Firstly, the octave violin appears to me to be the perfect solution to the non-existent problem. Just what purpose would it fulfill that a viola or cello would not do better? Secondly, an octave violin would have a scale length in the neighborhood of two feet! And a body width of about 18 inches just how would the player mount this instrument? Tucking it undet the chin would be a bit awkard to say the least.
The search for great technique does not always lead to great music, but the search for great music does always lead to great technique.
Scale length. It takes about five years to, more or less, become adequately accomplished on a violin. Few people have the time or the interest to indulge the slightly less but still significant amounts of time to become familiar with the different muscle memory for viola and cello. Octave strings provide the flavor of those instruments without the time investment.
The same gain can be made even easier via the use of electronics. Many people abhor electronic violins.
Without deviation from the norm, progress is not possible. —Frank Zappa
The future is already here—it’s just not very evenly distributed. —William Gibson
@JiminTexas - I've been experimenting with octaves on a standard 4/4 fiddle ( an FM Concert ) - and doing some detailed analyses of just how they respond on a standard instrument.
Octave strings are just that - same size (length) as normal - although heavier mass, and they are designed and manufactured specifically to tension (on a 4/4 fiddle) to a full octave down from normal strings (G2, D3, A3, E4 instead of G3, D4, A4, E5).
There are (as Pierre has mentioned here and elsewhere) certain "compensations" to be made when playing them - they respond much more slowly, especially the low G2 and D3 - and - because a normal violin is a "tuned, resonating body" ( a bit like a well tuned exhaust-pipe on a high performance car - well sort of - you know what I mean ) the lower frequencies are outwith (below) the normal frequency cut-off point on a standard violin (think of the instrument as being like a band-pass filter - like an equalization curve on a graphics equalizer on your stereo etc ).
You'll find some of the investigations, and results here - where I've had lots of useful feedback from @Irv as well - https://fiddlerman.com/forum/s.....gs/#p99365
I haven't done this directly (although I got close by installing them on an electric violin - and the results are quite impressive and mentioned in the thread I refer to) - but - on a standard size fiddle, I would imagine that a pick-up of the style that clips directly onto the bridge, or indeed has a transducer physically inserted into the bridge (like one of the Barcus Berry range) would "liven and widen" the response since it will be directly picking up the string vibration, and not so much the generated audio from the instrument which would be picked up by a normal microphone).
I guess the whole point of the exercise (from my point of view) was partly sheer curiosity, and partly to find another sound-canvas to mess around with, and try to understand what I could do with it.... (There is no help for me....)
I seriously recommend not copying my mistakes. D'oh -
Please make your own, different mistakes, and help us all learn :-)