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Driving a Piezo Tweeter ?

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ronp849

New Member
I have been looking at piezo sounders for another project and have looked at how the small 12volt alarms are put together.

The one I have uses a 26mm dia sounder running at approx +/- 110v peak (220v pp).

The high voltage is generated with a small auto transformer switched with a square wave from a 555 timer via a power transistor.
These units are designed to be ultra cheap so I doubt whether any of the components are special. The transformer is ferrite cored and the power transistor is a D313.
The power consumption was approx 200mA @12v.
Running frequency is approx 2.5 KHz

One point you might consider - running the sounder in free air gave a pathetic squeak - fitting it into the alarm housing nigh on burst my eardrums - conclusion - the accoustics of the disc housing has as much effect on volume as the electronics.

Regards

Ron
 
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audioguru

Well-Known Member
Most Helpful Member
I put a bottle cap near the rear of a little piezo transducer then tuned the frequency to the resonance.
Wow! It became very loud like a smoke alarm.
 

Sceadwian

Banned
**broken link removed**
The engineers guidebook on how NOT to build a bridge, and harmonics 101 from a signal mistake.. =)
Resonance is VERY powerful.
 
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unclejed613

Well-Known Member
Most Helpful Member
don't forget that Tesla almost ended up homeless as a result of putting a little "ticker" on one of the support girders in the basement of his apartment building and timing it to the amount of time it took for a hammer strike to echo from the device's location to the top of the building and back again. with his little device tapping on the girder for a few hours while he went out for dinner, the building was swaying and breaking windows as if in an earthquake by the time he returned. resonance can take small amounts of energy and continually add them with very little loss until something usually breaks. try to avoid resonant peaks in the piezo element's response for extended periods of time. an enclosure can greatly add to the efficiency of the device, and a horn (as in the super tweeter enclosures) can also add efficiency by "impedance matching" the air column. the wavelengths are small, so the airspace around the piezo element will be small as well, as will be the matching section of the horn.
 

Sceadwian

Banned
I don't believe that for a second unclejed.
Harmonics are powerful, but that 'little ticker' must have been DAMN big to shake a building, harmonic or not. Myth Busters did a piece on this with a several pound linear motor tuned to a real bridge's harmonic, they could detect it, but it wasn't bringing the bridge down. Something large enough to shake a building down would have had to have been hundreds of pounds, and the building design would have had to have been very primitive as well..
 
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