This short cw audio file from the text of TOM's , W4BQF's famous article, COPYING CW OVER 70 WPM, demonstrates how adding some audio harmonics to the pure sine wave cw tone, helps when trying to listen and copy morse code while listening on your speakers.  Using a VST PLUGIN called MWaveShaper,  you can "dial in", just enough and the "right kind" of harmonics to make listening to cw on speakers easier and more comfortable; minimizing ringing, echo, reverberation, cancellation, bounce back from walls that you normally get with a pure sine wave.
(The file alternates sending with PURE SINE WAVE and sending with HARMONICS added, so you can hear the difference)

ADDING SQUARE WAVE HARMONICS FOR BETTER CW COPY WITH SPEAKERS

chaseology