# An observation on crossover slopes



## FG79 (Jun 30, 2008)

I'm noticing more 24 dB slopes in general than 12 and 6 dB....

Curious why that's so often the trend? If you're just all about power handling and SPL, that's one thing, but the steep slope often has more holes in it than the shallower ones. Coherence favors shallower slopes (or no crossover at all).

I've found that 12 is often the best all around slope for me. If the driver's can handle it, I would go to a 6 dB slope when possible (like for instance, crossing a dome mid to a tweeter in the 7-10+ khz range). 

I can't recall seeing 24 dB slopes in home audio.


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## SHAGGS (Apr 24, 2011)

Unintentional phase changes that happen when a crossover is applied. 
6db = 90 degree phase shift
12db = 180 degree phase shift
18db = 270 degree phase shift 
24db = 360 degree (or no) phase shift

I didn't know about this, till someone posted it a couple months ago. Not sure if there are any other reasons.


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## 07azhhr (Dec 28, 2011)

SHAGGS said:


> Unintentional phase changes that happen when a crossover is applied.
> 6db = 90 degree phase shift
> 12db = 180 degree phase shift
> 18db = 270 degree phase shift
> ...


When you have these kinds of options you can use these shifts to your advantage to find what works best. Many read use 24db and just do it without looking for what is really the best one. But 24db slopes or any high slope can help to allow you to play lower/higher or take a weee bit more power. But this can come with it's own set of issues.

Sub to mb transition can be very difficult thanks to phasing issues. So for me when I am having a phasing issue there I play with each db setting to rotate them 90* at a time then reverse phase a few times to see if there is any difference made. When there is no difference made I know I am either 90* or 270* off. One 90* shift in either direction and bam there it is. Now reversing the phase will make a difference that can be heard and I can get them in phase.


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## fcarpio (Apr 29, 2008)

Let me see if I got this right, if there is more overlap in the frequency range between two drivers you can use a less steeper slope, the narrower the frequency overlap the steeper the slope?


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## ErinH (Feb 14, 2007)

one issue with shallow slopes that *can* be a problem, depending on the driver used and where the crossover is placed, is modal issues outside the nominal passband. for example, using a 5" driver, you expect to have modal issues above, say, 3500hz (this depends on material and speaker geometry). If it's bad enough and depending on where the crossover and slope are set, it can be heard. This is also a phase shift area that will interact with the tweeter playing that frequency and any harmonic of it which it turns creates real world, audible problems.

The overall transfer function is what you are trying to target. A speaker has a natural rolloff itself and textbook crossover slopes don't work. Your goal should be to match that rolloff point and slope in a way that works with the system and permits a smooth match to the other drivers and adds a level of driver protection for high output situations. Most of the folks here using active systems with preset crossover points have our hands forced to choose from a couple points and go with what best. But if you're building a passive or have a DSP that allows for specific frequency choosing, you should choose to match the drivers' natural rolloff so that you're not essentially putting (2) unlike crossover slopes and points on the same driver. 
Polar response falls under this same umbrella. 

In short, crossover points and slopes really isn't a trivial thing. We make it trivial because we don't' have the tools in most active DSPs to do much about it.


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## 07azhhr (Dec 28, 2011)

fcarpio said:


> Let me see if I got this right, if there is more overlap in the frequency range between two drivers you can use a less steeper slope, the narrower the frequency overlap the steeper the slope?


It is like this. Shallow slopes at the same x-o point for two drivers will cause overlap while steeper slopes will lessen the overlap.


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## BuickGN (May 29, 2009)

I'm probably in the minority but mine is easier to tune with 48db slopes. The speakers themselves will play much lower and with a shallower slope than what I have them at but it all sounds more coherent I guess with the steeper slope. The only over/under lap is the mid to tweeters which are underlapped.


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## 07azhhr (Dec 28, 2011)

BuickGN said:


> I'm probably in the minority but mine is easier to tune with 48db slopes. The speakers themselves will play much lower and with a shallower slope than what I have them at but it all sounds more coherent I guess with the steeper slope. The only over/under lap is the mid to tweeters which are underlapped.


 
You are only in the minority because most do not have 48db options . I only have up to 36 on my sub but only to 24 on all others. In relation to phase 48 is like 24 and is a 720* shift insted of a 360*. Either way gets you back where you started lol.


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## ADCS-1 (Dec 14, 2011)

I must be the minority of the minorities, with my Sony XES, and locked down to 70 dB slopes.


