Piezo Buzzers vs Magnetic Buzzers

[sirish]

Hello all the sane ppl in this insane world,

 First time here. I'm working on a product that has a piezo buzzer and it appears that the buzzer isn't too loud when inside casing. Especially in environments which are noisy. The part is PKLCS1212E4001-R1 and I see that its operated as per the datasheet ( 3Vpp, Square wave @ 4KHz ). From the datasheet I should be seeing a SPL of 85dB, but it doesn't sound that loud. The Vcc for the buzzer is 3.3V. I've given 5 and 12V and still surprisingly the sound hasn't increased.

I changed to a magnetic buzzer ST-04BH-P and at 12V this guy screams.

Unfortunately if I change to this buzzer, I have to change the footprint and trace routing. I'm trying to get away from that as its a little late in the project.

Is it true that magnetic buzzers are louder than piezo ? Or can I get a louder sound using the current Piezo. I've changed frequency to 4.2Khz and its improved a little, but not close to the magnetic one.

My other question is in the datasheet they say operating voltage range (Vp-p) as 25max. Whats this voltage ? the input square wave voltage or Vcc ? a little confused here.

Any help in this regards is much appreciated.

Thanks in advance.

Sirish

[Zero999]

What about adding a sound hole to the case?

How are you driving the buzzer? Please post a schematic.

[sirish]

Havnt explored modifications to the casing yet. That would involve a mold change and I'm not sure if management would be open to that. Won't hurt asking though.

I've attached the sch . The buzzer signal comes from an FPGA. Thanks

[thm_w]

I'm using the same part, although I haven't measured SPL it seems loud enough.

Use 5V if possible. Put a pot in place of the 1k and try tweaking it.
Whats the purpose of the diode? Does it get any louder with/without it?
Have you tried 3kHz as well?
Is FPGA output 3.3V?

[danadak]

Diode is to clamp the turnoff transient of the magnetic coil in buzzer,
to keep from blowing the MOSFET. Although there is a body diode in
MOSFET it has un-characterized switching performance, so BAT device
speed takes care of that issue.


Regards, Dana.

[Zero999]

It's a piezo buzzer, which doesn't produce back EMF. The diode will offer protection against voltages generated by the piezo if it's subjected to mechanical shock. Normally it's not a problem, if the piezo is driven from an IC, as the internal ESD protection diodes will clamp the excess voltage.

To get more power you need to drive the piezo transducer from an h-bridge. Attached is an example of using 74HCT04 logic gates which will shift 3V logic signals up to 5V and drive the transducer differentially. If you still need more power, then you could use a higher voltage and the CD4504B, CD40109B or a MOSFET driver: try the TC428. You might be able to get slightly more power by connecting logic gates in parallel to lower the output impedance.

Unfortunately this will require a PCB change. You might be able to find space to glue a tiny 74HCT3G04 to the board, dead bug style, and connect it to the piezo with bodge wires.

[bktemp]

An easy way of increasing the driving voltage for a piezo is adding an inductor in parallel. If you replace the resistor+diode with an small inductor (a couple of 100uH to 1mH), the voltage at the piezo will be much higher, making it much louder. It basically forms a step-up converter.

[Zero999]

An easy way of increasing the driving voltage for a piezo is adding an inductor in parallel. If you replace the resistor+diode with an small inductor (a couple of 100uH to 1mH), the voltage at the piezo will be much higher, making it much louder. It basically forms a step-up converter.

If you do that, you also need to remove the diode and ensure the driver transistor is rated to a high enough voltage.

[Seekonk]

On a product we made there was a pot to adjust frequency to resonance of piezo.  It was loud, so loud it fatigued the internal wires of piezo.  We were driving push pull from two inverters and that exceeded the spec for maximum drive voltage.  I agree with adding an inductor to existing design.

[Zero999]

The easiest way to design a circuit to drive a piezo at its resonant frequency, is to use a buzzer with an additional feedback terminal.

[danadak]

Piezo buzzers can look quite inductive.

http://electronics.stackexchange.com/questions/15421/whats-the-function-of-the-diode-in-this-driver-connected-to-a-piezo-buzzer

http://www.vtvt.ece.vt.edu/research/papers/08sas.pdf


Regards, Dana.

[KL27x]

You could also try alternating between 4KHz and 8KHz. Slow enough to hear the back and forth change in pitch. Much louder, IME. 8KHz will be an octave higher, and will also be a resonating frequency. Alternating really fast to mix up and alter the waveforms can make some crunchy sounding chirps that can also be subjectively louder, too. Some experimentation with frequencies may be needed. Not sure why this is the case, but most all alarms and sirens use more than a single frequency. It definitely works, IMO. Something about how the brain works, I guess. Like the eye it maybe detects changes better than absolute intensity.

An easy way of increasing the driving voltage for a piezo is adding an inductor in parallel. If you replace the resistor+diode with an small inductor (a couple of 100uH to 1mH), the voltage at the piezo will be much higher, making it much louder. It basically forms a step-up converter.

This is neat. Will have to try this.

First order of business, though, is to make sure you searched for available buzzers in the current footprint. They aren't all created equally. I would order one of each with most promising specs. A dozen or so, if possible, and do some testing. Results may be surprising. Maybe OP should also try 12V element if you are going to boost voltage. An enclosed 3.3V piezo maybe won't necessarily get much louder with more voltage, because of how it's built.

I have used the thin plastic housing as speaker. Adhere the bare piezo disc onto the inside of the housing. Then a hole isn't needed to allow the sound waves to exit. They are formed by the housing. Added assembly cost is an added concern, but at least you reduce size of pcb, a little bit, and in some cases can use a much larger element. Mainly I suppose useful if you want to make device very small.

High pitch 4KHz piezo element creates tiny sound wave, and the housing will suppress/absorb/block a lot of it, sans a hole. Hole doesn't need to be very big, at all.

[sirish]

Thanks everyone for the valuable suggestions. I never thought of adding an inductor. Very interesting idea. I'll give it a shot and see what happens. I did vary the frequency all that way to 8Khz and it really didnt make that much of a difference.

I've already ordered buzzers with similar footprint. Putting the buzzer on  housing is a good idea too. Gonna bring that up. I'm going to find out about adding a hole to the housing.

Thanks again !
Sirish