Passive Crossovers are simple to build, and as Greg stated above, when a single enclosure contains multiple Speakers, splitting and directing specific Frequencies per Driver type is almost prerequisite.
Not only do these Filters direct Frequencies to specific Speakers, they also keep the overall Load Impedance steady, as seen by the Power Amp (Power Amp drives into a more "Steady" Impedance throughout the spread of Frequencies).
I have an Application for designing Passive Crossover Networks, which may include Notch Filters, Impedance Equalizers, L-Pads, etc. for 1st through 4th order Networks built around Two Way and Three Way Loudspeaker Arrays - including Dual Voice Coil types.
There are some examples in the Tech Section, way at the end (some of the first drawings to be posted in the Tech. Reference area).
Send the Loudspeakers' Parameters (Data), along with where you prefer to roll Frequencies at (Crossover Points), and I can produce Xover Schematics for you.
You may wind the Inductors yourself, as that is the most effective way to achieve values close to the Design.
Capacitors may be stacked in Parallel, to achieve the Design Values.
Polypropylene or Mylar may be used.
I would stay away from the cheap Electrolytic Non-Polarized Caps.
The Xover Application may be used in conjunction with an Enclosure Design Application I also have, which makes for a complete Design Package.
As to building Pre-Amps and Power Amps with Op-Amps (i.e.: LM386 / LM387), I built a few Pre-Amps around these Op-Amps, and it was so much easier than the Phonograph Pre-Amp I built using Discrete Components!
It was for a Magnetic Cartridge Phonograph (35mv signal), typical RIAA Equalization "Reversal", with 3 level Tone Controls, Subsonic, Notch & Rumble Filters, and solid Line Level output.
Took eons to build and tweek!
Don't know what happened to that Pre-Amp. Someone took off with it back in 1993, as there were a few "Wannabee Electrical Engineers" hanging around where I used to practice at, and they liked "Fixing Things" which they deemed inoperable... you know the types!
These guys were acquaintances of the other Band we shared the Studio with, and probably attempted to use the RIAA Pre-Amp for something other than a Mag. Cartridge Phono (I am thinking Tape Deck).
When the Audio sounded bad, it was time to "Fix The Pre-Amp".
Things of that nature occur often when sharing a Studio!
Anyhow, good luck with the Project!
-- Scott (EE)
