It is crucial to match amplifiers to speakers correctly and use them with care. But in some cases you want extra protection from blowing up the speaker. I have thought of a ridiculously simple idea - to use zener diodes parallel to the speaker.

  • Zener diodes let through current only after certain voltage point (for example 5v) and by doing so they keep the voltage stable at that point. Zener diodes are mostly used as voltage regulators.

Not sure if it is wise to do so and how it will clip the sound when the diodes start letting through current of overvoltage but as I see it - it might clip the sound badly but it will still protect the speaker from too much voltage going in. I have found few circuits using this technique but descriptions are really lacking and I am not sure what to expect.

Sure, there are better options than using zener diodes as speaker protection circuit but for the sake of simplicity I am very interested if this would work as intented - protect speakers from over-voltage and power peaks.

My (simple) circuit design:

*Light diode acts as a clip indicator


simulate this circuit – Schematic created using CircuitLab

Similar circuit I have found online though it does not use any resistor in between them basically creating a 2ohm short for voltages over (in example) 5v. Could anyone comment how would amplifier handle such circuit design?

enter image description here

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    \$\begingroup\$ Speakers can take massive overloads but not continuously. Music produces a big peak wattage but a small average wattage. Do you get where I'm coming from? \$\endgroup\$ – Andy aka Jan 4 '17 at 18:18
  • \$\begingroup\$ The added circuitry is going to add some stray capacitance to your speaker circuit and will affect how the speaker sounds. I don't know know enough about zener diodes to tell you if it's going to be at all noticeable, but if you simulate this circuit make sure you're simulating the added capacitance. \$\endgroup\$ – Adam Jan 4 '17 at 18:24
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    \$\begingroup\$ @Adam, don't be silly. A few tens or hundreds of pF in a speaker circuit aren't going to make the slightest bit of difference, except maybe by helping to suppress RFI. \$\endgroup\$ – Dave Tweed Jan 4 '17 at 19:00
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    \$\begingroup\$ Yes, putting a resistor in series with the speaker would be stupid, for a load of reasons. But, really, I think I'm right. To work as a voltage regulator (or limiter), a zener needs to be put after a resistor in series with the supply. If you put the resistor in series with the zener, it is just useless. Look at your schematic: the speaker is still in parallel with the source. If you assume the source is perfect, the source voltage won't be lower at the speaker: there is nowhere to have a voltage drop. Now, of course, an amp is not a perfect source. But I'll maintain relying on that is ugly. \$\endgroup\$ – dim Jan 4 '17 at 21:35
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    \$\begingroup\$ Moreover, if, as you said earlier, "the whole point of doing this circuit is to prevent the amplifier going into clipping", you should maybe stop thinking about it. Clipping is not a problem for the amps. It is a problem for the speakers. And, with your circuit, you are basically making the speakers clip before the amp would clip them... \$\endgroup\$ – dim Jan 4 '17 at 21:51

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