"Ian Iveson" wrote in message
...
Keith G wrote

I'm in the process of chopping a nice little DD deck:

http://www.apah69.dsl.pipex.com/show/Chopper.JPG

Which is already much better since I removed the dodgy 'suspension' and
clamped it directly to a piece of, er, kitchen worktop - which has
produced a much richer and 'fatter' sound already, but I need some feet
which will work at least as well as (and look better than) two bath
sponges and a packet of Fusilli...??

Nick G has mentioned squash balls which, sitting in little wooden rings,
would work but I'm curious about wooden cones, which I can buy for a
coupla hundred quid or make for about 50p (still not decided...) - what I
want to know is which way up for best 'isolation' (energy dissipation) -
points up (from a concrete paving slab) or points down...??

Any Stress Engineers here? (Or I'll take the opinion of an ordinary
engineer who is at least a little bit wound up.... !! ;-)

Clamping the opposite of decoupling. Perhaps you could use clamps?

A thin layer of blu-tak or well-chewed gum under each corner should spread
the mass evenly and secure the deck against sideways forces and, er,
rocking couples.


Ooh, er....



Or bolt it down, as has been suggested, if you are inclined to worry about
high-frequency performance of blu-tak. Low frequencies won't be a problem
if the blu-tak is thin.

Cones don't dissipate energy unless they are squidgy. Squidgy cones are
unstable. Stiff cones dissipate compressive and sideways *forces* quite
well, if your objective is to raise something heavy above the ground so it
doesn't sway about. Think bridges, derricks, and the like.


Derrick's what...??



Generally pointy end up: the idea is to ensure that the cone is in
compression such that the supported weight, combined with relatively small
sideways forces, maintains the line of force from the point within the
boundary of the base, so every part of the cone is always in compression,
so the bridge doesn't fall over, even in a gale. This assumes that the
ground itself is stiff and that the bases cannot slide, and also means
that the supported weight doesn't need to be so stiff, because the pointy
ends cannot apply rocking couples to it, or vice-versa. Also to relieve
the points from the weight of the cones themselves, and because they are
easier to build that way because otherwise it is hard to climb, even with
a ladder. I guess that's why the Pyramids are point up.


I thought that was a 'Masonic' thing...???

(???)


In all these applications, the sharp end
should be effectively pin-jointed so whatever is resting on it can't
slide.

Just as cones spread force in one direction, they concentrate it in the
other. Hence they tend to make an effective pin-joint because the point
embeds itself under compression if the surface is relatively soft. If you
use them pointy-end down, as in spikes, then the bases must be prevented
from sliding. Whatever you are supporting must also be structurally stiff.

Quite what this has to do with your application I don't know. It only
makes sense for big things, so you don't waste time and materials on
unnecessarily bulky supports, reduce forces from wind and/or tide, and let
ships through. For coupling to a hard surface, thin blu-tak is better than
spiking, and chewed gum is even better, although it takes longer to run
in.


Do you recommend any particular flavour...??



Better still would be to embed the whole deck in cement. That would
relieve the bending forces on it between supports due to its weight. Not
good for cooling though.


OK, thanks for that - very reassuring to know I'm not the only nutter
here..!! ;-)