# Subwoofer phase question regarding head unit crossover settings



## randysicko (Oct 22, 2009)

I understand that phasing issues come into play when using crossovers, but I think there is something I am missing here...do these issues still affect the speakers when changing xover settings straight from a head unit?

As I understand it, in phase means the sub bass wave is reinforcing the low frequency wave from the 6x9s, or vica versa...as the cones for each are moving in and out at the same time. Well I have an alpine x305 deck and when I play the right piece of music, I notice cancellation and I have to switch the subwoofer phase from normal to reverse every now and then to get it louder/in phase. 

The only settings I ever play with on the HU are the eq, time correction and xover settings. On preset 1, I have the 6x9s and sub set to 80hz low pass and high pass with a slope of 24db. For preset 2, they are still set at 80, but the slope for each is 12db. The bass sounds louder and clearer on "normal" phase for preset 1, and louder/clearer on "reverse" phase for preset 2. 

Is this normal?


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## Avalanche (Jun 13, 2006)

Yes. When using a 12db slope the phase must be reversed on either the sub or the 6x9s to keep things in phase. 24db slope does not require this.


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## Sulley (Dec 8, 2008)

So what about a 18db/oct slope? on my headunit I have set filters at HPF of 12db and LPF of 18db.


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## Avalanche (Jun 13, 2006)

18db can be more problematic. You would need to experiment with xover points and listen closely to see if you can find a sweet spot that works. Certainly it can be done, as you will be in phase at some frequencies but not necessarily throughout the passband.


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## randysicko (Oct 22, 2009)

Thanks for the info! Now I'm wondering if the xover frequency point plays into this phase shift as well. I'm hoping not though because that would make for a lot more variables. So seeing that 12db would require a reverse phase setting... would that mean 6db and 18db will be out of phase no matter if I have it set to "normal" or "reverse"? Also, are there slopes that tend to work well together for sub, rears and fronts? 

I started reading about 90/360/etc. degree phase shifts, time delays, negative midrange responses.... head is sort of spinning now


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## Avalanche (Jun 13, 2006)

12db and 24db are the most common slopes used because the absolute phase issue is predictable. If you use 12db then reverse the phase on 1 set of drivers. This assumes that you have everything wired up correctly to begin with.

6,18,30db etc do not exhibit the same behaviour.

Now, when you also consider that time alignment, EQ and group delay will effect phase, it can be said with some certainty that no matter which slope is chosen, phase issues will exist. Using 12/24db slopes should eliminate some issues and make the other issues easier to resolve.

BTW-Group delay is usually modeled for subs. Typically there is several ms of delay at lower frequencies and little above 125hz. This is a function of the sub and enclosure design. 

Time alignment will dramatically effect phase response through the passband where the drivers overlap and play the same frequencies. Obviously, the steeper the slope the smaller this overlap is going to be. Getting TA dialed in will result in a much flatter frequency response throughout this area.

EQ also effects phase but there is not much you can do if you need the EQing.

Consensus of opinion is that those odd slopes mentioned above can be easier to integrate at freqs above 2k. These freqs are more level dependent than phase dependent. From my personal experience however, phase differences are audible even up to 5-6k but will have less impact than getting phase wrong at sub/midbass frequencies.

Trying to get a handle on all these variables inside your noggin is one thing-you will get it with enough reading. Applying what you have learned will lead to massive frustration in your vehicle. You will need to be patient and experiment. Set your slopes at 24db if possible and work from there. If I had to suggest one area to focus on it would be an understanding of proper TA.


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## randysicko (Oct 22, 2009)

Thank you very much for such a comprehensive reply...I will take the advice and do some research on my own to gain some more knowledge on these subjects


For now, I will stick with a 12 or 24db slope to minimize the phasing issues... I rarely us 6db and I never use 18db anyways. Im the kind of person that always tweaks stuff...even after I have it how I like it...so im no stranger to frustration when it comes to car audio tuning.

Proper TA is what Ive actually been trying to achieve for some weeks now. I started out using the IMPRINT tuning software, but I like how I can get everythng centered and sounding more "full" if I do the manual alignment. Lately, I've been going on what sounds good to me rather than what the exact speaker distance measurements are...but I notice that I have to tweak some settings MUCH more than originally measured. As an example, it looks weird TAing the FR to 40 inches more than any other speaker in the car, but to me, it sounds better. 

Most people say I want the LF with the most delay, but its the RF that has the clearest path to my ears.. plu im running 2ways AND the factory tweets up front so im sure that has something to do with the speed in which the higher frequencies reach my head. 

Im convinced this will be something Im always going to be toying with and its hard to enjoy the music until I know that im hearing it "correctly" if that makes any sense. But then again, some audiophiles would say that is where the fun comes in. I think Im starting to see it!


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## MarkZ (Dec 5, 2005)

randysicko said:


> Thanks for the info! Now I'm wondering if the xover frequency point plays into this phase shift as well. I'm hoping not though because that would make for a lot more variables. So seeing that 12db would require a reverse phase setting... would that mean 6db and 18db will be out of phase no matter if I have it set to "normal" or "reverse"? Also, are there slopes that tend to work well together for sub, rears and fronts?
> 
> I started reading about 90/360/etc. degree phase shifts, time delays, negative midrange responses.... head is sort of spinning now


It's not that easy. Although the speakers will be playing in phase if you reverse polarity on a 12dB/oct crossover, it may not arrive at your ear in phase. Especially if you haven't properly set your time alignment settings. And if you underlap or overlap your crossover points, you misalign the phase between the two speakers anyway.

Keep playing with the settings. If you're having trouble, start from scratch -- time alignment first, then crossover and polarity. Seek out someone with an RTA once it starts driving you nuts.


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## DarmoZ (May 20, 2016)

This was a good read, I too am discovering the joys and frustrations of tuning, months of fiddling (changing slopes on the HU, switching sub phase on HU, pulling my crossover out the door and trying all combinations of polarity shift).

But last night, I put all speakers back to the default of wired in phase, and then set the HU crossover at 24db slope...WOW everything sounds as it should now.

At 80hz crossover i get more clean punchy mid bass from the 24 then I do from the 12 or 18 even though they allow more low frequency to pass. before when using 6, 12 and 18 something always felt 'missing'. This must be because of the Phase because it sound correct now at 24db.

The way that I realised is by playing the Song 'Rio' by DJ Netsky at 3:17-3:20 there is a fast mid bass beat, this is mid bass because it only comes from the front and never the subwoofer (unless LPF is super high). Listen to this segment of the song over and over at the different Crossover slopes. Intuition tells you that the beat will have less punch as you move up into steeper slopes for High Pass (feeding less bass) and this is true, but when you reach 24 you should hear and hear it much more punchy and clean than the other slopes, as if the song has been restored!

Might not be the best or scientific way, but it worked for me and now every song of every genre sounds good now, no more fiddling with settings!

FYI: I use a Alpine HU, 4 channel amp to power the Components in the front (passive) and Coaxial in the rear, Sub is a JL Microsub+ (amp built in).


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