Sub level and how it effects phase alignment and crossovers

D

dumdum

Noob
So this is a follow on from Steve Weigner (@captainobvious) and Erins you tube podcast type thing...

someone asked if adjusting sub level would effect phase between the sub and midbass driver...

the answer is... it depends how good your timing/crossover settings are and any phase issues in the area

let me post some pictures of smaart with examples if I can get them to work of my own system...

so I’ve found an example that’s useable, let’s run with it... we have a phase trace of my sub and my right front mid... so as you adjust timing the line pivots around an imaginary point to the far left of the picture

so this pic is the same driver with different delay settings, that’s it, no phase (allpass adjustment in a helix) so as you see the lower the frequency the less effect time delay has on it, this is what your altering at a given frequency when you adjust time alignment

imagine this is a picture of a slice across frequencys of phase at the listening position
 
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So for my next pic this is the midbass added to the picture of the sub set to be in phase with the mid at the crossover region... which looking at these I’d make somewhere between 99.6hz where the crosshairs are and an octave further up around 200ish...
 
Good so far... ideally you’d want a big overlap of phase at various crossover points as increasing levels changes the crossover relationships

so with the sub on -6db you would end up with a crossover around 125, and as you can see we are in phase here and 1/3 of an octave below it, this would likely mean a good degree of summation at the crossover point...
 
So as we put the sub to -3db this is now putting the crossover right in the optimum place for the phase to be good above and below... this is where you’d put the crossover for maximum summation through the crossover and give a good impression of upfront bass, the relationship between the two drivers is as good as you can get given this phase relationship... this is good, you would get 6db of summation at the listening position and a good sense of the two drivers being as one and to be pulled to eye level on the dash

you can see the crossover in the bottom window is now moved up to approx 135 but this is a good place
 
Now with the sub level at 0db you can see the crossover has moved up some more to approx 150hz, this would still give a good summation through the crossover falling off a little bit at the top side where the responses phase drifts apart slightly (I normally aim for 30 degrees each way to get a good crossover...)
 
The level doesn’t change the timing, frequency to frequency will remain stable to the line in the phase graph for the sub will stay overlaying or running parallel to the midbass drivers trace

now to the rub, I have smaart and can do this because I can see phase live and tweak timing and phase to get it to overlay the midbass phase trace very well!

now then...

let’s try an extreme example... the settings of the first pics other sub angle, we would stand no chance of getting the crossover to work at 125-160 as per above... however imagin we wanted a crossover of approx 172... you adjusted your crossover so you got summation at a set sub level... you get 6db of summation but some funny dips either side (I don’t have a pic of this... but it would look mighty peaky... but this is an example so I’ll run with it...

so you set your crossover at 172 and get a good phase relationship at the freq and it drifts out either side... but you get 6db of summation so it’s good... or so you think...
 
Now let’s move the sub level up 3db and see what happens...

the crossover point now moves up to 183hz... you now have the phase correct below the crossover point, and drifting out of phase by 70 degrees at the crossover point and so you would then lose any sense of timing (even more above that) and the sub would likely pull to the subs location and you’d hear two different locations for each and they would seem out of time a fraction...

the same result would happen with a lower level away from the good phase crossover point...

the graphs all show the importance of good timing, I guess an easy way to check would be to move the crossover up 20hz and see if you still get 6db of summation... and the same for below... if you do then your timing is pretty good for the crossover...

the other thing worth noting is that in a reflective environment like a car you often get wrinkles and changes in phase as you move up the frequencys, sometimes delay settings are a bit off the charts with smaart, but you can sometimes get away with it by swapping phase and adding less delay or more delay and using a different delay... if I get chance I will show you just that, two good phase relationships... but with the drivers out of phase as we would think of it, but with different timings on each, one will normally be better than the other, but sometimes the phase plot is a gentle curve and you can do it both ways and get a good crossover
 
I hope this helps, I can’t recall who it was that asked the question... but if they are on here hopefully this helps... it’s always about timing and phase 👍🏼 Get that good and you can then often adjust a sub level and still get a good relationship at the listening position...

As an example I have two front subs and I have the phase and timing of the rear sub nailed... I can add 12db of bass at 20hz tapering down to 0db added around 80hz and it doesn’t pull back at all, only because the phase and timing at the listening positioning is nigh on as good as I can dial in... it drifts a bit at very low frequencys due to one being a 15 and one being a 10” (low frequencys often lag a little I think I have read somewhere more so with some drivers vs others...)

but at low frequencys due to wavelengths concerned it’s harder to get them in phase to a degree as the time has to be much larger and as long as you are within 60 degrees you still get a good amount of summation and don’t miss much...
 
dumdum said:
I hope this helps, I can’t recall who it was that asked the question... but if they are on here hopefully this helps... it’s always about timing and phase [emoji1360] Get that good and you can then often adjust a sub level and still get a good relationship at the listening position...

