In a Niibori Guitar Orchestra, the contrabass is tuned an octave lower than the prime guitar. The contra is therefore 5 notes lower than the bass.
The guitar is notated as if it were tuned conventionally, so that the instruction to play the open first string is written as an instruction to play (high) E. When played, an E comes out an octave lower - the same as the 2nd fret fourth string on a classical guitar.
The contra guitar reads from the same notation as classical (prime) guitar, and is played with the same technique - nothing is different except that the notes come out lower in pitch than the notation suggests. Because all the strings are overwound, more use is made of the thumb, to avoid the scratching that results when fingers with nails meet strings with attitude.
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Because the contrabass guitar is not proportionately as large (compared to the prime) as the increase in depth of its open strings, the contra strings are substantially thicker than the corresponding prime strings. Click for comparison table.
The contra strings require such a heavy over-winding (to bring the pitch down while keeping the tension high enough to avoid 'slap'), that the bottom two are too thick to tie at the pegbox and bridge. These strings are double wound (like piano bass strings), and taper to single windings at either end, meaning they are tailored to the exact length of the contra.