Publication: Study of an electroacoustic absorber
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2008-06
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2009
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Abstract
El problema de la atenuación del ruido de baja frecuencia todavía persiste pese a que ha sido ampliamente estudiado. Las técnicas para absorber ruido de alta frecuencia (superior a 500 Hz), como son los materiales porosos, resonadores de Helmholtz o espumas no ofrecen resultados aceptables a bajas frecuencias. Serían necesarios volúmenes impracticables de materiales porosos para intentar absorber frecuencias menores a 500 Hz, y lo mismo ocurre con los resonadores de Helmholtz. Esta ineficacia de los materiales pasivos absorbentes tradicionales ha motivado el desarrollo de nuevas técnicas para absorber el ruido reverberante de baja frecuencia, usando altavoces y materiales con control activo. En este trabajo se desarrolla un altavoz disipador pasivo, basado en el uso de una resistencia como absorbente de energía, y se optimizan los parámetros del altavoz y el valor de ésta resistencia disipadora. El principal objetivo de este trabajo era optimizar los parámetros de un altavoz para conseguir absorción total en un rango específico de bajas frecuencias. En este caso, el altavoz más útil es un altavoz pasivo, terminado en una resistencia, de forma que su funcionamiento sea similar a un resonador de Helmholtz. La frecuencia de resonancia es donde se puede obtener la absorción total. Moviendo esta frecuencia a lo largo del espectro, y cambiando su forma, es posible variar el valor de la masa mecánica y la compliancia. Con los diseños de MATLAB se ha visto que es posible conseguir absorción total en bajas frecuencias , a pesar de que son necesarios materiales extremadamente ligeros para construir el altavoz. Las pruebas experimentales con el tubo de impedancias han demostrado que el prototipo funciona, de forma que una vez conseguidas las características óptimas del altavoz, es posible construir paneles de este tipo de altavoces para controlar la reflexión de un recinto.-----------------------------------------------------------------------------------------
The problem of low-frequency acoustic noise attenuation still remains in spite of the fact that it has been widely studied. The techniques for absorbing high-frequency noise (greater than 500 Hz) such as the use of porous materials, Helmholtz resonators and mufflers not offer acceptable results at lower frequencies. Porous damping materials rely on the viscous damping of fluid low over a surface. And particle velocity is proportional to frequency, so for trying to absorb frequencies under 500 Hz, it would be necessary to use impractical volumes of material. The same problem appears with the Helmholtz resonators. They provide excellent attenuation of highly resonant acoustic modes but require restrictively large volumes for low frequencies. This inadequacy of the traditional passive damping treatments has motivated the development of new techniques for absorbing low-frequency reverberant noise with loudspeakers and active control materials. In this work we develop the design of a passive shunting loudspeaker, based on the use of a resistor as the energy absorber. The optimization of the loudspeaker parameters and the value of the shunting resistor are tested. The main objective of this work was to optimize the parameters of a loudspeaker for achieving total dumping at an specific range of low frequencies. In this case, the most useful loudspeaker is a passive one, ended in a resistor, so that the performing is similar to a Helmholtz resonator. The frequency of resonance is where a total absorption can be achieved. Moving this frequency through the spectrum, and changing its shape, is possible varying the value of the mechanical mass and compliance. With the MATLAB designs, it’s seen that is possible to achieve total damping at low frequencies, thought it needs the use of very light materials for the construction of the loudspeaker. The experimental testing with the impedance tube has demonstrated that the prototype works, so once achieved the optimal conditions of the loudspeaker, it’s possible to build panels of these loudspeakers for controlling the reflection of an enclosure.
The problem of low-frequency acoustic noise attenuation still remains in spite of the fact that it has been widely studied. The techniques for absorbing high-frequency noise (greater than 500 Hz) such as the use of porous materials, Helmholtz resonators and mufflers not offer acceptable results at lower frequencies. Porous damping materials rely on the viscous damping of fluid low over a surface. And particle velocity is proportional to frequency, so for trying to absorb frequencies under 500 Hz, it would be necessary to use impractical volumes of material. The same problem appears with the Helmholtz resonators. They provide excellent attenuation of highly resonant acoustic modes but require restrictively large volumes for low frequencies. This inadequacy of the traditional passive damping treatments has motivated the development of new techniques for absorbing low-frequency reverberant noise with loudspeakers and active control materials. In this work we develop the design of a passive shunting loudspeaker, based on the use of a resistor as the energy absorber. The optimization of the loudspeaker parameters and the value of the shunting resistor are tested. The main objective of this work was to optimize the parameters of a loudspeaker for achieving total dumping at an specific range of low frequencies. In this case, the most useful loudspeaker is a passive one, ended in a resistor, so that the performing is similar to a Helmholtz resonator. The frequency of resonance is where a total absorption can be achieved. Moving this frequency through the spectrum, and changing its shape, is possible varying the value of the mechanical mass and compliance. With the MATLAB designs, it’s seen that is possible to achieve total damping at low frequencies, thought it needs the use of very light materials for the construction of the loudspeaker. The experimental testing with the impedance tube has demonstrated that the prototype works, so once achieved the optimal conditions of the loudspeaker, it’s possible to build panels of these loudspeakers for controlling the reflection of an enclosure.
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Keywords
Electroacústica, Altavoces, Electroacustic absorber, Loudspeakers