I wired a Fostex FT17H to a YAMAHA R-S202D receiver and put a 1µF capacitor on the + line (like the manual suggests). If i play now a "normal" audio file (<20kHz) everything is great but when I play an ultrasonic audio file (>20kHz) the tweeter speaker emits a crack/pop sound when starting the audio and when its finished.
The speaker and receiver are brand new.
Why is this happening?

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    \$\begingroup\$ "when I play an ultrasonic audio file (>20kHz)" - what exactly is in this 'ultrasonic' audio file, and why are you trying to put it through an audio amplifier? \$\endgroup\$ – Bruce Abbott Jan 16 '18 at 14:07
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    \$\begingroup\$ It sounds like your audio file has a DC offset in it. Have you looked at it in an audio editor? \$\endgroup\$ – Dave Tweed Jan 16 '18 at 14:41
  • \$\begingroup\$ @DaveTweed I generated only a sine wave (without offset) and the crack persists. \$\endgroup\$ – pythonimus Jan 29 '18 at 13:26
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    \$\begingroup\$ How did you shape the beginning and end of your tone? If you just start and stop it abruptly, this creates wide sidebands that can be audible. If you ramp the signal level more gradually over a few milliseconds (e.g., linear ramp, raised cosine, etc.), this effect will disappear. \$\endgroup\$ – Dave Tweed Jan 29 '18 at 13:32
  • \$\begingroup\$ @DaveTweed I m shaping linear out. That helps, but to get the crack sound unnoticable I have to fade out a 22kHz tone over 1 second! This cannot be normal? \$\endgroup\$ – pythonimus Jan 29 '18 at 15:09

Because at ultrasonic frequencies the capacitor looks more and more like a short circuit - don't do it! Putting ultrasonic frequencies into speakers designed for the audio range can result in destruction of the tweeter

  • \$\begingroup\$ This has nothing to do with why there might be a "pop" at the beginning/end of the file. \$\endgroup\$ – Dave Tweed Jan 16 '18 at 14:44
  • \$\begingroup\$ Possibly not, but that will be the least of his problems if he ups the power. Tweeters rated at "80 wats RMS!" seldom take even a fraction of that power without smoking. \$\endgroup\$ – Dirk Bruere Jan 16 '18 at 16:14
  • \$\begingroup\$ The tweeter speaker is designed to play up to 50kHz, and the manual also states that you have to use a capacitor: madisoundspeakerstore.com/pdf/FT17H_OM_E.pdf Should I connect it directly to the amplifier? Because the manual states to not to. \$\endgroup\$ – pythonimus Jan 17 '18 at 9:43
  • \$\begingroup\$ @pythonimus No. The capacitor is there to block low fequencies. However, when tweeters are rated for "80W RMS" as I have seen in the past, they do not mean that the tweeter can take 80W of ultrasonic frequencies. Typically it is something like "typical distribution of frequencies in the audio music range" at 80W. Quite often this is approximated by Pink Noise \$\endgroup\$ – Dirk Bruere Jan 17 '18 at 13:19
  • \$\begingroup\$ @pythonimus Try and find out what the real power rating is for signals above (say) 20kHz \$\endgroup\$ – Dirk Bruere Jan 17 '18 at 13:22

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