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Potential of tree bark for the application as sound absorbing material Tree bark is a highly optimized natural material, which protects a tree from manifold damage at the peripheral layer. Hence, bark has some interesting technological properties, such as a low density and a good biological durability. In the wood‐industry, huge amounts of bark in pieces accrue, which are used to a low extend for high‐value applications. In this investigation, insulation panels from larch bark were produced and their inner structure was evaluated by means of CT. The sound absorption coefficient of panels with varying composition was investigated using impedance measurement and structure‐property relationships were evaluated. It was found that larch insulation panels can be applied as effective sound absorbers for frequencies higher than 500 Hz and that the frequency with the highest sound absorption can be affected changing the particle size of the panels. [ABSTRACT FROM AUTHOR]

Abstract: On the bass ratio in five acoustically outstanding concert halls. Until 1962 all renowned acousticians agreed that one should damp the low frequencies in the reverberation of a room as much as possible. From then on a doctrine was unfortunately spread out that a rise of the bass regime could give music and speech more fullness and warmth and the listener a comfortable envelopment. This imagination still dominates, even in standards, although the leading initiator and supporter of a bass ratio BR > 1 as a quality criterion for acoustics has discarded his own dogma in his book of 2004. In the meantime numerous buildings and reconstructions showed equally subjective evidence that BR ≤ 1 represents an important goal for the desired clarity of music and intelligibility of speech. The objective reason for otherwise unwanted inevitable low‐frequency hum may be found in destructive interference effects of the direct sound of a source with early reflections from the ceiling and walls. The latter should therefore absorb the bass. How well this is achieved may be deduced from the reverberation time in the unoccupied room without heavily upholstered seats, i.e. measured without their absorption always dominating at the irrelevant mid frequencies. In fact, most famous concert halls like Musikvereinssaal in Vienna (of 1877), Concertgebouw in Amsterdam (of 1888), Symphony Hall in Boston (of 1900) und Berliner Philharmonie (of 1963), as well as several other venues with excellent acoustics exhibit a bass ratio BR ≤ 1. The Elbphilharmonie in Hamburg (of 2017) may serve as another example which is highly esteemed by musicians as well as by conscious listeners. [ABSTRACT FROM AUTHOR]