Publications (11)1.55 Total impact
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Article: Low-frequency absorption using a two-layer system with active control of input impedance.
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ABSTRACT: Broadband noise absorption, including low frequencies, may be obtained by a hybrid passive-active two-layer system. A porous layer in front of an air layer provides passive absorption, at medium and high frequencies. Active control of the input impedance of the two-layer system yields absorption at low frequencies. The active control system can implement either pressure-release or impedance-matching conditions. A simple analytical model based upon plane waves propagating in a tube permits the comparison of both control strategies. The results of this simple model show that the pressure-release condition affords higher absorption than the impedance-matching condition for some combinations of geometrical and material parameters. Experimental results corroborate the good performance of the pressure-release condition under the prescribed geometrical setup.The Journal of the Acoustical Society of America 01/2004; 114(6 Pt 1):3211-6. · 1.55 Impact Factor -
Article: Microperforated insertion units: An alternative strategy to design microperforated panels
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ABSTRACT: Microperforated panels (MPPs) coupled to a rigid wall have been proposed recently as an alternative to porous absorbers in situations having concerns with bacterial contamination and small particles discharge, like food, pharmaceutical and microelectronic industries. There exists also an increasing interest for MPP absorbers in the transportation industry and civil engineering. In general, an optimally designed MPP with good broadband absorption requires many submillimetric holes distributed over a panel of also submillimetric thickness. Such thin plates or foils become so fragile that they need to be protected from mechanical damage. In this paper, an alternative strategy is investigated which allows the design of MPPs with panels of millimetric thickness while maintaining their acoustic performance. These absorbers, named microperforated insertion units (MIUs), avoid the structural problems of the classical MPPs. An assessment of the sound absorption properties of these structures is presented. Comparisons between calculations and measurements are also made under two experimental conditions: plane waves at normal incidence (impedance tube) and free field (anechoic room).Applied Acoustics. -
Article: Hybrid passive-active sound absorption in a standing wave tube using a thin plate actuator as secondary source
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ABSTRACT: Communication presented at the 18th International Congress on Acoustics (ICA 2004): "Acoustical Science and Technology for Quality of Life", Kyoto, 4-9 April 2004. This paper deals with the design and optimization of a hybrid passive/active liner for broadband noise reduction in a standing wave tube. The thickness of the multilayer absorbent is reduced in two steps: firstly a porous layer backed by an air gap is substituted by a microperforated panel followed by a reduced air gap; and secondly, the secondary loudspeaker is replaced by a thin plate driven by a piezoceramic patch. Experimental results show that high absorption may be achieved in a wide frequency range (100-900 Hz) with a thin hybrid passive/active absorber. This research has been funded by the Spanish Ministry of Science and Technology under Grant No. DPI2001-1613-C02-01. Peer reviewed -
Article: Control activo de la impedancia de entrada en absorbentes multicapa
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ABSTRACT: 6 pp.-- PACS nr.: 43.55.Ev.-- Comunicación presentada en los siguientes congresos: XXXIV Congreso Nacional de Acústica – TecniAcústica 2003. Encuentro Ibérico de Acústica. EAA Symposium on Architectural Acoustics. Expoacústica 2003 (Bilbao, 15-17 Octubre 2003). Publicado en número especial de la Revista de Acústica: Vol. 34, núm. 3-4 (2003). [EN] This work deals with the experimental design of hybrid absorbers for broadband noise control in ducts. The followed strategy is the control of input impedance of the multilayer system over a large frequency bandwidth, combining both passive and active technologies. Control of medium and high frequencies is afforded by a porous material backed with an air gap, while low frequencies are reduced with active control. Three active techniques are investigated: pressure-release in the back face of the porous layer, impedance-matching and zero-reflection condition. First experimental results of the developed prototype are shown. [ES] Este trabajo versa sobre el diseño experimental de absorbentes híbridos para reducir el ruido de banda ancha en conductos. La estrategia seguida es el control de la impedancia de entrada al sistema multicapa en un amplio margen de frecuencias combinando técnicas pasivas y activas. Las medias y altas frecuencias se controlan con un material poroso seguido de una capa de aire, mientras que en baja frecuencia se implementan técnicas de control activo. Se estudian tres estrategias activas: liberación de la presión acústica en la capa trasera del material poroso, adaptación de impedancias y condición de reflexión nula. Se muestran los primeros resultados experimentales obtenidos con el prototipo desarrollado. Este trabajo ha sido posible gracias a la financiación de la CICYT, a través del Proyecto DPI2001-1613-C02-01. Peer reviewed -
Article: Microperforated Insertion Units in free field: A case study
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ABSTRACT: 6 pages.-- Communication presented at ForumAcusticum 2005 Budapest: "Acoustics: Science and Technology for Knowledge Based Society and Healthy Environment" (Aug 29-Sep 2, 2005). In Internoise 2004 we reported the new concept of Microperforated Insertion Units, MIU, introducing their innovative acoustic and mechanical performances as an alternative to the traditional Microperforated Panel Absorbers, MPP. Theoretical and experimental results were compared in an impedance tube with diameters of 3 and 10 mm. In this work, we consider the angular dependence of the absorption coefficient of a large MIU panel (2.4 x 2.4 m2) in free field. Both theoretical and experimental results are presented, showing the acoustic absorptive capabilities of the device. We are grateful to the Spanish Ministry of Education and Science for funding this research under Grants No. DPI2001-1613-C02-01 and DPI2004-05504-C02-01. Peer reviewed -
