Helmut Fuchs

Sound-absorbing article effective over a broad frequency range

A sound-absorbing article which is one of a lining or a shaped element and which has a sound absorptive effect over a broad frequency range particularly useful in transportation vehicle when positioned proximate a reverberant wall, the article including at least one microperforated sheet absorber which has microperforations defined therein having at least one hole diameter ranging from 0.05 mm to 2 mm, which has at least one interhole distance ranging from 1 mm to 20 mm, and which has a proportion of hole area ranging from 0.2 to 4%, based on surface area of the at least one microperforated sheet absorber; and at least one absorber which is at least one of a foam absorber and a non-woven absorber and which is positioned at a preselected spatial distance from a reverberant wall.

Das neue Volkswagen-Akustikzentrum in Wolfsburg

Dieser Beitrag beschreibt einen neuen Standard fur die objektive Erfassung von Gerauschen in und an Kraftfahrzeugen im Labor. Im vorliegenden ersten Teil wird zunachst das Konzept eines auf die Bedurfnisse der Volkswagen AG zugeschnittenen Prufstand-komplexes dargelegt. Auserst niedrige Ruhepegel - selbst mit zugeschalteter leistungsfahiger Luftungsanlage - erlauben jetzt ungestorte akustische Untersuchungen. Die vom Fraunhofer-Institut fur Bauphysik (IBP) entwickelte reflexionsarme Raumauskleidung sowie die Gute der damit erreichten Freifeldeigenschaften sind Inhalt des zweiten Teils, der in der nachsten ATZ erscheint.

The New Volkswagen Acoustics Centre in Wolfsburg

The first part of this article in the last ATZ issue described the concept of a test bed complex that is tailor-made to meet the requirements of Volkswagen AG. Extremely low ambient noise levels — even when the powerful air conditioning system is switched on — allow acoustic examinations to be performed without any disturbance. This second part of the article deals with the anechoic room lining, which was developed by Fraunhofer IBP, and the quality of the free-field properties that can be achieved by this.

Broadening the frequency range of panel absorbers by adding an inner layer of microperforated‐plate

A disadvantage of panel absorbers, namely a panel backed by an airspace, is that the effective frequency range is usually rather narrow. It has been theoretically demonstrated that the absorption range can be broadened by introducing a microperforated‐plate between the panel and the back wall [J. Kang, IBP Report 1993]. In this paper, a series of experimental results on the effectiveness of this method is presented. The experiments were carried out using the single microphone FFT technology in an impedance tube. It is shown that with an inserted microperforated‐plate the acoustic resistance of the whole structure is greater than that of the outer panel alone. When the parameters of the microperforated‐plate are carefully selected, the absorption range can be effectively extended in both low‐ and high‐frequency directions. Typically the improvement is around 1 oct. The effectiveness of the microperforated layer is much less when its resonance frequency is considerably higher than that of the outer panel al...