Better Bass Scale for M&H A

[Delwin D Fandrich]

----- Original Message -----
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: "Pianotech" <pianotech@ptg.org>
Sent: November 02, 2002 12:32 PM
Subject: Re: Better Bass Scale for M&H A


>
> I can easily see where the common loop would make the back length very
stiff, but would that necessarily restrict bass bridge movement - the common
type should still pivot on the hitch pin - how does a more flexible rear
length free up the bridge?
>
> Terry Farrell

Terry,

To create much of any sound energy at very low frequencies the soundboard
has to move some significant amount. Probably the biggest restriction to
that movement is the backscale. The driving strings have to move the bridge
against the relatively short coupling between the back of the bridge and the
edge of the hitchpin riser. If the strings are at least moderately flexible
they present less restriction to that movement than they do if they are very
stiff. Try this yourself--make a mono-chord with a hitchpin and a tuning pin
some distance apart. About 1 m should do. Pull the string up to some
pitch--you just want it tight. Now, grasp the string with your fingers in
the middle and wiggle the thing up and down. Get a feel for how much force
it takes to deflect the string up 10 mm and down 10 mm. Next grasp the
string 100 mm from the hitchpin end and try again. Assuming you can still
deflect the string up and down 10 mm get a feel for how much force is
required and compare it to the force it took back in the middle. Now move
back to a point 25 mm from the end and see how far you can move it. That's
the restriction of the backscale. Changing a backscale length of 100 mm to
150 mm won't matter nearly as much as changing from 25 mm to 75 mm.

Del