Article: The influence of ocean waves in shallow water problems
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ABSTRACT: 5 pages.-- Communication presented at ForumAcusticum 2005 Budapest: "Acoustics: Science and Technology for Knowledge Based Society and Healthy Environment" (Aug 29-Sep 2, 2005). In this paper we present the influence of ocean waves in shallow water scenarios which have geometric dimensions of about several times the acoustic wavelength. Typically, this concerns coastal zones. It is well known that ocean waves are a source of scattering, have dispersive behaviour, and that at low frequencies are a source of noise. We will base our work on measurements realized in shallow water conditions, an attempt to model ocean waves and include them in existing codes of acoustic propagation using finite difference schemes. Additionally, we will compare the differences between measurements and prediction models and try to discuss the reliability of the models for the Shallow water case. Peer reviewed -
Article: Artificial neural network algorithms for active noise control applications
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ABSTRACT: 6 pages, 5 figures.-- PACS nr.: 43.50 Ki.-- Communication presented at: Forum Acusticum Sevilla 2002 (Sevilla, Spain, 16-20 Sep 2002), comprising: 3rd European Congress on Acoustics; XXXIII Spanish Congress on Acoustics (TecniAcústica 2002); European and Japanese Symposium on Acoustics; 3rd Iberian Congress on Acoustics.-- Special issue of the journal Revista de Acústica, Vol. XXXIII, year 2002. This paper shows the use of several methods commonly applied to training Artificial Neural Networks (ANN) in Active Noise Control (ANC) systems. Although ANN are usually focused on off-line training, real-time systems can take advantage of modern microprocessors in order to use these techniques. A theoretical study of which of these methods suit best in ANC systems is presented. The results of several simulations will show their effectiveness. This work has been supported by the Comisión Interministerial de Ciencia y Tecnología (CICYT) under the project DPI2001-1613-C02-01. Peer reviewed -
Article: Computed aided semiautomatic determination, at laboratory level, of the sound speed in solids, liquids and gases
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ABSTRACT: 6 pages, 5 figures.-- PACS nr.: 43.58.Dj.-- Communication presented at: Forum Acusticum Sevilla 2002 (Sevilla, Spain, 16-20 Sep 2002), comprising: 3rd European Congress on Acoustics; XXXIII Spanish Congress on Acoustics (TecniAcústica 2002); European and Japanese Symposium on Acoustics; 3rd Iberian Congress on Acoustics.-- Special issue of the journal Revista de Acústica, Vol. XXXIII, year 2002. This paper reports how can the sound speed, into any solid, liquid or gas media, be evaluated. The determination of the sound speed is done at laboratory level in a quick and simple way. The sole condition for the solid samples is to be limited in dimensions to fit into the sample holder of the measurement system; the fluids have to be put into some given receptacles. The system makes use of a generation and acquisition board controlled by a PC, that is not especially dedicated for this purpose. Some results are presented from which the accuracy of the evaluation can be shown. Peer reviewed -
Article: In situ absorption measurement of antinoise devices using pre-determined pulse waveforms
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ABSTRACT: 8 pages, 6 figures.-- Comunicación presentada en: XXXV Congreso Español de Acústica – TecniAcústica 2004, IV Congreso Iberoamericano de Acústica, IV Congreso Ibérico de Acústica y EAA Symposium "Environmental and Architectural Acoustics" (Guimaraes, 14-17 Sep 2004). Noise barriers can be characterized by using the Adrienne method which combines MLS signals with the subtraction technique. This paper deals with a method to shape the loudspeaker-microphone impulse response which utilizes inverse filtering techniques to design the waveform radiated by the loudspeaker according to some prescribed criterion. For instance, zero-phase cosine-magnitude waveforms provide minimum length within a given frequency band. Therefore, this technique allows approaching the microphone to the loudspeaker, and as a consequence, reduces the lowest reliable frequency of the absorption measurement. This research has been supported by the Spanish Ministry of Science and Technology, under Grant. Nº. DPI2001-1613-C02-01. Peer reviewed -
Article: Low frequency absorption by active control of impedance
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ABSTRACT: 8 pages, 5 figures.-- Comunicación presentada en: XXXV Congreso Español de Acústica – TecniAcústica 2004, IV Congreso Iberoamericano de Acústica, IV Congreso Ibérico de Acústica y EAA Symposium "Environmental and Architectural Acoustics" (Guimaraes, 14-17 Sep 2004). Passive systems are inherently unable to provide absorption in the low frequency range due to limitations in the size-to-wavelength ratio. Active control systems, on the other hand, perform at low frequencies. A hybrid passive-active system can then be conceived which complements the low frequency range of a passive absorber with active control. When properly configured, such a hybrid system is able to afford broadband absorption. This research has been supported by the Spanish Ministry of Science and Technology, under Grant. Nº. DPI2001-1613-C02-01. Peer reviewed -
Article: Measuring short impulse responses with inverse filtered maximum-length sequences
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ABSTRACT: Most loudspeakers have a non-flat frequency response which produces a long oscillating impulse response. An inverse filtering approach may be used to calculate the driving waveform necessary to equalize the response of the loudspeaker in order to radiate shorter acoustic pulses. When combined with the MLS technique, inverse filtering may be used to pre-emphasize the driving signal so that a shorter impulse response, with a prescribed waveform, is measured. This technique is described and illustrated by applying it to a distributed mode loudspeaker. Originally, this loudspeaker has a rather irregular response in a wide band. When the MLS signal is pre-emphasized with the proper inverse filter, a shorter impulse response is measured with a zero-phase cosine-magnitude spectrum.Applied Acoustics.
