Ted's Talk: Why get a ``C`` Extension for your Upright Bass?
Getting a “C” extension is really a matter of practicality; if the music you wish to play requires notes below the low “E” on your bass, then a “C” extension is the easiest way to achieve those low notes, without making radical changes to the instrument (or re-learning the fingering!)
I make custom “C” extensions out of hard maple, with a cap (a mini fingerboard) of ebony or dyed Wenge. I don’t use metal extensions because they are usually heavy, which can change the balance and sound of the bass. Also, every bass “scroll” and peg box are different, so I make every extension to order. The extension hugs the contours (see pic #2) of the box and scroll, and is shaped thickest where it needs the most support (see pic #3).
The brass capos or “gates” act as mechanical fingers to select the lowest note you want to play. (see pic #4) The larger “E” gate returns the bass to standard tuning. Some players prefer to finger the notes manually, and choose to install only the “E” gate. (see pic #5)
The meeting point of the extension and bass fingerboard ought to be the same as the string height at the nut: if the E string is normally almost resting on the edge of the board, then the extension can meet flush (see pic #6); if the E height at the nut is perhaps 1mm, then the extension overlaps the board by 1mm, and so forth.
In crafting an extension, we first create a mock (or beta) extension from soft wood. It is roughly fit in place and string alignment is determined. (see pic #7) We then copy the mock extension in hard woods. A slot is cut in the end, and a string pulley is installed. Depending on the size, shape and antiquity of the bass scroll, different methods of stringing are employed. Most brands of strings are available in C-extension length.