Room Acoustic Quality Research Articles

Real and Virtual Lecture Rooms: Validation of a Virtual Reality System for the Perceptual Assessment of Room Acoustical Quality

Enhancing the acoustical quality in learning environments is necessary, especially for hearing aid (HA) users. When in-field evaluations cannot be performed, virtual reality (VR) can be adopted for acoustical quality assessments of existing and new buildings, contributing to the acquisition of subjective impressions in lab settings. To ensure an accurate spatial reproduction of the sound field in VR for HA users, multi-speaker-based systems can be employed to auralize a given environment. However, most systems require a lot of effort due to cost, size, and construction. This work deals with the validation of a VR-system based on a 16-speaker-array synced with a VR headset, arranged to be easily replicated in small non-anechoic spaces and suitable for HA users. Both objective and subjective validations are performed against a real university lecture room of 800 m3 and with 2.3 s of reverberation time at mid-frequencies. Comparisons of binaural and monoaural room acoustic parameters are performed between measurements in the real lecture room and its lab reproduction. To validate the audiovisual experience, 32 normal-hearing subjects were administered the Igroup Presence Questionnaire (IPQ) on the overall sense of perceived presence. The outcomes confirm that the system is a promising and feasible tool to predict the perceived acoustical quality of a room.

Room acoustic survey of open and enclosed learning spaces in Finland

Use of open learning spaces for education has increased in schools while enclosed learning spaces are still used in most schools in overall. There is some debate that these two learning space types might differ in acoustic perceptions. If they do, room acoustic quality might be one explaining factor. Therefore, our purpose was to determine, whether these learning space types differ in room acoustic properties. We studied 10 schools with mostly enclosed and another 10 schools with open or flexible learning spaces in Finland. Altogether 73 learning spaces were investigated among the 20 schools. Measurements concerned reverberation time, Speech Transmission Index, and background noise level. Most of enclosed learning spaces (63%) met the new requirements of Finnish building regulations for enclosed learning spaces. Opposite to that, most of open learning spaces (91%) did not meet the regulations for open learning spaces. The results can be used in the root cause analysis of a teacher survey conducted in the same 20 schools. Teacher survey will be reported in another study. Parallel analysis of objective and subjective results is necessary to judge whether the current regulations are justified.

Measurement-based Auralisation to Predict Room Acoustics Quality of a Large Mosque with a Pyramid-Shaped Ceiling in Bandar Lampung

Acoustic standards in mosques are available, but most people have a lack of understanding of these measures. Auralisation is an audio technology that uses impulse responses, dry sounds and convolution software to create authentic auditory experiences. In Indonesia, objective room acoustic parameters are still unknown and the potential of auralisation is underexplored. The study aims to predict acoustic quality and people’s preference for auralisation in a pyramid-shaped ceiling using field measurements and subjective ratings. The methodology includes pre-survey, RIR measurement, dry sound recording, auralisation, and subjective surveys. Background noise, T30, D50, and C80 were measured, while auralised samples of lectures and Quran recitations were evaluated. Respondents’ preferences generally correlated with T30, especially D50 (47%) for lectures and C80 (44%) for Quran recitations. In conclusion, the study demonstrates the interplay between subjective preferences and objective measurements and suggests that these parameters can predict acoustic quality in pyramid-shaped dome mosques, paving the way for better design practices and improved listening experiences.

The effect of room acoustic quality levels on work performance and perceptions in open-plan offices: A laboratory study

A laboratory experiment was performed to explore the effects of acoustic quality levels on work performance and perceptions in open-plan offices. The accuracy rate of the serial recall task and the reported perceptions of the 41 participants were tested at two receiving positions in four office scenarios. According to the revised international standard for measuring room acoustic parameters in open-plan offices, ISO 3382–3:2022, the room acoustic qualities of the four office scenarios were classified into four levels (good, high-medium, low-medium, and poor). The results confirm the validity of the acoustic classification criteria in ISO 3382–3:2022 and highlight that people working in offices with good acoustic quality have significantly higher work performance and acoustic satisfaction than those working in offices with poor acoustic quality. Moreover, comparisons of objective and subjective results between the two receiving positions imply that maintaining a greater distance from people speaking improves work performance and acoustic satisfaction in offices with poor acoustic quality. However, this improvement is insignificant when working in offices with good acoustic quality.

