The main alteration investigated in respect to stage acoustics of the main hall of De Doelen is the introduction of a stage reflector. From comparison between subjective research and measurements it was concluded that increasing support (ST1) and Early Reflections Strength (G_(5-80)) would be required to improve stage conditions. The Early Reflections Strength (G_(5-80)) is not a standardized parameter but is proposed for this purpose. From scale model measurements and computer calculations it was found that the stage reflector as proposed increases the ST1 values (for own instrument) with 0.4 to 1.7 dB and increases the audibility of other instruments expressed in the Early Reflections Strength (G_(5-80)) with approximately 1 to 2 dB. The most significant influence of the stage reflector lies in filling the gap between very early reflections from the side walls and later reflections from walls and ceiling. The improvement is therefore expected to be modest but consistent. Proposed improvements in respect to timbre are: reduction of low frequency absorption and rougher surface finishing around the orchestra.
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