Piezo Buzzers - Controlling Volume?

[Arqiva BOC]

Probably a daft question, but I dont know the answer,

I have a project that contains a small DC driven piezo buzzer. Its too loud! Can the volume of these things be controlled, by simply reducing the DC drive voltage using a potentiometer?

I know I could just try it on the bench, but works getting in the way!

[Ambientnoise]

I have found that a series resistor works ok, needs a bit of trial and error.

Ken

[G6Tanuki]

It generally works OK, but in *some* cases you may find that feeding from a reduced voltage (or a supply with a raised source-impedance, as you'd get by simply putting a resistor in series) will cause the frequency of oscillation to change as well as the volume.

[Arqiva BOC]

Cheers chaps,

Not too bothered if the frequency shifts a bit. Its a sidetone buzzer in a 'Magic Morse' CW reader. I was just going to add a switch to turn it off as it annoys colleagues but thought i'd see if I could just quiet it down a bit!

Theres spare holes in the case sho I'll chuck a pot on it in series

[mole42uk]

I have a few of these in electronic flasher units for my old car. They are painfully noisy, but I find that a few layers of gaffa tape over the hole shuts them up quite easily.

[kalee20]

Err... wrap it in cotton wool?

[David G4EBT]

Yes, the volume is controlled by the supply voltage.

I guess the easiest way to determine the value of the series resistor needed to get the volume down to the desired level would be to temporarily wire a potentiometer in series, (say 1K, though that will depend on the supply voltage and the level to which it needs to be reduced). Then adjust the pot till you're happy with the sound level, note the resistance at that point, then select and wire in the necessary series resistor. Or it might just be simpler to have a few values of resistors to hand and substitute them till you get the optimum sound.

Have fun!

[Arqiva BOC]

Hi David,

I can try it either way on the bench. The idea is to allow me to vary the level, which is more ideal than turning it off or permanantly muffling it. Its ok when im using it and no one else is around, but its too loud if im with otherpeople as it annoys them (like lunchbreak practice in canteen!)

These piezo sounders can be incredibly loud for their size. Ive a 4S LiPo battery on my desk here and a 99p tester which has TWO of these, and its painful! I suppose it is intended to be heard over the noise of a model aero engine though...

[Biggles]

I have never proved it but someone once told me that blocking the hole where the noise comes out can cause the buzzer to fail. Probably worth taking the risk. We used to put a bit of electrician's tape over the darn things in the control room to stop the noise. If they are too loud I find it difficult to actually pinpoint where the noise is coming from. Not helpful when you have two or three alarms using the same buzzers dotted around the room.

[Cobaltblue]

The volume of pedestrian bleepers (on pedestrian crossings) are mostly controlled with a vane that progressively blocks the hole underneth the case from where the sound issues forth.

Its been that way pretty much unchanged for 50 years

Cheers

Mike T

[Herald1360]

Sticky Ty-Rap base over the 'ole!

Or Blu-Tak.

Series resistor can be iffy if the device goes GULP at startup, though a series zener may work.

[Boater Sam]

If you cut them up, they make good record cartridge crystal replacements. There is a youtube around.

[TonyDuell]

Originally Posted by Cobaltblue

The volume of pedestrian bleepers (on pedestrian crossings) are mostly controlled with a vane that progressively blocks the hole underneth the case from where the sound issues forth.

As is the ringer (bell) volume in at least some of the BT Ambassador/Statesman telephones. The volume control simply covers or opens holes in the underside of the chamber containing the transducer (which IIRC is a piezo element, but it's been some time since I've had one apart).

[Biggles]

You are right, Tony. We still use these at work believe it or not. The buzzer is a piezo element and has a little rotary shutter which has a limited effect on volume. They are actually a very robust telephone and take some breaking, although it has been done. If they are dropped on the floor the sounder can dislodge and fly out of the bottom of the phone. That's when you get a report of "telephone not ringing...outgoing calls ok"
Alan.

[TonyDuell]

Ah so that's how you get the sounder out of one... Dismantling the 'phone and trying to free it is a right pain

[Biggles]

They clip in easy enough but as you say they can be difficult to remove. We have lots of the sounders NOS in stores so we just break them out with the help of a large screwdriver. No doubt someone will say there was a proper service tool for doing this.