Acoustics of the saxophone

Bb soprano saxophone


Music Acoustics UNSW


a key depressed
a key not depressed
a hole covered
a hole uncovered
a part of the mechanism that is not normally touched
Details in fingering legend.

Acoustic schematic
a closed tone hole
an open tone hole

Non-specialist introduction to acoustic impedance
Non-specialist introduction to saxophone acoustics

Notes are the written pitch.
Frequencies are the sounding frequency, for Bb saxophone.
Unless otherwise stated, the impedance spectrum is for a Bb saxophone.

Impedance spectrum of a Bb soprano saxophone measured using fingering for D5.

This is the first standard fingering for a note in the second register – meaning that it plays at the second peak on the impedance spectrum. It differs from D4 (the corresponding note in the first register) in that it uses a register hole. This causes a leak in the bore that weakens (and mistunes) the first impedance peak, but has little affect on higher peaks – see register hole for an explanation, and compare with D4, whose impedance spectrum is almost identical except for the first peak. Above about 1 kHz, the curve is irregular: see the discussion in cut-off frequency.

Compare with the impedance spectrum for a tenor sax on written D5: same fingering but sounding one octave lower.


Sound spectrum of a Bb soprano saxophone played using fingering for D5.
For more explanation, see Introduction to saxophone acoustics.

Sound Clip

You can hear D5 played.

As noted above, this note plays at the frequency of the second peak in the impedance spectrum, the first being weakened by the register key. Note that the second and fourth impedance peaks are the only strong resonances corresponding to harmonics. Nevertheless, there are still many higher harmonics.

The higher harmonics occur because the vibration of the reed and the acoustic component of the air flowing past it involve nonlinear processes, such as the turbulent loss of kinetic energy of the air. This nonlinearity produces the higher harmonics. The reed motion becomes very nonlinear when it begins to strike the lay. At this dynamic level, the power of the fundament at f0 changes relatively little, and blowing harder instead adds more power to the higher harmonics, making the sound brighter. In its low range, and especially when played loudly, the fundamental of the saxophone is often weaker than some of the harmonics, in part due to the relatively weak first impedance peak. For more detail, see What is a sound spectrum?

In the second register, the first one or two harmonics coincide with peaks in the impedance spectrum, so the bore helps radiate them strongly. For high harmonics, there are usually no corresponding strong resonances. However, these radiate fairly well anyway, because the saxophone is a reasonably good megaphone at these frequencies. (The small peak in the sound spectrum at 2.9 kHz is probably broad band (breathy) sound being particularly well radiated by the bore resonance at that frequency.)

Alternative Fingering

Bb soprano saxophone


Impedance spectrum of a Bb saxophone measured using alternative fingering for D5.This fingering is not usually used for D5, except in trills from C5 or C#5. It uses the fingering for C#5 (no fingers!) plus one palm key to open an extra tone hole. So this fingering is still in the first register, and its impedance curve looks much like that for C#5, shifted up 6%, and quite unlike the curve for the second register D6 shown above.


Sound spectrum of a Bb saxophone played using alternative fingering for D5.
For more explanation, see Introduction to saxophone acoustics.

Sound Clip

You can hear D5 played with alternative fingering.
Fingering legend
How were these results obtained?

Contact: Joe Wolfe /
phone 61-2-9385-4954 (UT +10, +11 Oct-Mar)
© 1997-2009 Music Acoustics UNSW