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3 way DSP XO

Discussion in 'DIY Audio Forum' started by BE718, Nov 11, 2016.

  1. RayDunzl

    RayDunzl Major Contributor Central Scrutinizer

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    No.

    The room modifies the arrival time at the listening position of the reflected soundwaves emanating simultaneously from the two speaker locations causing their sum at the listening position to cancel.

    With either wave source operating alone the cancellation doesn't occur, or, is much less severe.

    By modifying the launch time (phase) of one speaker or of the other, or splitting the difference between both, the relative time of arrival of the wave peaks and troughs from each source via reflective surfaces at the listening position can be adjusted, thereby adjusting the amount of cancellation occurring at the frequencies of interest.

    No.

    Or Yes, with the following explanation.

    The direct wave from both speakers is not the source of the cancellation.

    The direct wave from left plus the reflected from left (causing some phase shift from the direct) does not cancel itself at the listening position.

    The direct wave from right plus the reflected from right (causing some phase shift from the direct that is different from that of the left) does not cancel itself at the listening position.

    The direct wave from both speakers, modified by the combined reflections from both speakers, at the listening position, does create a substantial null around 47hz.
     
    Last edited: Sep 24, 2017
  2. dallasjustice

    dallasjustice Addicted to Fun and Learning

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    IMG_1890.JPG My brain just blew up. Sorry I can't help.
     
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  3. watchnerd

    watchnerd Major Contributor Beer Hero

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    Experiment question:

    What happens if you wire one speaker with reverse polarity?
     
  4. RayDunzl

    RayDunzl Major Contributor Central Scrutinizer

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    The same thing that happens if I just reverse the channel polarity at the miniDSP, but it takes longer.

    Top - normal and then both inverted
    Bottom - right inverted and then left inverted

    upload_2017-9-24_0-52-19.png

    Wow.

    The out-of-phase playback traces register at a considerably lower level than I remember or have noticed before. The volume level wasn't changed.

    Smoothed out some to see that. -9dB at 1kHz

    upload_2017-9-24_1-3-3.png
     
    Last edited: Sep 24, 2017
  5. watchnerd

    watchnerd Major Contributor Beer Hero

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    Thanks, that makes sense.

    Do you think any changes would have to be made to a passive mid/tweeter crossover if you disconnect the woofer?
     
  6. Voldemaar

    Voldemaar Member

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    BE718, thanks a lot for detailed.

    At screenshots I see high pass at mixer soft. Can both frequency and slope /type of high pass be varied?

    Also, how do you like the sound? I see that at some conditions high order harmonics are dominant, this is usually not so good sounding subjectively..
     
    Last edited: Sep 26, 2017
  7. BE718

    BE718 Major Contributor forum experimenter

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    Hi Voldemaar,

    No problem. The filters in the mixer are limited, the HPF all you can control is the frequency. The other filters are parametric, set frequency gain and Q. Two of them can be set to shelf. Its not sophisticated enough to perform XO functions.

    upload_2017-9-26_18-57-52.png



    The Motu sounds very good, maybe not as good as my Chord Mojo, but the advantages of DSP XO are greater than the subtle differences between DACs. BTW it is using an ESS DAC chip.

    The distortion you mention needs to be put into context. The measurement was taken at 0dB full scale, with the output level at max of 10v rms. The scale is dBv so you need to subtract 20 to get the relative levels of those harmonics. The highest level seen is the 3rd at -116dB. that's actually pretty good for FS :) .


    [​IMG]


    This distortion disappears at lower signal levels. Noise floor is about -164dB with a 262000 point FFT (FFT processing gain is about 51 dB in this case)

    [​IMG]


    You can find some other measurements (loop back measuring itself with its own ADC) and internal pictures in this thread

    https://www.audiosciencereview.com/forum/index.php?threads/new-toy-motu-8a.1698/
     
    Last edited: Sep 26, 2017
  8. Voldemaar

    Voldemaar Member

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    I suppose if you go with AVB, it can sound superior vs Mojo USB connected
     
  9. BE718

    BE718 Major Contributor forum experimenter

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    No. The Mojo and 8A both work fine with USB, you wont see any improvement with AVB.
     
  10. Voldemaar

    Voldemaar Member

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    Interesting. Have you compared?
     
  11. BE718

    BE718 Major Contributor forum experimenter

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    I haven't, but there is no need. There are no USB related issues seen in any of the (excellent) measurements, so there is no basis to think that AVB will improve the measurements, let alone any chance that you would hear any difference.

    As an aside, don't get drawn into the USB cleaning nonsense seen elsewhere, its a non issue for well designed DACs :)

    Ill expand on this; galvanic isolation can be genuinely useful in certain circumstances. If the DAC is bus powered but has inadequate PSU regulation, a USB cleaner might help. Improving USB eye pattern/clocking beyond the USB spec requirements does sweet FA. :)

    If a DAC responds well to these USB cleaners it is just an indication of deficient design.
     
    Last edited: Oct 1, 2017
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