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Multi-Way Conventional loudspeakers with crossovers

Piezo in-line cap
Piezo in-line cap
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Old 29th October 2006, 04:48 PM   #1
sgatepunk is offline sgatepunk  United States
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Default Piezo in-line cap

Quick question (I hope), I figured someone here might be able to help me out with. I was planning on using a couple of piezo tweeters in a project I am doing (mostly because of the price point). I have never used them before but after a little reading I am under the understanding that these do not need to wired to the crossover network, which makes my design a little less complicated, that being the case though I would still like these speakers to be used for 5khz and up, I am also under the understanding that this can be done using an in-line cap. So heres my question, what would the value be for the in-line cap if I wanted wanted to use them for frequencies 5 khz and up?

THanks a ton!
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Old 29th October 2006, 05:41 PM   #2
omni is offline omni  United States
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Thats hard to tell because you don't know what the impedance is at 5000 Hz. But what you might try is to get an impedance reading at 5000 Hz if you can, then try a 6 db per octave crossover formula to figure the capacitor you need. Vance Dickasons Loudspeaker Cookbook has these formulas. You might also check out a website LALENA.com which has an application to figure component values on line. But you need to find a way to measure impedance at 5000 Hz first. With a frequency generator of some kind and a multimeter, and a 10 ohm precision resistor you can measure your impedance at 5000 Hz. Respectfully.........Omni
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Old 29th October 2006, 08:30 PM   #3
Andy G is offline Andy G  Australia
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Here we go again... The greatest mis-service ever done to a piezo was to say they can be used without a cross-over. Yes, from a mechanical pov they can, they will generally not disintegrate like a normal tweeter, but from a sound pov they should not be used without a cross-over !!!

The only piezo that I have heard do usable sound quality is the Motorola CTS variety. The lesser elcheapo ones....well, you get what you pay for !!

The easiest way to put a x-o on a piezo is to wire a resistor, generally 8 to 22ohms across the piezo, then use that value to calulate your cap value for your desired frequency. If the piezo level is too hot, try a few different resistors in series on the + side between the parallel resistor and the piezo.

The image here shows an eg of the wiring, the cap value is dependant on the parallel resistor and desired frequency


ps..... some amps don't like the high capacitance of a piezo and can go into oscillation. Making the series resistor at least 4ohms will solve this problem (with most Motorola piezos you will find you need 10-30 ohms to balance the top end to your woofer)
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Old 30th October 2006, 08:52 AM   #4
sreten is offline sreten  United Kingdom
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Hi,

read the wiki on piezo's here http://www.diyaudio.com/wiki/index.php?page=piezoXO

/sreten.
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Old 30th October 2006, 12:51 PM   #5
Andy G is offline Andy G  Australia
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Hi Sreten,

Glad to see that info is credited to Jon Risch. Jon and I and a couple of other guys discussed this quite a bit about 6-7 years ago. It was a great learning experience !!!

Because I don't want to spend heaps of funds, I still have the original KSN 1188's in both my sets of PA boxes and KSN 1142 in the foldbacks (Eminence woofs). Everyone who hears them who knows anything about music reckons the speakers sound pretty darn nice. Me happy !!!

Bit miffed the other week though, I could have worked with a guy from Canned Heat, but was already booked..
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