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Thread: JBL M552 CCBFREQ measured!

  1. #1
    Senior Member frank23's Avatar
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    JBL M552 CCBFREQ measured!

    Due to some (clever) thinking and linking up my macbook line in with my stereo, I have made some analysis with Audacity that I wanted to share with you.

    What I did was to measure a full range white noise frequency spectrum from:
    1) line out on my cd player
    2) high output on my M552 which is wired for CCBFREQ and was crossed over at 200Hz

    By comparing these using the spectrum analysis function of Audacity you can see the CCBFREQ effect from the M552. I am not too sure about the dB scale. That is why I crossed it at 200Hz to be able to see if I can find the 24dB/oct. This looks correct (see the about 24dB difference between 100Hz and 200Hz), so does this mean the CCBFREQ is really only about 6dB between 2000Hz and 17500Hz?

    first the full range line signal from the cd-player output:


    then the fullrange signal (hmm, actually it looks like it was crossed at a low frequency, but just look from 200Hz upwards) from the high output of the M552 with CCBFREQ:


    then the signal crossed over at 200Hz from the high output of the M552 with CCBFREQ:


    I'd love to hear what you think of it!

  2. #2
    Senior Member 1audiohack's Avatar
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    I think your very close. I measured the T.F. of one of my M552's set on CC comp for the 2360 so I could duplicate the curve in a DriveRack. The EQ spread I wrote into the DBX was -4.5 to + 3dB, as seen on the DBX screen at the bottom, 7.5dB total. The compared curve is shown below, the white line is the M552, the yellow one is from the DBX.

    I had the M552 crossed about 1kHz and I neglected to switch the TEF screen from dB Pascal to dBV so that scale is a guess.

    Good to see someone in else in the discovery stage! Keep it up and have fun.

    All the best,
    Barry.









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    Administrator Robh3606's Avatar
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    The cut and boost used for the 2360/2380 horns is published in the owners manuals for the M552/M553. Just download the manual. Unity gain is 5k for both curves.

    http://www.jblpro.com/pub/obsolete/M...s%20Manual.pdf

    Rob
    "I could be arguing in my spare time"

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    Senior Member frank23's Avatar
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    Quote Originally Posted by Robh3606 View Post
    The cut and boost used for the 2360/2380 horns is published in the owners manuals for the M552/M553. Just download the manual. Unity gain is 5k for both curves.

    http://www.jblpro.com/pub/obsolete/M...s%20Manual.pdf

    Rob
    Hi Rob,

    I have the manual, but that does not give you any info on the shape of the curve. Looking at zilch's link above, the FF compensation cards for other JBl crossovers have a bump lower down. In the M552 manual the only difference in specs (page 19) between the CC and FF is that CC is -5dB at 2000Hz and FF is -4dB.

    I wanted to see the curves. I will measure CC and FF side by side coming weekend.

  6. #6
    Senior Seņor boputnam's Avatar
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    Novel approach. Interesting.

    However...
    Quote Originally Posted by frank23 View Post
    ...(see the about 24dB difference between 100Hz and 200Hz
    ...that looks like -18dB/octave to me.
    bo

    "Indeed, not!!"

  7. #7
    Senior Member pos's Avatar
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    The problem with audacity is that you need white noise instead of pink noise.
    Or you have to export the data and apply some compensation.
    I am reluctant puting high level white noise into my full range speakers...

  8. #8
    Senior Seņor boputnam's Avatar
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    Quote Originally Posted by pos View Post
    The problem with audacity is that you need white noise instead of pink noise.
    I was wondering the same thing. I've never measured White Noise. Pink Noise (filtered White Noise) is a more relevant reference - it's use might change these observations.

  9. #9
    Senior Member pos's Avatar
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    from the first picture it looks like frank23 is using white noise, wich is what render a flat curve with audacity.
    Using pink noise gives you the classic descending curve, and the soft provides no mean of compensating it to flat.

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    Senior Seņor boputnam's Avatar
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    Quote Originally Posted by pos View Post
    from the first picture it looks like frank23 is using white noise, wich is what render a flat curve with audacity.
    Yes, he stated he is using it.

    Quote Originally Posted by frank23 View Post
    What I did was to measure a full range white noise frequency spectrum from
    I do not know how it would affect his plots of the CCBFREQ and the 552 crossover.

  11. #11
    Senior Member frank23's Avatar
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    Quote Originally Posted by pos View Post
    I am reluctant puting high level white noise into my full range speakers...
    I measured the output of the M552, so not the speaker output.

  12. #12
    Senior Member frank23's Avatar
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    Quote Originally Posted by boputnam View Post
    Yes, he stated he is using it.



    I do not know how it would affect his plots of the CCBFREQ and the 552 crossover.

    I think this method is ok with Audacity. I wil measure some other test signals next time that I know the dB difference of for sure to be able to calibrate the Audacity scale. Maybe it is correct as I've measured it, maybe not, I'll know next time.

  13. #13
    Senior Member pos's Avatar
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    It is correct. Here is what a pinknoise looks like in audacity.
    Attached Images Attached Images  

  14. #14
    Senior Member pos's Avatar
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    Makes me think:
    You could also use a sweap noise (limited to 23s...). But as for the white vs pink, you would have to use a linear sweap!
    I whish Audacity had a correction option to flatten the "pink" log spectral balance...

  15. #15
    Senior Member grumpy's Avatar
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    not main topic, but...

    I haven't played with Audacity's analysis function much, but it appears
    there is a "chirp" generator that -could- be used to good effect for such
    measurements. (tried it briefly using v1.3.8beta on a mac, onboard
    speakers and mic). Might have to work with it a bit, and perhaps get
    some expert feedback from an Audacity-centric forum, but a here's a
    brief comparison using Audacity (100-20000Hz log sine sweep) vs.
    Fuzzmeasure doing essentially the same thing (measuring mac laptop
    speakers and mic, -not- M552/3):
    Attached Images Attached Images   

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