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In a circuit I am designing there will be high frequency noise output into a speaker at -60 to -80 dBV. It's just that I opted to use a simple 2nd order LC filter (47 uH, 470nF) for delta-sigma quantization noise. Now the intuition tells me it's not going to harm my speaker, as its inductance itself is also going to attenuate that noise. But how do I prove it formally, or are there any sources backing this?

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  • \$\begingroup\$ I really doubt that you're going to break anything, but since you're looking for formal proof, I can only point you in a direction that looks good to me and let you run with it: Try thinking in terms of the speaker's impedance at those frequencies, from which you can get the power that it has to dissipate. It should become pretty clear that it's okay from a component-life standpoint. Whether it's acceptable or not to produce acoustic energy at those frequencies is a different problem. \$\endgroup\$
    – AaronD
    Jan 7, 2016 at 3:17
  • \$\begingroup\$ It's more like I'm trying not to write something that could be contested in my BSc thesis ;) It's going to be a 2W speaker, so obviously no fancy stuff like 2-way crossovers. I do know though, that careless people managed to blow their tweeters with udial.ape test file ;) \$\endgroup\$
    – Michał B.
    Jan 7, 2016 at 3:31
  • \$\begingroup\$ Yeah, tweeters in passive multi-way systems are not designed for the entire system power. The amp will be perfectly happy with a full-scale, ultrasonic signal, but the tweeter won't! \$\endgroup\$
    – AaronD
    Jan 7, 2016 at 3:34
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    \$\begingroup\$ @Michal B., supersonic generally implies 'above the speed of sound. Ultrasonic generally refers to sound above the upper theshold of hearing. I think you mean the latter. \$\endgroup\$
    – Transistor
    Jan 7, 2016 at 7:58

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-60 to -80 dBV is not going to hurt a 'regular' speaker, or any other kind.

Assuming the speaker has an impedance of at least 2Ω, the power at -60dBV will be in the region of 0.000001V2*2Ω = 2 picoWatts.

The primary reason for people blowing tweeters in audio systems is turning the volume up too high so that the amplifier goes into clipping. The resulting square waves are not only up to twice as powerful as the amp's rated sine wave output, but are also full of harmonics that will be fed into the tweeter through the crossover filter.

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