A horn generally has excellent efficiency. It can be as much as ten
times higher than that of a conventional loudspeaker. If a flare is
positioned in front of a diaphragm, the loudspeaker is able to
propagate its energy far more efficiently into the surrounding air.
Since the cross-sectional area inside the horn increases with length,
the area of the effective radiating surface is increased. In effect we
are shifting the radiation resistance of the throat (thin end of the
horn) to make it the radiation resistance of the mouth (opening of the
Horn speakers are not only available with tapered cross
sections, there is an infinite number of shapes and lengths and they
all have their own directivity characteristics. The increase in the
surface area inside the horn is also referred to as growth.
In an exponential horn, the cylindrical cross-section A increases
exponentially with distance x. Ax = Ah * e ^ ( k * x) Ax = cylindrical
cross-section at that distance x Ah = throat area k = flare constant
which determines how much the horn opens up along length x.
When you design a horn, you have several criteria:
- What frequency response you desire
- What driver you will use (and its parameters)
- How much compromise you are willing to accept (size, shape, materials, etc.)
The driver and frequency response determine the type and size of the
ideal horn, and for a bass horn the maximum size will affect the output
and probably the design criteria.
Note that many existing horn designs (and this is especially true
for bass horns) often have massive compromises or deviations from what
might be an ideal horn. Many Lowther rear-loaded bass horns have been
designed by large amounts of experimentation to achieve the best sound
given the compromises (often size) that are imposed. Beware when
designing your own horn that you understand why things were designed a
certain way. This is especially true if you are using or building on