At my last show I got to play Cate's new octave mandolin (known as the "Tenor Mandola" in Ireland) and I wondered what the tuning was supposed to be on it having never played one before. This led to the following investigation:
The 'cello (and viola) as well as the violin (and so, mandolin) are tuned in fifths (CGDA for cello and viola, and GDAE for the violin). The bass and the guitar (except for the B string) are tuned in fourths (EADG and EADGBE respectively). These last two instruments draw lineage through the Viol de Gamba (literally viol for the leg) which was an early 'cello and the Vihuela, an early form of guitar. The Viol and the Vihuela were both gut-stringed instruments and the tuning in fourths was more akin to that used in the lute. The Tenor Mandola is tuned as a mandolin only an octave lower, and so is tuned in fifths (as Cate had pointed out to me at the time ;).
Tuning in fifths was a later development and there were several reasons for it I've found:
- The harmonic relationship produces a richer set of overtones
- The size of an instrument and the fact that we have four fingers seems to make it more practical. Depending on the size of the instrument tuning in fourths could render the fourth finger useless
- It requires less strings for a given range. You need a five string bass to get as many notes as you can get on a four string bass tuned in fifths (note: I haven't actually ever tuned a bass in fifths)