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Thread: Summing at crossover - LR24db/BU24db

  1. Back To Top    #11
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Summing at crossover - LR24db/BU24db

    Quote Originally Posted by Cathul View Post
    Well, looks like those were created correctly.
    The three individual files also sum together correctly to the overall target.

    If you use the tape measure method for time alignment then it should work out nicely.

    I can only imagine you're doing something in REW or in your processor that you don't realize.
    Can you upload the REW save file so we can have a look?
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
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  2. Back To Top    #12
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    Re: Summing at crossover - LR24db/BU24db

    Quote Originally Posted by SkizeR View Post
    remember, you're almost never going to get a 6db sum in the car. reflections will show up as phase discrepancies in crossover regions. Also, why delay a half wavelength when you could just flip polarity?
    Good question.

    I don't know if this is true, but i've read that to have the bass and midbass in phase in the crossoverregion and account for the 360° phase shift due to LR24db (180° forward on highpass, 180° lag on lowpass) you have to add a wavelength of delay in addition to the calculated delay from distance.
    One wavelength at 63Hz is around 15.8ms, so larger than the max delay i can use. So i thought it would be a good idea to add halve a wavelength of additional delay to account for the additional delay caused by the crossover and flip the polarity to get back in phase again.

    If you say "screw that" i'll remove it and flip phase back to where it was.

    Edit: one thing i just remembered and that bugs me now is that when i only use the calculated delays i have a deep null at the crossover. I think i have to check the polarity of the speakers again.
    Also looked at the setup that the installer did after the physical installation of the equipment. He did use Butterworth 12db slopes all around with almost no eq and no polarity flip on any speakers, but some weird delay settings. Maybe instead of flipping delay as needed he just added delay until the speakers summed up.
    Last edited by Cathul; 05-20-2020 at 01:02 AM.
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  3. Back To Top    #13
    Noob Cathul's Avatar
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    Re: Summing at crossover - LR24db/BU24db

    Quote Originally Posted by Justin Zazzi View Post
    Can you upload the REW save file so we can have a look?
    Sure thing... 20200519_preset_4_stage1.zip
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  4. Back To Top    #14

    Re: Summing at crossover - LR24db/BU24db

    Quote Originally Posted by dumdum View Post
    All pass filters won’t work Likely because it’s a room mode, and it’s a result of the direct sound and a reflection cancelling, an all pass can’t do direct without effecting the reflection also, so the cancellation remains if that makes sense

    if your dash speakers don’t sum 6db lower down then they aren’t timed correctly or you have massive reflection issues if above the dash with glass around them
    Ok, I'm a little confused here. Earlier in this thread, you said this:

    "The only time I’ve ever got a full 6db of summation is while using smaart to actually set delays and phase by a mic positioned between the ears and then adjusted the delays to suit, of I do this I can sum my front midbass and get a full 6db between them, that means they are perfectly in phase"

    But now you are saying that I actually *should* be getting 6dB of summation with my dash speakers - at least "lower down" - and if I don't, then something is wrong. :-) Obviously, I'm not using smaart, so it sounds like I really *won't* be getting 6dB of summation after all.... ?

    I've had multiple people tell me that 3dB to 4dB of summation for my dash speakers is actually pretty normal and has something to do with the wavelengths and the size of the car interior - or something along those lines. I've measured, re-measured and re-re-measured the distances to my dash speakers, so I know they are correct. I'm sure that there most certainly are reflections with the dash speakers since they in stock locations and point pretty much straight up into the windshield.

    But what I'm trying to clarify is the 6dB summation part. From everything I've read, you'll rarely get a full 6dB of summation - especially for mid/high frequencies - and that you can sometimes get close to a full 6dB of summation with midbass frequencies (which I do get, for the most part).

    Just trying to get clarification.

    I'm curious to see what kind of summation @Cathul gets when he measures L+R speaker pairs.

    Thank you.
    Last edited by jtrosky; 05-20-2020 at 10:44 AM.

  5. Back To Top    #15

    Re: Summing at crossover - LR24db/BU24db

    Quote Originally Posted by jtrosky View Post
    Ok, I'm a little confused here. Earlier in this thread, you said this:
    "The only time I’ve ever got a full 6db of summation is while using smaart to actually set delays and phase by a mic positioned between the ears and then adjusted the delays to suit, of I do this I can sum my front midbass and get a full 6db between them, that means they are perfectly in phase"

    But now you are saying that I actually *should* be getting 6dB of summation with my dash speakers - at least "lower down" - and if I don't, then something is wrong. :-) Obviously, I'm not using smaart, so it sounds like I really *won't* be getting 6dB of summation after all.... ?

