Question

How do you account for the fact that two strings can be used to give notes of the same pitch and loudness but of a different quality?

Answer 1

 The ‘quality’ of a given note is determined not by its frequency and loudness but by the overall effect of the harmonics present in it. The harmonics are multiples of the fundamental or basic frequency of the ‘note’. Depending on the conditions under which vibrations are taking place, sometimes we get one set of harmonics and sometimes another set. The quality of the two notes would then be different even though their fundamental frequencies may be the same.