|Acoustics of the saxophone
Bb tenor saxophone
Notes are the written pitch.
In the acoustical sense, this note is still in the second register – it plays (normally) at the second peak on the impedance spectrum. This fingering uses a register hole. This causes a leak in the bore that weakens the first impedance peak (although both peaks will play comfortably with different embouchures). Above the second peak, the curve is irregular: see the discussion in cut-off frequency.
Compare with the impedance spectrum for a soprano sax on written E6: same fingering but sounding one octave higher.
Sound spectrum of a Bb tenor saxophone played using fingering for E6.
For more explanation, see Introduction to saxophone acoustics.
You can hear E6 played.