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## fcarpio (Apr 29, 2008)

bikinpunk said:


> one issue with shallow slopes that *can* be a problem, depending on the driver used and where the crossover is placed, is modal issues outside the nominal passband. for example, using a 5" driver, you expect to have modal issues above, say, 3500hz (this depends on material and speaker geometry). If it's bad enough and depending on where the crossover and slope are set, it can be heard. This is also a phase shift area that will interact with the tweeter playing that frequency and any harmonic of it which it turns creates real world, audible problems.
> 
> The overall transfer function is what you are trying to target. A speaker has a natural rolloff itself and textbook crossover slopes don't work. Your goal should be to match that rolloff point and slope in a way that works with the system and permits a smooth match to the other drivers and adds a level of driver protection for high output situations. Most of the folks here using active systems with preset crossover points have our hands forced to choose from a couple points and go with what best. But if you're building a passive or have a DSP that allows for specific frequency choosing, you should choose to match the drivers' natural rolloff so that you're not essentially putting (2) unlike crossover slopes and points on the same driver.
> Polar response falls under this same umbrella.
> ...


Excellent explanation. Now how do I know what the roll off is on my drivers? I would have to know this in order to match the crossover points and the slope, right? Is there as tool that could tell me what they are by monitoring a frequency sweep?


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## fcarpio (Apr 29, 2008)

07azhhr said:


> It is like this. Shallow slopes at the same x-o point for two drivers will cause overlap while steeper slopes will lessen the overlap.


I get that part, I was referring to the overlap between a mid driver and a tweeter. If there is a larger overlapping frequency range between them, the crossover points can be rolled more easily, but if there is less overlap the frequencies would have to be rolled over more sharply/steeper.

Bikingpunk answered my question with his post.

The other thing I got from his post is that the crossover slope has to match the frequency roll of the driver, but how do I find that frequency roll for my specific drivers???


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## Brian Steele (Jun 1, 2007)

fcarpio said:


> The other thing I got from his post is that the crossover slope has to match the frequency roll of the driver, but how do I find that frequency roll for my specific drivers???


With an RTA or good frequency response measuring tools. I like HolmImpulse, which is freeware, because it measures both FR and distortion. Adjusting the x-overs to accomodate the sloping response at a driver's upper and lower response range is one thing, but you may also want to ensure that the driver is filtered before distortion starts to rise. 

One more thing in favour of steep x-over points - when the impact of the distance between the drivers and the car's TF is taken into consideration, an overlapping response can result in deep notches in the response curve due to cancellation. I actually ran into this quite recently while investigating a deep 200 Hz suckout in my system - it was caused by my rear speakers being filtered a bit lower (I was trying to get a bit more midbass out of them). Even though there was a boost in output around 100 Hz, the choice of filtering also caused a deep notch at 200 Hz. Moving the HP filter up a bit eliminated the notch.


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## SPLEclipse (Aug 17, 2012)

Brian Steele said:


> With an RTA or good frequency response measuring tools. I like HolmImpulse, which is freeware, because it measures both FR and distortion. Adjusting the x-overs to accomodate the sloping response at a driver's upper and lower response range is one thing, but you may also want to ensure that the driver is filtered before distortion starts to rise.
> 
> One more thing in favour of steep x-over points - when the impact of the distance between the drivers and the car's TF is taken into consideration, an overlapping response can result in deep notches in the response curve due to cancellation. I actually ran into this quite recently while investigating a deep 200 Hz suckout in my system - it was caused by my rear speakers being filtered a bit lower (I was trying to get a bit more midbass out of them). Even though there was a boost in output around 100 Hz, the choice of filtering also caused a deep notch at 200 Hz. Moving the HP filter up a bit eliminated the notch.


This times a million. I underlap far more than I overlap.


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## fcarpio (Apr 29, 2008)

Brian Steele said:


> With an RTA or good frequency response measuring tools. I like HolmImpulse, which is freeware, because it measures both FR and distortion. Adjusting the x-overs to accomodate the sloping response at a driver's upper and lower response range is one thing, but you may also want to ensure that the driver is filtered before distortion starts to rise.
> 
> One more thing in favour of steep x-over points - when the impact of the distance between the drivers and the car's TF is taken into consideration, an overlapping response can result in deep notches in the response curve due to cancellation. I actually ran into this quite recently while investigating a deep 200 Hz suckout in my system - it was caused by my rear speakers being filtered a bit lower (I was trying to get a bit more midbass out of them). Even though there was a boost in output around 100 Hz, the choice of filtering also caused a deep notch at 200 Hz. Moving the HP filter up a bit eliminated the notch.


