Which is the highest note playable on the classical guitar?

Question

Let us consider a standard classical guitar with only 19 frets and 6 strings being played with the standard tunning E2-A2-D3-G3-B3-E4.

In this configuration, the classical guitar has a 'normal' playing range spanning the notes E2 - B5, comprising, thus, 3.5 octaves + 0.5T = 43ST -> 44 notes (T = tone and ST = semitone). This is exactly half of the playing range A0 - C8 of a standard piano with 88 notes.

The highest 'normal' note playable on top of the guitar fingerboard is B5 (19th fret of the 1st string). However, which is the actual highest note achievable on the classical guitar?

If we consider natural harmonics, by playing it on the 5th fret of the 1st string (or a little past half of the guitar's sound hole), one reaches E6, which is 2.5T above B5 (this E6 can be played as a 'normal' note on the 24th fret of the 1st string of an electric guitar).

If we consider artificial harmonics, it is not clear for me if one can produce clearly audible notes above E6. What do you know about it?

However, I was testing something unusual, and it is possible to go above E6 by playing on the 'wrong' side of the classical guitar neck. For instance, if one presses the 8th fret of the 1st string with any finger of the left hand and plucks the string with any finger of the right hand on the 'wrong' side of the guitar neck, it seems to me that B5 is produced. If one keeps doing the same thing but pressing the 1st string on the 7th fret, 6th fret, and so on, the notes produced become higher and higher. The last clearly audible note reached in this scheme, and the highest note I found on the classical guitar, is produced by doing the above technique with the 3rd fret of the 1st string pressed. However, I did not know by ear which note was this (it seems to me that the notes produced with this 'reversed guitar neck technique' do not walk in intervals of 1ST). By using the online note identifier https://www.flutetunes.com/tuner/ the program clearly identified this note as G7 (it is, therefore, 3 octaves above the 'normal' G4 of the 3rd flet of the 1st string, which is produced by playing on the usual side of the guitar neck)!

Does anyone know anything about the dynamics of the notes generated with this 'reversed guitar neck technique'? Any references about it?

And which is the highest note that you are aware of that can be played on a standard classical guitar with standard tunning?

Answer 1

Does anyone know anything about the dynamics of the notes generated with this 'reversed guitar neck technique'? Any references about it?

It's basic physics. The frequency of the note played on nth fret can be calculated as

fn = f0 · l0 / ln

where f0 is frequency of the open string, l0 is length of the open string and ln is length of vibrating part of the string

ln = l0 · [2 ^ (-n/12)]

These lengths result in equal temperament notes on each fret. But if you play a note on the "wrong" side, the fret positions will not obey these equations, so that the notes will be off in most cases... though that's not an obstacle for a creative musician. A notable example is the ending of Heitor Villa-Lobos Etude 2. See this link for reference:

https://classicalguitarrocks.com/cgr/approaching-etude-no-2-villa-lobos/

Interestingly, in the video mentioned in the link:

the author says he is unable to play this technique of his guitar (probably because the nut is too low (for this technique)).

The frequencies of the notes on the "wrong" side are:

fwn = f0 · l0 / (l0 – ln)

Below I list relative pitches in cents for the first 24 frets, obtained when you pluck the string on the "wrong" side

 2    4986   ← 4 octaves + major 2nd (too low)
 3    3836   ← 3 octaves + major 2nd (too high!!)
 4    3182   ← 2 octaves + minor 6th (too low)
 5    2733   ← 2 octaves + minor 3rd (too high!)
 6    2394   ← 2 octaves
 7    2126   ← octave + major 6th (too high)
 8    1906   ← octave + fifth
 9    1721   ← octave + fourth (too high)
 10   1563   ← octave + minor/major 3rd
 11   1426   ← octave + major 2nd (too high)
 12   1306   ← minor ninth
 13   1200   ← octave
 14   1105   ← major seventh
 15   1021   ← minor seventh (too high)
 16    944   ← major 6th/minor 7th, out of tune, but works for Villa-Lobos!
 17    875   ← major 6th (too low)
 18    813   ← minor 6th
 19    755   ← fifth/minor 6th
 20    703   ← fifth
 21    655   ← fifth/tritone
 22    611   ← tritone
 23    570   ← tritone (too low)
 24    533   ← fourth (too high)
 25    498   ← fourth

I described pitches of these notes, but many of them are out of tune. The closer to a multiple of 100 the value is the more in tune the note.

Please note that this calculation disregards fret width, and also the guitar nut doesn't have the compensation similar to the bridge, so the actual frequencies might differ a bit.

And which is the highest note that you are aware of that can be played on a standard classical guitar with standard tunning?

Sky is the limit, but the higher you go, the less feasible it is. You seem to reject harmonics below 5th fret too early. You can play the notes beyond the fretboard, especially with a slide. You can put on thinner strings and tune up. Oh you can also play the notes behind the nut. Applicability depends on a specific composition, specific musician technique, also specific instrument capabilities.