Acoustic absorbent panels with low perforation coefficient

8 pages, 8 figures.-- Comunicacion presentada en: XXXV Congreso Espanol de Acustica – TecniAcustica 2004, IV Congreso Iberoamericano de Acustica, IV Congreso Iberico de Acustica y EAA Symposium "Environmental and Architectural Acoustics" (Guimaraes, 14-17 Sep 2004).