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Thread: A SMAART Question......it's about phase

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    Noob Jdunk54nl's Avatar
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    A SMAART Question......it's about time (really phase but play on words)

    I posted this in my build thread but figured it might be good to have a dedicated thread to this so others can easily find the answer too. I think this is an important question that can lead others to get much better tunes.


    I finished my tune the other day with these moving mic measurement results: The really good looking pink lines are the house curves.
    Click image for larger version. 

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    I also have access to Smaart v8 to measure phase in real time and this is where my questions stem from:

    Copied and pasted from my build thread:

    Ok question for some of you that may know ( @dumdum or @Justin Zazzi)

    This was my tweeter phase response after getting it the best I knew how.

    Purple is my left tweeter and dark green is my right tweeter.
    I circled in green where my questions stems from.

    Here are my questions:

    1) Should I even worry about this area since my crossover for tweeters is at 3500hz acoustically and it gets the weird wrapping phase at about 3000hz and that is -12db down?

    2) If I were to worry about this, how would I fix it? As in, if this was somewhere at like 8000hz in the middle of the response. I tried some all pass filters on this and nothing would fix it. They would shift the weird wrap either higher or lower, but nothing would get rid of it.
    Click image for larger version. 

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    Here are my mids, anything you see I should fix here? This one has a break in the phase at about 1290hz in the left mid (green). The right mid is the dark red. I tried an all pass filter but it didn't really fix it. I tired 2nd order and different q's for it. Do you worry about those?

    Click image for larger version. 

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    Here are mids to tweeters: Left mid is green, left tweeter is orange, right mid is pink, right tweeter is blue.
    Click image for larger version. 

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    Here are mids to woofers: Left mid green, left woofer bright green, right mid ink, right woofer brown

    Click image for larger version. 

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    Here are my woofers and subwoofers, I don't see much to fix here. Subwoofer dark green, right woofer red, left woofer blue: Note* I forgot to lower the sub by 6db (since both woofers playing will raise the total response by 6db and I want my subs 10db louder than the woofers, in the below graph they are 16db louder than an individual woofer) in this below graph before grabbing the screenshot. I realized this and double checked the phase by lowering it 6db and it didn't change anything (as it shouldn't) phase wise but forgot to grab a new screenshot of that.
    Click image for larger version. 

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    2014 F150 Limited -> Factory HU programmed for 4v outputs -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 in Valicar Stuttgart Pods, Rear SB17's, Sub BM MKV's in MTI BOX. Alpine PDX-F6 -> Peerless SLS 6.5", SI M3 in Valicar Stuttgart Pods

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    Re: A SMAART Question......it's about phase

    Final question about all of the above:


    Once I was done doing that work, I got into the truck and was listening. My sound stage seemed to be shifted a few inches to the left of center. I tried changing left side overall levels by lowering them but the stage didn't shift at all. Should I mess with the timing? That seems like it would then mess up the phase responses. I tried that and it did shift the stage if I increased the delay on the right side as a whole by a couple clicks, but I know this definitely impacts the phase response.
    2014 F150 Limited -> Factory HU programmed for 4v outputs -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 in Valicar Stuttgart Pods, Rear SB17's, Sub BM MKV's in MTI BOX. Alpine PDX-F6 -> Peerless SLS 6.5", SI M3 in Valicar Stuttgart Pods

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    Re: A SMAART Question......it's about time (really phase but play on words)

    It seems we really need a tutorial about what delay and all-pass filters do to phase and how to properly "fix" phase problems.

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    Re: A SMAART Question......it's about phase

    Quote Originally Posted by Jdunk54nl View Post
    Final question about all of the above:


    Once I was done doing that work, I got into the truck and was listening. My sound stage seemed to be shifted a few inches to the left of center. I tried changing left side overall levels by lowering them but the stage didn't shift at all. Should I mess with the timing? That seems like it would then mess up the phase responses. I tried that and it did shift the stage if I increased the delay on the right side as a whole by a couple clicks, but I know this definitely impacts the phase response.
    You really do need to forget about the position of the speakers, you say the stage was a few inches left of centre… centre of what? The car or between the perceived location of the hard left and right of stage, the latter is what you should be listening for…

    most cars with pillars or dash mounted drivers have a reflection on the drivers side window

    think how we hear, we get the location of a sound source from all sources of sound, so if you have strong reflections from the side window and above the driver then we will ‘hear’ the source of the sound as being outside the speaker towards the side window…

    and also the passenger side we hear the sum of all the sound sources… it’s not uncommon to hear the passenger side several inches in from the pillar or speaker location…

    so we can have two sources of sound that are over to the left… what will that do to your centre if it is timed correctly and between left and right as our brain decides there location? Just what you experience

    people get hung up on the centre of the car being the centre, work out where your stage boundary’s are and then work out where the centre should be located… it’s likely not the centre of the car!

