use equaliser to put low pass filter in place

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    Profile photo of [XAP]Bob

    Not sure the signals paths match well enough to use the HPF and an antiphase version of the original signal 😉

    Id be interested by the output of an external crossover…

    Profile photo of Andreas

    Ok, here are three plots from a real crossover (LEM XO202) set at 200 Hz. As you can see from the plots, the numbers on the front do not necessarily match what you get, so measuring may be wise before using in production.
    LPF and HPF plots look somewhat expected, for me very interesing was the LPF+HPF plot which is nearly flat (about +/-1dB) up to the highest frequencies.

    Setup was:
    – PC via USB into Channels 31/32 (Qu32) those are send to Mix2 Output
    – Mix2 Out to XO input
    – XO LPF/HPF into Channels 1&2
    – Channels 1&2 send to Mix1
    – Mix1 master used to level at 0dB overall and recorded via USB
    So this also gives an overall impression of both DAC and ADC quality of the desc, and don’t forget the LEM is some analog gear in the middle.

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    Profile photo of [XAP]Bob

    Very different from the eq based plots…

    Profile photo of Andreas

    Sure, since this is a crossover which is built to give a flat response when summed and not a shelving PEQ or cluster of notch GEQs. Sadly there’s no spec in the manual about the rolloff, but from the plots its 24dB/octave. The Qu-GEQ has about 12dB/octave the Qu-PEQ shelving filter some 3dB/octave.

    Profile photo of [XAP]Bob

    Yes, I did expect it to be better, but even so…

    The figures are useful to quote, since you have the charts up… What’s the HPF dB/octave?

    (Feeling lazy, and want a consistent number recorded 😉

    Profile photo of Andreas

    The Qu-HPF is 12dB/octave. Could be steeper in my opinion…

    Profile photo of [XAP]Bob

    Same as the GEQ (but goes deeper)

    Profile photo of

    The original post was
    Can I use the EQ (mix8) to get a sub driven Aux
    There was never any mention of crossovers for mid way or for high end horns?
    and my response was:

    I do this all of the time into (powered 1200 watt B52’s) and non powered Subs using Lab Gruppen 4k amps
    However I cross at about 100 hz
    all faders (except 30hz left at 0db) 40 through to 100 I raise up. 125hz I leave at 0 (sometimes right off). the rest of the faders I bring down to off.

    Not technically Ideal however it works fine.
    Use your ears and be careful and actually go and look at your driver cones to make sure you are no pushing them too hard in those conditions.

    Never any mention of crossovers for mids of highs.

    When I use my powered B52 (and I have 12 of therm) I use the on board QU EQs from 100hz. The B52 already has a lousy crossover at 80hz and they have phase reverse etc and all the bells and limiters.
    I bont do any crossing for my high mids… they have a built in passive crossovers and i’m able to virtually leave the desk EQ flat! Brilliant! Never sounded better.
    However when I use my Lab 4ks to drive low subs (double 18’s 6 of them) I still use the EQ in the desk (Aux driven 7/8)
    however I use LAB GRUPPEN 3 way very high tech spec crossovers. Anologe 3 way Bal crossovers.
    Never would I cross over mid highs etc…
    However thanks for all of the info.
    Ive have built crossovers and know what’s involved.

    Must not forget that original post… at grass roots level…
    Some people just can not afford that wee extra peice of equipment.
    And remember once you own a peice of apparatus you can do anything you want with it.
    Even stand on ity like a tank commander.

    What we share is our opinions.


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