In general, the sound–post should stand from 1/8 to 1/4 of an inch to
the rear of the right foot of the bridge. Its outer edge should be in
line with the outer edge of the foot. From this position its upper or
lower end, or both, may be moved with advantage to secure certain
qualities of tone. It should in all cases fit the curves of the top and
back absolutely. Moving the lower end toward the centre favors the lower
strings. If the lower strings are weak and the upper at all sharp or
hard in tone, then a very loose post should be used. If the reverse is
the case, a long and tightly fitting sound–post is required. Moving the
upper end outward will help all the strings, if the tone before was hard
and shrill; but if the upper strings happen to be dull and heavy, then
the post should stand a little inside the line of the foot of the
bridge, and a little further back. The sound–post should be made of
fine–grained soft spruce. The grain should cross that of the top, as
this will prevent the marring of the inner surface of the top in putting
the post in and adjusting it.