Those little yellow speakers...

[MagnumForce]

How do those little yellow speakers that come in some cheap mcdonalds toys work?

These are also found in all PCs, it is the part that makes the little beep when the computer turns on. I can make them act like a normal speaker (although the sound isn't that great). They are also found in watches.

They also make a really interesting mic,

They don't seem to make sound the same way a normal speaker does.

I would like to know, since this type of technology interests me, but I can't seem to find any info on them on the internet.

Is there any special setup I would need to make act like a normal speaker? I can hook it up to a cd player, but it isn't very loud and they seem much louder in their native equipment (small toys/computers).

These things can act as a microphone as well, but they detect sound much differently then a normal mic, (which is basicly a really small speaker, but doesn't have all the parts needed to make sound that is audible to the human ear)

They seem to turn anything touching them into a gient mic. They can pick up sound in solid objects (and liquids possibly).But not any sounds that travel through the air.

 

[Dr.EM]

I presume your talking about piezo transducers, flat golden discs? They use a vibrating crystal element as opposed to a megnetic construction. They have much higher impedance than magnetic types, and so are easier to drive directly.

 

[MagnumForce]

Thank you so much. I am primerly interested in experimenting with them in a microphone setup. Any suggestions on how to do this. I have succesfully recorded sound from them on a computer, but I want to know if there is a better way of doing it.

 

[madmikejt12]

is this what you mean? **broken link removed**

 

[MagnumForce]

Exactly!

I want to know if there is a special setup to make them into a good Microphone. (I don't intend to use them like normal mics of coarse)

 

[Dr.EM]

I don't think they make very good microphones. You've noticed that they work well picking up sounds in solid objects though, they can be used as electric drum pad triggers. There are specialised ones for use as microphones, a crystal earpiece can work to some degree. To have much chance you'll need a FET input amplifier, as it is the only kind that can work effectively with such high impedance inputs, even then you'll want to keep the cable short. Using that, you may be able to achieve gains high enough to use it like an ordinary microphone. A big cone in front is likely to help too :lol:

 

[MagnumForce]

Thanks for the info.

It seems these are also used in ultra sound sensors. I just now did a web search on them.

 

[audioguru]

Piezo transducers make a lousy speaker, a lousy tweeter that sounds like a whistle and a lousy speaker. Because they have a very strong resonance at about 4kHz.

 

[Someone Electro]

Thats exsactly why thay sound so crapy.

They play sound around that freq. loud becose it cathes it resonace freq..

They can be drived directly from an output becose they have many KOhms inpendace.

There resonat freq. also makes then crapy mics. But they are still used becose they are small and can be stuck in nerly evrything.

Old mobile phones whithout poliphonic ringtones use piezos too.

If you hoock it up to your multmtere and set it to milivolt range you will see the voltage changing if you push it whith your finger.

 

[audioguru]

A piezo transducer makes a good beeper in a smoke alarm.

 

[Someone Electro]

Yea some can be REALY loud.

A lot of stufff that beeaps uses piezos becose there cheap and small.But if you try to play music whith it will sound realy crapy.

Piezos are also used in some cigarete lighters. The ones that click wen you push the button.That click is an piezo ignitor fireing.At that click an litle hamer inside it slams on an piezo and creates about 15 000V so make an spark that then ignites the gas.

You can esaly take them out and shock pepope whith them.

 

[audioguru]

I've seen and heard piezo tweeters that are just a photo of a tweeter stuck on a speaker.
I think they sound better than a real one.

Smoke detectors have the piezo transducer mounted in a resonant cavity.
My new "ding-dong" doorbell does the same for a smoother, louder chime.

I replaced the piezo beeper in my son's alarm clock with a 1" 8-ohm speaker and a tiny audio amp made with an MC34119 bridged power amp IC. Now it's loud enough to wake all the neighbours but not my son. :cry: