The disadvantage, however, is that indicators operate on a fixed frequency, reducing the flexibility offered to achieve an alternate frequency as application requirements change. Because of this, engineers do not need to worry about building a complex circuit to drive the buzzer. Then you can objectively decide whether it's "loud enough".As mentioned earlier in the presentation, piezo and magnetic indicators have the driving circuitry built into the design, creating a plug and play solution. by tweaking the volume while playing it through a speaker, then actually measuring the sound level at a fixed distance from the speaker using a sound meter. The mouth and fan unit (3d printed with fan bolted in) would be mounted inside, with just the pipe mouth exposed to the outside (plastic bits poking through a hole).īut most importantly: you should decide how loud that sound should be - e.g. The "pipe" can be a Helmholz resonator formed from the enclosure of the device itself, as long as the enclosure can be otherwise air-tight. It's not small but it can be fairly light for its size, and it doesn't get much simpler. Should work with just 1" of air pressure. This is not particularly light but can be simple: think an Altoids can soldered shut, filled with water or alcohol, with one or more flat transducers soldered to holes on one flat side, with the other flat side coupled to an acoustic resonator.Īnother solution to that problem is a (possibly folded) organ pipe (3D printed) with a small fan (1.5-2" diameter should be plenty) as air source. Since the piezo transducers are fairly stiff, there is quite an acoustic impedance mismatch between them and any chamber filled with air, and an intermediate low-viscosity fluid could be used to enlarge the coupling area. If you really think you need a vibrating membrane, then the membrane has to be tightly coupled to a resonating chamber. What I am trying to do is move as much air as possible with a vibrating membrane unit that is extremely light and simple You could just as easily use a binary counter and a little mickey mouse logic to get the same result if your divisor is a power of 2. People experienced in listening analytically, such as musicians, easily hear both the low and high tones.įor a commercial product that I engineered using this effect, I used a microcontroller running a simple program loop to "skip" one square wave in X to make the tone that I wanted. Interestingly, if you present this sound to someone who is not expecting a high, screechy tone, they often say that they only hear the low tone. I'm not sure why this works, but it works. You will hear a loud, raspy 125 Hz tone superimposed over a rather faint 4 KHz tone. You now have a "missing" wave 125 times per second in an otherwise continuous train of square waves at 4 KHz. One time in every 32 square waves, inhibit the pulse.Make a square wave at 4000 Hz to drive the transducer.Your desired frequency is in the ratio 1:32 of the natural resonant frequency. Say you have a piezo disc with a natural resonant frequency of 4000 Hz but you want a tone at 125 Hz. (I can't help you if it's a piezo "buzzer" that has its own fixed-frequency driver powered by DC.) If you have a bare piezo transducer which you are driving with your own circuitry, I have a way for you to get a loud, arbitrarily low-frequency sound.
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