- Isobarik loading
has
become pretty
popular for car audio use in the last few years. Again this is not a
new
concept, having been originally introduced by Harry Olson in the early
1950's. Technically, "isobarik" is not really an enclosure type; it is
a loading method. This loading method involves the coupling of two
woofers
to work together as one unit. This is typically accomplished either by
placing two woofers face to face or by coupling two woofers with a
small
chamber. The result of coupling the two speakers is that the coupled
pair
(iso-group) can now produce the same frequency response in half the box
volume as a single speaker of the same type would require. For example,
if a speaker is optimized for performance in a 1 cu.ft. sealed
enclosure,
one iso-group of the same speakers can achieve the same low frequency
extension
and overall response characteristics in a 0.5 cu.ft. sealed
enclosure.
- There is, of
course,
a penalty involved.
Whenever you use isobarik loading, you are sacrificing 3dB of
efficiency
compared to a single driver in twice the air space. In practical terms,
this is not usually a big deal since the powerhandling is doubled (two
speakers instead of one) and the impedance is typically cut in half if
we parallel the two speakers (twice the power, assuming the amplifier
can
deliver the necessary current.) The end result is about the same output
as the single driver in the bigger box but at twice the amplifier power
(and twice the speaker cost.)
- Isobarik loading
can
be used within
any enclosure type, including bandpass designs. The ported and bandpass
isobarik designs can be difficult to design and build due to very small
enclosures with large port requirements. Isobarik bandpass designs, in
particular, can be literally impossible to build with certain speakers.
There are some things to look out for with each type of isobarik
design,
such as mechanical noise and uneven heat dissipation which can present
potential sound quality and reliability problems. All the methods which
involve opposite cone motion require that the speakers be wired in
reverse
polarity relative to each other. These designs also provide a
performance
advantage in that their opposed cone motion averages out suspension
non-linearities
(differences in inward and outward suspension control,) which reduces
distortion.
- If you are
strapped
for space and
can afford the extra speakers and more complex enclosure, the ability
to
have a compact subwoofer system with no real sacrifice in performance
is
well worth the extra effort and expense. On the other hand, if you have
a lot of space and are looking to get the maximum amount of output
without
sacrificing sound quality, using multiple iso-groups can give you the
best
cone area/box volume ratio while still retaining good fidelity.
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