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Old 18th March 2003, 07:54 PM   #1
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Default Is Peizo destroyable?

I just got my piezo horn tweeter drivers in the mail and I ordered twice as many as I needed, in case they blew out, but then I realized they're piezo, and I don't know if I can blow them out.

The site says they're "rated" at 100 watts RMS, but then, this site isn't known for having accurate specs.

Anyone ever blow up a piezo element? Or might it overheat and set the paper cone on fire? (Yes, there is a paper cone attached to the piezo element...)

Need I worry?

Thanks guys!
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Old 18th March 2003, 07:56 PM   #2
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Yes. Piezos can crack, they can heat up excessively and delaminate from their attached structures, they can have thermal failure at the wire attach. I've killed them in each of these ways, there may be others accessible to those more creative than me.
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Old 18th March 2003, 08:22 PM   #3
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Heh, I just did some testing with one of the spares.

I was able to run 100 watts through it at 3 khz no problem--didn't even flinch.

However, when I went down to 1 khz, the poor thing "died" after a few seconds at 10 watts. (I had the thing under a mountain of pillows so I could only barely hear it, so I wasn't quite sure when I'd killed it.) I pulled it out, opened it up, and was amazed at how warm the element had gotten.

Then, just to be sure, I hooked it up again. As it turns out, after cooling off for a minute, it works again! (Anyone have any more "scientific" explanations? Please enlighten me!)

well, now I know what I need to know--my midrange is going to be the most easy-to-kill, and my little amplifier does have enough juice to do it, if I handle things wrong.

Thanks guys.
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Old 18th March 2003, 09:00 PM   #4
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Heat could mess with the molecular structure of the crystal I suppose..
More likely, some difference in thermal expansion, but that would likely produce delamination from the metal parts.

Oh well. IANAP (P=Physicist).

Tim
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Old 18th March 2003, 09:29 PM   #5
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Some models of piezo tweeters have in-built overload protection through a light bulb(acting as a variable resistor) and a poly-switch(acting as a resettable fuse). That is why the tweeter worked after the `fuse' cooled down.

In models that do not have the protection feature, you will normally find a 30E 3watt resistor as a shunt load. This gets burnt first. If you replace this with a nominal 30 to 47E 5watt resistor, the unit will work again as good as normal.

Ofcourse, there are times, despite the above elements, the piezo element crumbles.
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Old 18th March 2003, 09:50 PM   #6
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From my experience of piezos about 15 years ago they were also very vulnerable to mechanical shock, of course they may be better now
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Old 19th March 2003, 12:06 AM   #7
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Default not fond of DC

They will sink 100 watts, but at what minimum frequency. I dont think piezos are fond of DC.
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Old 19th March 2003, 01:04 AM   #8
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I guess it really depends on what 100 watt amplifier your using.

A Nikko Alpha 130 will kill Piezo's everytime. From
Frequencies 5 Khz - Up non clipped signal.
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Old 19th March 2003, 07:58 AM   #9
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The rating in Watts for piezo tweeters is quite strange anyway. It is the voltage that sets the main limit on these. For the former Motorola piezos there was an average maximum of 20 Volts stated and a short term maximum of 30 Volts stated.

Although they can bear frequencies down to zero (=DC) they (and the user as well !!) benefit greatly if you keep low frequencies away from them.

Regards

Charles
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Old 19th March 2003, 02:47 PM   #10
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That's the thing that weirded me out.

I measured whilst testing and found that I had sent >35 VAC through it at 3 khz and it didn't even flinch! (I didn't know my amp could handle that much power!) I had the poor thing under a pile of coats so it didn't blow my ears out, but it didn't sound clipped at all.

Drop the frequency to 1khz, and suddenly the driver realizes its mortality! It only took about 10 VAC to make it stop responding, and then the strangest part, how pulling it apart made it start working again....

What a bizarre thing to be dealing with. I know now that there's no way I blow out these tweeters; unfortunately I don't have such a guarantee for the midrange. (I'm using the same drivers for the midrange as for the high-range.) Since it's crossed over at 1.2k, there's still a risk of suddenly losing midrange during a gig.

*sigh* Oh well. C'est la vi.
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