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Schalldämpfung in dünnwandigen, rechteckigen Lüftungskanälen

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In ventilation ducts, e.g. made from thin sheet steel, a damping of several dB per metre of duct length is found at low frequencies. The damping begins at the frequency of the deepest natural flexural vibration of the duct wall and terminates at approximately the frequency at which the mass impedance of the canal wall is equal to the acoustic characteristic impedance of the air.

By means of measurements in model ducts and in those practically constructed the influence of the ducts' transverse dimension, of the mass of the duct-walls per surface unit and of any sound-damping such as that of a thermal insulation jacket for the duct are shown in the damping of the duct. By the planning of the sound insulation of a ventilation installation the damping in thin-walled ducts can be determined so that the necessary length of ducts lined with porous material could be approximately reduced by half.

Zusammenfassung

In Lüftungskanälen, z.B. aus dünnem Stahlblech, ist bei tiefen Frequenzen eine Dämpfung von einigen Dezibel je Meter Kanallänge vorhanden. Die Dampfung beginnt bei der Frequenz der tiefsten Biegeeigenschwingung der Kanalwände und endet ungefähr bei der Frequenz, bei welcher der Massenwiderstand der Kanalwand gleich dem akustischen Kennwiderstand der Luft ist.

An Hand von Messungen in Modellkanälen und praktisch ausgefährten Kanälen wird der Einfluß der Kanalquerabmessungen, der Masse der Kanalwände je Flächeneinheit und eines schalldämmenden bzw. wärmeisolierenden Kanalmantels auf die Dämpfung im Kanal gezeigt. Bei der Planung der Schalldämmung von Lüftungsanlagen kann die Dämpfung in den dünnwandigen Kanälen berücksichtigt werden, wodurch sich die notwendige Länge porös ausgekleideter Dämpfungskanäle etwa halbiert.

Sommaire

Dans les canalisations d'aération, en tôle d'acier mince par exemple, on constate aux basses fréquences un amortissement de plusieurs dB par mètre. Cet amortissement commence à la première fréquence propre de flexion de la paroi et disparaît approximativement à la fréquence pour laquelle l'impédance massique de la paroi est égale à l'impédance caractéristique de l'air.

Des mesures effectuées sur des maquettes ou sur des canalisations réelles permettent de mettre en évidence l'influence des dimensions transversales des canalisations, celle de la masse unitaire des parois et celle d'une garniture d'isolation thermique ou acoustique. Si l'on tient compte de cet amortissement lié à la minceur des parois, on pourra diviser par deux la longueur des revêtements poreux nécessaires pour insonoriser une installation d'air conditionné.
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Document Type: Research Article

Publication date: February 1, 1981

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  • Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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