The Fixed Chamber Reed
The photograph on the left shows the area scraped away (using a small radius scraper tool, such as the ProPrep #200 with Pointed Channel scraper blade) to accept the section of tube that will be embedded as the fixed chamber. The reed is formed with a temporary butt wire which is removed and the chamber tube is inserted. The butt wire is replaced and the tube is wrapped with a rubber band to conform to the forming mandrel. The brass tube used is 7/32″ x 0.014 (or could be 5mm) in diameter. The metal tube length is 5-6mm, with the top end placed just below the 2nd wire position.
The lower end of the tube sits just in front of the bocal penetration point (9-10mm). This size tube produces a large fixed throat which gives the reed not only more consistency because the reed tube does not shrink, but also gives the reed more expressive “room” and flexibility in the middle register. Smaller diameter tubing is certainly possible, and a much smaller tube inserted into an existing reed seems to increase response in the extreme high register.
This technique was also recently done on contrabassoon reeds in two different throat sizes with great success. Aluminum tubes were used in this case, and may be the preferred tubing to use vs. brass.
Note: The reed shape should have a fairly wide tube to accommodate the insert and close the gap. Some reed shapes have a slight bulge beyond the second wire by design. With narrower shapes a large chamber can be carved into the gouge as shown below to create a larger chamber. See also the Bulge Chamber reed and mandrel below.
The tubing is available at hobby shops and is also available in brass or aluminum.
Steve Harriswangler Reeds
The bulged chamber reed and mandrel:
Bulge chamber mandrel made by Rieger
Bulged mandrel prototype by Steve HarrisWangler