Solved problem? Yes, long ago.
However:
Perfect? No, not as close to perfection as electronics (i.e., amplifiers, DACs, etc.). Frequency response and harmonic distortion in speakers still is significantly worse than the best electronics. On top of that, add phasing issues between drivers in the vertical axis, combing issues in multi-channel systems, imperfections with passive crossovers, etc. But, speaker technology continues to improve.
However:
Perfect? No, not as close to perfection as electronics (i.e., amplifiers, DACs, etc.). Frequency response and harmonic distortion in speakers still is significantly worse than the best electronics. On top of that, add phasing issues between drivers in the vertical axis, combing issues in multi-channel systems, imperfections with passive crossovers, etc. But, speaker technology continues to improve.