Recording - March 2014 - 53

While I've read anecdotal reports of
sonic improvement with this method, it
doesn't address the whole situation. With
inertia blocks there are other laws at
work, specifically the conservation of
momentum and the conservation of energy I spoke of. And no block movement is
required to transmit sound. Once again
we're back with the Newton's Cradle.
So like the balls in Newton's Cradle,
the kinetic energy from a speaker cabinet
can still be transmitted to the supporting
surface through the inertia block, explaining its less-than-optimal performance. So
in our application, increasing inertia
alone only has a limited effect.
On needles and pins
Another concept in speaker isolation is
that the smaller the contact area supporting a given object, the greater the resistance of that interface to transferring kinetic energy. This is called high loading in
acoustical-science circles. So theoretically,
if you could support your speaker cabinet
on an infinitely small point, no kinetic energy could cross the interface. That ideal situation is not possible in our world, but if
we restate the concept as "a smaller area
of contact will have a higher resistance to

energy transfer", we now have something
that can be put into practice.
Since only the point of contact needs to
be as small as possible, you can isolate
your speaker using pointed cones or
spikes on your speakers or speaker
stands without being concerned about the
shape of the body of the spike or cone.
It's the point that matters. See Figure 2.

This works better than the inertia block, but
there are still two issues that limit the performance of cones or spikes. The first is that the
point can dig into the surface of the speaker
or the floor, which is usually made from
wood or some other material that a sharp
point can penetrate. It may not be much initially, but over time the point will dig deeper,
increasing the surface area of contact, and
reducing its attenuation. This is fixed by

putting something hard, like a small, hard
metal disc, between the point and the surface. Some spikes come with these.
But there's another way the efficiencies of
cones and spikes are compromised. Kinetic
energy traveling from side to side or front to
back in the cabinet sees a high impedance
interface where the point contacts the cabinet, as this energy is traveling at right
angles to the axis of the spike or cone. But
there's also energy traveling in the cabinet's
vertical axis-for reasons I won't go into
here, it has an easier time crossing the
point of contact. Remember Newton's
Cradle again? The energy passes through
the tiny point of contact between each two
spheres, moving in the direction of the interface. So spikes and cones do reduce the
energy migration. A great improvement,
but we can do much better.
Float like a butterfly...
Let's say you could make your speakers
float in midair. That would certainly isolate
them! There would be no point of contact,
and no path for energy moving in any
direction. We can't make this happen, but
believe it or not, we can come very close.

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Recording - March 2014

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