Design of Simple Acoustic Materials for High School Hall Using Software CATT

Good acoustic quality is essential to consider in designing a multipurpose room. Unfortunately, school halls usually have poor room acoustics. Lack of funds and lack of knowledge about acoustics cause the acoustic quality of the room to be very poor. The purpose of this research is to design a simple acoustic material application concept for a high school hall based on the Ministry of Education and Culture manual to meet the requirements for speech, music, and sports functions. Simple acoustic materials exist in everyday life, such as corrugated cardboard, cork, multiplex boards, newspapers, egg racks, and cloth. The research applied a simulation method using CATT v8 software. The parameters used to measure room acoustic quality were RT60, C-80, D-50, STI, EDT, and LF The simulation compared the hall's acoustic performance without and with the simple sound absorbers. The absorbers were applied to 39% of the walls and 55% ceilings. The absorbers reduced T-30 (500Hz) from 3.8 seconds to 1.5 seconds with an omni sound source and 1.3 seconds with speakers. The averaged Speech Transmission Index (STI) was improved from 38% to 60% with the omni sound source and from 43% to 65% with speakers.

Sound Environments in Large Public Buildings for Crowd Transit: A Systematic Review

Sound environments in large public buildings are likely to be different from those of performance spaces, as well as those not specifically designed for acoustic “performance”, but where sounds still play an important role because of the function they can promote (or disrupt). The aim of this study was identifying common strategies and empirical approaches researchers have been implementing for these acoustically complex enclosures and to provide some methodological indications for future studies on the topic. Studies conducted in three building types for crowd transit, such as museums/exhibition spaces, shopping malls, and transportation hubs/stations, which were collecting data about either physical outcomes or individual responses for such sound environments, were selected. The Scopus databases were searched for peer-reviewed journal papers published in English without time limitations. An additional manual search was performed on the reference lists of the retrieved items. The general consideration on inclusion was to meet the requirement that the case belonged to the three building types, and then the specific inclusion criteria were: (1) including at least an objective acoustic measure of the space; or (2) including at least a subjective measure of the space. The search returned 1060 results; after removing duplicates, two authors screened titles and abstracts and selected 117 papers for further analysis. Twenty-six studies were eventually included. Due to the limited number of items and differences in measures across studies, a quantitative meta-analysis could not be performed, and a qualitative approach was adopted instead. The most commonly used objective measures were SPL, and more specifically often considered as LAeq, and T. The intervals across studies were currently of inconsistency, and the selection is recommended to take space scale factor into account. The used subjective measures can be classified into four categories as annoyance, affective quality, room-acoustic quality, and acoustic spatiality. Four basic perceptual assessments concerning dynamic contents are accordingly suggested as “annoying-not annoying”, “crowded-uncrowded”, “long-short (reverberation)”, and “far away-nearby”. The other descriptors can be project-specific. The methodologies involve measurement, questionnaire/interview, listening test, and software simulation. It is necessary for the former two to consider temporal and spatial features of such spaces, and the adoption of the latter two will lead to better understanding of users’ exposure in such spaces, e.g., acoustic sequences and user amount. The outputs of investigations inform that background noise level, e.g., 90 dB in museum/exhibition spaces, and sound reverberation, e.g., 4.0 to 5.0 s in shopping malls and transportation hubs/station, are of fundamental importance to the design of such spaces. Sufficient acoustic comfort can be achieved with integrated design of indoor soundscape.

Improved Room Acoustics Quality in Meeting Rooms: Investigation on the Optimal Configurations of Sound-Absorptive and Sound-Diffusive Panels

This work deals with the improvement of the room acoustic quality of two medium sized meeting rooms through the investigation of the optimal placement of absorption and diffusive panels on the walls and ceiling. Acoustic measurements have been carried out in the existing untreated rooms with ODEON 13 room acoustics measurement and prediction software, and the Adobe Audition plugins Aurora. Simulations of different combinations of sound absorption and diffusion treatments have been carried out with the updated version of the software, ODEON 15. The panels were positioned in the meeting rooms following the guidelines of the DIN 18041 standard and the scientific literature. The results advise the application of absorptive materials on the ceiling or around the borders, creating a reflective middle area, and on the upper part of one the lateral walls, including the rear wall. Configurations with diffusers do not generally bring significant improvements. The Speech Transmission Index (STI) is a less sensitive parameter for the different acoustic scenarios, compared to Reverberation Time (T) and Clarity (C50). The research also outlined a design workflow, useful to successfully design meeting rooms and rooms for speech in general, which allows to determine the optimal number and location of acoustic panels and to minimize the costs.

