Not quite sure i have a thorough understanding of active crossovers. i am under the impression that you can do a 2 way active crossover by hp the amp on the tweeters and lp the amp to the mids. then i noticed ppl intsisting on dsp/external crossovers, and saying only certain hu were active capable.

i've searched this site and a couple car audio forums and haven't really found an explanation of what an active crossover is and what is required equipment wise.

 

Well to be truelly active this is what would need to happen:

In a 2 way setup - Two tweeters, two mids - each speaker has to hve its own amplification so 4 channels of amplification.

Now mids need a bandpassed signal, tweets just need a high pass. Only way to accomplish that is with a headunit that is capable of goign active or an outboard active crossover.

 

i assume a bandpassed signal means a signal that is lp and hp to only include certain frequencies.

that assumption being true, wouldn't an 4 channel amp with a 30hz infrasonic filter (hp) and a lp filter on 2 channels and a hp filter on channels 3/4 do the job all by itself? to get a little more specific, this amp:

http://mobile.jlaudio.com/products_amps.php?amp_id=438

 

Why couldn't you use a h/u that has a hpf on the preouts and lpf on the amp to get the bp filters

 

is that question for me or are you wondering also? i was thinking that too, using the lp/hp crossovers on the hu.

also when ppl say "that head unit is not active capable" do they just mean the hu itself can't do it, but it could be done externally?

 

Technically *could* be done this way, although most people would want flexibility of adjusting the slope as well. If you want a more steep or shallow slope on one or both ends you dont have the ability. It has and can be done the way mentioned above, but not withstanding limitations.

 

You can but you are very limited as to what you can do. Much simpler than getting 3 seperate amps for each driver range.

Also a hpf of 30hz is far too low for most midbass's.

 

Yep.

 

my midbass is a cdt m6 which is rated at 20hz as a component set or 40hz when used by itself ( i assume an active set up falls into this category). so it should be ok right?

the jl amp has adjustable slope 12/24db.

but how would you do it the right way. i'm just going by how the cdt website.

 

Thats way to low to crossover over your midbass unless you plan to lowpass the sub at 20/30/40hz.

The easiest way is to get a 4 channel amp and a headunit that is active capable.

 

Just wondering how much signal are left.

Assume your HPF filter let signals above 30KHz pass. All signals (components) below 30KHz are abandoned.

Then you pass this "above 30KHz" signal through a LPF which only allows signals below 50Hz to pass.

----> Finally, all signals are filtered out. You get no signals.


Basically, LBF + HPF makes Band Reject filter. Band pass filter does the opposite thing.

 

If you HP say 80Hz on the HU and LP say 2k on the amp then you would create a BP between 80 and 2K. This would consist of using one set of preouts.

 

Sub LP @ 20 will yield you hearing Nothing. Then again those midbasses arent going to play down to 20 in real world anyway.

 

OK, this makes senses.

 

Well some peeps use the subs for rumble only to feel it but in that scenerio you need something that is capable of playing down to 10-15hz... LOL.

 

Me thinks he meant 30hz.

 

i plan on not using a sub. so if i use the hp/lp on the hu to set the range and the lp/hp on the amp to split it then i should be good right. also on that jl amp i posted there is bp crosseover on channel 1/2, does that mean the frequency filter is for the hp on channels 1/2 and the filter on channels 3/4 set the lp on 1/2 and the hp on 3/4?

 

No sub means youll be losing alot of lowend.

 

WHAT? No it means that channels 1/2 can be bandpassed.

 

yeah i know, but the trunk will be full, might possibly tuck a 10" somewhere, but install is in the future a bit

i understand that, i'm just trying to figure out how by looking at the image of the adjustment panel. it says that if bp is selected the lp on 1/2 is set by the channel 3/4 frequency filter. just wondering how the hp for 1/2 is set.