RTA software, off course. As far as the cancellation goes, time alignment should take care of that. If anything you should get more peaks and less valleys.


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## Neil_J (Mar 2, 2011)

For the record, which will give better impact and transient response, shallow or steep slopes? I know the answer but want to see what others think, both from a theoretical and practical/anecdotal perspective.


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## 07azhhr (Dec 28, 2011)

fcarpio said:


> RTA software, off course. As far as the cancellation goes, time alignment should take care of that. If anything you should get more peaks and less valleys.


Sounds like you like having multiple drivers to play a bunch of the same frequencies.


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## fcarpio (Apr 29, 2008)

07azhhr said:


> Sounds like you like having multiple drivers to play a bunch of the same frequencies.


Good observation, but I try not to.


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## Libertyguy20 (Jun 6, 2012)

I know ive seen Andy suggest that when setting up a system initially the best way to get an idea of where your drivers roll off is to remove/turn off all crossovers on the driver, and look at the responce on the RTA...that will tell you where it starts to roll off naturally, then use that information for you initial x/o and slope setting cause your driver isn't gonna do anything much more below or above that anyway without distortion. 

This comment was made obviously for mids and subs in mind.....not tweets cause you will fry them naturally if you turn off/remove the x/o and turn up the volume. With that said most people know their tweets limitations and recommended x/o designs.


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## Libertyguy20 (Jun 6, 2012)

BuickGN said:


> I'm probably in the minority but mine is easier to tune with 48db slopes. The speakers themselves will play much lower and with a shallower slope than what I have them at but it all sounds more coherent I guess with the steeper slope. The only over/under lap is the mid to tweeters which are underlapped.


lol, my old Sony XDP-4000x has 72db x/o point for the sub.....talk about a brick wall


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## thehatedguy (May 4, 2007)

On paper, the shallow slopes have better transient behavior.

Power

Stored_energy_2




Neil_J said:


> For the record, which will give better impact and transient response, shallow or steep slopes? I know the answer but want to see what others think, both from a theoretical and practical/anecdotal perspective.


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## dvsntt (Nov 17, 2009)

SHAGGS said:


> Unintentional phase changes that happen when a crossover is applied.
> 6db = 90 degree phase shift
> 12db = 180 degree phase shift
> 18db = 270 degree phase shift
> ...



I was reading the document on tuning my amplifier, and it stated that 6db of slope puts the frequency out of phase by 45 degrees. But for practical terms, is it 90 because the signal is playing at 2 speakers?


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## minbari (Mar 3, 2011)

dvsntt said:


> I was reading the document on tuning my amplifier, and it stated that 6db of slope puts the frequency out of phase by 45 degrees. But for practical terms, is it 90 because the signal is playing at 2 speakers?


yes and no. technically if you took 1 speaker and HPF'd this speaker with a cap, for a 6db/oct slope. lets assume that speaker can cover the 80hz to 20khz range. Then that 1 speaker would see a 45° shift.

people say it is 90° because they will use a 6.5" at 80hz HFP and a 12" sub at 80hz LPF. if they are both 6db/oct, then they both experience a 45° shift for a total of 90°.

but! if you have a 6.5" speaker with no LPF on it and a tweeter with a 6db/oct HPF on it, you will actually only get a 45° shift since the midbass has no filter on it at all.

also the shift really only happens at or near the filter point, get very off away from that filter point and the phase shift goes away.

just something to keep in mind.


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## dvsntt (Nov 17, 2009)

I see...sort of. So I was intending to calculate my phase adjustment by the slope, it's a 6db High pass for the tweets, a 6 db band pass for the mids, and a 12db low pass for the single sub. I adjusted the tweets and midst to 90 and the sub to 180. I'm uncertain how to actually calculate it though, these were calculated from fuzzy understanding at best. I'm sure one should have a 0 value, and the others adjusted to match it.


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## minbari (Mar 3, 2011)

dvsntt said:


> I see...sort of. So I was intending to calculate my phase adjustment by the slope, it's a 6db High pass for the tweets, a 6 db band pass for the mids, and a 12db low pass for the single sub. I adjusted the tweets and midst to 90 and the sub to 180. I'm uncertain how to actually calculate it though, these were calculated from fuzzy understanding at best.


the phase shift for the mid/tweet region would be 90°.

the phase shift for the sub/mid area would be 135°. but, since they are different slopes, the effect will last longer for the 6db mid.

the real short answer is, if it sounds good, dont worry about it.  This is all electrical phase. dont forget that there is also acoustic phase and that changes based on freq for each driver. your phase will also flip based on distance. sometimes many times. best to listen to the speakers, then flip the phase on each driver until it sounds the best.


