Short Reverberation Time Research Articles

Amplified music and variable acoustics—Controlled low frequencies and envelopment at high

Subjective ratings from 25 professional musicians and sound engineers were obtained to assess two Danish rock venues of similar size and similar low frequency reverberation times, but different high frequency reverberation characteristics. The musicians rated one hall outstanding and significantly better than the other, substantiating a hypothesis that pop venues can have a longer reverberation time at mid to high frequencies at least in the empty condition with no seats installed. Possible causes for this is an enhancement of the musicians’ ease of expressing dynamics as well as of their ability to sense the audience for whom they are playing. It has formerly been shown, that what characterizes the best halls for amplified music is a relatively short reverberation time at low frequencies. However, in this study, a fairly long reverberation time in the 63 Hz octave band is found to be acceptable, especially in the hall with the longer mid-high frequency reverberation time, pointing towards a tolerance for longer reverberation in this band in general. Further, this hints at the possibility that mid-high frequency reverberation can mask, at least 63 Hz band challenges. The 125 Hz octave band RT, which thereby remains the single most important to control for amplified music, is app. 1 sec in the two venues that hold some 700 standing audiences

Chinese speech intelligibility of children in noisy and reverberant environments

Reverberation time and signal-to-noise ratio in classrooms are critical factors to speech intelligibility. In this study, the combined effect of reverberation time and signal-to-noise ratio on Chinese speech intelligibility of children was investigated in 28 elementary school classrooms in China. The results show that Chinese speech intelligibility scores increase with an increase of signal-to-noise ratio and the age of children, and decrease with an increase of reverberation time in classrooms. Younger children require higher signal-to-noise ratio and shorter reverberation time than older children to understand the speech. The A-weighted signal-to-noise ratio combined with a wide range of reverberation time can be used to predict speech intelligibility score and serve as a criterion for classroom design for elementary schools.

Speech intelligibility under realistic classroom acoustics

Speech recognition is fundamental in everyday communication environments, especially in school classrooms where the teaching-learning process takes place. Extensive literature is available that refers to speech intelligibility studies on the effect of artificially added reverberation and speech-shaped noise, whereas there is a little number of works that account for realistic acoustics. This work investigates the effect of measured classroom acoustics on speech intelligibility, accounting for the effect of informational and energetic masking, distance teacher-to-listener between and binaural unmasking. Speech reception threshold (SRT) corresponding to signal-to-noise ratio yielding 80% of speech intelligibility was measured in two acoustically different primary school classrooms. The acquired binaural room impulse responses were convolved with anechoic speech and noise stimuli, then presented via headphone to a group of adult normal-hearing listeners. The results show that SRTs were lower (better) under optimal classroom acoustics, i.e., with reverberation time of 0.4 s. Also, SRTs under informational masking noise were averagely higher (worse) by 6.6 dB than SRTs under energetic masking, proving that the former masker is more competing than the latter and needs to be deepen in future research. The binaural unmasking was observed only for a short teacher-to-listener distance in the room with a shorter reverberation time.

Effects of Reverberation on Sound Localization for Bilateral Cochlear Implant Users

The purpose of this study was to examine the effects of reverberation on the ability of listeners with bilateral cochlear implants (BCIs) to localize speech in anechoic and reverberant environments. Two specific research questions were addressed: (1) how do listeners with BCIs localize sounds in different environments compared to listeners with normal hearing (NH)? and (2) at what reverberation time (RT60) does localization performance begin to decline for both groups of subjects? Six adults with BCIs and ten with NH participated. All subjects completed a virtual localization test in simulated anechoic and reverberant environments (0.0, 0.2, 0.6, and 0.9 s RT60) in quiet. A three-word phrase was presented at 70 dBSPL from nine simulated source locations in the frontal-horizontal plane (± 900). Root-mean-square localization error (RMSLE) in degrees was calculated. Results revealed localization accuracy significantly decreased as reverberation time increased for both groups of subjects. Listeners with BCIs had significantly poorer localization accuracy than listeners with NH in all conditions. Their RMSLE changed from 320 in anechoic condition to 600 in RT60 0.9s condition, while corresponding change for listeners with NH was only from 170 to 220. In addition, localization performance of listeners with BCIs started to decrease at a shorter reverberation time (RT60 0.6s) compared to those with NH (RT60 0.9s). In conclusion, reverberation significantly degraded localization performance, with a greater influence on listeners with BCIs than listeners with NH. In addition, bilateral experience is likely to help listeners with BCIs achieve a better localization outcome over time. It is important to apply the information obtained in this study to optimize binaural benefit for listeners with BCIs in everyday listening situations.