Reproducibility of Voice Parameters: The Effect of Room Acoustics and Microphones

Computer analysis of voice recordings is an integral part of the evaluation and management of voice disorders. In many practices, voice samples are taken in rooms that are not sound attenuated and/or sound-proofed; further, the technology used is rarely consistent. This will likely affect the recordings, and therefore, their analyses. The objective of this study is to compare various acoustic outcome measures taken from samples recorded in a sound-proofed booth to those recorded in more common clinic environments. Further, the effects from six different commonly used microphones will be compared. Thirty-six speakers were recorded while reading a text and producing sustained vowels in a controlled acoustic environment. The collected samples were reproduced by a Head and Torso Simulator and recorded in three clinical rooms and in a sound booth using six different microphones. Newer measures (eg, Pitch Strength, cepstral peak prominence, Acoustic Voice Quality Index), as well as more traditional measures (eg Jitter, Shimmer, harmonics-to-noise ratio and Spectrum Tilt), were calculated from the samples collected with each microphone and within each room. The measures which are more robust to room acoustic differences, background noise, and microphone quality include Jitter and smooth cepstral peak prominence, followed by Shimmer, Acoustic Voice Quality Index, harmonics-to-noise ratio, Pitch Strength, and Spectrum Tilt. The effect of room acoustics and background noise on voice parameters appears to be stronger than the type of microphone used for the recording. Consequently, an appropriate acoustical clinical space may be more important than the quality of the microphone.

A measuring instrument for the auditory perception of rooms: The Room Acoustical Quality Inventory (RAQI).

With the Room Acoustical Quality Inventory (RAQI), a measuring instrument for the perceptual space of performance venues for music and speech has been developed. First, a focus group with room acoustical experts determined relevant aspects of room acoustical impression in the form of a comprehensive list of 50 uni- and bipolar items in different categories. Then, n = 190 subjects rated their acoustical impression of 35 binaurally simulated rooms from 2 listening positions, with symphonic orchestra, solo trumpet, and dramatic speech as audio content. Subsequent explorative and confirmative factor analyses of the questionnaire data resulted in three possible solutions with four, six, and nine factors of room acoustical impression. The factor solutions, as well as the related RAQI items, were tested in terms of reliability, validity, and several types of measurement invariance, and were cross-validated by a follow-up experiment with a subsample of 46% of the original participants, which provided re-test reliabilities and stability coefficients for all RAQI constructs. The resulting psychometrically evaluated measurement instrument can be used for room quality assessment, acoustical planning, and the further development of room acoustical parameters in order to predict primary acoustical qualities of venues for music and speech.

언어명료도에 기반한 창문 개방 조건 교실의 배경소음 기준 고찰

Speech intelligibility in classrooms, determined by signal-to-noise ratio and room acoustics quality, is important for communication between teachers and students. This work reports on the current situation of speech intelligibility evaluated using useful-to-detrimental ratio (U50) in 12 unoccupied classrooms near roads. To examine the influence of traffic noise transmitted into classrooms on the speech intelligibility, on-site measurements were carried out according to closed and open window conditions. The results showed that the average U50 values were 2.68 ㏈ and –3.73 ㏈ for closed and open window conditions, respectively, indicating the importance of background noise control in classrooms. Based on the measured U50 values and the precedent study, proper background noise levels in classrooms in case of an open window were 43.3 ㏈A and 47.8 ㏈A to meet the minimum level for a “good” class (USUB50/SUB = 1.5 ㏈) and the middle level for a “fair” class (USUB50/SUB = –1.0 ㏈).