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## Hanatsu (Nov 9, 2010)

The acoustical slope are rarely gonna be the same as the electrical slope you set. In several cases I've noticed that 12dB or 18dB/oct equal a 24dB/oct rolloff. The closer the natural rolloff you set the crossovers the more "unpredictable" the real slope gets IME.

24dB/oct means 360degree phase shift, this is not the same as 0deg phase shift. The signal gets delayed an entire cycle. The impulse response and transient response will be messed up with a tall order filter but it might not be that much of an issue. Using shallow slopes can present serious challenges. An exception is shallow slopes pretty high on tweeters, might actually sound really good in some setups IME. 

For the record, I'm using 24dB/oct LR filters in my home audio towers. So it's not entirely uncommon in home audio as far as know


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## Hanatsu (Nov 9, 2010)

Posted this video in some other thread. Great explanation on phase.


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## thehatedguy (May 4, 2007)

If you have a processor that allows two seperate XO points, you can use those to get flat phase response.

If you have your FR and impedence data, you can use that in a program like lspCAD or Passive Crossover Designer to look at your phase relationship between the drivers with various crossover points and slopes.

But bewarned, when you go off axis in those programs, it is near impossible (if not impossible) to get a flat phase response.


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## ErinH (Feb 14, 2007)

Neil_J said:


> For the record, which will give better impact and transient response, shallow or steep slopes? I know the answer but want to see what others think, both from a theoretical and practical/anecdotal perspective.


would you trade overshoot in the time domain with the potential for audible modal ringing outside the passband? that's the real question.


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## Neil_J (Mar 2, 2011)

bikinpunk said:


> would you trade overshoot in the time domain with the potential for audible modal ringing outside the passband? that's the real question.


Very well put


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## LovesMusic (Mar 29, 2012)

Neil_J said:


> For the record, which will give better impact and transient response, shallow or steep slopes? I know the answer but want to see what others think, both from a theoretical and practical/anecdotal perspective.


bottom line:

More power = faster work


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## minbari (Mar 3, 2011)

LovesMusic said:


> bottom line:
> 
> More power = faster work


what does that even mean as it pertains to crossover slopes?


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## Eric Stevens (Dec 29, 2007)

FG79 said:


> I'm noticing more 24 dB slopes in general than 12 and 6 dB....
> 
> Curious why that's so often the trend? If you're just all about power handling and SPL, that's one thing, but the steep slope often has more holes in it than the shallower ones. Coherence favors shallower slopes (or no crossover at all).
> 
> ...


24dB or steeper slopes have potential benefit beyond the most obvious.

There is lobing effect through the crossover band (area that both drivers are contributing to output at the same frequency) which would be evident in the polar response both horizontal and vertical. The lobes in the response create peaks in some axis and dips on others as a rough way to describe the effect. With a 6dB slope you get larger lobes and and larger dips, when I say larger I mean they cover more degrees or a larger angle of the axis of output. Steeper slope will have lobes and dips that cover much smaller degrees or smaller angle. This can be demonstrated with single speaker and walking in an arc in front of it while it is playing, use Piano and you will hear the lobing effects as you walk. With 6dB this effect is very easy to hear and sounds downright bad in some axis, 24dB is much more difficult to identify and sounds better even at the worse axis of output.

The same effect listed above is further exacerbated by driver offset, or unequal path lengths and causes some strong frequency steering effects with peaks and dips in the FR. The 6dB slope will have the most significant peaks and dips and the steeper slopes such as 24 or 36 will have much reduced peaks and dips causing FR steering effects.

Add to the above the range of frequencies in which the driver interaction will have an effect is reduced with a steeper slope. This simplfies tuning making good or excellent results easier to achieve.

In the car I prefer steeper slopes, In the high end home environment I tend towards shallow 6dB slopes.

Just some food for thought 

Eric


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## bbfoto (Aug 28, 2005)

^Thanks, Eric. Great info given in simple terms.



Hanatsu said:


> Posted this video in some other thread. Great explanation on phase.


And thanks for posting this video, Hanatsu. Makes it much easier for my pea-sized brain to comprehend. 

Great discussion. Sub'd


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