TL;DR: I am looking for a the best way to amplify all external sound but cut off at a hearing safe level.

I am attempting to incorporate active ear protection into an old SPH-4 helicopter helmet. I have a pair of earmuffs that have external microphones that first amplify all external sound then cut it off at a certain level to avoid hearing damage. These are great because you can have a conversation with someone without having to shout. There is a knob on the side that controls the volume and you are even able to turn it up past what you would be able to hear normally and get "super-hearing". I find all this functionality very helpful and would like to add them to my helmet.

My current best idea on how to accomplish this is using an SparkFun Sound Detector (SEN-12642) which has a built in electret microphone and outputs the audio signal, an analog signal representing sound intensity and a pin that goes high when sound is above a certain level (adjustable with a through hole resistor). If I connect a potentiometer to the adjustment traces and a NOT gate to the high/low pin I should get a signal that is high any time the audio signal is at a safe level. If I use that pin to enable an amplifier that takes in the audio signal from the electret mic and connect that to the speakers built into the ear cups, I think that will accomplish my goal.

My question is: is there a better way to do this? It seems like it should work but it does come with some drawbacks including shutting off all sound when sound levels are high enough to trigger the sensor, needing to manually adjust the cutoff and output volume levels with a pair of potentiometers as well as being a fairly bulky solution. I would much prefer the ability to clip the loudest parts of the audio signal rather than shut it off entirely.

  • 2
    \$\begingroup\$ What you are describing is a compressor or limiter in audio terms. \$\endgroup\$
    – JYelton
    Commented Jul 27, 2023 at 19:45
  • \$\begingroup\$ I agree with @JYelton . You describe compression. These have a threshold (volume level), a ratio ( the actual compression applied to reduce the dynamic range), and an attack (how fast it reacts) and release (how long it stays engaged.) Then there's the makeup part, which gets back the gain you lost by having the rest operating. (There's also sidechaining, ducking, and deessing, for another time.) Anyway, look for some kind of compressor, I think. \$\endgroup\$ Commented Jul 28, 2023 at 11:59
  • \$\begingroup\$ Thank you for giving me the search terms I need. I've had a bear of a time trying to find info on this but not knowing what to google. I keep finding info on avoiding clipping which isn't what I need \$\endgroup\$
    – David G
    Commented Jul 28, 2023 at 15:55

1 Answer 1


My question is: is there a better way to do this?

I've seen anti-parallel diodes across handset earpiece transducers. They are used to limit the risk of acoustic shock on telephone handset earpieces. It may not be better but it's a whole lot simpler. The diodes clamp the peak to peak voltage to around 1.4 volts.

Of course, your earphones may be more sensitive but, you can use series resistors to ensure that the amplifier cannot deliver a level that can cause acoustic shock.

So, does better mean just as effective but far simpler and requires no DC supply or, does better mean something else?

  • \$\begingroup\$ That is a very clever solution and I will try it first. Simpler defiantly counts as better. The big thing I'm looking for is trimming too loud sounds instead of cutting them off like the sparkfun design would do so that also qualifies as "better" imo \$\endgroup\$
    – David G
    Commented Jul 28, 2023 at 15:58

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