Critical methodological assessment of the distraction distance used for evaluating room acoustic quality of open-plan offices

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 from speech transmission index (STI) calculations. This study examines how the ISO 3382-3 metrics, especially rD, are affected by certain aspects of STI calculation, by using acoustic measurements of 20 offices. Results show that rD values calculated using ISO 3382-3 speech spectrum were significantly different to those calculated using other standard and proposed speech spectra. The choice of standard octave-band transmission index weights, e.g., male/female, used in standard STI calculation as per IEC 60268-16 (2011), did not significantly affect rD values. However, compared to the standard STI calculation, the pre-standard weights from the STI model from 1985 that is used in some important studies cited in ISO 3382-3 yielded much shorter rD values; RASTI yielded an increase in rD of less than 1 m; whereas STIPA (IEC 60268-16: 2011) did not affect rD. The effect of auditory spectral masking in standard STI calculation was negligible overall, but there were cases where the auditory masking reduced rD by up to 0.5 m. The effects of speech spectrum on two other relevant metrics in ISO 3382-3, namely spatial decay rate of speech, and A-weighted sound pressure level of speech at 4 m distance, were not significant. Overall, sensitivities of rD to several aspects of STI calculation are highlighted, which should contribute to the interpretation of studies that informed ISO 3382-3 development, support the current implied practice of using male STI weights for genderless speech in the calculation of rD, and provide guidance on potential refinements.

Model of Thailand Speech Intelligibility (T-SI) in the Large Classrooms from Public University

The objectives of this research are to evaluate acoustic environments and to forecast STI values from spatial component variables in the large classrooms of the Thai public university that were specially controlled the same room finishing materials including the floor, walls, and ceiling. Whereas the five spatial component factors included (1) Room Volume (RV), (2) Ceiling Height (CH), (3) the Ratio of Depth to Width (Rdw), (4) Total Room Surface (TS), and (5) Percentage of Absorbing Surface areas (PAS). The research tools were the smartphones that used the applications for acoustical evaluation and speech intelligibility analysis. The Speech Transmission Index (STI), Reverberation Time (RT), and Background Noise Level (BNL) were collected by the calibrated microphone in the nine points distributed across the entire room. And also, the sounds for testing were simulated such as balloon burst, and STIPA signal via a sound generator. The Thailand Speech Intelligibility (T-SI) model was developed by the multiple regression analysis with a statistical at a confidence level of 95%.The results showed that this T-SI model depended on the strongly positive relationship of PAS and the slightly positive relationship of CH, TS while the RV, Rdw were slightly the negative relationship and which predicted STI values. Moreover, the highest affecting variable of T-SI model was CH and the lowest was PAS. However, this research implies that the improving room acoustic quality would be adjusting the sound absorbing surface areas i.e., increase the cloth curtain or appropriate methods.

A room acoustical quality inventory

In a two-step procedure, a new psychological measuring instrument has been developed for the acoustical perception of room acoustical environments for speech and music. As a first step, an expert focus group of room acoustical scholars and consultants was formed in order to reach a consensus on a vocabulary as complete as possible to describe room acoustical qualities. In a second step, this inventory was used for the evaluation of 35 different simulated room acoustical environments presented by binaural synthesis to 190 subjects of different age and expert level. Based on the ratings of this room sample, a comprehensive psychometric analysis was performed in order to evaluate the preliminary item battery with respect to reliability, discriminative power, and redundancy. The resulting room acoustical quality inventory, together with the database of room acoustical models as well as their monaural and binaural transfer functions and their perceptual evaluation, can be used as a ground truth for the validation of existing and newly developed room acoustical parameters.

The perceptual evaluation of acoustical environments II: Natural environments

The perceptual evaluation of natural acoustic environments requires an assessment of the “room acoustical impression.” After some theoretical considerations on the nature of this perceptional construct and the shortcomings of existing tools, we present a new, empirically substantiated approach for the development of a corresponding measuring instrument. It relies crucially on the room acoustical simulation of a representative pool of acoustical environments for speech and music and their auralization for different acoustical sources. The resulting room acoustical quality inventory, together with a database of room acoustical models and their monaural and binaural transfer functions, can be used as a ground truth for room acoustical analysis and perception.

