuitry preferably.