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Do piezo horns require a crossover?

Discussion in 'Amps [BG]' started by eleveniseven, Oct 31, 2007.

  1. eleveniseven

    eleveniseven Guest

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    the situation im in is that i built a cabinet with a 15" driver and a horn, the horn is crossed over using a peavey crossover, i dont know any more about it than that, but, i have a popping and cracking noise coming from the horn. i would like to just replace the horn with a piezo or two even??
    i have read they dont require crossovers, but my questions are: do they take crossovers? and how does a piezo horn figure into the ohm equation?
    if you add one, or two or 10 for that matter, do you figure the ohm rating for the cabinet the same way as you would a regular speaker?
    i have consulted google...i cant find a real answer, let me know what you think. thanks!!
  2. rodl2005

    rodl2005

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    I built some PA bins a while back & used the Motorola 400w horn-piezo & didn't need a cossover!!! I did put a resistor in line before it so it wasn't so harsh & it's sounded sweet ever since!!! Dunno re your one OR whether ALL piezo horns dont need X-overs tho!
  3. pharaohamps

    pharaohamps Supporting Member

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    Popping and crackling from your horn could be a lot of things. If your horn is crossed over too low it could be distorting, or it could be driven too hard even if crossed over correctly.

    Piezo's don't typically need x-overs, because they have much much too high an impedance at low frequencies and thus they ignore them.

    Impedance is a funny thing - 8 ohms impedance (for example) is measured at some frequency. Impedance is an AC measurement unlike DC resistance and so changes with the reactance of the speaker (goes down for lower freqs and up for higher ones.) A piezo horn / tweeter might have an impedance of 8 ohms at 5 khz, but at 1khz it might be 500k or 1 meg ohm.

    Thus if a piezo and a conventional woofer were wired in parallel, the piezo gets most of the power at high freqs. At low freqs, the woofer gets most (or all, if the piezo impedance is really high.)

    A horn on the other hand is really just a small speaker. It has a much lower reactance (its voice coil has inductance and so it's XsubL is a fairly large number) and will take more power at low freqs. The problem is that low freqs have a lot of energy and heat the voice coil without doing much other work (the speaker can't reproduce the tones since it can't move far enough or doesn't have a large enough surface area,) and thus its voice coil burns out. Crossing over the horn with a high pass filter prevents much energy from the low freqs. from getting to the coil, and protects the speaker.

    Have fun!
    Matt Farrow

    At 1kHz, the woofer has an impedance of 8 ohms
  4. eleveniseven

    eleveniseven Guest

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    so if i were to remove the x-over, and replace the horn with a piezo...or two, would my amp still see an 8 ohm load, or would i reducing the load? i understand that the piezo's load changes with frequency, but as a general rule? would you wire them parallel or series?
    i hate to be asking such questions, but i just cant seem to find a clear explanation anywhere?
    i can just remove the horn, but i hate to do that, because i may use this cabinet as a stand alone at some gigs, so i would like to have the highs present...anyway, thanks for all the helpful input so far!
  5. billfitzmaurice

    billfitzmaurice

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    Looking in the wrong places you must be.
    http://www.partsexpress.com/pdf/piezo.pdf
  6. eleveniseven

    eleveniseven Guest

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    thank you bill, this is great. i was hoping you would see my thread.
    thanks again!
  7. eleveniseven

    eleveniseven Guest

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    after reading all that, some of which i dont really understand...why arent piezos used all the time, seems to be a pretty awsome product...that answered my questions, and i am going to use them in my cabinet project. thanks for all the help.
  8. koobie

    koobie Supporting Member

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    I can't say I dislike all piezos I've heard, but probably most of them. Are piezos ever utilized in anything aside from cost-constrained designs?
  9. billfitzmaurice

    billfitzmaurice

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    Piezos properly employed work at least as well as compression drivers, and when cost is taken into account they work considerably better. The problem is that 99.9% of the time they aren't properly employed.
  10. KJung

    KJung Supporting Member

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    Interesting stuff. I am one who mostly hears the piezo tweeters used in lower end cabs sounding very harsh. However, from reading the great link you provided, my guess is that most of these manufacturers don't include that extra 'filter' that was mentioned in the article to eliminate the upper mids that can still be present with a piezo with no crossover. I assume this is why many of the executions can sound quite 'ganky'.

    Is that what you mean by 'properly employed'?
  11. eleveniseven

    eleveniseven Guest

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    +1 to KJung, also, what type of filter should you use to properly employ the horn?
  12. billfitzmaurice

    billfitzmaurice

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    The upper mids aren't a problem. Piezos are usually used along with woofers that have little to no midrange, and it's the lack of mids that makes the high frequencies seem too strident. BTW, to the original poster, you shouldn't go direct from a fifteen to tweeters, you need a midrange driver too.

    Piezos are often used in cabs that are poorly designed, because they are inexpensive. It's the entire package responsible for its sounding bad, not the tweeters. They're a favorite in cheap PA boxes, lined up three or four abreast. That tells you right off that the box is bogus, as tweeters should almost never be horizontally arrayed.
  13. KJung

    KJung Supporting Member

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    Makes sense. Thanks.
  14. eleveniseven

    eleveniseven Guest

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    ok...that sounds good, do you have crossover plans available on your site that i could buy and build one that would allow me to add an effective mid speaker to my setup including a piezo..?
  15. billfitzmaurice

    billfitzmaurice

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    No, only complete cabinet plans, sorry.
  16. BassmanPaul

    BassmanPaul Gold Supporting Member

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    I think Bill's been watching too many Star Wars movies. Thank you Yoda!

    I personally don't like piezos that much but I admit they are simple to implement. I usually put a 0.1 mfd cap in series with them as well as a 10-20 ohm resistor.

    Paul
  17. eleveniseven

    eleveniseven Guest

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    so what effect does adding the .1 mfd capacitor and the 10-20 ohm resistor create? what does that do exactly,
  18. qts

    qts

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  19. billfitzmaurice

    billfitzmaurice

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    Explained in the link I gave you.
  20. eleveniseven

    eleveniseven Guest

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    ok...ill re read

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