Acoustical characteristics of classrooms of tropical climate

This paper presents in-situ objective acoustical measurements and assessment of acoustical characteristics for the analysis of the classroom acoustics of the Visvesvaraya National Institute of Technology (VNIT) located in Nagpur, India as a representative case. Nine classrooms of VNIT, Nagpur as representative classroom typologies are assessed and presented in this paper. The analysis based on in-situ measured indicators of room acoustic quality, such as reverberation time (RT30), clarity (C50), background noise (BN), and the speech transmission index (STI), permit the identification of certain salient features of classroom acoustics in a tropical climate like India and complementary practical challenges associated with natural ventilation. The paper concludes by outlining acoustic concerns observed in the objectively identified and investigated classrooms of a tropical climate of the representative case. The conclusions are also supplemented with few recommendations for acoustical retrofit measures.

Time-compressed speech intelligibility in different reverberant conditions

The aim of this study was to determine how different reverberant conditions affect subjective perception of fastened speech. The objective parameters used for a description of room acoustics quality were Reverberation Time (RT) and Speech Transmission Index (STI). In relation to these parameters the Time-Compression Threshold (TCT) had been measured for normal hearing listeners younger than 30. The measuring test was based on artificially generated room impulse responses, MATLAB implementation of a phase vocoder, the Polish Matrix Test (PMT) combined with the 1-up/1-down adaptive procedure. As expected, the value of TCT decreases with an increase of RT and is highly correlated with STI. Therefore, the TCT parameter can be treated as an another sufficient estimator of acoustical quality of an enclosure in the context of speech intelligibility.

Relationships between perceived room acoustic quality and perceived reverberance, listener envelopment, and tonal quality.

In order to effectively design performing arts venues, the subjective qualities of a room's acoustics must be first identified and then corresponding objective measures must be developed to predict listeners' perceptions. Many attributes have been proposed and tested, and previous work has shown that these attributes not only allow listeners to distinguish between spaces, but also relate to subjective perception of room acoustic quality. However, several attributes remain vaguely defined and the relative importance of each of these attributes to overall preference is unclear. A better understanding of this relationship will allow for clearer design targets when evaluating and designing spaces.Based on an extensive review of the literature, the four attributes most commonly cited are loudness, proximity, reverberance, and clarity. Loudness is one of the most easily perceived attributes of a real or simulated sound field (Kimura, 1976 as summarized in Cremer & Muller, 1978; Lehmann & Wilkens, 1980) and correlates strongly with overall preference (Barron, 1988; Beranek, 1962; Lokki, Patynen, Kuusinen, & Tervo, 2012; Sato et al., 2013). Proximity, or the apparent closeness of the sound source, is a subjectively significant parameter (Hawkes & Douglas, 1971; Lokki et al., 2012; Sotiropoulou, Hawkes, & Fleming, 1995) and is somewhat related to sound level (Sotiropoulou et al., 1995). This parameter has recently been found to correlate highly with preference ratings, even when all recordings presented in subjective testing were taken at the same distance from the sound source (Lokki et al., 2012). These results suggest that perceived proximity depends on more factors than distance alone.A majority of research to date has included the attribute of reverberance, also referred to as liveness and resonance. Reverberance appears to be an independent factor for distinguishing between spaces (Beranek, 1962; Hawkes & Douglas, 1971; Katoh & Terashima, 2013; Lokki et al., 2012) and is closely linked to overall preference ratings (Barron, 1988). An attribute that is often inversely related to reverberance is known as clarity or definition. Previous studies have shown that both of these terms, clarity (Katoh & Terashima, 2013; Lehmann & Wilkens, 1980; Lokki et al., 2012; Sotiropoulou et al., 1995) and definition (Hawkes & Douglas, 1971; Lokki et al., 2012; Schroeder, Gottlob, & Siebrasse, 1974 as summarized in Cremer & Muller, 1978), are important discriminatory factors and they have been shown to correlate with preference (Sato et al., 2013; Soulodre & Bradley, 1995).Three additional categories of attributes, spatial impression, intimacy, and spectral content, have also been cited, but are not as well defined as the first four described above. Spatial impression is thought to have two components: apparent source width (ASW) and listener envelopment (LEV; Bradley & Soulodre, 1995), and both ASW (Jeon & You, 2010) and LEV (Barron, 1988; Jeon & You, 2010; Lokki et al., 2012) have been shown to contribute to overall preference. Intimacy is an important distinguishing factor between sound fields and spaces (Beranek, 1962; Hawkes & Douglas, 1971; Katoh & Terashima, 2013) and has been found to correlate strongly with overall preference (Barron, 1988), but may represent a similar perceptual attribute as spatial impression (Beranek, 1992).The final main subjective parameter group describes the spectral content of the sound and encompasses a wide variety of related terms: bassiness (Lokki et al., 2012), brilliance (Hawkes & Douglas, 1971), warmth (Barron, 2005; Beranek, 1992), timbre (Lehmann & Wilkens, 1980), treble (Soulodre & Bradley, 1995), balance (Hawkes & Douglas, 1971), blend (Hawkes & Douglas, 1971), and tonal quality (Sotiropoulou et al., 1995). All of these terms have been found to relate to overall preference, but the degree to which they overlap has not yet been determined. …

Requirements for low-frequency reverberation in spaces for music: Part 2: Auditoria for performances and recordings.

(ProQuest: ... denotes formulae omitted)A large number of contemporary concert and assembly halls are criticized for their mediocre acoustics, although most elaborate model tests and computer simulations are at our disposal for the large-scale planning and small-scale interior design of an enclosure. On the other hand, we have inherited numerous spaces with excellent acoustics that were built without any powerful prediction and calculation tools. Acousticians or sound engineers may complain that nowadays, architects almost exclusively consider the visual of a structure. Only rarely do they consider the acoustic aspects (Blesser & Salter, 2007, p. 1). But are we able to provide the builders with a firm and generally applicable guideline for achieving acoustical quality and comfort in a room for a specific musical or lingual destination?Concerning the less concrete, more complicated sonic processes such as hearing (meaning, the detection of sound) and listening (as active attention or reaction to the meaning, emotions, and symbolism contained within sound), one may refer to Blesser and Salter (2007) for a profound synopsis of the various of architects, interior designers, and sound engineers. As an acoustician, one may retreat to the standard International Organization for Standardization (ISO 3382, 1997) on p. 2: This standard continues to specify room acoustic quality by reverberation time T alone . . . T measurements are important in the field of noise control (e.g., in public buildings, libraries, swimming halls or work places) as well as for the assessment of rooms for speech and with... (1)where V is the room volume in m3 and both T in s and the equivalent absorption area A in m2 of the room are strongly frequency dependent in the range between (at least) f 63 Hz and 8,000 Hz relevant for room acoustics in general. ISO 3382-1997 in its Note 17 states, The frequency range should include the octave bands from 125 Hz to 4 kHz or the one-third octave bands from 100 Hz to 5 kHz. In concert halls the 63 Hz octave band should be added. When it comes to additional quantities, meant to be subjectively important according to ISO 3382-1997, Annex A, like early decay time, strength (G), clarity (C80), definition (C50), center time TS, and lateral energy fraction (LF), however, the focus is only on a much more restricted mid-frequency (mf) spectrum between 500 Hz and 1 or 2 kHz (also for the averaged singlenumber ratings that prevail in practice) intended to summarize measurement results, see Beranek (1996, Appendix 1). As a result, one rarely finds acoustics criteria for the complete frequency spectrum. Instead, standard recommendations usually just refer to a correspondingly averaged Tm as a function of room volume.In this context, Beranek et al. (2010) may be cited:I am convinced that we need to work with the whole spectrum of human hearing-we must not ignore the universes of very high and very low frequency sound that are presently unattended in our data gathering and analysis. Half the instruments of our orchestra have their fundamental pitches below 125 Hz. We need to design for strength in the fundamental sounds of those instruments. Fundamental pitches of low frequency instruments support intonation and bloom for the full orchestral sound. Fundamentals are fundamental! (p. 7)At the same meeting, Bradley (2010) stated that there is not much evidence to support the idea that mid-frequency values are most representative of the perceived broadband changes of all measures (p. 7). Burkowitz (2011), an experienced sound engineer, suggests that recognizing the musical structure and architecture in the contra- and sub-contra ranges is just as important as doing it for the formants (p. 279).The present authors recognize and deal with the prominent role that the performance spaces play in all music making and listening. Hundreds of venues of different size and use have taught them that the complete reverberation characteristic has an enormous impact on any type of music performances, well knowing that modern recording equipment may, to a certain extent, help to cope with adverse acoustics. …

Perceptual relevance of location of reverberation in a concert hall.

