Why do CD basses installed on theorbo/Chitarrone sometime break (mostly on the 5th course), even if there are no sharp edges and they were installed properly?

 

Tiorba (1882)
Source: Biblioteca de la Facultad de Derecho y Ciencias del Trabajo Universidad de Sevilla / CC BY (https://creativecommons.org/licenses/by/2.0)

The CD strings (from 110 CD up to 220 CD) are designed for renaissance & d minor Lute basses only .
For the long diapasons of medium extensions, the CDL type strings are available.
The thinner CD strings (82 CD up to 105 CD) instead, are designed for 5th courses and octaves for the very lower bass strings of renaissance & d minor lutes.

On theorbo/chitarrone these rules sometime do not work: why?

While on the traditional lute/archlute the 1st string works with the higher FL product (220-230 Hz.m), any kind of theorbo/chitarrone works with an exceptional, longer vibrating string length, far longer than what was calculated for lute, hence the fact that the 1st and 2nd strings are forced to be tuned an octave lower. For example, while a renaissance lute tuned in A at modern pitch has a scale around 57 cm, a theorbo in A at the same standard pitch has a scale of 85-88 cm (the FL product of the 3rd string b note -that actually is the canterelle- is 220 Hz.m)
In these conditions, the range of the FL products typical of a 5th course of a renaissance Lute (79-81 Hz.m) or the 6th course of a d minor lute (71-74 Hz.m) allows the use of CD strings of the thinner range with no problems, while on a theorbo instead, the FL product raises up to 109-115 Hz-m, and it is too high for strings designed as basses.
In practice, the FL product of a 5th course on a theorbo is the same of a 4th course on a renaissance lute.
This is the explanation of why a CD string installed on the 5th course of a theorbo can sometimes break: the FL product is too high (it’s not a matter of tension; tension has no influence in the FL product).

In conclusion, the proper place for the CD strings is – in the higher position – the 5th course of the renaissance lute, or the 6th , 7th  and 8th fretted theorbo basses. For the 5th course of a theorbo/chitarrone, the right strings to use are NNG or CDL type.

 

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