The effect of reed hardness
In the preceding section we have ignored the compliance of the reed, discussed above. This acts in parallel with the bore, and its impedance decreases at high frequency, so its effect is to reduce the rise in impedance with frequency: softer reeds give lower overall impedance at high frequency. Further, the very high resonances are weaker and occur at lower frequency when you use a soft reed.
On this figure, the single dots are the experimentally measured impedance spectrum for E3, with a value of the compliance corresponding to a hard reed. The continuous line (actually the experimental points joined together) shows the spectrum for a soft reed. At low frequencies, there is not much difference, but you can already see a slight difference in frequency: the hard reed plays sharper, all else equal. As you go to higher frequencies, you see that the soft reed gives lower peaks. Lower peaks are harder to play, so the hard reed makes it easier to play high notes. (Unfortunately, a hard reed also makes it easier to play squeaks.)
To understand more about the detailed shape of these impedance curves, see the discussion of the experimental results for E3.