What lowers the pitch when the mouthpiece is pulled?

[jbtsax]

As an experiment I warmed up an alto saxophone and found the placement on the cork that A=440 and A=880 were best in tune and marked that spot.

I then inserted a 1/2" long delrin bushing whose id matched the id of the end of the neck and whose od matched the id of the shank of the mouthpiece into the shank of the mouthpiece. I then slowly pushed the mouthpiece up to the mark on the cork and played again. The pitch was 20 cents sharper for the low A concert and even more for the octave higher.

In effect the volume inside the mouthpiece was reduced without the physical length of the saxophone being changed and there was a pronounced effect on the pitch. The test could be done in the reverse as well, tuning with the insert in and then removing the insert to increase the volume inside the mouthpiece.

This simple experiment seems to suggest that it is the increase in volume inside the mouthpiece when it is pulled that lowers the pitch and not the increase in the length of the instrument to the tip of the mouthpiece. However, it is probably not that simple since in the real world both the volume and length change when the instrument is tuned.

John

 

[Gandalfe]

So when you blow louder...

 

[Heckelphone]

Cf. A. Benade

As an experiment I warmed up an alto saxophone and found the placement on the cork that A=440 and A=880 were best in tune and marked that spot.

I then inserted a 1/2" long delrin bushing whose id matched the id of the end of the neck and whose od matched the id of the shank of the mouthpiece into the shank of the mouthpiece. I then slowly pushed the mouthpiece up to the mark on the cork and played again. The pitch was 20 cents sharper for the low A concert and even more for the octave higher.

In effect the volume inside the mouthpiece was reduced without the physical length of the saxophone being changed and there was a pronounced effect on the pitch. The test could be done in the reverse as well, tuning with the insert in and then removing the insert to increase the volume inside the mouthpiece.

This simple experiment seems to suggest that it is the increase in volume inside the mouthpiece when it is pulled that lowers the pitch and not the increase in the length of the instrument to the tip of the mouthpiece. However, it is probably not that simple since in the real world both the volume and length change when the instrument is tuned.

John

If I remember right from Benade's book, the internal volume of the mpc is supposed to approximate the volume of the truncated bore it replaces. "Truncated"? If the sax tapered all the way to a point it would be too hard to blow: the bore is truncated at the end of the neck. Unfortunately, it is not a straightforward calculation, because the flexibility of the reed also factors in: the softer the reed, the greater the apparent (for acoustical reasons) internal volume. (NB: this is why it is a mistake to make single-reed mpcs for oboes and bassoons by trying to carve the shape of a double reed inside the chamber of a mpc blank. The solid mpc appears much smaller than a double reed of the same dimensions. And the shape doesn't really matter.)

So, yes, you are correct that it is the change in internal volume of the mpc that matters in tuning.