Interestingly, it probably mainly the integrated amplifier (or Bluetooth receiver - I can not say) - so the electronics are to blame.
If you connect the speakers with line-in with a high end Bluetooth receiver / amplifier, so the Lautsprecherchen play equal time to significantly fresher, fuller and louder.
In short ... for the price certainly not a bad buy and delivered will be promptly and perfectly. For me clear 5-star value. Thanks!