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The Acoustical Effect of Audio Equipment and Furniture in a Mixing

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The Acoustical Effect of Audio Equipment and Furniture in a Mixing Acoust. Sci. & Tech. 26, 2 (2005) The acoustical effect of audio equipment and furniture in a mixing room Atsuro Ikeda1;Ã, Masataka Nakahara1;2, Chizuru Kai1 and Akira Omoto3 1SONA Corporation, 2–19–9 Yayoi-cho, Nakano-ku, Tokyo, 164–0013 Japan 2Kyushu Institute of Design, Shiobaru 4–9–1, Minami-ku, Fukuoka, 815–8540 Japan 3Faculty of Design, Kyushu University, Shiobaru 4–9–1, Minami-ku, Fukuoka, 815–8540 Japan ( Received 21 September 2004, Accepted for publication 20 November 2004 ) Keywords: Mixing room, Loudspeaker response, Absorption coefficient PACS number: 43.55.Fw, 43.55.Gx [DOI: 10.1250/ast.26.233] 1. Introduction A mixing room is the room where the mixing engineer sits soundproof absorption at the listening position and operates the various audio 2.86 layer layer equipment with listening to the playback sound reproduced by the loudspeaker. These equipment and furniture, which are R 0.39 RS1 RS2 usually of large dimensions, have to be installed into the SUBR ° C 160 1.37 mixing room after the architectural construction is done. ° 125° RS3 ° 1.13 1.15 95 However, the acoustical effect of them is rarely discussed. On Room 0.56 45 Center 6.40 the other hand, in respect to the acoustic design for LS3 0.56 1.13 auditoriums, the acoustical effect of chairs and the audience 1.15 SUBL are often considered in order to estimate the acoustical 1.37 LS2 properties under the actual environment. In recent research, L LS1 0.25 0.39 the acoustical effect of equipment in a mixing room is 0.25 1.5 1.35 reported [1]. Focusing on this point, the authors conducted mixer's acoustical measurement in the existing mixing room with and position Unit [m] without equipment and furniture. This letter shows the (receiver) 6.80 measurement results and reports the acoustical effect of equipment and furniture on a mixing room. C 2. Measurement 2.70 1.76 2.11 2.03 1.95 Impulse responses were measured in the mixing room 1.20 shown in Fig. 1. The mixing room is a medium sized post- production studio in Tokyo [2] whose floor area and room volume are 35 sq meters and 83 cu meters, respectively. The eleven loudspeakers, nine full-range loudspeakers and two Fig. 1 Examined mixing room with the condition subwoofers, are installed in order to work for the multichannel ‘empty’; there is nothing in the room. Loudspeakers; programs. Therefore, 11-kinds of impulse responses are able full-ranges, L/C/R/LS1/LS2/LS3/RS1/RS2/RS3, to be measured at one receiver position in the room. and subwoofers, SUBL/SUBR. The impulse responses were measured under three conditions as follows. the full-range loudspeakers, and SUBL and SUBR indicate (1) ‘empty’: There is nothing in the room (Fig. 1). subwoofers which reproduce only the low frequency sound. (2) ‘console in the room’: Only the mixing console is The loudspeaker responses, namely the transfer functions located in the room (Fig. 2). from the loudspeakers to the mixer’s position including the (3) ‘all equipment in the room’: All equipment such as the loudspeaker characteristics, were measured. mixing console, audio equipment (racks) and furniture (tables, sofas, chairs) are located in the room (Fig. 3). 3. Measurement results The loudspeakers, amplifiers, measurement tools and 3.1. Loudspeaker responses receiver positions were consistent though all conditions. The One of the most important things for the acoustical positions of loudspeakers, sources, are shown in Figs. 1 to 3, property of the mixing room is the frequency characteristics where the L, C, R, LS1, LS2, LS3, RS1, RS2 and RS3 indicate of a loudspeaker response at the mixer’s position. This section shows the differences of the responses from C, RS1 and RS3 Ãe-mail: [email protected] loudspeakers due to the presence of a mixing console and 233 Acoust. Sci. & Tech. 26, 2 (2005) empty console in the room all equipment in the room RS1 R RS2 C SUBR C RS3 Room mixer's position Center (receiver) 10dB LS3 RS1 mixing console SUBL LS2 L LS1 Unit [m] 10dB relative SPL [dB] Fig. 2 Plan view of the mixing room. ‘console in the RS3 room’; only the mixing console as the grayed object is in the room. 10dB 10 100 1k 10k frequency [Hz] RS1 R RS2 Fig. 4 The variation of the loudspeaker responses at the SUBR mixer’s position due to the presence of equipment and C RS3 furniture. From the top, the responses from C, RS1, and RS3 loudspeakers. The solid lines, the dashed lined and Room Center the dash-dotted lines indicate the responses of ‘empty,’ LS3 ‘console in the room’ and ‘all equipment in the room,’ mixing console respectively. Results are averaged at 1/24 octave SUBL intervals. LS2 L LS1 mixer's position (receiver) ‘all equipment in the room’ - ‘empty’ 20 RS3 RS1 Fig. 3 Plan view of the mixing room. ‘all equipment in 10 the room’; equipment and furniture shown as the grayed objects are in the room. 0 -10 C SPL difference [dB] -20 other equipment shown in Figs. 1, 2 and 3. 