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In this thread i want to propose the design idea of ultra-long scale tapping instruments, which i feel have a very exciting potential as low-tuned bass-guitar-like instruments.

Scale length of bass guitars

Scale length is a critical specification for bass instruments. Leo Fender chose a 34" scale for bass guitar as a compromise between tone and playability, but that was for a lowest string at E1. Since then, although the more flexible roundwound strings have helped, a modern lowest string at B0 on a 34" or 35" scale has significant problems due to the stiffness of the large gauge, more specifically, the gauge relative to the scale length.

Most string sets have the low B at a lower tension than the other strings, to minimise the gauge and the issues caused by stiffness. But a low tension makes the low B rather loose and floppy. Larger mass strings inherently need more tension to support their vibration, so these standard gauge low B strings are borderline undertensioned. But more tension requires a larger gauge, which is stiffer and negatively affects tone.

Strings are limited in how flexible they can be made, so the only solution is a longer scale length, for example the Dingwall basses at 37" or the Kalium basses at 40".
This helps in 2 ways:
For the same tension, a thinner gauge can be used, increasing flexibility and therefore improving tone and sustain.
Additionally, the string effectively becomes more flexible because it is longer.

Ultra-long scale tapping instruments

Tapping instruments use a string damper, this reduces the usable scale length by 1 or 2 frets. Many tapping instruments that use a 34" bridge to nut distance therefore have their tappable scale reduced to roughly 32" or 30", which has a very significant effect on the tonal quality of the lowest bass strings. This is a good reason to use a longer scale.

The tapping technique creates a bright, clear tone, this is ideal for very low notes.

Below i list the primary problems of ultra-long scale bass guitars and how a tapping instrument solves them:

* Reach

A bass guitar is already a very long instrument, a longer scale moves the nut and the bridge, and therefore the hands, even further away from each other.
With a tapping instrument, one hand does not need to be near the bridge, so the bridge can be moved away, out of reach, to increase scale length, while also leaving the nut unmoved.

* Fret spacing

A longer scale results in the frets being further apart. With a bass guitar the fretting hand has to either stretch or shift more.
A single-region tapping instrument allows both hands to be present on the fretboard, which doubles the length of the fretboard covered relative to a single fretting hand.
If the tuning is fourths, the scale length can be significantly increased while also making it easier to cover a particular number of frets. To cover 5 frets, the hand nearest the nut only needs to cover 2 frets, the other hand only needs to cover 3 frets.

* String availability

Most tapping instrument companies already have custom strings made for them.

An example using string 'slenderness'

Roughly, string flexibiity can be thought of as being determined by its gauge (width) relative to its length.
It's useful to be able to put a value to flexibility, so i came up with a rough measure of string flexibility i call 'slenderness', which is scale length in inches divided by gauge in inches.

I will use a Stick for this example, because Stick Enterprises has very high standards for the behaviour of their strings and has stated the maximum gauge they find tonally acceptable.
All modern Stick instruments have a 36" bridge to nut distance, the lowest tappable fret is fret 1 which therefore has a 36 * 2 ^ (-1 / 12) = 33.979" scale.

Stick Enterprises currently uses a maximum gauge string of .128 to avoid excessive stiffness and inharmonicity. The slenderness at the lowest tappable fret is 33.979 / 0.128 = 265.46. This gives us a slenderness value to preserve.
The tension of a .128 tuned to it's lowest official pitch (at fret 1) of Bb0 on a 33.979" scale is (approximating using Kalium's tension calculator) 31lbs.

Now for example let's imagine a Stick instrument that is 3 frets longer.
The longest tappable scale is now 33.979 * 2 ^ (3 / 12) = 40.408".
The bridge to nut scale is now 36 * 2 ^ (3 / 12) = 42.811".
A string preserving a slenderness of 265.46 can now be of gauge 40.408 / 265.46 = 0.152".

Now the nice surprise, this instrument doesn't play only 3 semitones lower.
A string of gauge .152 on a 40.408" scale and at roughly 31lbs will tune to (approximating using Kalium's tension calculator) F0, which is 5 semitones lower than Bb.
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