One of the things we see here is a planar tweeter crossed over at far too low a frequency. With very few exceptions, planar and ribbon tweeters generate a *LOT* of harmonic distortion if crossed over below 4 or 5 kHz.
This speaker has what looks like a HIiVi or Beston type planar tweeter with horn loading. You really can't use those things down to 2,000 Hz like it seems they tried to do here - the driver has OK amplitude response at such frequencies but horrible THD.
Note- For AMT type tweeters- they have more "excursion" and so produce sound down to the ~2,000 range without all this distortion, generally speaking.