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  1. #1
    Veteran Member Four Rings cspcrx's Avatar
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    test tones and DMM?

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    I have a thought on how I can test the frequency output from the B&O amp to the factory subwoofer and would like your thoughts.

    If I connect my digital multimeter in place of the stock sub and play a 60hz test tone I should see voltage because the amp is passing it. Now if it did the for various frequencies say 20, 40, 60, 80, 100, 120 etc I should be able to see where I no longer get voltage thus telling me where the stock amp crosses over the sub channel.

    I my theory solid?
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    THEN THEN THEN Rinse & Repeat!

  2. #2
    Active Member One Ring
    Join Date
    Jun 25 2012
    AZ Member #
    95820
    Location
    Texas

    Quote Originally Posted by cspcrx View Post
    I have a thought on how I can test the frequency output from the B&O amp to the factory subwoofer and would like your thoughts.

    If I connect my digital multimeter in place of the stock sub and play a 60hz test tone I should see voltage because the amp is passing it. Now if it did the for various frequencies say 20, 40, 60, 80, 100, 120 etc I should be able to see where I no longer get voltage thus telling me where the stock amp crosses over the sub channel.

    I my theory solid?
    In theory, yes, solid.

    Get an 8 ohm, non inductive resistor - you need to keep the load constant instead of a fluctuating one like a speaker has.
    Then you need to measure the RMS voltage across the resistor while you play sine waves at different frequencies into the resistor. Each time you play a different frequency sine wave, you will record a different RMS voltage and then you can build a simple table with frequency vs. voltage. Then you can plot these in X-Y to see what the frequency response looks like. Ideally you would want to test all the speakers frequency response to see what you have. Raise your resolution even more and you'll be able to tell the slope.

    I just got a '13 S5 and I can tell you from the last week of driving around that I suspect there's more trickery happening than just a simple cut-off point. I'm positive this is volume based and, as weird as this sounds, fader based. It sounds to me that the slope and response are changing based on these two values. Yes, I know about GALA and that junk is turned off.

    I was an installer for car and home audio in my youth and am still pretty active. I can test this within the next week or two and get back to you (Working alot right now). If you're impatient or just want to gather the equipment/skillset you can do this a laptop, voltage divider circuit and Room EQ Wizard (REW).

  3. #3
    Active Member One Ring
    Join Date
    Jun 25 2012
    AZ Member #
    95820
    Location
    Texas

    Subwoofer signal testing - right from the leads to the sub via pink noise from the Autosound2000 test cd:

    Bass and Treble set to mid point, no gala, surround at lowest point, fader in center, car parked:


    Same as above with gala active:


    Bass set to high, no gala:


    The car was stationary. I'll be testing this tomorrow with the car moving as soon as I make some adjustments to the rig and have someone available to drive the car.

    If you have any specific settings you'd like to to see, just let me know.
    Last edited by toitle; 08-03-2018 at 08:53 PM.



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