19
The Diminishing Line Source technology
In the past, the point source was considered the ideal in loudspeaker
design. The smaller the driver, the broader the dispersion pattern at rising
frequencies. However, this simple model overlooked one important factor.
In the real world, distortion from a transducer is roughly proportional to
displacement. The longer the throw (or smaller the piston area) required to
generate a given volume displacement, the greater the distortion
generated for that given displacement (or loudness level).
Let’s look at a simple equation for the volume displacement of a circular
piston.
Volume Displacement = Travel x Surface Area
As you can see, if we want to keep travel at a minimum, then surface area
must increase accordingly. In fact, for a given size piston, displacement
requirements increase by a factor of FOUR every time we drop one octave
infrequency. It’s now quite clear that the ideal model should be revised to
one which maintains constant directivity while increasing in piston area
with falling frequency.
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