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Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Measured sound pressure levels in the open system for (a) white, (b) pink, (c) brown noises, as well as for (d) frequency sweep from 10,000→20 Hz for systems with plain isolators, and the active system at two different cavity depth levels.