The crwth consists of a fairly simple box construction with a flat, fretless fingerboard and six gut strings, purportedly tuned gg´c´c´´d´d´´.
The original report of that tuning  (Edward Jones, Musical and Poetical Relicks of the Welsh Bards; London: 1784), from which most subsequent others appear to draw their information, uses arbitrary pitch designations for illustrative purposes.
Jones also states that the tuning procedure began by tightening the highest string as much as possible without breaking it, subsequently tuning the others to it intervallically.
Such was not an uncommon practice in the days before standardized pitch and was, in fact, mentioned in other manuals on string instrument playing.

While Jones's report was widely read and used as the basis of a number of subsequent accounts, and therefore today is often considered to be evidence of a standard tuning, it is more likely that a variety of tunings were experimented with and in some cases employed, as was and still is the case with many other string instruments, particularly those within folk cultures.
A second tuning, reported by William Bingley (A Tour Round North Wales; London: 1800), features the drones tuned in octaves, with the strings over the fingerboard tuned in paired fifths rather than seconds.
However this tuning is almost certainly derived from later violin playing and is impractical given that the crwth is equipped with a flat bridge and therefore designed to play all six strings simultaneously.

Traditionally the soundbox, or resonator, and a surmounting yoke in the shape of an inverted U (see picture of player), were carved as a single unit from a block of maple or sycamore.
The soundboard, or belly, a separate piece (the upper surface, nearest the strings), was most often made of deal or some other soft wood, and the bridge was usually made of cherry or some other fruitwood.
Two soundholes, or circular openings about an inch to an inch and a quarter in diameter, were cut into the soundboard to allow pulsating air from the soundbox to escape and strengthen the tone.
The two G strings (to use Jones's terminology - see above) ran parallel to the fingerboard, but not over it, so those strings were used as fixed-pitch drones which could be plucked by the player's left thumb.
The remaining strings, which were tightened and loosened with metal harp wrest-pins and a tuning key or wrench, were usually bowed with a horsehair and wood bow.
One characteristic feature of the crwth is that one leg of the bridge goes through a soundhole (see picture of player) and rests on the back of the instrument (the bottom of the soundbox).
Although it has been conjectured that this is a primitive attempt at a sound post, or anima, something the instrument lacks, it is equally likely that it is designed to take some of the downward pressure of the tightened strings off the soundboard.
Since that piece is flat, unbraced, and usually made of soft wood, it is much weaker than the belly of a violin.

All surviving pictures of crwth players show a playing position with the lower end of the crwth braced against the chest, supported with a strap around the player's neck (see picture).
The sound of the crwth was described by medieval poet Gruffydd ap Dafydd ap Hywel as 'in the hand a hundred voices' (yn y llaw yn gan llais'), referring to the rich sound of six strings sounded simultaneously in harmony.
Along with the harp and timpan, the six-stringed crwth was one of the three main string instruments of the Welsh according to the medieval Triads, and an instrument of the aristocracy with its own native repertoire and a strict examination system though which a master crwth player had to pass.
A three-stringed version also existed which required less skill and was played by minstrels.

The tone of the crwth is softer and rougher than the modern violin, and has a comfortable melody range of an octave by the use of third position, although it is possible to reach an octave and a half by the use of higher positions.
It's sound that goes well with the timbres of the harp and pibgor
The crwth consists of a fairly simple box construction with a flat, fretless fingerboard and six gut strings, purportedly tuned gg´c´c´´d´d´´. The original report of that tuning  (Edward Jones, Musical and Poetical Relicks of the Welsh Bards; London: 1784), from which most subsequent others appear to draw their information, uses arbitrary pitch designations for illustrative purposes. Jones also states that the tuning procedure began by tightening the highest string as much as possible without breaking it, subsequently tuning the others to it intervallically. Such was not an uncommon practice in the days before standardized pitch and was, in fact, mentioned in other manuals on string instrument playing.
While Jones's report was widely read and used as the basis of a number of subsequent accounts, and therefore today is often considered to be evidence of a standard tuning, it is more likely that a variety of tunings were experimented with and in some cases employed, as was and still is the case with many other string instruments, particularly those within folk cultures. A second tuning, reported by William Bingley (A Tour Round North Wales; London: 1800), features the drones tuned in octaves, with the strings over the fingerboard tuned in paired fifths rather than seconds. However this tuning is almost certainly derived from later violin playing and is impractical given that the crwth is equipped with a flat bridge and therefore designed to play all six strings simultaneously.
Traditionally the soundbox, or resonator, and a surmounting yoke in the shape of an inverted U (see picture of player), were carved as a single unit from a block of maple or sycamore. The soundboard, or belly, a separate piece (the upper surface, nearest the strings), was most often made of deal or some other soft wood, and the bridge was usually made of cherry or some other fruitwood. Two soundholes, or circular openings about an inch to an inch and a quarter in diameter, were cut into the soundboard to allow pulsating air from the soundbox to escape and strengthen the tone. The two G strings (to use Jones's terminology - see above) ran parallel to the fingerboard, but not over it, so those strings were used as fixed-pitch drones which could be plucked by the player's left thumb. The remaining strings, which were tightened and loosened with metal harp wrest-pins and a tuning key or wrench, were usually bowed with a horsehair and wood bow. One characteristic feature of the crwth is that one leg of the bridge goes through a soundhole (see picture of player) and rests on the back of the instrument (the bottom of the soundbox). Although it has been conjectured that this is a primitive attempt at a sound post, or anima, something the instrument lacks, it is equally likely that it is designed to take some of the downward pressure of the tightened strings off the soundboard. Since that piece is flat, unbraced, and usually made of soft wood, it is much weaker than the belly of a violin.
All surviving pictures of crwth players show a playing position with the lower end of the crwth braced against the chest, supported with a strap around the player's neck (see picture). The sound of the crwth was described by medieval poet Gruffydd ap Dafydd ap Hywel as 'in the hand a hundred voices' (yn y llaw yn gan llais'), referring to the rich sound of six strings sounded simultaneously in harmony. Along with the harp and timpan, the six-stringed crwth was one of the three main string instruments of the Welsh according to the medieval Triads, and an instrument of the aristocracy with its own native repertoire and a strict examination system though which a master crwth player had to pass. A three-stringed version also existed which required less skill and was played by minstrels.
The tone of the crwth is softer and rougher than the modern violin, and has a comfortable melody range of an octave by the use of third position, although it is possible to reach an octave and a half by the use of higher positions. It's sound that goes well with the timbres of the harp and pibgor
Crwth