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Thread: Do you time align your drivers ?

  1. #1
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    Do you time align your drivers ?

    Hello to Everyone
    First of all thank you very much for this extremely interesting source of audio informations.
    Second, I am very beginner but eager to learn as well.

    I understand that when the centers of emission of drivers are not equally distant from the listening point they must be time aligned.
    1) Is there a tolerance on this distance difference ? an acceptable gap ?
    2) How do you perform this alignment ? actively with an active crossover or passively ?
    3) Is this issue overrated for home applications ?

    Thank you sincerely and kind regards,
    Gino

  2. #2
    Senior Member BMWCCA's Avatar
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    Sounds like a question intended for the D.I.Y. forum. There are several examples of time-aligned consumer systems from JBL such as the L250, 250ti, and the L-series such as the L7 which simply use slanted baffles to "correct" driver alignment passively if that's what you're asking. Since you seem to be specifically asking about consumer systems, and it's early here and I've nothing better to consider :

    Personally, from an untrained and uneducated audio dabbler, I just don't get the physics of the concern. Knowing the speed of sound and that even the worst case of miss-alignment in a normal home system is usually not much more than ten-inches, if we call it twelve-inches (on English foot) that would make the differential in time for the sound to hit your ears of even the most-poorly aligned drivers at something like 0.0009 seconds, regardless of your distance from the speaker. Without compression drivers and horns (L7, 250ti) that disparity is even a fraction of that tiny figure.

    I realize the human brain and hearing's ability to discriminate such differences is truly amazing, and important to the species' survival much as is binocular vision, and I have no idea what the threshold of that ability to discriminate the difference, or correct for it, is. I'm sure there's more to the issue that I'm missing, like perhaps harmonics, but the name "time alignment" seems to imply a simple application of physics and the known speed of sound. If I'm missundertanding it, I'm sure the engineers here will correct my assumptions. Even those from the land down-under where they have their own laws of physics.

    As a competitive swimmer (in a distant past), we were always taught to launch on the smoke or spark from the starter's gun rather than the sound, so I realize we're a remarkable species in how we process subtle difference in sight and sound even over short distances.

    My assumption has always been that true time-alignment is important only in live-sound reinforcement for large installations or where repeating systems are used for PA or SR over a large area. I'm happy to be properly educated concerning the problems in my assumptions and how the phenomenon really applies.
    ". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers

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    Thank you very much for your kind and helpful reply.
    Moreover I am really sorry to have posted in the wrong forum.
    I would be grateful if anyone could redirect this 3D in the correct forum.

    Kind regards,
    gino

  4. #4
    Administrator Robh3606's Avatar
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    I try too when I build my DIY stuff. I use the step response to see how well integrated they look. You have to remember that the alingment is only good in a specific window, point in space, so you shoot for alignment in your listening window.

    1) Is there a tolerance on this distance difference ? an acceptable gap ?
    Good question obviously you don't want extreme path lengths it also skews the null lobes which can be an issue. You don't want a null on axis.

    2) How do you perform this alignment ? actively with an active crossover or passively ?
    I used physical driver alignments with a passive crossover. My active system I have not really addressed it and never measured to see what the step response looks like. It sounds fine so don't fix what's not broken.

    3) Is this issue overrated for home applications ?
    Who knows? Looking at the step response of a 4344 the integration is not all that good at all but it doesn't stop it from being a fine sounding speaker. That said I feel better when the step resonse looks good

    Rob
    "I could be arguing in my spare time"

  5. #5
    Senior Member rdgrimes's Avatar
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    Having the L250 with it's time-aligned baffle I have assumed that at least some of what I really like about this speaker is just that. It has a "cohesiveness" and clarity that really shouldn't be due to the drivers or XO themselves. (Having similar drivers and XO in other systems where I don't hear the same level of clarity). In short, I'm sold on the alignment for lack of anything better to point to for the origens of this clarity. It just sounds "right", and listening fatigue is non-existent. It's also true that in the case of the 250s, there are other design features that may well be contributing.

