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Help designing 2-way audio crossover

  1. Oct 4, 2014 #1



    asdf.jpg Links: https://www.parts-express.com/vifa-oc25sc65-04-1-textile-dome-tweeter--264-1018 https://www.madisoundspeakerstore.c.../silver-flute-w17rc38-04-ohm-6-1/2-wool-cone/

    For tweeters, they say to take the resonant frequency and multiply that by 2.5x, and that figure should be the lowest you should cross your tweeter over. The resonant frequency of my desired tweeter is exactly 1,520hz. If you do the math, that's 3,800hz.

    Why is this?

    Is a 3.8khz crossover point the absolute lowest my tweeter will be able to cross at the lowest possible slope, which would be a 6dB/octave? I understand I can cross lower if I'm using a steeper slope, but I just want to make sure this is correct.

    Also, that mid-woofer plays relatively flat up to about 5khz with the exception of that little peak. If I wire a 10uF poly cap in series with my tweeter giving me a x-over point of 3.8khz at 6dB/octave, then where should I cross my mid-woofer over? Should I overlap? How much?

    Do you guys think it would be better to cross with a steeper slope on my tweeter or just use a notch filter on the mid-woofer? I really don't want my mid-woofer playing past 3khz because of the peak at 5khz. However, I'd be breaking rules if I crossed my tweeter under 3.8khz.

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  3. Oct 9, 2014 #2
    Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Oct 9, 2014 #3

    jim hardy

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    Well, think about it - if you send your tweeter a signal at its resonant frequency, won't it sound too loud? That'll be annoying if a certain note blasts out louder than everything else.

    Similarly, what if your crossover has a frequency gap between high end of midrange and low end of tweeter ? Wont there be a dead spot in frequency responsive, ie certain notes won't get made into sound ?
  5. Oct 10, 2014 #4

    jim hardy

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    Wouldn't you place their respective -3db points right atop one another, so that as one fades out the other is fading in ?
  6. Oct 10, 2014 #5
    I know you didn't arbitrarily choose that 3dB figure, so I'm asking where you got it from. I see the 3dB figure all the time. For instance, if you double the power, you only get a 3dB gain. I'm not interested in why that is now, I just want to know where everyone is getting the 3dB figure from or why it's so common. I mean why not 5 or why not 10? Does this have something to do with the way humans perceive sound? Is it not linear?

    And I didn't even think about that for the resonant frequency. That makes sense, thanks.
  7. Oct 10, 2014 #6

    jim hardy

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    3db being half power, when both are down by half their sum will be one. So your response will be fairly flat.

    What would be sum if both were down by 90% at your crossover frequency? Maybe a dead spot?

    Don't be afraid to look for simple thinking, it is usually the right direction.

    3db point falls nicely from the math of filters. So it's very common.

    In a simple RC filter, it's the frequency at which XC = R and each sees 0.707 of Vsupply since it's a vector summation.
    It's called "corner frequency" .
    0.707 being 1/sqrt(2) , at corner frequency power dissipated in the R is (Vsupply2)/(sqrt(2)2)/R

    which = Vsupply2/2R , half power...

    Filters is another whole world in which the math and real world behavior are sooo closely related that it's fascinating. I recommend you learn all you can for it will greatly enrich your audio hobby experience.
    Look for old LM833 appnotes......
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