setting active xover point for sub amp

[lithium 358]

my sub amp is a kenwood excelon. u cant bypas the xover... right now i just cranked it 200hz at a fixed 18db slope. and use an 80 hz 18 (or 12) on the hu.

i forget if the 2 frequencies combine or if there separate of each other.... i think it was explained to me once awhile back that they somehow combine so i would have like a 75 hz with 36db slope....

what would u recommend i do...

[bassahaulic 155]

You need to set the amp and HU about the same, no bass above 80Hz is even getting to the amp.

And tell your friend that doesn't make sense lol Well doesn't to me.

Edited February 28, 2009 by bassahaulic

[johnecon2001 82]

They don't add together. Which ever one is set lower will take precedence over the other.

[lithium 358]

i thought so too.... ill mess with it tomorrow. i think how i have it now. it sound pretty decent. i think i actually have the sub at at the next step down on my hu which is 63 hz. i was thinking about just using the sub's xover by it self and setting it at about 75 hz...

ehh either way ill get it sound nice sooner or later. being able to tune this much is pretty fun.

[lithium 358]

They don't add together. Which ever one is set lower will take precedence over the other.

makes perfect sense to me. idk where i heard that other explanation... d

[KU40 173]

well, i believe they do add together in sorts, but at the slope side of things, not the frequency. In that case you'd have a -18db slope from 80 hz down from your head unit, then 36db slope down below 200 hz. It won't hurt anything to have it like that. It's just a steeper slope.

[johnecon2001 82]

The slopes won't add together. Not the way it works.

If you had two crossovers, both at 80hz with a slope of 24dB. You wouldn't have a final slope of 48dB because they'd both be right on top of each other doing the same thing. It'd still be a 24dB slope.

[dbjunior 0]

The slopes won't add together. Not the way it works.

If you had two crossovers, both at 80hz with a slope of 24dB. You wouldn't have a final slope of 48dB because they'd both be right on top of each other doing the same thing. It'd still be a 24dB slope.

the crossover reduces the signal by an amount so if the amp is getting a signal that is already reduces it will be further reduced from the original. but it doesnt just drop off from 80hz if it is set at 80hz. if you have a 12db cross over its 12db down from an octave away. there for 40hz would be 0db down 60hz 6db down 80hz 12db if you set the other crossover at 160hz odb would be at 80hz but 80 is already 12db down 160hz would be 24db down from the first crossover plus 18db or whatever the second crossover is, making 160hz 42db down from the original signal

[KU40 173]

The slopes won't add together. Not the way it works.

If you had two crossovers, both at 80hz with a slope of 24dB. You wouldn't have a final slope of 48dB because they'd both be right on top of each other doing the same thing. It'd still be a 24dB slope.

the crossover reduces the signal by an amount so if the amp is getting a signal that is already reduces it will be further reduced from the original. but it doesnt just drop off from 80hz if it is set at 80hz. if you have a 12db cross over its 12db down from an octave away. there for 40hz would be 0db down 60hz 6db down 80hz 12db if you set the other crossover at 160hz odb would be at 80hz but 80 is already 12db down 160hz would be 24db down from the first crossover plus 18db or whatever the second crossover is, making 160hz 42db down from the original signal

I think the slopes do add together because the second crossover (amp) doesn't know that the first crossover is there (head unit). I think it still just crosses it over as it would without the first one there. I think this only works with active crossovers. Passive crossovers vary because the capacitors and inductors would interact with each other differently whether you wired the crossovers in series or parallel (just like dual voice coils). Your crossover points would shift. http://www.bcae1.com/ on page 54 shows the passive crossover stuff. I may be wrong on active though. hmm. The more I think about it the less sure I am. haha.

However, dbjunior, I think you're incorrect on the specifics of the crossover slope. In your example, if a 12db crossover is set at 80 hz, it doesn't start reducing the signal from one octave down, 40 hz. The crossover point is the -3db point. So 80 hz would be -3db. But then 160 hz would be 12 db down, 320 hz 24 db down, etc. Where the crossover begins reducing the signal varies depending on the crossover slope. Page 27 of bcae1.com shows a graph with different crossover slopes in it.

[johnecon2001 82]

I think the slopes do add together because the second crossover (amp) doesn't know that the first crossover is there (head unit). I think it still just crosses it over as it would without the first one there.

This is where it gets tricky. Take the example of both of them being at 80hz/24dB. It'll still be at 80hz/24dB. If one is set to 160hz/24dB and the other is 80hz/24dB however, the point of the 160hz point will overlap the 80hz one. Which effectively makes the 80hz point useless. It doesn't combine.

[SoCalSQ 0]

use one crossover.

set it at the slope you want.

you'll never match them up correctly unless you spend a lot of time with an RTA

a 24 Db slope is plenty, i almost never go over 12 except on sub/midbass

[KU40 173]

I think the slopes do add together because the second crossover (amp) doesn't know that the first crossover is there (head unit). I think it still just crosses it over as it would without the first one there.

This is where it gets tricky. Take the example of both of them being at 80hz/24dB. It'll still be at 80hz/24dB. If one is set to 160hz/24dB and the other is 80hz/24dB however, the point of the 160hz point will overlap the 80hz one. Which effectively makes the 80hz point useless. It doesn't combine.

hmm. Maybe it's different than I think. How is it determined which one is used in the 80 hz and 160 hz example?

[danssoslow 0]

I think the slopes do add together because the second crossover (amp) doesn't know that the first crossover is there (head unit). I think it still just crosses it over as it would without the first one there.

This is where it gets tricky. Take the example of both of them being at 80hz/24dB. It'll still be at 80hz/24dB. If one is set to 160hz/24dB and the other is 80hz/24dB however, the point of the 160hz point will overlap the 80hz one. Which effectively makes the 80hz point useless. It doesn't combine.

The slopes have to be additive.

Let's take two 80hz/12dB crossovers for example. The output signal of the radio is playing at a level of 100dB pink noise. Through the first crossover, the output signal is now 88dB at 80hz going into the second crossover. That 88dB signal will then get cut another 12dB at 80hz to now arrive at an output signal of 76dB, or 24dB from the original signal.

Every crossover is going to cut the signal coming into it, regardless of what the original signal was.

Correction:

As KU40 has said, 80hz would be the point where it is 3 dB down; but even so, through the second crossover the signal would be 6dB down from the original signal.

Edited March 1, 2009 by danssoslow

[johnecon2001 82]

Man I need to get some pictures to show you guys this stuff.

You don't add slopes, because you can't change how steep they are when you overlap them. It doesn't work like that.

In the 80hz/160hz example, the crossover set higher (160) will overlap the lower one because by the time you get to 80hz in the 160hz xover, you're already at 0dB @ 80hz (on a 24dB slope).

fake edit: I made a couple of graphs on my PM5D

80hz

And leaving that 80hz on and overlapping it with a 160hz.

[lithium 358]

thanks for the answers guys.

but im wondering what would happen if u had lpf at lets say 80 with a 6 db slope and then a second point kinda close at like 90 hz with a higher xover slope like 18 or 24.

i can picture it in my head but i would be nice if u could model it up for me johnecon just so i know if im right.

thanks