SPEECH PRIVACY DISTANCE IN 3 OPEN-PLAN OFFICE LAYOUTS: COMPUTER MODELLING AND SIMULATION APPROACH Joko Sarwono, Annisa E. Larasati, F.X. Nugroho Soelami, and Indra Sihar Department of Engineering Physics, Institut Teknologi Bandung, West Java, Indonesia. e-mail: jsarwono@tf.itb.ac.id Sentagi S. Utami Department of Engineering Physics, Universitas Gadjah Mada, Yogyakarta, Indonesia. Acoustical problems that occur within open-plan offices are related to communication comfort between co-workers. Problems include distortion of speech intelligibility due to interference by unwanted sound, lack of speech privacy and interruption during the communication by other co-workers. Studies of comparison between open and closed-plan offices have shown the psychological effect on occupants due to these acoustical problems within the open-plan offices. This paper explores the characteristic of room acoustics in open-plan offices that enhance the ability for speech comfort, particularly to support speech privacy. Computer modeling and simulation approach were used to determine in particular the speech privacy distance on 3 types of open-plan office layout. It was found that there is a unique difference of speech privacy distance among the 3 types of layout. This result would be useful for designing the working space layout in open-plan office with regards to speech privacy and intelligibility. 1. Introduction The issue related to energy efficiency has demanded improvement of many aspects in the human life; one of the improvements due to this issue is by the usage of open plan office. Open plan office is an office where the entire workstations are located in one room without wall partition as high as the ceiling; each workstation is separated only by screen partition. By the collective usage of energy such as lighting and air-conditioning for occupants in the office, the open plan office increases the energy efficiency and saves a lot of construction fee. Other advantages of open plan office are the communication improvement between workstations; easier idea exchange and more convenient conversation happens between occupants. These advantages create a better working environment in some way [1]. Despite of the improvements and advantages that open plan office has, it also has disadvantages regarding to acoustical problems. Noise such as speech and laughter, phone ringing tones, footsteps, ventilation noise, external noise, appliances noise, cleaning noise ICSV20, Bangkok, Thailand, 7-11 July 2013 1
and artificial masking sound are exist in the open plan office. Among of these noises, speech is the most annoying and the loudest sound source in the open plan office [2]. Common speech problem in open plan office is about the surrounding intelligible speech. Speech can make distraction to other workstation and leads to a lower individual working performance. Moreover, conversation confidentiality problem exists especially to the. To handle this problem, the characteristic of open-plan office room acoustic characteristics is studied in this paper; especially about how to enhance the ability for speech comfort, particularly to support speech privacy. To study this characteristics, computer modelling and simulation approach were used. The idea of using computer modelling and simulation for the open plan office has already conducted by Rindel [3]. Moreover in this paper, computer modelling and simulation is used to determine parameters of speech privacy on 3 types of open-plan office layout arrangement and variations on workstation screen partition. 2. Simulation and Related Standard The ISO 3328-3:2012 is a standard that specifies measurement method which results in several parameters that indicate the general acoustical performance of the open plan offices. In this paper, the parameters that become focus of attention are the Index (STI) based parameters which are STI in the, distance ( ), and the distance ( ). The details on the calculation method can be seen in related standard [2]. The parameters on distraction and privacy distance are derived from listener STI condition along the workstation on open plan office. distance is a distance when STI falls below 0.5 and privacy distance is a distance when STI falls below 0.2. The condition when STI < 0.2, it means the negative effects of speech transmission to the listener work performance is disappear, and when the STI is