Maximize the Sound from a Buzzer

Hi Frank,

I doubt if it will make much difference but you can squeeze an extra volt into the Buzzer if you use an N Channel MOSFET  instead of the NPN Transistor. Depending on how you are driving the transistor it may work without modification or you may need a 10K resistor to pull the gate to ground.

John

Hi John,

I am a retired mechanical engineer and still learning electronics so much appreciated.   I have been using bipolar transistors up until now for the most part but did get some BS170 N-Channel MOSFETs a while back.   I will probably be driving the transistor with a MSP430 at ~3 V.  No problem putting a 10K pull-down resistor on the gate if needed and will keep that in mind.  I note from the datasheet that the BS170 has very low Drain-Source current with Vgs of 3V.  Assuming I am reading this right, it would be a poor choice.  I will have a look through what is available but suggestions are welcome.

Hi Frank,

I have traditionally used an NTD 4906 for these applications as they are logic level and will saturate by 3 volts. I just set up a test with 5 volts on my load to the drain of an NTD4906 and I was able to get full saturation at 2.9 volts under a 750 mA load.

There should be some equivalent N ch MOSFETS out there as these are listed as obsolete now. The trick will be to make sure they will handle the current of the buzzer and that they are specified as "logic level" or have a Vth low enough to work.

John

I took a look at the BS170 data sheet and its Vgsth is slightly higher than the NTD4906 but the big short coming is that at full saturation it has a much higher DS resistance.

John

Piezo buzzers will provide higher sound pressure level with lower input power than magnetic buzzers. The input power is minimized and the output sound pressure level is maximized when the buzzer is operating at its resonant frequency.

You can get 125 dB with 200 mA if you really want it that loud.

A PUI (AI-5025-TWT-R) generates 115 dB with 75 mA at 12 V.

At 5V you can get 95 dB with 5 mA. (Mallory PT-3529PQ).

You can put several in parallel if you want louder sound.

Another option could be to do something mechanical to provide better impedance-matching of the buzzer to the air: essentially some way to make the buzzer move air more efficiently. Some kind of waveguide (like you get for bass on ported music speakers) can work well. Your frequencies won't be low, so the waveguide won't be large.... but you need some way to design it.

As dougw said, because your frequency is fixed, resonance will help you. Attaching the buzzer to another, larger, object that has the same resonant frequency can help you get more air moving (so higher SPL).

Hi Frank,

Interesting topic I've looked in the past for good buzzer circuits too, and it seems quite hard to find an off-the-shelf single chip to do this these days. One trick I recall was to use a schmitt hex inverter or quad NAND integrated circuit, and parallel up some of them for drive, and put the piezo buzzer across it, so that it is in parallel too, for doubled-up Vp-p. It would be possible to use one of the gates for an RC oscillator.

Thanks for the great responses  I am pretty sure the "correct answer" is "all of the above".  I will publish what I come up with after working through it.

Frank

Good point dr-jhc . A horn shape is likely the best way to match impedance, although which horn shape is best, is a complicated question.

Awesome link.  This is something I actually worked on (more accurately struggled with) one summer as a student project many years ago.  I will never forget the professor who thought most of the derivations and math “obvious from inspection”.