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    I try too when I build my DIY stuff.
    I use the step response to see how well integrated they look.
    You have to remember that the alingment is only good in a specific window, point in space, so you shoot for alignment in your listening window.


    Thank you very much for your kind reply.
    I realize that the all procedure involves sophisticated equipment I cannot access to, unfortunately.
    I will try to get points of emission alignment in a vertical plane, caring to keep the middle point between the drivers on ear axis (please excuse my very poor english. I have not been able to improved it even if I am trying)

    Good question obviously you don't want extreme path lengths it also skews the null lobes which can be an issue.
    You don't want a null on axis.
    I used physical driver alignments with a passive crossover


    This is much more difficult for me to understand. Too technical I am afraid.

    My active system I have not really addressed it and never measured to see what the step response looks like.
    It sounds fine so don't fix what's not broken. Who knows?
    Looking at the step response of a 4344 the integration is not all that good at all but it doesn't stop it from being a fine sounding speaker.
    That said I feel better when the step resonse looks good
    Rob


    But this is very important I think.
    If I understand well you are listening to a 4344 system without any kind of time alignment and nevertheless get an accurate response ?
    How is the soundstage rendition of the system ?
    Do you even get a good image depth ?
    I know that also the listening room plays an important role
    I am looking for that so much amazing effect when it seems that sounds come from points beyond the front wall.
    I live in a small flat ... this would give a nice sensation of living in a much bigger space ...

    Thank you very much indeed
    Kind regards,
    gino

  7. #7
    Senior Member BMWCCA's Avatar
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    Quote Originally Posted by ginetto61 View Post
    If I understand well you are listening to a 4344 system without any kind of time alignment and nevertheless get an accurate response ?
    How is the soundstage rendition of the system ?
    Do you even get a good image depth ?
    I know that also the listening room plays an important role
    I am looking for that so much amazing effect when it seems that sounds come from points beyond the front wall.
    I live in a small flat ... this would give a nice sensation of living in a much bigger space ...
    I have the 4345s in a tiny living room. Nothing time-aligned about those big boxes! And yet when I sit on the couch and close my eyes I'm immersed in the performance. Granted some recordings are much better than others, but my impression of the soundstage is that it's darn good. But then I'm the guy who thinks L7s aren't that finicky when it comes to placement and I enjoy walking around them in the same room and enjoying the feeling of being in the middle of the performance. So, once again...:dont-know
    ". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers

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    Administrator Mr. Widget's Avatar
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    Re: Do you time align your drivers ?

    This is an interesting question and one that I hope to someday do some serious studying of.

    First of all, audio is full of pseudo scientific BS and worse. Bearing that in mind, if a speaker is advertised as being time aligned, I wouldn't assume it necessarily to be true.

    So what is time alignment? As far as I know there are three types.

    A full frequency driver such as a single full range cone or an electrostatic panel. These will inherently be time aligned.

    A properly designed coaxial driver can be time aligned.

    Lastly we have the vast majority of speakers claiming to be time aligned. These typically have a sloped baffle or a series of baffles that are stepped back. This design can only be really time aligned on axis and at one specific listening height. I am not so sure these designs are truly ever time and phase coherent in absolute terms in the real world.

    So how important is time alignment?

    That is a huge question. as Mr. BMW said, his 4345 clones are far from time aligned, a horn based speaker with a baffle mounted 2405 will have a step (impulse) response that shows a distinct separate arrival time from the tweeter and horn by several milliseconds. Does this make them unlistenable? No. Can everyone hear this? No. Can anyone hear this? I don't know. I'd like to find out.

    That said, when you take a system like the 4345 and correct it's time alignment, it will sound different... better? I am not sure. This is an area that I find most interesting.


