I think that big difference between old and new series is because, new series (HTM1D-HTM2D-HTM3S and HTM4S) have loudspeakers redesigned.
New series use a simple crossover (6dB/oct) because loudspeakers byself limited the frequency response.
Old models have need a more complex cross-over filter to obtain the same output curve.
With less cross over components the sound might be more clear
New series use a simple crossover (6dB/oct) because loudspeakers byself limited the frequency response.
Old models have need a more complex cross-over filter to obtain the same output curve.
With less cross over components the sound might be more clear