The Structure of the Bassoon
[Experiment1]Comparing the Sound of Tone Holes cut Obliquely and Perpendicular

Does the sound change according to whether the bore of a tone hole is cut obliquely or straight? We performed an experiment with a vinyl chloride tube.

Experiment procedure

1. Prepare two vinyl chloride tubes (PVC pipe) of the same length, and cut a hole at the same position in both.
2. Attach a straw to each hole, either perpendicular to the tube or obliquely.
3. Cut the straws so that they extend to the same perpendicular distance from the surface of the PVC pipe.
4. Attach a bocal, blow into it and compare.

The PVC pipe simulates the bore of the bassoon, while the straw acts as the bore of the tone hole. The position at which the straw is attached to the PVC pipe is the same whether it is attached perpendicular to the pipe or obliquely. This is to control the conditions of the experiment aside from the angle and length of the straw.
Comparing the sounds produced in the two experiments, the pitch of the sound produced with the oblique straw is a little lower than that produced with the perpendicular straw. This is because the tube extends farther when the straw is attached obliquely. The 6 centimeter difference in length of the two straws, of 7 centimeters and 13 centimeters respectively, is expressed as the difference in the pitch of the sounds. On a real bassoon, there are no parts that are actually this thick. The deepest is the 4 centimeter bore of the tone hole on the tenor joint. When designing a bassoon, there are a variety of tuning methods by which the pitch can be made very slightly lower. These include adjusting the angle of the tone holes to lengthen the bore, as was done in this experiment, making the tone holes smaller, adjusting the position of the openings of the pipe so as to lengthen the bore, and other methods. That said, because the number of tone holes and the size along the whole length of the bore have an effect on the sound, fine tuning of the pitch is not straightforward.