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    Administrator Robh3606's Avatar
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    Hello Gino

    Just to see what we are talking about here are a couple of Step Response measurements. First one is a DIY biamped 3 way and the second a biamped 4344. The step response from a 4345 is going to be very similar. You can see all 4 drivers with the 2405 first the 2122 a close second then the woofer out of phase with the 2425 right in the middle of the woofers response. It's the physical offset of the 2425 mounted on the 2307 that really skews the time alignment. When you start talking about soundstage and so on I would hazard to quess that "Time Alignment" may contibute but it certainly is not going to be the deciding factor. To many other variables to consider.

    Rob
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    Senior Member jcrobso's Avatar
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    This can be a can worms!

    Passive X-overs can add phase shifts, different distance of the voice coil from the mounting baffle can cause time shifts. How can we survive all of this ??
    The speed of sound for most of us is close to 1 foot per mill-second, this is a general rule of thumb that I have used.

    If your speakers have all cone drivers, most of the VCs will be within a few inches of each other, so don't throw your speaker out!
    Now if you have horns, the difference could be a whole foot! In the case of my K-horns the woofer is about 6' in back of the mid-range driver. This is because if the horn were straight it would be about 6' long.
    When I wired everything up I did swap the woofer polarity back and forth to get the best sound, I don't remember which way it's set. Phase/time delays are more critical at higher frequencies than at low.
    I remember years ago I went over to a friends house to listen to his new speakers, he said he like them but was disappointed with the bass. I listened then went over to one of the speakers and reversed the leads, yes he had wire one backwards. All of a sudden there was plenty of bass. I knew what to listen for, so I knew what the problem was.
    As others have said everything is a comprise, To get sound of a full range horn system I have accept a small amount of time misalignment.
    Could I fix this? Yes I could, I could bi-amp and put a 6 mill-second delay in the high frequency feed to that amp. So far I not felt the need to do this, everything you do cost you something.

  11. #11
    Senior Member grumpy's Avatar
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    R. Heyser's excellent Klipschorn review from Audio, 1986:

    http://forums.klipsch.com/forums/sto...n%20Review.pdf

  12. #12
    Administrator Robh3606's Avatar
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    This can be a can worms!
    Yes but I certainly wouldn't loose any sleep over it. Damn near every commercial speaker system out there is not time aligned and any vertical driver array is only aligned in a small window. A coax driver is the way to go and they are few and far between.

    Rob
    "I could be arguing in my spare time"

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    Quote Originally Posted by rdgrimes View Post
    Having the L250 with it's time-aligned baffle I have assumed that at least some of what I really like about this speaker is just that.
    It has a "cohesiveness" and clarity that really shouldn't be due to the drivers or XO themselves. (Having similar drivers and XO in other systems where I don't hear the same level of clarity). In short, I'm sold on the alignment for lack of anything better to point to for the origens of this clarity. It just sounds "right", and listening fatigue is non-existent. It's also true that in the case of the 250s, there are other design features that may well be contributing.
    I have never seen directly a L250, unfortunately
    I read that is one of if not the most prestigious JBL home speaker.
    I understand that the front panel being not vertical but sloped aligns in the vertical plane the centers of emission of the various drivers.
    Is this the real situation ?
    Thanks a lot and regards,
    gino

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    Quote Originally Posted by BMWCCA View Post
    I have the 4345s in a tiny living room.
    Nothing time-aligned about those big boxes!
    And yet when I sit on the couch and close my eyes I'm immersed in the performance.
    Granted some recordings are much better than others, but my impression of the soundstage is that it's darn good. But then I'm the guy who thinks L7s aren't that finicky when it comes to placement and I enjoy walking around them in the same room and enjoying the feeling of being in the middle of the performance. So, once again...:dont-know
    Very clear to me, thank you
    Maybe this issue is overvalued after all.
    As I understand from another 3D the role of the listening environment is much more important and decisive to get an accurate reproduction
    Thanks again and regards,
    gino

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