    as for the phase, don’t get hung up on worrying about phase wraps above midranges and somewhere around 2khz, tbh I only tend to use all pass below 1khz max, installation location of drivers to get clean phase is far more important in the first instance

    clean phase between two drivers gives depth of stage, along with correct eq work and freq response

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    Re: A SMAART Question......it's about phase

    @Justin Zazzi's response in my build thread: https://www.caraudiojunkies.com/show...-Limited-Build
    Copied and pasted

    I would not worry about phase alignment above 1kHz 'ish. If your tweeters are Goofy at 8khz, I wouldn't bother.

    If you wanted to though, I think all pass filters are a good start. They can only bend the phase trace one direction so if you're not getting what you want, try all pass filter on the other channel instead.

    It is curious to see the knee in phase response though. Usually I see a sharp transition like that when I'm measuring a 2 way or a coaxial set because the acoustic center of the midrange and tweeter are different distances from the mic. So in that case the phase plot would be two straight lines that intersect somewhere, and you get a shape that looks much like your tweeter phase does.

    I would double check that the frequency response is what you think it is. Frequency and phase response are linked so adjusting one can help the other match.

    Oh, also reflections.



    Second Response from Justin Copied and Pasted:

    A couple clicks of time alignment is insignificant phase change in the lower frequencies where phase becomes more meaningful. If you can improve your stage with a small time adjustment, go for it?

    I would also focus on what frequencies in the stage are not centered. Have you tried playing bandwidth limited pink noise tracks? I would try that with only one pair of channels engaged at a time, like woofers only, then mids only, etc. Somewhere around here we have some Tuning Stones that work great for this
    2014 F150 Limited -> Factory HU programmed for 4v outputs -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 in Valicar Stuttgart Pods, Rear SB17's, Sub BM MKV's in MTI BOX. Alpine PDX-F6 -> Peerless SLS 6.5", SI M3 in Valicar Stuttgart Pods

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    Re: A SMAART Question......it's about phase

    Quote Originally Posted by dumdum View Post
    You really do need to forget about the position of the speakers, you say the stage was a few inches left of centre… centre of what? The car or between the perceived location of the hard left and right of stage, the latter is what you should be listening for…

    most cars with pillars or dash mounted drivers have a reflection on the drivers side window

    think how we hear, we get the location of a sound source from all sources of sound, so if you have strong reflections from the side window and above the driver then we will ‘hear’ the source of the sound as being outside the speaker towards the side window…

    and also the passenger side we hear the sum of all the sound sources… it’s not uncommon to hear the passenger side several inches in from the pillar or speaker location…

    so we can have two sources of sound that are over to the left… what will that do to your centre if it is timed correctly and between left and right as our brain decides there location? Just what you experience

    people get hung up on the centre of the car being the centre, work out where your stage boundary’s are and then work out where the centre should be located… it’s likely not the centre of the car!

    as for the phase, don’t get hung up on worrying about phase wraps above midranges and somewhere around 2khz, tbh I only tend to use all pass below 1khz max, installation location of drivers to get clean phase is far more important in the first instance

    clean phase between two drivers gives depth of stage, along with correct eq work and freq response

    It was left of center of dash. You are right, I need to rethink what center should be.

    I did find out one of the reasons, apparently I sit shifted to the left, if I sit in the middle of my seat like you are supposed to, it is centered. I moved my head about the same distance the center image was off and this fixed most of the issue. I guess if I want to continue to sit like that, I need to make sure my microphone is actually in that position that my head would be in, and not in the middle of the headrest like I had it when measuring in the above. It is a difference of a few inches.


    Also, thanks for the info on phase, it corresponds with Justin's advice too. This is why I asked. I figured it was something that the data is showing me but my ears can't really interpret. I know at those frequencies it is usually more volume dependent than it is phase dependent for positioning. Sometimes we need to learn to ignore some of the information our measurement devices are giving us. I have been better at this with REW, but not with smaart.


