elf speaker sens.qxd

elf speaker sens.qxd
BAG END
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INFRA PROCESSOR vs DSP
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An often asked question is how to emulate our Infra processor in commercially
available DSP's.
There are a number of Bag End loudspeakers installed using a commercial
DSP set to emulate the Infra processor.
This does work, although there are
some drawbacks. It is useful to listen
and compare as including an Infra
processor is often worthwhile.
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Graphs show the typical difference
between a DSP processor set to imitate
the Infra processor and the Infra
processor. The loudspeaker response
is an accurate computer model, not an
acoustical measurement.
In the frequency domain even a modest
DSP as the one in the graph can duplicate the frequency response well enough
to make the bass mostly sound like a
Bag End bass system. Looking at the
Infra processor in comparison, you can
see the noise in the upper range (above
500 Hz) is much lower and while this
seems better (and it is) realistically it is
not important as the response of the
woofer cone is falling off so the higher
noise floor is not reproduced audibly.
In studio and mastering facilities or
other critical listening environments the
lower extension is useful for monitoring
and also sounds noticeably better.
Many DSPs do not respond below 20
hertz. The graph shows the extension
with the Infra processor is another
octave lower.
One very important aspect of making our
systems practical is the protection
scheme. The Dynamic Filter leaks the
integrators via a voltage controlled
detector. You set the detector threshold
as you would with a limiter but rather
than limiting the entire band the dynamic filter dynamically reduce the bass
extension. This is an elegant
solution to protect the system as it is
not audible. In comparison the conventional approach is a band limiter which
reduces the entire bass range. This also
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1. Response of Bag End Infra and DSP
processors. The Infra processor
continues to rise below 20 hertz.
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3. Response of DSP processor and loudspeaker simulation with and without limiting protection. The DSP limiter reduces
the entire bass band there by changing
the upper crossover frequency.
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The Bag End Infra bass processor is an
analog dual integrator developed in the
late 80's and commercially introduced
in the early 90's. The integrator has
110 dB of dynamic range and typically
-100 dBu self noise. The implementation of this simple circuit has been perfected over time.
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2. Response of processors with loudspeaker simulation. The DSP has higher
noise in the upper range, this noise is
not audible as the bass speaker
response does not reproduce it.
changes the crossover point and is audible. Crossing the threshold, the Dynamic
Filter reduces the lower bass level but
still plays the note at the maximum safe
level and leaves the rest of the middle
and upper bass unaffected. This allows
practical use of the extended bandwidth
as there is no power penalty for allowing
the low extension. It allows the system to
be used safely to its maximum level while
never sounding compressed or protected
making any design more efficient.
Reducing the low bass is not audible as
there are many sounds in nature that do not
have low bass content. Unless you know the
material and are expecting low bass content
you do not miss it. Full band compression is
not natural and is audible.
It is easy and reliable to set the protection
threshold so systems do not distort or
Infrasub™ and BAG END® are trademarks of Modular Sound Systems, Inc.
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4. Response of Bag End Infra processor
and loudspeaker simulation with and
without dynamic filter protection. The
Dynamic filter reduces the lowest
frequencies as required protecting the
system where the most power is
required. It does not effect the middle
and upper bass range and leaves the
upper crossover point unaffected.
break. First, size the amp to the speaker
then, set the threshold on the processor
to engage just before the amp would clip,
thus preventing it from clipping. Self
processed powered systems have this
internally set.
BAG END Loudspeakers
22N272 Pepper Road
Lake Barrington, Illinois
60010 USA
Voice 847 382 4550
Fax 847 382 4551
www.bagend.com
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