Proceedings of Meetings on Acoustics

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1 Proceedings of Meetings on Acoustics Volume 19, ICA 2013 Montreal Montreal, Canada 2-7 June 2013 Architectural Acoustics Session 1aAAb: Cultivating the Sustainable in Architectural Acoustics 1aAAb8. Audio and acoustic design of the University of Sydney s Indoor Environmental Quality Laboratory Densil Cabrera, Luis Miranda*, Robert Crow and Richard De Dear *Corresponding author's address: lmir9852@uni.sydney.edu.au The quality of indoor environments such as commercial offices is affected by many factors, including temperature, humidity, air movement, illumination, ambient sound and room acoustics. In 2012, a new laboratory was established at the University of Sydney to examine how such factors affect human occupants. In terms of sound, the design of the laboratory has three components: the acoustic design of the testing rooms; the audio system design (for introducing artificial soundscapes); and the design of generic soundscapes to support experimental work in the laboratory. Acoustic design considerations of the laboratory allow for the testing rooms to be configured as high grade office environments. The laboratory has a 24-channel audio system for introducing realistic and potentially complex sound fields into the testing rooms, both from within and outside the rooms. Parametrically controlled soundscapes are being developed for interior sources (such as building services noise) and exterior sources (such as transport noise). This paper describes the laboratory's acoustic conditions, audio system and soundscapes. Published by the Acoustical Society of America through the American Institute of Physics 2013 Acoustical Society of America [DOI: / ] Received 22 Jan 2013; published 2 Jun 2013 Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 1

2 INTRODUCTION The quality of indoor environments as experienced by their occupants can have significant effects on comfort, productivity and health. The overall quality of indoor environments comes from a combination of factors including air quality, temperature, illumination and acoustics. In 2012, The University of Sydney opened a new Indoor Environmental Quality Laboratory (IEQ Lab) that is designed for scientific research on such factors and their interaction, and this paper describes the acoustic and audio aspects of the laboratory. Such laboratory-based research complements field-based studies of indoor environmental quality of spaces such as commercial offices. Together, research using laboratory and field methods can develop improved approaches to the design and evaluation of buildings in the context of increased environmental rating demands, so that reducing the environmental footprint does not result in reduced quality in the internal conditions for occupants. GENERAL DESCRIPTION OF THE IEQ LAB The IEQ Lab is built within a pre-existing building, and it has two rooms in which the indoor environment is controlled (Chambers 1 and 2 see Figure 1). Chamber 1 is the larger one, designed to accommodate 8-12 workstations and their occupants in an open-plan office configuration. It has a floor-plan of approximately 60 m 2 (8.85 m x 6.85 m x 2.60 m high), and the ceiling is suspended (using plasterboard tiles), and the floor raised 0.3 m above the concrete slab for under-floor air distribution. The shorter two walls have windows, including two operable windows on each. On one of these walls, the windows interface directly with the building s outdoor environment, while the other wall s windows interface with a laboratory corridor that can be used to simulate external environments (the other side of the corridor has windows that interface directly with the outdoor environment). Heavy panels can be installed on the inside of the exterior windows to block visual access to the outside, eliminate access to daylight and increase sound insulation from external noise sources. Chamber 1 can be cross-ventilated naturally using the windows, or using mixed mode, or full-time mechanical ventilation. It includes options for a variable air volume (VAV) ceiling-based air-conditioning, or a floor-mounted displacement ventilation option based on an underfloor-plennum, divided into two zones (perimeter and interior). Details of the air-conditioning and control systems of the IEQ laboratory are given by Nathwani et al. (in press, 2013). FIGURE 1. Plan of the IEQ Lab, indicating the approximate positions of the loudspeakers. Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 2

