@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....)