The Same Reverberation Time in Two Identical Rooms does not Necessarily Mean the Same Levels of Speech Clarity and Sound Levels when We Look at Impact of different Ceiling and Wall Absorbers

For setting the acoustic conditions in a classroom for teaching and learning activities, it is common to only measure Reverberation Time (RT). To calculate the RT in rooms with ceiling absorption is common but this data can also be misleading. Indeed, we measured the similar RT values in two identical rooms with different acoustic treatment, even though the calculations predicted significant differences and interestingly the rooms are also be perceive quite differently in reality.Taking the human response to sound into account the measured RT data alone leaves us in the dark when seeking to explain the difference in human user perception. Measuring additional room acoustic parameters such as speech clarity and the difference in sound levels, identifies other important differences between the two unoccupied but furnished rooms with the same RT and points to why only one of the two rooms seems fit for purpose as a group activity room.We will discuss how to achieve room acoustic comfort in classrooms; short RT, low sound levels and high speech clarity. In addition to commonly accepted short RT values we will discuss recommended objective values for good Speech Clarity to support good speech communication activities in typical teaching and learning rooms in real life situations.

Comparison of Acoustic Performance Depending on the Location of Sound Absorptive and Diffuser in Small Auditoriums Using 1/10 Scale Models

This study investigated how the location of sound absorptive materials and sound diffusers affects the acoustic performance of small auditoriums. It was conducted for a standard model established with the averaged dimension of 36 auditoriums which had opened since 2000 in Daehak-ro, Seoul. In this study, the installation area of finishing materials was calculated upon a back wall which had the smallest installation effective area of finishing materials. To analyze the changes of acoustic performance according to installation location of finishing materials, experiments were carried out using the 1/10 down scale models for 8 cases which were made by classifying the installation location of ceiling and side wall into the front, middle and rear part.The used acoustic parameters were reverberation time (RT), early decay time (EDT), clarity (C80), definition (D50) and speech transmission index (STI). In result, the index related to the amount of reverberant sound (RT, EDT) showed the great changes when evaluating it through just noticeable difference (JND), but the one related to clarity (C80, D50, STI) hardly indicated the changes. In case to obtain short reverberation time, it was most effective to control reverberation time through the side walls when installing sound absorptive and diffusive materials, and side wall front was the location which could get the shortest reverberation time.

Acoustical design for public address announcements in an underground subway station

The public address (PA) is a part of the passenger information system in an underground subway station. A sample station named Xingzhong Road on metro line 9 in Shanghai is considered in this paper. A ray-tracing model for acoustical simulation of the PA system is established. Verification is performed by comparing the simulated and the measured sound pressure levels (SPLs), early decay time (EDT), reverberation times (RTs) and clarity (C50). Several sound samples are simulated by changing the ceiling absorption materials of the subway station model. Jury tests of these sounds are conducted by using the paired-comparison method (PCM). We found that people prefer a shorter RT, which demands higher sound absorption materials. The relationship between the RTs and the averaged absorption ratios of the ceiling materials suggests that the RT around 1 s is the best in the Xingzhong Road station, and the values of the objective parameters, such as the SPL, EDT, speech transmission index (STI) and echo speech, are acceptable to PA system. The method presented in this paper can be regarded as a useful tool for acoustical optimization design of the subway station PA system.

Amplified music and measurement results regarding inflatable membrane absorber technology

Previous studies and experience have shown that what distinguishes the best from the less well liked venues for pop and rock music is a shorter reverberation time in the 63–250 Hz octave bands. Since a longer reverberation time in these bands is needed in order to obtain warmth at classical music concerts, variable acoustics must address these frequencies in order to provide the best results in multipurpose halls. This paper will expand on research on recommendable acoustics for amplified music. Certified measurements from reverberation chambers and installed systems on a patented, inflatable, on/off absorption technology are presented. Since the technology can be used in the entire ceiling area, the T30 of a hall can be lowered by almost 50% in the important octave bands for pop and rock music. Absorption coefficients are almost constant across the frequency bands from 63 to 1000 Hz. The technology, which is the only passive solution to enable variability also at the important lower frequencies, is meant to be used in any hall where both classical as well as amplified music is being played, such as in music schools and performing arts centers.

