I love these threads.
It is an enduring question - how to best get this large instrument down to low C? - a question that can never be fully resolved as each solution is a compromise. 5-string basses have closer spaced strings and additional tension on the top, but can be played down to low C in the same position one is familiar with from a 4-string bass. Extensions leave the string spacing the same and don't add the tension of an additional string to the top, but require a different technique to finger notes up around the scroll. Each one may work for different people in different contexts, and some people will heartily defend the direction they've chosen. The novice or amateur who chooses to explore this question will quickly find that their inquiry has no clear answer - ultimately each musician must figure out what works best for them. That can involve significant investment of time and money; it can be difficult to get one's hands on each type of instrument and then spend enough time with the instrument, with a sufficient variety of repertoire, to determine one's personal preference.
It is a question for which this forum will never be able to provide sufficient information, but to save a bit of that time and money we all wish it could.
And then, sometimes you'll get crazy people popping in to say
but wait, there is a third way -
just change everything you've been doing and tune your bass in fifths, CGDA. And before anyone takes offense at "crazy," well, I wanted to pop in here to say that it is worthwhile to consider tuning your bass in fifths. It is again a compromise, but with different tradeoffs. You get to keep four strings and get an expanded range without an extension, but you have to have a more flexible approach to moving around the fingerboard.
I was inspired to try fifths tuning by some of the previous arguments about 5-strings vs. extensions on TalkBass. I probably wouldn't have stuck with it except that I had spent some of our recent collective downtime doing David Allen Moore's Fractal Fingering exercises on Discover Double Bass. Those aren't directed at fifths tuning, but the course improved my overall understanding of the fingerboard and offered exercises that really helped to hone my left hand shape. Thus, when I decided to give fifths tuning a whirl, it wasn't like walking into a wall - more like stepping onto the moving loading platform of one of those continuously-moving amusement park rides. An adjustment was required, but it wasn't like I forgot how to walk.
While certainly not for everyone, a set of strings tuned in fifths is cheaper than an extension or a fifth string, so it may be an easier option to explore for some people. The 41.25" string length on my Shen plays C just fine - though its purpose is just for practice and your mileage may vary in performance settings.
People of TalkBass, let us always remember all the ways we can play low C. With perseverance and dedication, we can ensure that the double bass continues to not be a standardized instrument well into the 21st century. May it never be a boring old
violin.
For further reading, I found these articles interesting, if you haven't seen them yet:
The Fifths System of Tuning Through the Ages — Joel Quarrington
The Double Bass Tuned in Fifths — Joel Quarrington