This paper ties in to a previous Convention Paper by the same authors (AES 115th Convention, 2003, #5944, ) and presents a current set of commercially available passive and active low frequency absorbing devices. One item in particular is of an experimental nature – a wood box loaded with conventional membrane loudspeakers. These are not connected to an amplifier, but to a variety of different passive electronics networks (parallel, serial). Reproduci-ble acoustical measurements have been taken in a completely untreated rectangular concrete room, sequentially with and without a total of eight different absorbing devices. Results are compared and conclusions are presented.
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