Xover Adjustment?

[PollyCranopolis 10+ year member]

Just purchased a Concept 2410 from the Cybe. Great unit, very impressed. My question concerns the xover settings on the amp. I have my 880PRS set @80hz for the subs. Why is it when I turn the amp xover above 80hz, It sounds like the frequencies are still going up? I figured if the HU is only sending the amp frequencies 80hz and below, then jacking up the amp xover should have very little effect. I mean, how can the amp produce frequencies it's not recieving from the HU? The amp does have a 24db xover, which may have somthing to do with it. Any suggestions?

Another thing is I'm finding it hard to dial in the amp xover with any sort of accuracy. The unit has only 2 printed frequencies located at the beginning and end of the adjustment (50hz start, 350hz end). How am I suppose to know when I have this thing set at say 80hz, with so much of an unmarked range in between?

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[PollyCranopolis 10+ year member]

Just to add some additional info, The sub amp xover is 24db, while the slope from the HU can be set at 18,12 or 6. I understand there should be some roll-off, but I am still able to notice a major diffrent in output if I turn the amp xover above 80hz, after being set to this opint from the deck.

 

[headless 10+ year member]

Crossovers are additive, and they aren't solid - they work on a curve...an 18db crossover stacked on a 24db crossover would cut out way more sound than just an 18db crossover. It's not that your deck is cutting out ALL sound below 80hz...80hz is the crossover point...that's where the signal is 6db quieter than 'normal'. If you stack 2 crossovers on top of eachother @ 80hz, then sound @ 80hz would be 12db quieter than it should be, not 6db. By natural extension of this concept (not a solid wall where sound is cut off, but a gradual lessening) you can see that around the crossover point, sound would be effected in the same way -- by the time you're one octave away, you've got an additive 'cut' of 24db MINUS another 18db...36db?!

 

[PollyCranopolis 10+ year member]

A buddy of mine suggested that diffrent xover slopes can actually be in/out of phase. For example, it would be better to have a 12db paired with a 24db, vs. 24/18. Any credance to this? Also, if my subs are crossed over from the HU @80hz, why would cranking the 24db amp xover up to 350hz make a diffrence? Would it be better to set the xover from the HU at 200hz, then adjust down to 80 from the amp? Would this mean that for every notch at the amp with the HU set at 80, im actually raising/lowering the slope by 36?

 

[headless 10+ year member]

A buddy of mine suggested that diffrent xover slopes can actually be in/out of phase. For example, it would be better to have a 12db paired with a 24db, vs. 24/18. Any credance to this? Also, if my subs are crossed over from the HU @80hz, why would cranking the 24db amp xover up to 350hz make a diffrence? Would it be better to set the xover from the HU at 200hz, then adjust down to 80 from the amp? Would this mean that for every notch at the amp with the HU set at 80, im actually raising/lowering the slope by 36?

I wouldn't double crossover any signal at all without doing a ton of graphing + math to figure out what effect it would have. The reason why changing your 24db x-over from 80hz to 350hz effects anything is because the existing 18db crossover slopes from under 80hz to well over 80hz in 18db increments, lowering the volume. Some signal under 80hz is removed, and then as it increases in frequency, more and more is cut out -- at a rate of 18db per octave. If you stack a 24db crossover on it, you end up with a totally different curve on TOP of that...

From what i understand, while an 18db/octave crossover hitting -6db @ 80hz might start cutting sound off at 1/3rd of an octave higher, a 24db xover slope would start cutting sound at only 1/4th of an octave higher. So not only is your new crossover effecting bass around AND below the 80hz mark, as you move the 24db crossover slope higher, you are going to hear a change well above 80hz...because the 18db 80hz crossover is still going to be letting through a reasonable amount of (well) above 100hz and the 24db crossover on top of that is going to cut that slow decline off sharply.

A signal sent through a 12db crossover that is then sent through another 12db crossover both centered on 80hz is not the same as a 24db/oct crossover...the slope would be different on a single 24db/octave crossover

 

[PollyCranopolis 10+ year member]

Interesting...So any idea on how I would go about setting these? Sucky thing is that I can't turn the xover totally off on either the HU, or the Amp. Maybe set the HU slope to it's lowest at 6db, then adjust from there? You think it would make any diffrence to set the HU slope high, adjust down at the amp, or vice versa? What about actually trying to match both?

 

[headless 10+ year member]

Interesting...So any idea on how I would go about setting these? Sucky thing is that I can't turn the xover totally off on either the HU, or the Amp. Maybe set the HU slope to it's lowest at 6db, then adjust from there? You think it would make any diffrence to set the HU slope high, adjust down at the amp, or vice versa? What about actually trying to match both?

You've gotta be kidding me...there's got to be a way to turn one of them off... //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif at least on the HU, if the amp won't let you... :/

 

[PollyCranopolis 10+ year member]

You've gotta be kidding me...there's got to be a way to turn one of them off... //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif at least on the HU, if the amp won't let you... :/

Nope..not from what I'm reading in the manual. I can turn the slope down to 6db, 50hz on the HU (880prs), but theres no way to completley set it to all pass. Funny how I can set the front and rears to allpass, but not the Sub pre-outs! The amp xover is always on.

 

[helotaxi 5,000+ posts]

It's not that your deck is cutting out ALL sound below 80hz...80hz is the crossover point...that's where the signal is 6db quieter than 'normal'.

The crossover point is the 3dB down point, not 6. Small point.

My suggestion would be to set the amp x-over at the highest freq and use the one on the HU since it is easier to adjust and you know what freq it is set to.

 

[headless 10+ year member]

The crossover point is the 3dB down point, not 6. Small point.
My suggestion would be to set the amp x-over at the highest freq and use the one on the HU since it is easier to adjust and you know what freq it is set to.

Ah, thanks for the correction. Did i mess anything else up? (I'm still a newb about alot of things re: audio)

Good idea on the x-over...the 18db x-over should have had enough effect by 250hz that the 24db on top of it probably wouldn't make an audible difference

 

[PollyCranopolis 10+ year member]

Thats what I was thinking as well. I know theres going to be that roll-off, but once the amp xover is set high enough away from the 80hz HU, the diffrence should be nill.

 

[PollyCranopolis 10+ year member]

Went ahead and tried this, but it still sounds like adjusting the amp xover (24db variable) even up to 350hz, noticably changes the sound, when the amp is recieving it's 18db/63hz signal from the HU.

 

[headless 10+ year member]

Went ahead and tried this, but it still sounds like adjusting the amp xover (24db variable) even up to 350hz, noticably changes the sound, when the amp is recieving it's 18db/63hz signal from the HU.

What's the highest xover freq you can set on your deck? try the 24db @ 80hz on your amp and then set your deck's to 6db @ 300hz or something. That's probably your best case scenario, unless you do something creative like split one of your other preouts that aren't being crossed over at the deck (if there are any)

 

[PollyCranopolis 10+ year member]

What's the highest xover freq you can set on your deck? try the 24db @ 80hz on your amp and then set your deck's to 6db @ 300hz or something. That's probably your best case scenario, unless you do something creative like split one of your other preouts that aren't being crossed over at the deck (if there are any)

Highest on deck would be 200hz @6db. So your basically saying to set the deck high, then adjust down on the amp.

Amp range- 50-350hz 24db variable

HU range- 50-200hz 18,12,6db

 

[headless 10+ year member]

hmmm. I'm still pondering this math.