Little has been published about the repercussions of different source locations and measuring positions for the Low-Frequency Effects (LFE) loudspeakers in cinemas and dubbing theatres. The aim of this study is to determine the effects of the number and position of the loudspeakers on the uniformity of the response over the listening area, and to assess the effect of the measuring of those responses by the choices made regarding the positioning of the microphones within typically used arrays. Some organisations issuing recommendations for the installation of LFE loudspeakers have long suggested that they should be installed asymmetrically, below the screen. The reason given for this is to avoid the symmetrical driving of the low-frequency modal responses of the rooms, the sources typically being centred about 20% of the distance from one side-wall and 33% of the distance from the opposite side wall. However, other organisations, and many designers, have recommended the mounting of the LFE loudspeakers in tighter-packed clusters. Furthermore, it has long been suggested that a single microphone position is inadequate for measuring the response of an LFE channel because the long wavelengths involved make spacial variation in the measurements inevitable. Typically, 4, 5, 8 and 10-microphone arrays have been used, but as rooms differ so much in size, shape and acoustic properties, no universal instructions exist about precisely how to place the microphones in such arrays. This paper examines how the choice of low-frequency source positions, and the microphone positions in a 5-microphone array, can affect the measured average responses over the designated listening areas. It also discusses how the positioning of the loudspeakers can affects the evenness of coverage. The results of the spacially averaged responses are compared with the responses at individual microphone positions, in order to assess how representative the averages are of the responses at specific locations.

Authors: Newell, Julius; Newell, Philip; Holland, Keith
Affiliations: Acoustics Consultant, Moaña, Spain; Newell Acoustic Engineering, Lisbon, Portugal; University of Southampton, Southampton, UK(See document for exact affiliation information.)
AES Conference: 57th International Conference: The Future of Audio Entertainment Technology – Cinema, Television and the Internet (March 2015)
Paper Number: 2-2
Publication Date: March 6, 2015
Subject: Acoustical design and performance of motion picture theaters

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