    Unfortunately, I am not skilled enough nor do I want to get into all of the work it takes to proper position drivers beyond what they are. My tweeters and mids are currently in Valicar pods and the tweeters (swivel mount option) are angled to the best I could get with their swivel mounts and within their location limitations to mount them without doing way more work or cutting things I am unwilling to cut.
    2014 F150 Limited -> Factory HU programmed for 4v outputs -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 in Valicar Stuttgart Pods, Rear SB17's, Sub BM MKV's in MTI BOX. Alpine PDX-F6 -> Peerless SLS 6.5", SI M3 in Valicar Stuttgart Pods

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    Re: A SMAART Question......it's about phase

    Also, I really love that we can have these deeper conversations on this forum, as in, there are people that can answer and I trust their answers.
    2014 F150 Limited -> Factory HU programmed for 4v outputs -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 in Valicar Stuttgart Pods, Rear SB17's, Sub BM MKV's in MTI BOX. Alpine PDX-F6 -> Peerless SLS 6.5", SI M3 in Valicar Stuttgart Pods

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    Re: A SMAART Question......it's about phase

    It's a little off but closely related to the topic but... Justin Zazzi mentioned the "Tunning Stones" method which always makes me smile I have been playing around with using the NPR Tiny Desk Concert Series to help with visualizing the staging. I stole it from Matt Schaeffer and Gary Bell as they talk about it on their podcast, its something they use when verifying staging in their work and when demoing vehicles for the customer. I wonder what your experience would be with it??? I have been fortunate enough to hear your latest tune which sounds fantastic and when i was in the driver's position everything appeared to play very transparent, sounds came from where they should, i could mentally see what i was hearing and the overall experience left me rethinking my approach and as you set a high bar for me to try to reach!!!

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    Re: A SMAART Question......it's about phase

    I wish I could chime in helpfully here... but I can't.
    I'm going to be playing with my first AP filters in my own DSP install, first I've ever personally owned, and first I've taken further than an initial tune - which still isn't complete.

    I definitely want to get my hands on SMAART because so SO SO much is hidden invisibly and potentially frustratingly, after you've done your EQ-ing, aligning, and even acoustical interior treatments. I've never had it that tool OR a way to mitigate those issues, so being able to actually MEASURE those phase shifts, apply AP filters, then observe your impact in the phase realm - just awesome.


    I suspect your phase anomolies are actually DUE to your crossovers - as the sound rolls off below the high-pass frequency, there is a phase shift, no matter whether you picked bessel or butterworth or linkwitz-riley or anything - in fact that's the reason system designers have historically tried to use as few drivers as possible. Ideally a single point-source driver would most accurately reproduce the sound because it is perfectly phase-correct. Even if you had a mid and tweeter that were theoretically perfectly flat in dB level from 20hz up to 20khz and beyond, you need that crossover point - which even if perfectly aligned so there's no dip in frequency response, it does mess up the phase on both side of the Xover point... for the tweeter, below it, and for the mid, above it.
    The steeper the slope, the faster they roll off, but also the faster the phase shift happens.
    Traditionally it's been impossible to really correct for this - but it seems like with the right tools and DSP/filters - I mean wow, this really is one of the old-school fundamentals being tackled here.

    If - *if* you could actually flatten the frequency response across a crossover point, AND flatten the phase response across the crossover point, you absolutely could dramatically improve your imaging.
    I almost typed "to the degree where you emulate that theoretical-ideal point-source driver", but unfortunately the complex reflections in our car interiors would prevent us from QUITE getting to that perfect ideal, since the two drivers do need to be in two different locations in space physically - but maybe it would open the door for systems more like my current install (sub... midbass... midrange... wideband... tweeter... read "way too many Xover points for phase coherence) to be as good as my old-school ideal systems for imaging (sub... 6.5 midbass/midrange... tweeter that can reach from below 2khz to over 20khz). The old school ones WERE difficult to nail imaging particularly right around the Xover point - which had everything to do with this phase shifting, and that's a fascinating aspect of Psychoacoustics...
    Consciously, you can't really "listen" for phase.... other than being aware that the image isn't correct. And it's entirely your subconscious recognizing that the sound isn't exactly correct. It's completely what led me to be fascinated with the very concept of imaging.
    Still - what a tool, so effing cool... At least to a geek like me.

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    Re: A SMAART Question......it's about phase

    It really is an amazing tool. Especially to use polarity flips, all pass filters, other ways to impact phase. Once you are done, there is no second guessing your time/phase alignment. Much like when you are done with REW, there is no second guessing your frequency magnitude response (unless you did something wrong). I can't go back to not using SMAART just like I can't stop using REW (well if smaart would ever implement an EQ window like REW has I would stop using REW)

    If you don't have smaart though, head on over to https://opensoundmeter.com/en/
    It is a free version of smaart that does nearly everything smaart does.
    2014 F150 Limited -> Factory HU programmed for 4v outputs -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 in Valicar Stuttgart Pods, Rear SB17's, Sub BM MKV's in MTI BOX. Alpine PDX-F6 -> Peerless SLS 6.5", SI M3 in Valicar Stuttgart Pods

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