|Acoustics of the clarinet|
Notes are the written pitch.
Note how similar this spectrum is to that for A3. (Of course, the clarinet overblows a 12th.) The only substantial difference is the reduction in the first peak. The purpose of the speaker key is just that: to destroy the fundamental resonance so that the instrument will not 'drop down' to the lower register. See register hole for details.
Although it doesn't feel like it to your fingers, acoustically speaking, this fingering is actually a cross fingering: it has a closed tone hole below the first open one. This is responsible for the shape being more irregular from about 1.0 to 1.6 kHz than the curves for D#5.
For a general discussion of the clarino register, see the description on B4.
Sound spectrum of a Bb clarinet played using fingering for E5.
For more explanation, see Introduction to clarinet acoustics
You can hear E5 played.