passive crossovers are networks built using capacitors and inductor coils. active crossovers are generally line-level electronic signal processors that work between the amplifiers and the signal source. active crossovers are generally "better" due to no phase shift, or loss of energy, and no coloration from the components in a passive filter. the disadvantage is that every speaker needs its own amplifier channel, and the system gets more expensive and complex doing things that way. active crossovers are generally adjustable as well, whereas most passives are not, or if tehy are, it's very limited.
2shay. in addition: (as per sqeak from caraudio.com)
"Ok, passive crossover networks are unpowered crossovers (i.e. no external power source) that split the frequencies between the speakers in a component set. They send the higher frequencies to the tweeter and the lower frequencies to the mid(s). They accomplish this by using a combination of capacitors and coils to create certain crossover points and slopes. They are wired in line with the speakers, between the speakers and the amplifier. The amplifier's output is connected to the passive's input, then the mid(s) and tweeter are connected to the passive's output.
Now, when two speakers (a mid and a tweeter) are on a passive crossover, the mid and tweeter are not wired in series or parallel. Two 4ohm speakers (a mid and a tweet) do not make a 2ohm load or an 8ohm load. Two 4ohm speakers on a passive crossover network create a 4ohm load on the amplifier. Two 8ohm speakers on a passive xover create an 8ohm load. A 4ohm mid and 8ohm tweeter on a passive xover creates a 4ohm load for the mid's frequencies and an 8ohm load for the tweeter frequencies. Reason for this has to do with the fact that passive's are based on frequency distribution and not power distribution.
When you have components sets with passive crossovers, the power from the amp is not split between the speakers. If you have a 70 watt amp, then each speaker is going to receive 70 watts (assuming all speakers are the same impedance). If you are sending 70 watts @ 4ohm to the component set, and the mid is 4ohm and the tweeter is 8ohm, then the mid will receive 70 watts but the tweeter will only receive 35 watts.
This probably isn't a very technical explanation....but it gets the point across none-the-less Let's pretend theoretically that we are running a 70 watt @ 4ohm amp full range. That amp (theoretically) puts out 70 watts at all frequencies at 4ohms, correct?? Now, pretend that we are running that amp to a component set (with all 4ohm speakers) through a passive crossover with a crossover point of 3500hz. So, we are taking that full range signal from the amp and splitting up the frequencies between the mid and tweet at 3500hz. Now, since we are splitting the frequencies and nothing else, there is still going to be 70 watts worth of power at all frequencies below the crossover point and at all frequencies above the crossover point, just the same as there was before we split the signal (since it was putting out 70w at all frequencies).
yop. all active. i just recently sold the passives. I did try them out though. at the time i was running an active RF epx2 xo w/12 db slopes. too much lows were getting into my 3" causing excursion. not a good thing, especially for a 3" dome driver. the dynamics were so much better with the active than the passive xo. also, the passives ate up a tremendous amount of power. and i was already overpowering my 3ways. so basically, i drive my 6.5 and 1" with my vga 500.4 with about 140wx4. and 120w goes to each of my 3" via the 400.2 (the ears are the most sensitive in this region, anyway). the alpine pxa-h702 offers extreme capability with the eq and xo. i am able to xo all 6 channels individually, raise/lower gain, as well as turn on/off any pair of drivers. but when it comes to the subs, i can turn on each one or both. i highly recommend going active if you have the proper slopes, and time to tune. this one offers 6, 12, 18, 24, and 30db/octave. again, very versatile.
"yop. all active. i just recently sold the passives. I did try them out though. at the time i was running an active RF epx2 xo w/12 db slopes. too much lows were getting into my 3" causing excursion. not a good thing, especially for a 3" dome driver."
Don't feel too bad, my dome mid uses a 6db/oct crossover. Of course, it's crossed at 700hz, though. At least with 12db/oct you're keeping excursion constant as frequency goes down, one reason 2nd order is a minimum for most tweeters.
But of course. I was referring to it in the sense of cone flutter and general resonance issues, just it's capability to play midrange frequencies accurately. Off axis you'll get around 1khz out of it before it starts dropping off in response (that's assuming 90 degrees). At 30 degrees off axis I'd say dispersion would be pretty good until about 2khz.