between 0.5 and 0.2 the negative effects on work performance is start to vanish, lastly when STI >0.5 the listener cannot concentrate on his work or simply open plan office has poor speech privacy [2]. The variation on the STI can be represented on distraction and privacy distance, which is preferably shorter than the distance between each workstation. In this paper, simulations of several open plan office layouts are conducted to get STI condition along the open plan offices. The simulations in each case are made to resemble measurement setup that stated in ISO 3328-3:2-2012. The object that used in this simulation is an open plan office plan that occupied by 36 employees. The basic scheme of the office can be seen in figure 2.1 (a), with height of the room is 2.75 m and flat ceiling condition. The workstation scheme can be seen in figure 2.1(b), where default height for the screen is 1.22 m, 1.4 m table length and 0.6 m in width. (a) (b) Figure 2.1 a. Open Office Plan Basic Scheme b. Table Sketch for Open Office ICSV20, Bangkok, Thailand, 7-11 July 2013 2
There are 12 simulation cases based on workstation layout arrangement, source-receiver position paths, and height of the workstation screen. There are 3 workstation layouts used in this simulation, Layout 1, 2, and 3. In each layout, there are two source-receiver position paths. First path is straight path that parallel to the length of the room, the term used in this paper is Length Path; and then the second path is the non-straight path parallel to the width of the room, and the term used in this paper is Width Path. For each path, 1 source and 4 receiver points are used; all source and receiver positions are located at 1.2 m height from the ground, 0.5 m from table border, and at least 2 m from the closest wall. The schemes on the 3 layout arrangements and source-receiver position paths are shown in figure 2.2 - figure 2.4. In the scheme, source is indicated by red dot and receiver points indicated by number (Length Path) / alphabet (Width Path). In case of screen height variations, simulation is conducted only for Layout 3 (Figure 2.4). Screen heights are 1.22 m, 1.3 m, 1.4 m, and 1.5 m. The tool that used to simulate the acoustic condition in paper is CATT-Acoustic. CATT- Acoustic is one of acoustic prediction software based on ray-tracing and image source method. The condition of absorption coefficients and background noise that used in these simulations are given as in table. 2.1 and Table 2.2. Figure 2.2 Layout 1; Length Path and Width Path. Figure 2.3 Layout 2; Length Path and Width Path. ICSV20, Bangkok, Thailand, 7-11 July 2013 3
Figure 2.4 Layout 3; Length Path and Width Path. Table 2.1 Absorption Coefficients for Open Plan Office Simulation Oject (Material) Absorption Coefficients in Each Octave (α) 125 Hz 250 Hz 500 Hz 1k Hz 2k Hz 4k Hz Window ( Thick Glass) 0.18 0.06 0.04 0.03 0.02 0.02 Wall (Brick and Plaster) 0.01 0.02 0.02 0.03 0.04 0.05 Ceiling ( Acoustic Panel) 0.7 0.66 0.72 0.92 0.88 0.75 Floor (Thick Carpet Cover) 0.02 0.05 0.14 0.37 0.5 0.65 Table (Wood) 0.28 0.22 0.17 0.09 0.1 0.11 Table 2.2 Background Noise for Open Plan Office Simulation Octave Band Frequency (Hz) Background Noise (db) 125 250 500 1K 2K 4K 8K 45 38 32 28 25 23 21 3. Simulation Results and Discussions From the simulation, the STI value for each position is obtained. From the obtained STI, relation between STI and the source-receiver distance can be interpolated by regression model. Finally by the regression model, distraction distance ( ) and privacy distance ( ) can be calculated. The calculation results of these parameters based on the layout arrangement can be seen in table 3.1 and table 3.2. Meanwhile, the results based on the variation for the height of screen in layout 3 can be seen in table 3.3 and table 3.4, among all tables r is the receiver distance from the source. ICSV20, Bangkok, Thailand, 7-11 July 2013 4
3.1 Variation on the open office plan layout arrangement Layout Table 3.1 Simulated Parameters for Length Path 1 STI = -0.02 r + 0.67 7.88 21.58 0.66 2 STI = -0.02 r + 0.63 6.99 22.7 0.61 3 STI = -0.06 r + 0.86 6.43 11.83 0.88 Layout Table 3.2 Simulated Parameters for Width Path 1 STI = -0.04 r + 0.86 8.7 15.88 0.76 2 STI = -0.05 r + 0.91 9.05 15.66 0.93 3 STI = -0.05 r + 0.85 7.08 13.23 0.91 3.2 Variation on the partition height on Layout 3 Height (m) Table 3.3 Simulated Parameters for Length Path 1.22 STI = -0.06 r + 0.86 6.43 11.83 0.88 1.3 STI = -0.05 r + 0.87 6.98 12.68 0.88 1.4 STI = -0.05 r + 0.89 6.69 12.05 0.88 1.5 STI = -0.06 r + 0.88 6.54 11.65 0.88 Height (m) Table 3.4 Simulated Parameters for Width Path 1.22 STI = -0.05 r + 0.85 7.08 13.23 0.91 1.3 STI = -0.05 r + 0.88 7.06 12.62 0.91 1.4 STI = -0.06 r + 0.90 6.89 12.26 0.91 1.5 STI = -0.06 r + 0.90 6.51 11.37 0.90 ICSV20, Bangkok, Thailand, 7-11 July 2013 5