20 100 1k Figure 4 shows the frequency characteristics from three frequency [Hz] kinds of the loudspeaker to the mixer’s position under three room conditions, ‘empty,’ ‘console in the room’ and ‘all Fig. 5 Differences between the loudspeaker responses equipment in the room.’ Because of the horizontally sym- with equipment and furniture and ones without them; ‘all equipment in the room’ — ‘empty.’ The solid metrical shape of the room, the responses from the loud- lines, the dashed lined and the dash-dotted lines speakers on the right hand are shown. Figure 5 shows the indicate the responses from C, RS1 and RS3 loud- effects of the equipment and furniture, namely the differences speakers, respectively. between the responses of ‘all equipment in the room’ and ‘empty.’ Because of the little difference at higher than 1 kHz, the results in the range from 10 Hz to 1 kHz are shown. In reverberation time is often reported as the measurement result Figs. 4 and 5, results are averaged at 1/24 octave intervals. of a mixing room. According to the results shown in Figs. 4 and 5, we ascertain Therefore, the apprehension for the variation of the that the equipment and furniture affects the loudspeaker absorption characteristics due to the presence of equipment response at low frequency range. and furniture may be useful for the acoustic design of a 3.2. Reverberation times mixing room. Figure 7 and Table 1 show the reverberation The reverberation time is not usually considered on the times under three conditions, ‘empty’ (solid line), ‘console in acoustic design of a mixing room, because a mixing room is the room’ (dashed line) and ‘all equipment in the room’ (dash- usually surrounded by the highly sound absorbing materials, dotted line). The gray solid line indicates the measurable and is no longer the diffuse sound field. On the other hand, the minimum reverberation time due to the limit of the measure- absorption characteristics is one of the most important ment system, e.g., the duration of the band pass filters et al. subjects for the acoustic design of a mixing room, and the Reverberation times were averaged by the values at five 234 A. IKEDA et al.: EFFECT OF FURNITURE IN A MIXING ROOM receiver1 h=1.2m empty all equipment in the room receiver 3 receiver2 h=1.8m console in the room ceiling and walls (mixer’s position) h=1.2m 0.8 0.7 0.6 Source (C speaker) 0.5 0.4 absorption coeffiecient 0.3 250 500 1k 2k 4k 8k 1/1 octave band center frequency[Hz] receiver 4 receiver 5 Fig. 8 Variation of the average sound absorption co- h=1.2m h=1.2m efficients under three room conditions; ‘empty’ (solid line), ‘console in the room’ (dashed line), ‘all equip- Fig. 6 The source (C loudspeaker) position and the five ment in the room’ (dash-dotted line). The gray solid receiver positions for the measurement of the rever- line indicates the average sound absorption coefficients beration time. of walls and the ceiling of the ‘empty’ condition. empty all equipment in the room Table 2 The average absorption coefficients of the measurable minimum RT console in the room mixing room under three room conditions. 0.3 mean free path 2.73m 1/1 octave band fc [Hz] 2505001k2k4k8k 0.2 empty 0.48 0.46 0.49 0.50 0.48 0.48 α empty + console 0.48 0.48 0.50 0.50 0.49 0.51 empty + all equipment 0.59 0.59 0.59 0.56 0.56 0.57 0.1 0.0 63 125 250 500 1k 2k 4k 8k Reverberation Time [sec] 1/1 octave band center frequency [Hz] Table 1). This suggests that the equipment and furniture have a certain sound absorption power which cannot be omitted for Fig. 7 Variation of the reverberation times due to three the acoustic properties of a mixing room. room conditions; ‘empty’ (solid line), ‘console in the Because of the high sound absorption and the small room’ (dashed line), ‘all equipment in the room’ (dash- volume of the room, the acoustical properties of a mixing dotted line). The gray solid line indicates the meas- room cannot be expressed by the statistical theories based on urable minimum reverberation time due to the limit of the diffuse sound field. However, in reality, these theories the measurement system. such as a reverberation formula are often used for the acoustic design and the representative values of the measurement data of a mixing room.
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