14 Replies Latest reply on Jan 12, 2018 12:28 AM by fmilburn

    Maximize the Sound from a Buzzer

    fmilburn

      I am working on a gizmo that will alert the user to an event using sound and light.  It will be in a small enclosure.  My objective is to make the buzzer as loud and annoying as possible, with an option to soften it. This is what I have to work with power wise:

       

      • 5V from USB
      • 3V logic from microcontroller
      • gizmo will include a radio so want to avoid a switching boost converter

       

      I put together the following circuit on a breadboard which works more or less as expected:

       

      I don't need to vary pitch and the buzzer I just happened to have on hand is an active buzzer (that is to say it will buzz with only DC) which frees up a timer on the microcontroller.  I have looked through the E14 offerings and 85 dB seems to be about the best I can expect at 5V.  Before I blindly pick one and move on here are my observations and questions:

       

      1) There is a sharp transition between loud and soft.  It seems subjectively like it goes from a soft buzz to full throttle with a small change in R5 on the schematic.

      2) Are there high efficiency buzzers I am missing or is the only way to get higher volume with higher power and thus, higher voltage.

      3) I might consider an amplifier with speaker but it would have to be simple, sturdy, and compact.

       

      Thoughts and ideas are greatly appreciated!

       

      Frank

        • Re: Maximize the Sound from a Buzzer
          jw0752

          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

          4 of 4 people found this helpful
            • Re: Maximize the Sound from a Buzzer
              fmilburn

              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.

                • Re: Maximize the Sound from a Buzzer
                  jw0752

                  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

                  4 of 4 people found this helpful
                  • Re: Maximize the Sound from a Buzzer
                    jw0752

                    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

                    3 of 3 people found this helpful
                • Re: Maximize the Sound from a Buzzer
                  dougw

                  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.

                  4 of 4 people found this helpful
                  • Re: Maximize the Sound from a Buzzer
                    dr-jhc

                    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).

                    5 of 5 people found this helpful
                      • Re: Maximize the Sound from a Buzzer
                        dougw

                        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.

                          • Re: Maximize the Sound from a Buzzer
                            fmilburn

                            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”.

                              • Re: Maximize the Sound from a Buzzer
                                rachaelp

                                fmilburn  wrote:

                                 

                                I will never forget the professor who thought most of the derivations and math “obvious from inspection”.

                                I had a lecturer at university who was like that. He was supposed to be our maths lecturer but when everything is "by inspection" it gets hard to follow! Oh, that and he wrote in circles around the board and as he was cancelling out things or rearranging an equation he would just wipe them off the board and rewrite the updated version, which made it very hard to keep up and write down in our log books!

                                 

                                Best Regards,

                                 

                                Rachael

                                • Re: Maximize the Sound from a Buzzer
                                  dougw

                                  I can certainly relate to the notion of profs who were legendary for all the wrong reasons.

                                  Profs who spent their lecture time telling stories and never covering the subject matter at hand.

                                  Profs who write so fast or flip slides so fast it is impossible to keep up, much less understand what they are trying to get across.

                                  Profs with such strong accents, it was impossible to understand what they were saying.

                                  Profs who mumble incoherently.

                                  Tyrannical Profs who were on a power trip.

                                  But they do make you appreciate the gems even more.

                                • Re: Maximize the Sound from a Buzzer
                                  dr-jhc

                                  Thanks for the link - that will keep people busy for a while!

                                   

                                  I'd start with a horn that looks like it might work reasonably well (based on that article) then 3D print some variations of these and test them. I'm sure you'd get something good enough quite quickly doing this.

                                  1 of 1 people found this helpful
                              • Re: Maximize the Sound from a Buzzer
                                shabaz

                                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.

                                5 of 5 people found this helpful
                                • Re: Maximize the Sound from a Buzzer
                                  fmilburn

                                  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

                                  • Re: Maximize the Sound from a Buzzer
                                    fmilburn

                                    Thanks again for the great response to my question and the help provided.  There is a preliminary schematic posted here that shows the current state of the circuit I am building:  AIS Alarm - Schematic