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Desde 1978, AudioPro ha
diseñado y fabricado altavoces que han merecido su reconocimiento en todo el
mundo, especialmente dentro de la especialidad de subwoofers activos. La
historia de los altavoces de Audio Pro comenzó con un producto único, el
modelo B2.50, un subwoofer poco común que incorporaba un amplificador y un
crossover activo. El B2.50 incorporaba la técnica ACE-Bass (amplificador
controlado eufónico Bass). Se trata de una técnica patentada, diseñada para
reproducir las frecuencias bajas de los pequeños recintos. El ACE-Bass en el
B2.50 utilizaba altavoces subwoofer duales, controlados por servos para
hacer los ajustes convenientemente. ACE-Bass fue inventado por Karl Erik
Ståhl, un joven ingeniero sueco que centro su labor en conseguir unos graves
de gran intensidad, sin estar por ello la caja acústica supeditada a grande
volúmenes. La tecnología ACE-Bass fue presentada por vez primera en la 61ª
Convención de la Sociedad de Ingenieros de Audio, de Nueva York en noviembre
de 1978. La sorpresa entre los audiófilos fue considerable, y la calidad de
AudioPro pasó a ser mundialmente reconocida. Especialmente impresionante
eran los graves, que daban sensaciones sónicas que pocos habían
experimentado fuera de la sala de conciertos. La tecnología ACE-Bass ha
seguido desarrollándose durante todos estos años y actualmente se sigue
utilizando en la fabricación de los subwoofers de AudioPro. |
Explicación en Inglés
ACE-BASS is an abbreviation for Amplifier Controlled Euphonic Bass.
A more tecnical description of ace-bass
In Elektronikvärlden (a Swedish hi-fi
magazine) No. 8, 1988, Bertil Hellsten wrote a very good and instructive
description of the ace-bass technology. Below is an abstract of the article:
General
There are many ways to accomplish good bass
in a loudspeaker. One is to have a large cabinet and a large woofer.
In practice, the lower limit for a woofer is set by the lower resonance
frequency, which can be lowered by increasing the membrane's mass. By adding
weights, you can go lower and lower in frequency. But, at the same time, the
speaker will respond increasingly slowly.
In addition, the membrane's compliance and damping will no longer match, so
the result isn't useful. To achieve a very low limiting frequency in a small
woofer, a combination of mass, compliance and damping is needed, and this is
impossible to achieve mechanically.
Audio Pro's solution - electronic mechanics
Seen from the amplifier's point of view, the loudspeaker is an electrical
component with its mechanical attributes transformed into electrical
magnitudes. The mass corresponds to a capacitance, and the compliance to an
inductance that is in parallel with the capacitance. The attenuation
corresponds to a resistance that is in parallel with both of the above.
By adding more inductances, resistances and capacitances, one should easily
be able to change the loudspeaker's mechanical attributes. This is the main
idea behind Audio Pro's ace-bass loudspeaker constructions.
But there is a catch. The drive unit's voice coil has a resistance that
lies serially with the parallel 'mechanical' components. This means that we
can't parallel-connect directly to the woofer's mechanical parameters. It is
not connected to the amplifier firmly enough.
If we were to increase the damping by parallel-connecting the amplifier
output with a resistance, we would still never get a lower value than what
the voice coil's resistance gives, and that is not good enough. The same
thing happens to the other attributes. They are 'hidden' by the voice coil's
(and the speaker cable's) resistance.
Negative resistance
The solution is to serially connect the amplifier output with a negative
resistance. But you can't buy that at your nearest electronics parts shop.
It can only be achieved by positive feedback in the amplifier's output stage.
There are several sensitive factors that can easily cause the system to
self-oscillate. However, correctly trimmed, you can achieve a system that
exactly equalizes all the resistances that are in series with the drive
units' properties. In this way, you can also reach and affect the
loudspeaker's mechanical attributes electrically.
You can also choose to let this influence decrease with increasing
frequency, where it's no longer needed.
By using this feature fully, Audio Pro maintains that you can decrease the
speaker's physical volume by 90%, compared to a conventional bass reflex
box!
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