As an example I have two front subs and I have the phase and timing of the rear sub nailed... I can add 12db of bass at 20hz tapering down to 0db added around 80hz and it doesn’t pull back at all, only because the phase and timing at the listening positioning is nigh on as good as I can dial in... it drifts a bit at very low frequencys due to one being a 15 and one being a 10” (low frequencys often lag a little I think I have read somewhere more so with some drivers vs others...)

but at low frequencys due to wavelengths concerned it’s harder to get them in phase to a degree as the time has to be much larger and as long as you are within 60 degrees you still get a good amount of summation and don’t miss much...
Click to expand...
If you're using Windows 10 on that computer, you can press "Windows button"+Shift+S to take screenshots, full screen, just a window, or a smaller area. It's better than a phone pic.
Currently, I'm using a 160 hz low passed signal (varied by subwoofer level control) that is mixed into my midbass and is also low passed for my subs, it seems to alleviate some of these problems. What are your thoughts on that?
 
ckirocz28 said:
If you're using Windows 10 on that computer, you can press "Windows button"+Shift+S to take screenshots, full screen, just a window, or a smaller area. It's better than a phone pic.
Currently, I'm using a 160 hz low passed signal (varied by subwoofer level control) that is mixed into my midbass and is also low passed for my subs, it seems to alleviate some of these problems. What are your thoughts on that?
Click to expand...
Are you using virtual channels in a helix dsp? If you mean the bottom end of the midbass level also changes with the sub level then that will make the crossover remain the same as if the sub goes up by 6db so does the adjoining part of the midbass, if that’s what you’ve done it’s a good solution... it means your phase relationship will remain the same as it’s at the same point whatever the sub level is set to 👍🏼
 
Hey Dumdum, what version of Smaart are you using? Di or V8? Also what microphone(s) and I/O device if you are using one? I am very tempted to finally purchase my own copy and am leaning towards the di version.....
 
Also, for those that want to play with phase, you can do a little of that with REW and the alignment tool. To get to it, you need a newer version of REW.
Take IR measurements by pressing the measure button (not RTA).
Go to the ALL spl tab and click the gear icon.
Click the alignment tool.
Select the two drivers you want to phase align
Adjust the delay of one or the other to get the phase to match up around the crossover.
If negative delay, the speaker is closer than the other, if positive, it means that speaker is farther away than the other.

You can also see how the FR above is impacted by the delay. This isn't "real time" like Smaart, but you can at least take one measurement of each driver, use the tool, then make a change and see how it works. It used to be every change you had to take another measurement.

YMMV with this, I haven't had great luck using this and setting the delays suggested, the center image is always off when I do.....I am sure it is user error.

Note 1* Unfortunately the dsp I am using for this vehicle has maximum delay of 8ms :(
Note 2* Make sure if you are doing this, you set your sub level appropriately for measuring against a single speaker. My subs are 6db higher than a single speaker but with both mids playing the sub level crosses with both mids at 80hz.

View attachment 15062


This is the generated minimum phase version and levels adjusted (via rew and measurement action button), maybe this is what I need to use ???

Edit* just played around with this, it gave me the same time alignment of ~2.20s for EVERY driver except sub at 0...This would not give me a center image....
View attachment 15063
 
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Jdunk54nl said:
Hey Dumdum, what version of Smaart are you using? Di or V8? Also what microphone(s) and I/O device if you are using one? I am very tempted to finally purchase my own copy and am leaning towards the di version.....
Click to expand...
Smaart di2 which is a stripped down version of 8 with only two inputs and one transfer function at a time

i use a focusrite 2i2 and a Dayton mic currently, although I am considering an earthworks m23 :)
 
dumdum said:
Are you using virtual channels in a helix dsp? If you mean the bottom end of the midbass level also changes with the sub level then that will make the crossover remain the same as if the sub goes up by 6db so does the adjoining part of the midbass, if that’s what you’ve done it’s a good solution... it means your phase relationship will remain the same as it’s at the same point whatever the sub level is set to [emoji1360]
Click to expand...
MiniDSP 8x12, with a physical loopback for both front and subs (both to avoid differing delays from the extra pass through the dsp).
 
dumdum said:
Are you using virtual channels in a helix dsp? If you mean the bottom end of the midbass level also changes with the sub level then that will make the crossover remain the same as if the sub goes up by 6db so does the adjoining part of the midbass, if that’s what you’ve done it’s a good solution... it means your phase relationship will remain the same as it’s at the same point whatever the sub level is set to [emoji1360]
Click to expand...
I don't think the virtual channels in the Helix allow that, but I don't own one, I just read the manual. It would be nice if that were possible in any dsp's software without the extra external connections.
 
Jdunk54nl said:
Also, for those that want to play with phase, you can do a little of that with REW and the alignment tool. To get to it, you need a newer version of REW.
Take IR measurements by pressing the measure button (not RTA).
Go to the ALL spl tab and click the gear icon.
Click the alignment tool.
Select the two drivers you want to phase align
Adjust the delay of one or the other to get the phase to match up around the crossover.
If negative delay, the speaker is closer than the other, if positive, it means that speaker is farther away than the other.

You can also see how the FR above is impacted by the delay. This isn't "real time" like Smaart, but you can at least take one measurement of each driver, use the tool, then make a change and see how it works. It used to be every change you had to take another measurement.

YMMV with this, I haven't had great luck using this and setting the delays suggested, the center image is always off when I do.....I am sure it is user error.

Note 1* Unfortunately the dsp I am using for this vehicle has maximum delay of 8ms :(
Note 2* Make sure if you are doing this, you set your sub level appropriately for measuring against a single speaker. My subs are 6db higher than a single speaker but with both mids playing the sub level crosses with both mids at 80hz.

View attachment 15062


This is the generated minimum phase version and levels adjusted (via rew and measurement action button), maybe this is what I need to use ???

Edit* just played around with this, it gave me the same time alignment of ~2.20s for EVERY driver except sub at 0...This would not give me a center image....
View attachment 15063
Click to expand...
Mute one channel of input before the subs are mixed in to get an appropriate level.
 
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