3 Chamber 2 is designed to accommodate 4-6 people seated at individual workstations, and has a floor area of approximately 25 m (4.20 m x 5.63 m x 3.38 m high). It has options of displacement ventilation from an underfloor air distribution system, but instead of a suspended ceiling it has structural concrete coffers painted black, but visible above building services (luminaires and chilled beams hung at 2.5 m above the floor). Active and passive chilled beams offer alternative air conditioning options to the under-floor air distribution system. One of the most important design criteria guiding the IEQ lab s development was the experiential realism of the facility, to maximize external validity of the research conducted in them. For example, if a particular research project was focused on temperature effects on office productivity, the lab must look and feel like a real office so that research findings from samples of human subjects in the facility can be generalized to actual office conditions real office workers in real office buildings. This focus on experiential realism is the most distinctive unique feature of the facility, and it demanded that special attention was given to the acoustic performance of the chambers, plus the installation of a dedicated audio system. The audio and acoustics aspects of the IEQ Lab are the focus of this paper. ACOUSTIC CHARACTERISTICS OF THE ENVIRONMENTAL CHAMBERS The background noise in the IEQ lab is not as low as would be required for a more conventional acoustical laboratory, but this is not a significant limitation for the envisaged studies because the lab is intended to simulate realistic office, residential and transportation vehicular environments. With the external windows open, road traffic noise from a relatively busy inner city road is clearly audible. Closing the windows and adding the heavy panels reduces this to barely audible noise in the low frequency range. Chamber 2, which has no exterior walls, is quieter than Chamber 1, and Chamber 2 s passive chilled beams contribute very little noise to the room. Active airconditioning in either room introduces steady aerodynamic noise, and examples of background noise levels are given in Table 1. TABLE 1. Examples of background noise levels measured in the IEQ Laboratory mid-morning on a weekday, using a Brüel & Kjær 2250 sound level meter, with and without air-conditioning operating. Values are derived from five spatially separated measurement positions using a 60 s integration time at each position. In the examples, the variable air volume (VAV) system (Chamber 1) and active chilled beams system (Chamber 2) were run at their maximum intended operating level. Room and Condition A-weighted Leq (dba) Extended Noise Criterion Chamber 1, no air-conditioning Chamber 1, VAV system Chamber 2, no air-conditioning Chamber 2, act. chilled beams The reverberation time of Chamber 1 in the mid-frequency range is 0.7 s (measured when unoccupied and sparsely furnished). Due to the lack of a suspended ceiling, that of Chamber 2 is longer (0.9 s) despite that room s smaller volume. However, there is space to insert sound absorbing material within the exposed coffers of Chamber 2, which should significantly reduce its reverberation time if required. In 2013 we are developing a regenerative artificial reverberation system for Chamber 1, so that its reverberation time can be increased if required. A door allows access directly between Chambers 1 and 2 (which is an important feature in experiments focusing on the effect of transitions between environmental conditions). The door is solid, with seals around its edges (including a drop seal) to aid in acoustic separation between the chambers when it is closed. The weighted level difference, D w, from Chamber 1 to Chamber 2 has been measured as 31 db (D ntw is 33 db). The chambers are not large (compared to some real-world open plan offices), and so the ISO (2012) parameters tend to indicate a potentially high degree of speech distraction between occupants (in Chamber 1; Chamber 2 is too small to assess using ISO ). Measured without office partitions or the introduction of electroacoustic masking noise, the distraction distance (r D ) in Chamber 1 is greater than the room dimensions (r D = 18 m when the VAV air-conditioning is running). AUDIO SYSTEM A 24-channel sound reproduction system is installed to introduce sound into the two chambers and the corridor (with two of the channels used for monitoring in the control room). Chamber 1 has twelve flush-mounted ceiling Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 3

4 loudspeakers: model Quest QTC-2080BC, which is a two-way coaxial loudspeaker (with a back can and ports). These have a manufacturer s specified frequency range from 80 Hz 18 khz. The twelve loudspeakers are individually controlled. Their spatial distribution is necessarily somewhat irregular due to the high density of building services above the suspended ceiling. Also hidden above the suspended ceiling, within the coffers of the structural ceiling, are four custom-built subwoofers (installed close to each other, and used together via a single audio channel). The cross-over frequency between the subwoofers and ceiling loudspeakers is 100 Hz. Chamber 2 has a much simpler audio system, consisting of four individually controlled loudspeakers, each mounted near the corner of the room within the ceiling coffers. These loudspeakers are Quest MS801 two-way monitor style loudspeakers, with a rated frequency range from 55 Hz 20 khz (±4 db). There is no subwoofer in Chamber 2. The audio system for the corridor is designed to simulate outdoor soundscapes, which sometimes can be characterized by high sound pressure levels. Four independently controlled public address loudspeakers are used along the corridor: model Quest QA3004, each rated at 400 W rms. Two subwoofers are used in parallel at the end of the corridor. Equipment for control and amplification of the audio system is housed in the control room. The computer program Max is the primary platform used to generate, play, process and distribute signals to the amplifiers (and hence the loudspeakers). DEVELOPMENT OF SOUNDSCAPES A collection of parametrically controlled soundscapes is being developed for the laboratory. At the time of writing, the soundscapes that have been implemented include parametrically controlled HVAC-like noise for Chambers 1 & 2, and outdoor noise scenes (road traffic, rail traffic and aircraft) which principally use the corridor loudspeakers. The soundscapes are hosted in the computer program Max, which provides a simple graphical user interface to control the soundscape parameters. The HVAC-like noise is synthesized from filtered pink noise, and has four preset spectra: neutral, hiss, roar and rumble, based on the Room Criterion mark II rating system (Blazier 1997). Nevertheless, the spectrum can easily be further modified if the user wishes. Apart from the noise spectrum, the adjustable parameters are gain and amplitude modulation. The outdoor soundscapes are based on four-channel recordings of real outdoor environments in Sydney. In many of these recordings, microphones (cardioid or omnidirectional) were positioned in a line to match the line of four loudspeakers in the IEQ Lab s corridor in an effort to maintain some spatial realism in the reproduction. Calibration tones were recorded to facilitate reproduction at a realistic sound pressure level. For the aircraft and rail traffic soundscapes, discrete recordings of passing aircraft or trains were extracted, allowing these to be reproduced with arbitrarily generated periods of silence between them. In the graphical user interface, a slider determines the maximum period between sound events (the actual period of each silence is determined by a pseudo-random number generator). The road traffic recordings are continuous (and are simply looped), and the density of the traffic can be increased by playing more than one recording at a time. It is possible, though not necessarily desirable, to play all of the soundscapes simultaneously. The operable windows between the chambers and the corridor allow the outdoor soundscapes to enter the chambers either directly via the open windows, or as sound transmitted through closed windows and other building elements. Optionally, subtle reinforcement of an outdoor soundscape using the loudspeakers within each of the chambers can be used if required (for example, the subwoofers in Chamber 1 can help increase the low frequency sound and vibration in the room). More soundscapes are being developed for the IEQ Lab in 2013, including multichannel speech babble. CONCLUSION The University of Sydney s IEQ Lab is capable of a wide range of experimental studies into the quality of indoor environments, especially offices. The air-conditioning system is highly versatile, and can create a very wide range of environmental conditions. Lighting levels (including daylight and artificial light) can also be adjusted over a wide range. This paper has described the acoustic and audio aspects of the IEQ Lab, which allow the effects of background noise or soundscape on comfort or productivity to be studied, as they interact with other aspects of indoor environmental quality. Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 4

5 ACKNOWLEDGMENTS The authors thank Group Technologies Australia Pty. Ltd. for the donation of audio equipment for the IEQ Lab. Some acoustic measurements reported in this paper were made by students in the Master of Design Science (Audio and Acoustics) degree: Daniel Clinch, Grant Cuthbert, Justin Leong, Jason Obadiah, Todd Power, Jeremy Skellern, Martin Thorpe, and Nicholas Vandenburg. REFERENCES Blazier, W.E. (1997). RC Mark II: a refined procedure for rating the noise of heating, ventilating air-conditioning (HVAC) systems in buildings, Noise Control Engineering Journal, 45: International Organization for Standardization (2012). ISO : Acoustics Measurement of room acoustic parameters Part 3: Open plan offices, Geneva, Switzerland. Nathwani, A., de Dear, R., Candido, C. and Cabrera, D. (in press, 2013). The next generation of experientially realistic labbased research: The University of Sydney's Indoor Environmental Quality Laboratory, Architectural Science Review. Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 5