Update: This was the first design attempt. An alternate approach to creating a Low A extension is detailed here.
The Low A “Insert”: The important thing about this extension is that it does not effect the intonation of your instrument. Shoving a cardboard or plastic tube in your bell to lengthen the bassoon is a nice and cheap way to do it, but other notes (surprisingly some of the ones in the staff like the one finger E) tend to go way out of tune.
My extension is not something that you stick in the end of your bassoon. Instead this “Bb bell extension” is a small piece which goes *in-between* the bass joint and the bell. It effectively makes the bassoon a few inches longer and lets you play low A. Here’s a video that shows the manufacturing process, and also how it works and sounds:
The best part about this design is that you play everything normally, but to play low A all you have to do is turn the extension 90 degrees and it changes whether you’ll play Bb or A.
I made my extension by taking parts from a pretty cheap but quite broken 1960’s bassoon.
The next thing is to saw the bell of the “donor” bassoon down to 8 inches in length. Next, I got the help of a friend who’s got a really nice woodshop who carefully turned “donor” bell on a lathe so that my normal bell would fit on the end.
Note: The inside diameter of a bassoon actually varies a LOT from one manufacturer to another. This means that its not possible to make bell extension that will work on every bassoon. They have to be done carefully one at a time. So, I did a lot of sanding and eventually the extension fit onto the bass joint of my bassoon and the bell fit on the top. UPDATE: I have since added a 3/4″ divot in the wood to allow for some cork which allows for more variability in bell diameter as well as wood expansion due to humidity.
With the woodworking done, I fabricated a new metal key to make it all work. The extra key closes the pad on the extension as well as the one above on the bell.
A huge thank you to John at www.neil-woodworking.com for helping with this project!