By overall simulation results, it is concluded that from all layouts and screen heights good speech privacy doesn t achieved, but there is a unique difference of speech privacy conditions among 3 types of layout. For example, Layout 3 has STI values of the are 0.88 and 0.9 respectively in length and width path; this shows that receiver can notice clearly the speech from the source. But on the contrary, it has the shorter privacy and distraction distances compare to the other layouts. This condition happens because screen does not exist separating the nearest workstation, but this layout give more privacy between area of workstations group. Other example is layout 2 at Table.3.1, in this condition the STI value of the is 0.61, which is the lowest among other layout, but in the same time it also has the longest privacy distance. These contradictions between each parameter set up different interpretation of open plan offices. Based on distraction distance and privacy distance, the best layout for open plan office is layout 3, but it has high STI value of the. Due to this fact, layout 3 is suitable for an office where there are division of occupants based on job that they are doing. Each group can be located in adjacent workstation with no screen existed. In case of office type where occupants working individually and need high concentration to the work, the layout 1 is the most suitable for office, because it has the lowest average privacy condition compare to the layout 2. The simulation of layout 3 due to the variation of heights shows that the three speech privacy parameters are not varying significantly. Intention behind the height variation was to get significant improvement in speech privacy condition. From table 3.4, shorter distance of privacy distance and distraction distance exists but not significantly. One reason behind this condition is coming from the diffraction phenomenon on low frequency that cannot be simulated in ray-tracing method [4], this drawback leads to underestimation of the STI. Another reason that can cause this condition might come from the increment of both reflecting and absorption surface area on the partition which create almost constant STI distribution among each screen heights. 4. Conclusions The computer modeling and simulation on the open plan office to evaluate speech privacy parameters has been conducted in this paper. 3 types of open-plan office layout show different speech privacy characteristics, even though the amount of absorption area, screen height, and background noise are constrained to be the same. The variations of the privacy distance, distraction distance, and the STI value to the suggest one type of office layout is better for number of people that working together as a group and other type of layout is better for individual working type of office. Moreover, each speech privacy parameters should be carefully observed because the physical interpretation will give different conclusion of privacy. From this study is also concluded that screen height variation doesn t influence the speech privacy condition. The drawback on the ray tracing method might be the cause of this problem due the inability to model the sound wave diffraction phenomena. The further studies on this matter should be conducted. REFERENCES 1 2 3 4 Zahn, L. G., Face to Face Communication in an Office Setting: The Effects of Position, Proximity and Exposure, Communication Research, 18, 737-754, (1991). Standardization, I. O, ISO 3382-3 Acoustics - Measurement of room acoustic parameters Part 3: Open-plan offices, (2012). Rindel, J. H., Prediction of acoustical parameters for open plan offices according to ISO 3382-3, Proceedings The Acoustics 2012 Hong Kong Conference, Hongkong, 13-18 May (2012). Elorza, D.O., Room acoustics modeling using the raytracing method: implementation and evaluation, Licentiate Thesis, Department of Physics, University of Turku, (2005). ICSV20, Bangkok, Thailand, 7-11 July 2013 6