View Full Version : Active Crossover Questions

05-11-2007, 10:47 AM
I posted this in the general questions and asked the Mod's to delete that post (or close it). With that being said:

I have a pair of JL Audio VR650-csi components. Tweeter, driver and a passive crossover.
I also have an alpine processor H701 which allows me to run them active, which i am currently doing and loving it. (no passive crossover being used)
I was thinking about crossovers, slopes and ranges today and when i went active on my JL's I basically followed the slope settings that the passive crossover was:

1st order low-pass circuit and 3rd order high pass (ie: -6db slope and -18db slope)

What is the benefit of the -6db and -18db slope on these components vs. -12db or -24db?

Because the components are 1st order low-pass circuit and 3rd order high pass, should I have the slope setting between the driver and my sub as -6db or -18db? Or should i have that slope setting -12db or -24db?

So basically to sum it up, I currently have my settings as:

tweeter ==> 4.5khz -18db slope high-pass
driver ==> 4.5khz -6db slope low-pass and 90hz -12db high-pass
Sub ==> 90hz -12db low-pass

Phase at zero for all.

Also should I have my phase set to 180 for any of my speakers because of the slope settings? Should I have my slope settings changed? if so, any reason why? Sorry for the noob questions but I figure if I ask some of the experts i'll get a much better sound in my car.

Please let me know if I'm missing any info in here and I'll include it.

Id like to add one more thing... Am I crossing over the tweeter/driver correctly?
If I bought the tweeters seperately they are rated at: 4 KHz - 25 KHz 3 dB
The VR650-csi (which includes that tweeter i just mentioned, are rated at: 59 Hz - 25 KHz 3 dB
Is it smart to cross them over at 4.5khz? or should it be lower or higher?

Please someone give me a lil push in the right direction and dont flame me for askin

05-11-2007, 11:54 AM

thats kind of what you are looking at with your crossovers. the thing about different slopes means, you can let the speakers play higher or lower because the slope gets them to be able to play further into each frequency band without having the negative breakup that they exibit...

here is an example of a frequency response of a driver.


so with a higher crossover slope you can play further up or down the frequency spectrum of a give driver. therefore the fidelity of the system can be increased because having single speaker play more tends to yield a better soundstage, and height.

05-11-2007, 12:32 PM
WOW! i am impressed with the trueRTA program.. Thats sick!

So lemme ask you this, based upon what I am currently doing, do you think something should be changed? or maybe a recommendation?

05-11-2007, 01:37 PM
the whole point of going active is playing with different crossover points and slopes. we can recommend but really its very install dependent. just play with different points and slopes. at least to start, hi pass the mids at like 80hz @12/oct and play around from there.

05-11-2007, 02:53 PM
Thank you Alphakenny... Yea i gues I really just wanted a decent starting point for the hi-pass mids and a decent starting point between the mids and tweeter.

05-11-2007, 05:32 PM
I really doubt that having everything in phase works in your car either. Almost every install I have heard active requires switching the phase on at least one of the drivers. Usually a mid. Requires is obviously subjective but nonetheless what I have found.

Experiment with everything and enjoy tweaking that is half of the fun of it.l

05-11-2007, 10:23 PM
I really doubt that having everything in phase works in your car either. Almost every install I have heard active requires switching the phase on at least one of the drivers. Usually a mid. Requires is obviously subjective but nonetheless what I have found.

Experiment with everything and enjoy tweaking that is half of the fun of it.l

Correct. About the only time you'll really find yourself keeping drivers in phase (mid/tweeter) is in a kickpanel location when both on the same plan and axis.

I find when designing passives, that a 12 db low pass, and an 18 db high pass is a good starting point when using a standard mid in door, tweeter in a-pillar/sail panel locations. It allows for the tweeter to operate a bit out of phase of the mid, and gives you the opportunity of swapping phases on the tweeter so you can get pretty good alignment. By doing a 6 and 18, you're 180 degrees out of phase. May be good, may not. Of course depends on install.

Your mid also plays a key role in how steep of a slope you should use. If the driver plays flat, and has a natural roll off up high, then 6 db is fine. For something like the RS180 or other metal coned drivers, you have to deal with cone breakup, and in the case of the RS180 it's very severe. You want a very steep slope to compensate for it, or a very low crossover point. Since there aren't many tweeter that like 1000 hz, a steeper slope is a better option.

Like the others have said. Play around a bit. If the mid you're using has a smooth roll off, then 6 db will probably be very nice sounding. Try a 12 db slope on the tweeter, and swap around phases and see how that sounds. Then try a 24 db slope, and see if you can achieve a lower crossover point on your tweeter to help with the off-axis response of your mid.

There's lots of playing you can do. Just wait till the "I want to try some DIY drivers" bug hits you. You're screwed then.

Here let me help you. Because I'm a sadistic bastard.


05-12-2007, 06:29 PM
guys.. again thank you very much!

When you guys say swap the phase on the mids or on tweeter do you mean swaping the phase on both the left and right channel or is it just one channel? I assume if i swap the phase on the mids, i should do both left and right mid otherwise they would cancel themselves out. But i could be wrong/

05-12-2007, 07:22 PM
you got 4 speakers up front. start playing with the wires and switch them around.

play. see what sounds best. you will (well, you should be able to) know when it sounds worse.


05-12-2007, 09:04 PM
You can change phase on each driver at the processor without messing with wires at all. The other nice thing about using digital processing for an active setup is you should be able to use whatever slope works out without the order of the filter messing with the phasing and group delay of the output since those artifacts are a result of the components used in an analog filter. Same with equalization.

05-12-2007, 10:05 PM
Thanks guys.. Yea I have an Alpine processor H701 running optical from my DVA-9831 HU. Under the TCR settings i can change the phase from 0 to 180 on each channel. I'll start playing around and see what i like best

Should I have the Sub turned off during the phase testin for the front channels..

Note: I do not run any rear speakers. Only front components running active.

05-12-2007, 10:08 PM
You'll want to adjust the sub phase, too, to get it to blend as well as possible with the front stage.

05-12-2007, 10:11 PM
Turn the sub off while you adjust your comps. Add it later and adjust it if necessary. Good luck tuning you active setup. Im getting there, but it seems like when I get it sounding good, I change the song, and am back at it again. :suicide: