
Densil CabreraThe University of Sydney · Sydney School of Architecture, Design and Planning
Densil Cabrera
BMus, Grad Dip Com, MA, PhD
About
208
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Introduction
My research interests are in architectural acoustics, psychoacoustics, audio, signal processing, and related areas. Projects in recent years have been in areas such as auditorium stage acoustics, open-plan office acoustics and acoustic retroreflection.
Additional affiliations
February 1996 - present
Publications
Publications (208)
Open-plan offices are well-known to be adversely affected by acoustic issues. This study aims to model acoustic dissatisfaction using measurements of room acoustics, sound environment during occupancy, and occupant surveys (n = 349) in 28 offices representing a diverse range of workplace parameters. As latent factors, the contribution of $\textit{l...
The adaptive capacities of building occupants have so far been primarily investigated in relation to the thermal climate through the adaptive thermal comfort model. However, the concept of adaptation extends beyond thermal conditions and is relevant to other sensory modalities, such as acoustics. This is significant for both human health and well-b...
A room was treated to be predominantly retroreflective in the high frequency range by introducing arrays of cube corner retroreflectors (CCRs) over most surfaces (excluding the floor). In a small room (volume 55 m3), 156 CCRs in the form of square trihedra with 350 mm edge lengths were used as wall and ceiling treatment. The horizontal plane distri...
Time reversal acoustics (TRA) has tremendous potential for focusing, or sound concentration, in reverberant architectural environments. While TRA provides an inherently simple means of achieving a high degree of spatiotemporal focusing, its appropriateness for listening applications in the built environment is challenged by the need to accommodate...
Retroreflective acoustic treatment of architectural spaces can concentrate early-reflected sound onto the respective arbitrarily located sources. Typically, this is achieved by arrays of corner reflectors (CRs) or cube corner retroreflectors (CCRs). Still greater sound concentration can be achieved by focusing retroreflectors—achieved by curving th...
Introducing retroreflection into rooms can change the distribution of reflected energy, concentrating early reflections on the source. But what is a retroreflective room, and how could it be implemented? This paper introduces concepts including retroreflective arrays andretroreflective focusing, which achieve much more than the trivial case of a re...
Although focusing might normally be an architectural acoustician’s nightmare, combining it with retroreflection is potentially beneficial. Focusing acoustic retroreflectors concentrate early reflected sound onto arbitrarily located sources. Dihedral and trihedral retroreflectors can be made to focus by curving one or more of their faces in either o...
Human echolocation, in the form of flash sonar, can support spatial awareness and navigation for vision-impaired people. This paper examines the potential of acoustic focusing retroreflectors to support echolocation within an area. Parabolic dihedra and trihedra, along with other variants of focusing retroreflectors, return much stronger reflection...
The stage view qualities in 56 acoustically categorized music auditoria from around the world were analysed using a stage-view quality prediction method derived from laboratory subjective experiments. The prediction results were examined in relation to the acoustic quality, size, and architectural form of the auditoria, comprising rectangular, hors...
Enjoying a music concert is a multisensory experience, which mostly involves auditory and visual perception. However, the quality of acoustics and view may vary greatly within an auditorium. This study investigates preference at various seats within two size variations of an auditorium, through a virtual-reality subjective experiment with realistic...
In a concert auditorium, conditions at different seats vary greatly, and are mostly affected by the view of the stage and the received sound of the performance, the former of which has been much less studied. With a focus on visual seat location, this study systematically investigates the effects of three visual factors: distance, lateral angle, an...
This paper aims to study the effect of room acoustics and phonemes on the perception of loudness of one's own voice (autophonic loudness) for a group of trained singers. For a set of five phonemes, 20 singers vocalized over several autophonic loudness ratios, while maintaining pitch constancy over extreme voice levels, within five simulated rooms....
The irrelevant speech effect (ISE) characterizes detriment to cognitive task performance in the presence of irrelevant speech. This paper examines whether the ISE varies due to the number of simultaneously active nearby talkers (for up to two talkers), or the overall sound level, within the context of a simulated open-plan office. Two experiments w...
This paper investigates variability in the key ISO 3382-3:2012 metrics, based primarily on the repeatability and reliability of these metrics, using repeated measurements in open-plan offices. Two types of repeated measurements were performed in offices, Type1 (n=36), where the same path over workstations was measured from opposite ends, and Type2...
Within the soundscapes of open-plan offices, irrelevant speech has consistently been reported as the most distracting, and causing performance decrements for workers. Notwithstanding this generalization, the 'babble' created by multiple simultaneously active talkers can sometimes provide beneficial sound masking, but due to spatial release from mas...
Open-plan offices (OPOs) have been around for more than half a century now, chronicling the vicissitudes of workplace topography amongst other factors. This paper addresses one such factor - the sound environment in occupied OPOs in relation to several objective workplace parameters, using measurements in contemporary OPOs and comparisons with stud...
Activities conducted outdoors have reduced risk of disease transmission and yield positive mental and physical effects, but outdoor environments commonly suffer from acoustic problems such as urban noise, rapid spatial sound decay and insufficient acoustic support. This paper addresses the last problem, i.e., people's poor self-hearing due to lack...
How much sound can a building surface reflect to a source, the location of which is not exactly known? This paper considers this question particularly for a planar surface acting as an array of retroreflectors, or of focusing retroreflectors. The question is investigated using finite-difference time-domain acoustic simulation, using ideal retrorefl...
Audiovisual integrations and interactions happen everywhere, including in music concerts, where combined visual and auditory perception contributes to overall enjoyment. Thirty-three participants evaluated their overall subjective preference at various seats in four virtual auditoria, which comprised congruent and incongruent auditory and visual re...
Based on an online survey, this study investigated the effect of various factors, including those related to performance, acoustic condition, visual condition, price, comfort, architectural design, and social aspects, on participants’ selection of concert, seat, and their experience of attending classical concerts. From 153 valid responses, it was...
Construction noise is one of the most important and prevalent occupational hazards in the construction industry. The negative effects of construction noise can be mitigated by implementing an efficient noise management process during pre-construction and construction stages. Current research themes in the area of construction noise management are f...
This paper examines acoustic retroreflection from a polytrihedral dome that was used in creative-arts practice-led research as a unique, high voice support singing practice space. The polytrihedral dome is investigated with laboratory measurements, field recordings of singing practice, and by finite-difference time-domain (FDTD) simulation of sound...
Retroreflection is rarely used as a surface treatment in architectural acoustics but is found incidentally with building surfaces that have many simultaneously visible concave right-angle trihedral corners. Such surfaces concentrate reflected sound onto the sound source, mostly at high frequencies. This study investigated the potential for some Ind...
Noise disturbance in open-plan offices (OPOs) has been a systemic issue throughout their history. This paper presents preliminary results from a study where an occupant survey (N = 366) was conducted in 30 office spaces within 9 buildings, along with measurements using the ISO 3382-3 method, and measurements of the sound environment during occupanc...
Acoustically retroreflective surfaces can reflect the sound of a person's voice back to them, thereby increasing voice support and potentially influencing the talker to reduce their speaking level (the 'room effect'). This paper gives an overview of experiments with acoustically retroreflective surfaces: existing building façades, fabricated arrays...
One's own voice (autophony) is transmitted to the ears as direct airborne sound, bone conduction, and indirect airborne sound from reflections characterized by overall gain and spectro-temporal features. This study investigates how the spectral profile and gain of simulated indirect airborne sound, quantified as voice support (ST V), affect the spe...
A broadband point source loudspeaker, referred to as a 'gap source', is described. The source is driven by four compression drivers configured as two identical two-way sources connected to two symmetric pipe structures. The sound source radiates from a small gap between the pipe openings, yielding sufficiently powerful omnidirectional radiation in...
Seat preference in a concert hall is affected by both auditory and visual conditions. While traditional concert hall preference studies have mainly focused on auditory preference, visual preference has drawn more recent attention , as the importance of audiovisual interaction has been emphasized. For combined audiovisual studies, using virtual real...
Open-plan offices (OPOs) have been around for more than half a century now, chronicling the vicissitudes of workplace topography amongst other factors. This paper addresses one such factor – the sound environment in occupied OPOs in relation to several objective workplace parameters, using measurements in contemporary OPOs and comparisons with stud...
Going to a concert involves both visual and auditory senses, which have been found to influence each other in many ways. The visual design of a concert hall contributes to the visual experience of seeing a concert, and color is one of the most obvious elements of the visual design. While some studies have reported that color affects vehicle loudnes...
This study investigates acoustic reflection from three building façades, each of which forms an array of corner cube retroreflectors. The façade of Latimer Hall (Berkeley, USA) has deep rectangular balconies that typically provide 56 simultaneously visible retroreflective elements; the Ainsworth Building (Sydney, Australia) has a sawtooth façade wi...
Among current adoptions of standard industrial robotic arms for automation and mass customisation in the building industry, robotic fabrication is of interest for bespoke manufacturing and advancing mobile and onsite construction processes. The use of robotic arms can be of significance particularly where access and site conditions limit further co...
This paper investigates variability in the key ISO 3382-3:2012 metrics, based primarily on the repeatability and reliability of these metrics, using repeated measurements in open-plan offices. Two types of repeated measurements were performed in offices – Type1 (n = 36), where the same path over workstations was measured from opposite ends, and Typ...
Characterizing stage acoustics using objective parameters has seen some recent resurgence—several studies have noted the importance of the directionality of early stage reflections to musicians, which is not adequately represented using existing omnidirectional stage-support parameters. This study examines the subjective impressions of 19 chamber m...
The irrelevant speech effect (ISE) characterizes detriment to cognitive task performance in the presence of irrelevant speech. This paper examines whether the ISE varies due to the number of simultaneously active nearby talkers (for up to two talkers), or the overall sound level, within the context of a simulated open-plan office. Two experiments w...
Acoustically retroreflective surfaces reflect sound back to the source, over a wide range of possible source positions. This paper explores their potential use in architecture, in the form of an extensive array of square trihedral corner cubes which could be used for reducing speech distraction in multi-talker environments. The retroreflective effe...
This paper examines acoustic retroreflection from a building façade that includes an array of 255 square trihedral corner cube reflectors with edge lengths of 300 mm. The façade is investigated by field impulse response measurements in its vicinity, laboratory measurements of reflected energy distribution from a single 300 mm corner cube and an arr...
ISO 3382-3:2012 is the international standard for measuring the acoustics of open-plan offices. These measurements are performed in unoccupied offices, and it has recently been shown that some of the ISO 3382-3 metrics, especially distraction distance, are useful in predicting the occupants’ perceived disturbance due to noise. The current research...
Vacuum insulating glazing (VIG) is a relatively new glazing technology that was first developed primarily for its thermal insulation properties. This research aims to continue a preceding study about the acoustic performance of VIG and to analyse the effects of dissimilar thickness and additional damping to the sound insulation performance of VIG....
This paper presents a case study for the production of retroreflective ceiling treatment in an open work environment. In this setting with multiple talkers, speech distraction can be a significant cause of dissatisfaction and loss of productivity. Ceiling treatment in open plan work environments can provide an important way of ameliorating distract...
ISO 3382-3, the international standard for evaluating the acoustics of open-plan offices, includes metrics based on measuring spatial decay, over workstations, of speech sound pressure level, and speech intelligibility. The speech intelligibility metrics, out of which distraction distance (rD) has recently been shown to be most useful, are derived...
Open, flexible workspaces were introduced decades ago, but architectural design approaches to ceiling systems have not changed substantially. This paper discusses the development of strategies and prototypes for a lightweight, integrated ceiling structure that is robotically woven. Through geometrically complex, fibre-reinforced building elements t...
Acoustic support of one’s own voice affects speech, and increased support can foster more relaxed voice projection, which reverses the Lombard effect. While hearing one’s own voice in typical rooms shows subtle influences of “global” room acoustics, local treatment can yield stronger effects for talking-listeners. This paper considers two types of...
Irrelevant speech from co-workers has consistently been listed as one of the major nuisances within open-plan work environments. To explore the psychoacoustic basis of the so-called irrelevant speech effect (ISE; which causes cognitive decline and increases acoustic distraction) within a multi-talker context, a series of laboratory-based experiment...
It is generally acknowledged that speech related noise is a common distractor in many work environments, e.g., open-plan offices. There are many studies and some standards that address these noise related issues, but they generally do not consider sound propagation through corridors. This study investigates how certain spatial arrangements of ceili...
Within the soundscapes of open-plan offices, irrelevant speech has consistently been reported as the most distracting, and causing performance decrements for workers. Notwithstanding this generalization, the 'babble' created by multiple simultaneously active talkers can sometimes provide beneficial sound masking, but due to spatial release from mas...
This study compared psychoacoustic reverberance parameters to each other, as well as to reverberation time (RT) and early decay time (EDT) under various acoustic conditions. The psychoacoustic parameters were loudness-based RT (TN), loudness-based EDT [EDTN; Lee, Cabrera, and Martens, J. Acoust. Soc. Am. 131, 1194–1205 (2012a)], and parameter for r...
This paper presents empirical research into the acoustic performance of randomized robotically fabricated patterns. Randomness is introduced as degrees of variations in code, both supported by quasi-predictable variations in a computational process, and the select changes through multiple variables in precise robotic fabrication that extend the spe...
Objectives: This paper aims to the study the effect of room acoustics and phonemes on the perception of loudness from one’s own voice (autophonic loudness), for a group of trained singers.
Methods: For a set of 5 phonemes, 20 singers vocalised over several autophonic loudness ratios, while maintaining pitch constancy over extreme voice levels, wi...
Local acoustic treatment around a person’s head and body can influence the transmission of speech to and from the person, the perception of background noise, and the sound they hear of their own voice (autophony). This paper demonstrates ways to systematically quantify these acoustic effects in terms of oral, binaural and oral-binaural gains. Two p...
Early reflections are known to be important to musicians performing on stage, but acoustic measurements are usually made on empty stages. This work investigates how a chamber orchestra setup on stage affects early reflections from the stage enclosure. A boundary element method (BEM) model of a chamber orchestra is validated against full scale measu...
Although auditorium acoustics has been extensively studied from an audience perspective, studies of musicians’preferences on stage are far more limited. The present work tests and extends the hypothesis, suggested in recent studiesby others, that the directional distribution of early reflected energy on stage is subjectively important to musicians....
Randomness can introduce degrees of variation as part of a highly controlled design process, which can be of particular significance in the context of acoustic performance in architecture. This paper presents research into robotic fabrication of surfaces with acoustic micro-patterns that can change the acoustic response of space. It explores the de...
Objectives:
This paper aims to study the effect of room acoustics and phonemes on the perception of loudness of one's own voice (autophonic loudness) for a group of trained singers.
Methods:
For a set of five phonemes, 20 singers vocalized over several autophonic loudness ratios, while maintaining pitch constancy over extreme voice levels, withi...
The acoustic conditions on stage for musicians are traditionally assessed with an omnidirectional receiver; however, with the use of a spherical microphone array the directionality of on-stage sound fields can be examined. This paper explores the issues around using such a microphone for stage acoustic measurements. As part of this study the 32-cha...
Vacuum insulating glazing can be very effective as a thermal insulator, which makes it potentially useful in reducing energy loss through building facades. This article examines its effectiveness for airborne sound insulation. Measurements of intensity sound reduction index were made of samples of single glazing and commercially manufactured vacuum...
In room acoustics measurement, calculating reverberation time from room impulse responses is often done, aided by software. This paper compares the performance of nine software implementations for calculating octave band reverberation time, including two written by the authors. Synthetic impulse responses are used to test decays without and with a...
In the context of acoustic performance in architecture, this paper presents research into the computational design and robotic fabrication of surfaces with micro-geometries that can change the acoustic response of space. It explores the design affordances for acoustically efficient patterns for sound scattering - between complex geometries, acousti...
Through a collaboration with the Australian Chamber Orchestra (ACO) and their sister group ACO2, subjective musician assessments of the acoustics in sixteen Australian concert venues have been obtained. The musicians were asked to rate venues on key acoustical aspects, including on Reverberance, Hearing Self, Support, Ensemble, Clarity, Warmth, Tim...
Although final mixing and mastering is monitored over loudspeakers, the majority of music listeners use headphones on mobile devices. Preferences for spatial process depend on the method of reproduction. For a variety of program material using headphones, listeners often prefer a stereophonic image that is created by simulating nearfield crosstalk...
Messa di voce (MDV) is a singing exercise that involves sustaining a single pitch with a linear change in loudness from silence to maximum intensity (the crescendo part) and back to silence again (the decrescendo part), with time symmetry between the two parts. Previous studies have used the sound pressure level (SPL, in decibels) of a singer's voi...
Over the past 50 years, upper hemisphere immersive loudspeaker systems in anechoic environments have supported research into the perception of room acoustics. A newly completed laboratory facility consisting of an upper hemisphere 196-loudspeaker array is described, along with available methods to deploy room acoustics auralization within the facil...
This study examines the effect of speech level on intelligibility in different reverberation condi-tions, and explores the potential of loudness-based reverberation parameters proposed by Lee et al. [J. Acoust. Soc. Am., 131(2), 1194-1205 (2012)] to explain the effect of speech level on intelligi-bility in various reverberation conditions. Listenin...
A hemispherical array of 196 independent loudspeakers has been constructed for laboratory re- search on spatial hearing, auralization, sound-field quality and spatial audio signal processing. The array of small loudspeakers is supported by a geodesic frame with a radius is 2.4 m. With this relatively high spatial density of sound sources, spatially...
Standard calculations of the Speech Transmission Index (STI) are most frequently determined using specialised test signals, but methods have also been developed that estimate an STI value by using real speech as the stimulus signal. However, these methods have previously been studied in highly controlled scenarios, and have rarely been tested using...
This paper outlines the steps in objectively estimating the time-varying loudness of one's own voice in a room (i.e. auto-phonic loudness). voice recordings, made with a near-mouth microphone, are converted to the sound that reaches the two eardrums of the talking (or singing)-listener by convolving them with the impulse responses from the mouth to...
There are many factors that can affect the measured values of the speech transmission index (STI), and this paper examines how and why identical inputs into STI calculation software are yielding varying results. The study involved a survey of a number of software implementations of the Indirect Method for computing the STI from an impulse response,...
Complex curved surfaces posit challenges for manufacturing, but become more available through the range of toolpaths that come with 6-axis robotic fabrication. In this chapter, we present an in-progress report that explores the way in which an industrial 6-axis robot can become an interdisciplinary research tool that produces space that is both imm...
AARAE is a MATLAB-hosted environment for measurement and analysis of room acoustics and audio systems, designed to support education and research in audio and acoustics. While it already provides a wide range of test signals, and measurement, processing, and analysis methods, one of its main features is easy extensibility. Students new to signal pr...
Although looking at a room gives a visual indicator of its ‘size’, auditory stimuli alone can also provide an
appreciation of room size. This paper investigates such aurally perceived room size by allowing listeners to hear the sound of their own voice in real-time through two modes: natural conduction and auralization. The auralization
process inv...
This paper investigates the use of psychoacoustic loudness analysis as a method for determining the likely emotional responses of listeners to musical excerpts. 19 excerpts of music were presented to 86 participants (7 randomly chosen excerpts per participant) who were asked to rate the emotion category using the emotion-clock-face continuous respo...
A 3-year longitudinal study was conducted to investigate changes in vocal quality as a result of singing training at a tertiary level conservatorium in Australia. Singers performed a messa di voce (MDV) at intervals of 6 months over the 3-year period of training. The study investigated the evolving acoustic features of the singers' voices exhibited...