    I've had multiple people tell me that 3dB to 4dB of summation for my dash speakers is actually pretty normal and has something to do with the wavelengths and the size of the car interior - or something along those lines. I've measured, re-measured and re-re-measured the distances to my dash speakers, so I know they are correct. I'm sure that there most certainly are reflections with the dash speakers since they in stock locations and point pretty much straight up into the windshield.

    But what I'm trying to clarify is the 6dB summation part. From everything I've read, you'll rarely get a full 6dB of summation - especially for mid/high frequencies - and that you can sometimes get close to a full 6dB of summation with midbass frequencies (which I do get, for the most part).

    Just trying to get clarification.

    I'm curious to see what kind of summation @Cathul gets when he measures L+R speaker pairs.

    Thank you.
    Smaart enables you to see live phase traces and set delays very accurately, and note what I said about the lower midrange and 6db of summation, upper midrange and treble as you say you are lucky to get 3-4db of summation

    smaart is relatively new to me, so when I say the only time... it’s because it’s the only tune I’ve actually concentrated on it, I’ve not tried phase aligning mids and then summing them also, it should give a good amount of summation though... I will check the laptop later and see if I have any graphs I can utilise 👍🏼

    dash speakers play into the 500hz region so I would consider it a win if I got 6db of summation at the bottom end of there register, that means reflections not withholding the bottom end at least is in phase... as you get higher the wavelengths are indeed shorter and so it’s far harder to measure them and get good phase traces, it’s far better to measure around the ears and check for the best summation at the crossover points As the brain is far less phase dependant at higher frequencys

    i am about to make new a pillars and have a dashboard back for the first time in ages so I will be measuring lots of times in both smart and rew perhaps (rew has some greater functionality when it comes to averaging two measurements which smaart does have, but I’ve worked with rew for ages and i feel far more confident playing with it), I will doubtless post up lots of measurements so I will endeavour to share them in here as well as my build thread
    Last edited by dumdum; 05-21-2020 at 02:48 AM.

  6. Back To Top    #16

    Re: Summing at crossover - LR24db/BU24db

    I’ve just had a look and I do have a trace that illustrates 6db of summation...

    it also shows a phase issue at 350 which I’ve moved to the centre of the phase trace view and the resulting dip in the response where summation sucks ass

    i don’t unfortunately have the other sides response at the same input level as I adjusted the mic input for other traces, but you can clearly see I get 6db of summation at a fair few places (the reason I appear to get a little more in some places and less in others is the responses don’t perfectly match due to a static mic, but the midbass do match pretty well as a static mic is effective at those frequencys
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  7. Back To Top    #17
    Noob Cathul's Avatar
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    Re: Summing at crossover - LR24db/BU24db

    Quote Originally Posted by jtrosky View Post

    I'm curious to see what kind of summation @Cathul gets when he measures L+R speaker pairs.

    Thank you.
    Up to 6db in Bass/Midbass and up to 3db for left+right in midrange/tweeters... So exactly like you.
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  8. Back To Top    #18

    Re: Summing at crossover - LR24db/BU24db

    I actually had a look on rew after I posted the phase trace above and I found the below...

    I do get 6db through my mids in bunches with 3-4 between and the old phase issue where I get 1, but a good sign is getting at least 6db in a fair few places, if not you perhaps need to reposition drivers to make the summation better (I’ve been through 20 odd locations and aimings on top of my dash before settling on where my mids are now to get individual sides as good as they are now )

    it’s not a nice task and I get that most can’t do what I’ve done (in the sense of cutting the top off a dash board and trying loads of places! Not I’m some kind of special... well I am special... but not like that lol), but sometimes it’s only 2-3” away from the screen or a different aim that can transform a stage from average to excellent 👍🏼

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    Noob Cathul's Avatar
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    Re: Summing at crossover - LR24db/BU24db

    Well, my last measurement from left and right was before i redid the time delay, so i have to remeasure anyway... will do that in the next days.
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  10. Back To Top    #20

    Re: Summing at crossover - LR24db/BU24db

    5-6db from 150, phase issue at 350 the good summation after that, then a mixed bag of 3-4 after that 👍🏼 At the top end it gets hard with a moving mic to see how the summation goes, but the lower registers sub 5-700 are good to test even with mids for how well your drivers are phase aligned, that’s 1/48th octave with zero smoothing...
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