6
Why anchor the movement caused by the cone?
For a driver to produce a sound, theoretically only the cone need move
forward to create the air pressure wave that we hear. However, as we all
learnt at school, Newton’s Third Law of Physics states: to every Action,
there is an equal and opposite Re-action. Depending on whether the
speaker cabinet is anchored or unanchored, the interaction of the speaker
cabinet with the cone movement is like the difference between diving off
the concrete edge of a swimming pool and diving off a small rowboat on
the water.
If the swimmer is compared to the speaker cone, then diving from the
concrete edge is like having a speaker coupled to/on a stand on spikes,
whereas diving from the rowboat is when the speaker cabinet is not
anchored by spikes or is not on a stand. Diving from a rowboat, the
energy of your forward/upward movement is partly lost because as you
push down against the boat, it moves away in the direction your legs
push it (i.e. downwards/backwards). This results is much less
forward/upward energy, and is far less controlled than when pushing
against the solid pool edge.
This image of the lost energy of motion parallels the losses in the quality
of sound when the speaker assembly (cabinet, driver frame, stand, spikes)
moves independently of the cone. When the cone moves forward, how
much of the motion/energy is translated into an accurate sound wave will
depend on how much cumulative movement there is in the total
‘assembly’. For a speaker on a stand without spikes, the cabinet
responds, in effect, like a punching bag on a pole. The speaker’s weight is
uppermost; the movement is a forward/backward rocking motion. Even if
the speaker is placed directly on the floor rather than a stand, the
backwards rocking effect will occur/be the same, though the lack of
height provided by the stand will create less of a levering action/effect.
The addition of a stand provides a rigid platform to hold the speakers
securely. It also increases the overall mass (adding lead shot can further
enhance this). The combination of a stand with spikes will have the
greatest effect on minimizing speaker movement. Whether anchored
directly by spikes or placed on a stand with spikes, the rocking of the
speaker cabinet will be lessened (though it cannot be removed
altogether). All the same, these measures create an improvement in the
sound quality that is most definitely audible.