Almost OT: Anyone know how I could make this louder (piezo)

[ExpAnonColin]

http://www.discovercircuits.com/PDF-FILES/beeper4.pdf

Will the piezo I use effect how loud it is?  Is there any specific piezo I should get?  Does size matter?  Can anyone explain to me exactly what the piezo is doing here, I'm not very familiar with them.

-Colin

[casey]

i think it's acting as a crude "speaker" to transfer the beeps that
the circuit produces to an audible sound.  it appears as if the
schematic suggests a particular piezo for the best performance.

[Peter Snowberg]

Can anyone explain to me exactly what the piezo is doing here, I'm not very familiar with them.

The piezo element is just acting like a speaker here. The higher the voltage, the greater the piezo effect. Usually in watches, the piezo element is driven by the high voltage inductive kickback that comes from charging a small coil.

That schematic shows 120dB @ 12" which is enough to cause permanent hearing loss. Be careful your hearing. I have tinitus and I can tell you first hand you don't want it.

There is a local science museum that has a piezo demonstration exhibit that involves pressing on a crystal (using a little lever) about an inch long and it makes enough voltage to create 1/4" arcs. The Piezo effect works both ways... squeeze the crystal and you get high voltage out.... or add high voltage and it squeezes the crystal. (in this case making sound)

Will the piezo I use effect how loud it is?

Yes it will. Larger crystals can be MUCH louder. The mounting of the crystal also makes a huge difference in how loud the output is. This is a place where hard epoxy like JB-Weld works very well. Soft adhesives like silicone rubber will eat the sound.

Is there any specific piezo I should get?

Ideally, you want a piezo transducer with a resonant frequency that is similar to the sound you're putting into it or getting out of it.

Larger crysatals and/or larger mountings will have a lower resonant frequency.

As you experiment, try to use the largest variety of crystals you can find. The difference between random crystals can be quite huge.

Take care,
-Peter

[ExpAnonColin]

Excellent peter, thanks

I'll be sure to be careful about hearing loss with this thing, 120db is way up there, I was just worried because I want the sound to carry pretty far.

How big do you think the piezo should be for an application where I need it to be really loud?

-Colin

[Boofhead]

You will need a piezo that will cope with the large voltage swing.  You can get units targeted for alarm systems.

Like Peter said you need to get a Piezo unit which is tuned to the frequency range you want.  This is part of the acoustic design of the Piezo - you can't control this so you have to buy one that matches.  High-efficiency units have a some form of Helmholtz resonator or horn on the front.   Those cylindrical piezo beepers with a hole on one surface  are made that way for a reason - it's part of the acoustic (helmholtz) resonator. Usually there is trade-off between efficieny and the bandwidth of the device.  For this reason it is important to choose the right device.  Tuning the oscillator frequency to match the unit is also possible - provided the final frequency is acceptable.

Unfortunately when you buy low cost Piezo units there is very little information available.