I'm pretty sure if you're going to send 3-4 different signals to be amplified, you're going to need 3-4 channels of separate amplification.

Edit: Otherwise you're going to separate all your frequencies at the crossover/eq and mash them all back up again through the amp.

 

passive crossovers are used between the amp and the drivers. so the passive xover splits the frequencies to two speakers with one channel from an amp. why cant an active xover do this, or are there any made that can do it? i wouldnt have a problem buying a bit1 or ms8 if only i didnt also have to fill my trunk up with amps

 

You could also do this for way less then 1700. The JBL GTX47 goes for like 70 shipped and new, that will allow you to go 4 way active. Then you would only need two 4 channel amps (1 for tweets and mids, the other for midbass and sub). You could probably find to very suitable amps for around 500. If you want a DSP with more control you could get 2 MiniDSP's for like 250 I think. So it can be done for far less then 1700, you might not be able to get top of the line amps but you could get very good amps.

 

Basic Car Audio Electronics

great site to learn some electrical theory as it pertains to car audio

 

yea ive installed both passive and active crossovers before. I dont really understand why you posted pictures of exactly what i had just described. So anyways, to reiterate my question:

Is there something principally different between an active and passive crossover that prevents the creation of an active crossover that can operate post-amplification; so you can use one channel of an amplifier to operate a woofer, midrange, and tweet and maintain active control of the xover points?

 

Is there something principally different between an active and passive crossover that prevents the creation of an active crossover that can operate post-amplification; so you can use one channel of an amplifier to operate a woofer, midrange, and tweet and maintain active control of the xover points?

Yes.

 

I could say something constructive, but it won't make a difference to the OP apparently. Instead I'll just be a minor troll and watch the carnage from afar...

 

If not, then why? It seems like you could save alot of money and space running active 3 or 4 way off a single amplifier.

Because in the purest sense, "active" is one channel of input and one channel of output. One channel of amplification per driver.

Now, take an active crossover and put it in place of the passive in the diagram. What's the difference? Even if you can adjust the crossover points, it's still technically passive (or "quasi-active"). You'd still be feeding the amp(s) a full range signal, then it passes through the XO/processor where it's split. One channel of amplification per driver is not present.

I'm not saying it's not worthwhile to pursue--in fact, why not use a 2-way + sub active headunit then build a simple passive to highpass the tweeter at like 8kHz? Driver's don't need time alignment over 4kHz. Or, and I've thought of doing this, would be to split the "sub" signal using the amp's XO...so the HU gets set to 200Hz lowpass (or whatever), you split the signal at the amps, sub gets an 80Hz lowpass from its amp, midbass gets an 80-200 bandpass on its amp. Midrange is set to 200-8000Hz in the headunit, tweeter gets set to 8kHz highpass in the same way. Just an example or two...

 

So very eloquently put by bill.
Thank you for that excellent explanation.

 

You're welcome, hope the OP gets the drift.

BTW, there's a "Thanks" button, it doesn't seem to get used near enough...

Best,
Bill

 

It seems to me that you are looking for a variable passive crossover network. Most of the time when these are used it is to determine crossover points before building your final passive crossover network (provided you have the proper measuring devices to figure out exactly where you're crossover point is). Some prebuilt passive crossover networks allow for minimal adjustment but I think your looking for something more along the lines of this:

Vidsonix Crossover Box

This is more or less "test equipment" and would require a lot of effort to setup but it would let you play with different crossover points in a passive environment.