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Thread: Time alignment dimension

  1. #1
    Senior Member jbl4ever's Avatar
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    Time alignment dimension

    Does anyone know the offset for the following components for time alignment
    2370 horn with 2426 verse 2225 woofer
    Thanks

  2. #2
    Senior Member rdgrimes's Avatar
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    AFAIK you just want the voice coils to line up in the vertical plane.

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    Quote Originally Posted by jbl4ever View Post
    Does anyone know the offset for the following components for time alignment
    2370 horn with 2426 verse 2225 woofer
    Thanks
    That sounds like a JBL 4671 or one of its variants. I don't know if JBL ever published a time alignment offset spec for it or not as it was almost always used with its own crossover (3110). On the 5234 and 5235, I'm pretty sure they didn't have any dedicated modules for the 2370 the way they did for some other horn/driver/systems. There was one module, late in life for the 5235 where one could stuff their own resistors for time alignment (they gave you two positions so you could use 1% resistors to make the value you needed).

    If I were to hazard a guess, it would be on the order of .7msec. But that would all depend on how you mount the systems relative to each other. If you have freedom in mounting, play a tone at the crossover frequency and adjust until it maximizes at your listening position. There shouldn't be too much offset when you're done.

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    Senior Member gdmoore28's Avatar
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    What RDGrimes said. Physical alignment is nothing more than what the name implies: the various drivers are positioned on the cabinet so that their voice coils/diaphragms are vertically aligned along the same line. Simple as that.

    GeeDeeEmm

    Here's a vivid example of vertical time alignment from Technics.

    From the interweb: Technics SB-E100

  5. #5
    Senior Member Ian Mackenzie's Avatar
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    Without getting into s long winded discussion time alignment has several factors

    The phase relationship of a driver can vary considerably to the point that the actual acoustic centre is not the voice coil.

    A crossover network introduces phase shift and group delay within the filter typically the low pass filter.

    A simple way of determining if your physical alignment is right (assuming the acoustic crossover slopes are correct) is to reverse the polarity of the woofer and adjust the distance of the horn. A deep 20 dB notch should uniformly form at the crossover point. You will find it’s quite sensitive once you are near the correct offset.+-5 mm is critical as you approach correct phase tracking of the crossover transfer function.

    The offset is only valid for one 3 dimensional point in space in front of the loudspeaker

    I hope this helps clarify your post

    Ian

  6. #6
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Ian Mackenzie View Post
    The offset is only valid for one 3 dimensional point in space in front of the loudspeaker.
    Exactly, so the idea that there are time aligned speakers is mostly bunk. Do they know where I’ll be sitting?

    Now, a speaker like one of the Altec 604 series, the Urei speakers, or the dual concentric Tannoy speakers can be time aligned since the distance from the two drivers to the listener’s ears will not shift due to listening height/distance, but even these are mostly not really perfectly aligned either.


    Widget

  7. #7
    Senior Member Ian Mackenzie's Avatar
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    Loudspeakers like the the Wilson WAMM (Dave Wilson RIP) can be adjusted so the individual drivers are in alignment at the listening position. That’s complicated and very expensive.

    In the diy space you are not bound by commercial or marketing constraints so you can fiddle around with this phenomenon to your hearts content and believe what you want to believe subjectively.

    At the extreme early movie horn loudspeaker had significant time delay due to the long horns used.

  8. #8
    Member Mitchco's Avatar
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    Here is a link to an article that shows a JBL 4722, which has a large z offset between the CD/waveguide combo and bass drivers, being time aligned, including subs, using modern DSP: https://www.computeraudiophile.com/c...diolense-r712/ There are several before and after time domain measurements using Audiolense and REW.

    In the article, I also tried an experiment where one FIR filter contained the time alignment and the other filter, same frequency response, but no time alignment. In a blind test, I was able to discern the difference.

    Below is a step response display of a time aligned 3-way horn loaded system (i.e. high and mid horns, 15" direct radiator) measured over 14 positions across a 6' x 2' grid at the listening area. Note the direct sound is time aligned regardless of measurement position:

    Name:  REW LR speakers Step 14 measures across 6ft by 2ft grid at LP plus target.jpg
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Size:  80.9 KB

    Of course, after the direct sound, room reflections enter into the picture, but not so much as to still follow the target timing response. Modern DSP allows for accurate and precision alignment of drivers. In the cases above, using linear phase digital XO's in software, along with frequency and time domain adjustments, including excess phase correction, ensures the sound arriving at one's ears, has a smooth frequency response, is time aligned, with minimal phase and group delay disturbances. Meaning one is reproducing the source media with very little frequency and time domain distortions.

    While my results are anecdotal, many others have noticed similar improvements, as I have found, described in the article. I hope more research continues in this interesting area of psychoacoustics.

    @jbl4ever, I hope you find an appropriate method to time align your drivers. Cheers, Mitch

  9. #9
    Senior Member 1audiohack's Avatar
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    Each speaker has a delay of its own plus additional delay caused by the dividing network, (unless FIR filtering is used.)

    The network delay is due to its function as a transmission line so it does not matter if its high level or low level, the delay will be here. The delay is partly due to the high frequency cut off and partially due to the substantially larger inductance value of the woofers voice coil.

    Woofers have more delay than tweeters. In the absence of added signal delay on the HF driver the correct location of a tweeter is inevitably behind the woofer.

    My experience with precision time alignment mirrors Mitch’s.

    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

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    Quote Originally Posted by sguttag View Post
    That sounds like a JBL 4671 or one of its variants. I don't know if JBL ever published a time alignment offset spec for it or not as it was almost always used with its own crossover (3110). On the 5234 and 5235, I'm pretty sure they didn't have any dedicated modules for the 2370 the way they did for some other horn/driver/systems. There was one module, late in life for the 5235 where one could stuff their own resistors for time alignment (they gave you two positions so you could use 1% resistors to make the value you needed).

    If I were to hazard a guess, it would be on the order of .7msec. But that would all depend on how you mount the systems relative to each other. If you have freedom in mounting, play a tone at the crossover frequency and adjust until it maximizes at your listening position. There shouldn't be too much offset when you're done.
    this was the 53-5333 crossover board, working only in 5235 as the board needs power supply. It was passible to modify the crossover frequency by changing a resistor network component, and the same for the delay. There are two delay sections, by defaut of 350us each.

    This card is very difficult to get.

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    Yup, that's it! I remember setting them up for the 4675 and 4670 speakers a bunch, back in the day. Even printed up Avery labels to apply so the little window on the crossover frame would show how it was configured. I couldn't recall if JBL actually published a spec for that card for their cinema speakers (of which the 4671 was considered a small cinema speaker). I see it wasn't in the 53-5333 manual but perhaps from the Cinema Installation manual, from that era, the same way that they now publish (well how ever often, or not, they update it) for current speakers and the DSP values (I believe based on the Drive Rack 260).

  12. #12
    Senior Member jbl4ever's Avatar
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    Thank you very much for every ones reply. A lot more variables come into play, not just centers of VC's

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