Easy BBC modular wideband sound absorber

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Here, are some very interesting links, but in English because from the tests of the BBC, which compare between them the effectiveness of absorbent resonator panels at low frequency from 50hz. Efficiency curves in support.
http://downloads.bbc.co.uk/rd/pubs/reports/1992-11.pdf

And to deepen the comparison of the different types of panels
http://downloads.bbc.co.uk/rd/pubs/reports/1992-10.pdf
room acoustics
http://downloads.bbc.co.uk/rd/pubs/reports/1992-09.pdf

The first two documents compare, measure and identify the defects of each. The effectiveness of different resonators according to their nature are thus analyzed:
Helmholtz resonators with vent
Helmholtz resonators with perforated panel
Helmholtz membrane resonators.

They conclude that boxes described below are absorbent at a low frequency and over an extended frequency range.
They also do not have the multiple resonance faults of the tuned panels of the other modules studied.
58 * 58 cm on the side
183,5mm deep
made of 9.5mm plywood
with a background of 4mm
filled with 175 mm of rock wool (density between 40 and 60 kg / m3)
closed by a 3mm thick panel perforated at 20% of 3mm holes at 6mm centres.

Attention only one of these boxes are not enough to treat a room, it speaks to cover one of a dozen m2 with these boxes (like any type of low frequency absorber)
Bye
 
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