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Thread: Measuring Amplifier Frequency Response Part 2

  1. #21
    Devil's Advocate Adam_MSS's Avatar
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    Glad to see it's working as expected. What other tests are you planning?
    You don't use science to show that you're right, you use science to become right. - R.Munroe

    The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. - W.L.Bragg



  2. #22
    The MicMate seems unnaturally tilted... My Icicle was much flatter than that IIRC.
    "Of course, the laws of science contain no matter and have no energy either and therefore do not exist except in people's minds. It's best to be completely scientific about the whole thing and refuse to believe in either ghosts or the laws of science. That way you're safe. That doesn't leave you very much to believe in, but that's scientific too."

  3. #23
    Big Daddy Chad's Avatar
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    Quote Originally Posted by VP Electricity View Post
    The MicMate seems unnaturally tilted... My Icicle was much flatter than that IIRC.
    that's it's self-noise.

  4. #24
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    Quote Originally Posted by Adam View Post
    Glad to see it's working as expected. What other tests are you planning?
    I am going to check a few things that I have laying around the house. If my wife lets me, I am going to test the "premium" sound system in her 2011 Genesis Coupe.

    Of course, with that said, the mystique surrounding my "servo" has been discovered. Although I haven't tried higher volumes where it is supposed to augment the amount of boost through corrective feedback, I've come to realize that it is just a radical bass boost designed to alter the output of a subwoofer. The subwoofer has to be installed in a sealed enclosure where its resonates at 70 Hz in order to achieve the best results from my device.

    I just thought it did more than it did since it's been beat into my head that this device compares input to output with the model of an ideal subwoofer environment being the constant. It was supposed make corrections based on the ideal model through the application of corrective feedback at the inputs of the amplifier. I think it is more along the lines of this gizmo with an additional feature or two: Sub-Woofer Controller where the equalization is applied differently to take advantage of cabin gain in the automobile.
    Last edited by ChrisB; 10-28-2010 at 04:14 AM.

  5. #25
    Tester Extraordinaire ErinH's Avatar
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    curious to see the results should you decide to use rightmark.


    one other thing to consider trying is to put a load on your preouts/prein and see how/if that effects the FR. I did this by simply soldering a 550ohm resistor to the rca between the tip and shield. I did the same with a 22kohm resistor. I did it to measure the clipping point so I haven't tried it to measure FR.
    Your ears: The best tools you have... and they're free, too!

  6. #26
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    Well, here it is with Rightmark now that I finally have a USB MobilePre:


    Uncle Chad was right, what I have on my hands is a bass boost box with a twist. It monitors output and applies corrective feedback at the input of the amplifier when things get too rowdy.

    In other news, I think I am turning into an audio nerd!

    EDIT: I also tested a couple of other amplifiers that I had laying around. It would appear that the "Punch EQ" that everyone talks so much about didn't carry forward through every Rockford Fosgate amplifier on the market:



    The Power 351s seems right in line with the Zapco Z100S2.
    Last edited by ChrisB; 07-06-2011 at 08:14 PM.

  7. #27
    Devil's Advocate Adam_MSS's Avatar
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    Pretty cool. How did you arrive at the conclusion about the feedback? Not questioning the conclusion, just interested in the process.

    Also what is the distortion scale on the first plot?

    Both the power 351 and the zapco are pretty damned flat. I'm really impressed.
    You don't use science to show that you're right, you use science to become right. - R.Munroe

    The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. - W.L.Bragg



  8. #28
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    Quote Originally Posted by Adam_MSS View Post
    Pretty cool. How did you arrive at the conclusion about the feedback? Not questioning the conclusion, just interested in the process.

    Also what is the distortion scale on the first plot?

    Both the power 351 and the zapco are pretty damned flat. I'm really impressed.
    After doing the first measurement, I started thinking that it was nothing more than a Linkwitz Transform circuit so I spoke to one of the designer's friends. The designer's friend referred me to the patent and explained the analog comparison circuit to me which sadly, went over my head. While it would be a royal pita to measure the corrective feedback, I noticed that the boost was volume dependent and it would even RTA differently depending on output level. I'm halfway tempted to implement this again in my vehicle since my wife doesn't want it any more.

  9. #29
    Devil's Advocate Adam_MSS's Avatar
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    Well that's certainly an effective way of getting the info.

    I figured that you had observed some changes at different levels to support the conclusion, I just didn't see it in the graph. Very cool stuff. Glad the setup is working out for you.
    You don't use science to show that you're right, you use science to become right. - R.Munroe

    The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. - W.L.Bragg



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