At 09:26 AM 12/5/01 -0800, you wrote:
> > ... If burrowing insects, such as the larger Buprestid and
> > Cerambycid adults can tunnel a cylindrical straight hole
> > through healthy hardwood for 30 cm,
> > there MUST be some noises associated with this.
>
> I think dry hardwood would transmit the sound better than healthy
>hardwood, but it does seem like you should be able to hear them to some
>extent. I once called the pest-control guy after hearing something chewin=
g
>beneath the floor of my house. Turned out to be carpenter ants. They wer=
e
>quite audible to the unaided human ear. The wood, of course, was dry, not
>wet or green.
>
>--Brian M. Godfrey
>
Dear Brian:
I bet you may be right.
Of course it is very hard to measure many properties of green wood, since
the total moisture content varies daily. Trees are designed,
interestingly, to do all their volumetric changes with moisture in a radial=
manner, not a longitudinal direction. That is from wet to dry they get
fatter, not taller.
This is also why furniture makers have, until the very recent development
of plywoods and permanent glues, always carefully observed the grain
direction in designing especially large panels, such as for doors and
drawers. Designers have always made the assumption that along-the-grain
dimensions will never change, but that radial or tangential widths will
grow and shrink with summer and winter cycles every year. The development=
of water-resistant finishes was, in part, an attempt to control this yearly=
change in shape.
If you have never done it, I recommend looking carefully at some
old-fashioned panelling. A cupboard door, for example, has four edges made=
so the longitudinal (in a tree up and down) grain sets and fixes the
outside size of the door, fitted with various kinds of joints in each
corner. This stays the same from season to season so the door can open and=
close in the space provided. Each of these four has a deep groove cut in
its inner edge to receive the panel. The panel has four tapered edges,
which are designed to glide into and out of this groove as the seasons
pass, and humidity changes. People, in their misunderstanding of the
workings of such things, are wont to varnish these working edges fast,
making the door split or warp eventually. But I do ramble.
The design of musical instruments, such as the violin, have also been the
subject of many interesting scientific investigations and articles. I
recall a Sci Am atricle on violins from the early sixties which I read four=
times but now can only recall the amazement I felt. It seems the post
inside the violin sets the "wolf note", below which frequencies are coupled=
in one mode and above which in another. Coupled from string, through
bridge to wood then air, that is.
>my very best,
Marty Michener
MIST Software Associates
75 Hannah Drive, Hollis, NH 03049
coming soon : EnjoyBirds bird identification software.
________________________________________________________________________
________________________________________________________________________
|