Room in Room Acoustics: the Influence of the Direct/Diffuse Sound Field Ratio in a Listening Room on Played Back Recorded Acoustics

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Constant Hak

Eindhoven University of Technology

Wednesday 3 june, 2015, 09:40 - 10:00

0.9 Athens (118)

Room acoustical properties in music and voice recordings such as reverberation, definition, clarity and speech intelligibility are influenced by the acoustics (including electro-acoustics) of the listening room. Playing back recorded acoustics through loudspeakers in sound control rooms, lecture rooms, congress halls or cinema’s affects the intended acoustics of the recording. In earlier investigations, the impact of listening room impulse responses on recording room impulse responses was shown by convolving many random combinations of practical (more or less) diffuse field room impulse responses. In this new study the influence of the direct sound contribution has been investigated. To this end, three typical loudspeaker sources were used for playing back recorded acoustics: an omnidirectional loudspeaker source (dodecahedron), a single loudspeaker (box) and a loudspeaker array (column). In order to have a sufficiently large measurement distance, this was done in a large (non-diffuse) sports hall (functioning as the 'listening room'). At various distances from the loudspeaker sources, from direct near field (0.1 m source-receiver distance) to more or less diffuse far field (10 m source-receiver distance), the influence of this hall and type of loudspeaker sound source on the played back recorded acoustics was determined using convolution techniques. The results are presented as a function of the source-receiver distance and as a function of the direct/diffuse sound energy ratio, directly derived from the measured impulse responses. The audibility of the difference between recorded and perceived acoustical properties is judged based on the JND (Just Noticeable Difference). It is found that a directional loudspeaker sound source in a room (high directivity index Q in the listeners direction) does not necessarily better reproduce the played back recorded acoustics.

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