Two tension bars sufficed, neither of them breaking into the
scale: the first, nearly straight, being almost parallel with the lowest
bass string; the second, presenting the new feature of a diagonal bar
crossed from the bass corner to the string-plate, with its thrust at an
angle to the strings.
There were reasons which induced Mr. Broadwood to somewhat modify and
improve this framing, but with the retention of its leading feature, the
diagonal bar, which was found to be of supreme importance in bearing the
tension where it is most concentrated. From 1852, his concert grands
have had, in all, one bass bar, one diagonal bar, a middle bar with
arch beneath, and the treble cheek bar. The middle bar is the only one
directly crossing the scale, and breaking it. It is strengthened by
feathered ribs, and is fastened by screws to the wooden brace below. The
three bars and diagonal bar, which is also feathered, abut firmly on the
string plate, which is fastened down to the wooden framing by screws.
Since 1862, the wooden wrest-plank has been covered with a plate of
iron, the iron screw-pin plate bent at a right angle in front. The
wrest-pins are screwed into this plate, and again in the wood below.
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