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Thread: phase/time alignment

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    Member Sponsor [WBF Founding Member] rblnr's Avatar
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    phase/time alignment

    Some speaker companies such as Vandersteen place heavy emphasis on time aligning the drivers so the signal from each arrives to the listener at the same time. Others, such as Revel, use a flat front baffle. There seems much less concern about lining up the voice coils/time alignment.

    What are your thoughts/experiences on this?

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    [WBF Founding Member] Addicted to Best! JackD201's Avatar
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    There are some speakers with flat front baffles that are time aligned electrically via the crossover networks. I owned a pair of Von Schweikert VR-4 Gen IIIs that were done this way. The later generations with the sloped cabinets use mechanical time alignment. According to their designer going from electrical to mechanical added to transparency. Makes sense. Less parts in the way.

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    [WBF Founding Member] Gregadd's Avatar
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    Although the speed of sound varies it is about 13,200 inche or 1100 feet per second. At an average listening distance of 10 feet it would be a very small difference in arrival time. I am sure there is some research on the subject.
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    Member Sponsor [WBF Founding Member] rblnr's Avatar
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    Don't know any research specifically, but seem to recall some manufacturers such as Harman citing your argument in downplaying the importance of it. Other manufacturers however insist on the importance of time coherence. Off the top of my head KEF, Tannoy, Vandersteen, Ascendo, Reference 3A, Thiel, et al. Ascendo and some others allow for forward/back adjustment of the head unit to compensate for listening distance. Matters too whether the drivers are wired in phase.

    I will say that in reviewing some passive ATC speakers and comparing them to my active ATC 20-2s that are time phased electrically, there certainly seems to be more soundstage depth w/the actives. Obviously, I can't isolate the reason for this.

    On another note, single driver speakers almost always image well and have great timing. Again, this could be because of a number of reasons.

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    [WBF Founding Member] Gregadd's Avatar
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    Check this link provided by Myles Astor- http://www.physics.sc.edu/kunchur/pa...---Kunchur.pdf
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  6. #6
    I did some experiments with phase and time alignment many years ago. I built a pair of "pot-bellied" speakers so the voice-coils were in alignment. I loved the sound from these so much that they were my mainstay speakers for 20 years (living through two woofer upgrades). I also tried a phase alignment using fill-in speakers from B&O technical papers. These were put into a tower with a side-firing woofer. Bottom line was they stayed in my workshop because I never could get them to sound better than mediocre. The B&O speakers that I used as a reference would always blow them away, so it was probably my choice of components rather than basic concept.

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    Member Sponsor [Technical Expert] DonH50's Avatar
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    Hey Gregadd -- the link did not work for me? I wanted to read it before commenting as I'm getting tired of pulling my feet out of my mouth. - Don
    Don Herman
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    [WBF Founding Member] Gregadd's Avatar
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    Quote Originally Posted by DonH50 View Post
    Hey Gregadd -- the link did not work for me? I wanted to read it before commenting as I'm getting tired of pulling my feet out of my mouth. - Don
    Your oral fixations notwithstanding try it this way. Go here then click on the second link http://www.whatsbestforum.com/showth...0500#post10500
    Be civil to all, sociable to many, familiar with few, friendly to one, and enemy to none.
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    [WBF Founding Member] Moderator RBFC's Avatar
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    Unity Audio used a capacitative network in their speaker crossovers to actually time align the various frequencies that propogated from each individual driver. Apparently, in a driver's bandwidth, the lowest frequencies arise from the periphery of the cone and the higher frequencies are emitted toward the center. So, in a cone configuration, there is time domain smearing from an individual driver. On top of this, the alignment of multiple drivers is the secondary (and possibly overlapping) source of misalignment. Imagine that a single frequency near the crossover frequency is played by both the midrange and the woofer (for example) so that there is smearing of the same note from two drivers.

    Time domain smearing can be a complex problem, indeed.

    While I don't know the exact science or implementation behind the crossover design in the Unity Audio PARMs I had, they sure sounded coherent. They also received rave reviews at CES, etc. Unity Audio founder Bob Grost, who now heads Cerious Technologies, was an engineer for sound cancellation in Corvettes for GM, if I'm correct. He's a good guy, and I hope he comes out with some statement projects for our community to examine.

    Lee

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    Member Sponsor [Technical Expert] DonH50's Avatar
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    Thanks!

    Glad I kept my mouth shut. I never would have guessed 6 us was the threshold! Now, I suspect the culprit is the impact on the time response (which could also be expressed in the frequency domain) that in turn causes significant distortion. If you think about it, 6 us is a goodly amount of jitter, and in this case might it be loosely (OK, very loosely) compared to having a deterministic (signal-dependent, and coherent) jitter of that level? Actually, I would model it as a non-linear group delay (or phase error). Might have to piddle with that a bit.

    Helps explain why planar speakers do well in tests, and why so many companies spend so much effort time-aligning the speaker systems (including the crossover networks) to maintain a coherent wavefront to the listener.
    Don Herman
    "After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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