Standard reference texts as well as the International Organization for Standardization (ISO) standard on room acoustic quality (see, e.g., Beranek, 2004; Barron, 2010; and ISO3382-1:2009) focus on temporal distribution of energy [e.g., reverberation time T, G, and C80] and binaural aspects [lateral energy]. Kahle (2013) suggested that this description is insufficient when working with concert halls and that spatial aspects of sound fields need to be taken into consideration beyond binaural aspects. Furthermore, spatial aspects should be considered independently and separately for the (source presence) and the (room presence; see, e.g., Kahle, 1995, for details on source presence and room presence). For source presence, lateral reflections have different effects than ceiling reflections; this difference is taken into account by the objective criterion of lateral energy and the subjective factor of apparent source width. For room presence, listeners prefer to be fully enveloped by room sound; when talking to musicians and experienced listeners it is clear that this must not be limited to the frontal hemisphere and the question of lateral energy. All of the room around the listener should be active and this includes the parts of the room above us and behind us. Finally, when accepting the concept of segregation into a foreground source stream and a background room stream, a generalization of the cocktail party effect suggests that segregation is facilitated when the center of gravity (or direction of arrival) of the source is spatially separated from the center of gravity (or direction of arrival) of the room stream. Room reverberation should hence ideally be spatially homogeneous or come from a different direction than the source stream. In this paper, case studies are examined that show how spatial aspects of late sound can influence the perception of early sound and how frontal noise can influence the perception of both source presence and room presence. This suggests that spatial direction of arrival can strongly influence the perception of room acoustic quality.Case Study: Electro Acoustic Enhancement System Stockholm Concert HallThe Stockholm Concert Hall (Konserthuset, see Figure 1 for a photo of the hall) had been plagued with acoustic problems for decades (Dahlstedt, 1974) and has undergone several renovations. During the 1972 renovation, an electro-acoustic enhancement system was installed the hall, but apparently decommissioned after few months of use (Dahlstedt, 1974). The reasons for the decommissioning of the system are unknown, but probably the increase of natural reverberation during the renovation was at the time considered as being sufficient. Further renovations 2000 and 2005 decreased reverberation time and as a consequence the audibility of the late room response was significantly below optimum after 2005.As already indicated, it was found that one of the main reasons for the insufficient reverberance (what musicians described as lack of bloom) was the presence of a semitransparent technical ceiling installed under the lighting bridges for practical and esthetic reasons. The semitransparent expanded-metal ceiling (which can be seen at the top of Figure 1; Figure 2 shows a more detailed side view) created a slight transmission loss both on the way in for sound into the volume under the roof and on the way out. As a consequence, no reverberation could be heard coming from the top of the room and the ceiling was felt as being acoustically absent.First as a tryout and then as a final solution, an electro acoustic enhancement system based on the multiple channel amplification of reverberation (MCR) principle (de Koning, 1983-1984; Mulder, 2001) was installed the volume above the semitransparent ceiling, with microphones picking up the sound under the stretched-metal ceiling and loudspeakers enhancing the sound above the stretched metal ceiling. …

Sound source influence to the room acoustics quality measurement

Objective parameters of the room acoustics quality are obtained from the impulse response, which is measured using the appropriate PC based acoustic measurement system with two types of loudspeakers. Such measurement gives the impulse response that is the result of measurement of the entire system, which consists of the room and electro acoustics equipment. In order to investigate the real influence of loudspeakers on the measurement results, the research was made in the same measuring conditions. Impulse responses were measured with the same measuring system. Measuring point was selected at the optimum listening position in the room, and all measurements were carried out in the same place. The loudspeakers were placed at the optimum and characteristic positions in the room, and rotated around their axes in order to determine the impact of their position and directivity characteristics on the measurement of objective parameters of room acoustic quality.