Classroom acoustics and hearing ability as determinants for perceived social climate and intentions to stay at work

Background noise and room acoustics may impede social interactions by interfering with oral communication and other cognitive processes. Accordingly, recent research in school environments has showed that social relationships with peers and teachers are described more negatively in rooms with long reverberation times (RT). The purpose of this study was to investigate how RT and hearing ability (i.e., hearing thresholds [HT] and distortion product oto-acoustic emissions) were associated with school teachers' perceptions of the social climate at work and their intentions to stay on the job. School teachers (n = 107) from 10 schools that worked in classrooms classified by acoustical experts as "short RT" (3 schools, mean RT 0.41-0.47 s), "medium RT" (3 schools, mean RT 0.50-0.53 s), and "long RT" (4 schools, mean RT 0.59-0.73 s) were examined. Teachers who worked in classrooms with long RT perceived their social climate to be more competitive, conflict laden, and less relaxed and comfortable. They were more doubtful about staying on the job. Even if the teachers were generally satisfied with their work the results suggest that the comfort at work may have been further improved by acoustical interventions that focus on reducing sound reflections in the classrooms. Yet, due the study design and the novelty of the findings the potential practical significance of our observations remains to be evaluated.

Noise Problems in Restaurants

The gathering of many people in restaurants, bars, canteens and other kinds of eating establishments is often very noisy, and for that reason verbal communication can be difficult, or even impossible for people with reduced hearing capacity. Although a complicated acoustical problem due to the feed-back influence of noise on the speech level, a simple prediction model for the ambient noise level due the speech is suggested. It is found that the noise level increases by 6 dB if the number of people is doubled. In order to achieve a sufficient quality of verbal communication a high volume and a short reverberation time is needed. A minimum of 3–4 m2 absorption area per person is needed for sufficient conditions, and 6–8 m2 for satisfactory conditions. It is suggested to label the rooms with the “Acoustical capacity”, i.e. number of people which should not be surpassed for sufficient quality of verbal communication.

On a variable broadband absorption product and acceptable tolerances of reverberation times in halls for amplified music

Previous studies have shown that what distinguishes the best from the less well liked halls for pop and rock music is a short reverberation time in the 63, 125 and 250 Hz octave bands. Since a quite long reverberation time in these frequency bands is needed in order to obtain warmth and enough strength at classical music concerts, variable acoustics must address these frequencies in order to obtain desirable acoustics in multipurpose halls. Based on the results of a previous study of Danish rock venues as well as three newly built halls, acceptable tolerances of T30 were investigated. The results suggest that T30 can be at least 1.4 times as long in the 63 Hz octave band as in the 125 Hz band and attain values of +/- 15% at higher frequencies compared to previously determined values. A variable broadband absorption product is also presented. Absorption coefficients are approx. 0.8 in the 125, 250, 500 Hz bands, 0.6 at 1 kHz and decreasing at higher frequencies and in the 63 Hz band when in the ON position. In the OFF position the product attains absorption values between 0.0 and 0.2.

Glass as an aid and as a challenge in acoustics treatment

A new installation for a broadcast center that included recording and transmission studios had to be constructed in an all transparent glass facade building in a major street in Mexico City. Together with all the acoustical specifications requested and needed for proper response of the studios, it was also requested from the very beginning of the project that the building facade could not be modified at all, i.e., all the glassing could not be obstructed in at least a couple of meters from the edge of the building in order to preserve the look of the building as it was originally constructed. This meant that enough sound insulation for the studios and control rooms as well as the short reverberation times, and resonance control needed by the acoustic conditioning treatment had to be attained with plenty of glass area, which could not be moved, plus all the glassing needed for visual communication between rooms to allow for normal operation of the studios. Construction details and results are presented.

Determinants of noise annoyance in teachers from schools with different classroom reverberation times

A high proportion of school teachers report that they are disturbed by noise during teaching. The aim of the study was therefore to identify determinants of self-reported noise exposure and disturbance attributed to noise among secondary school teachers ( n = 419) in 10 schools in Copenhagen, Denmark. The schools were selected to show contrasts in classroom reverberation times (RT), and were classified as “Short RT” (3 schools, mean RT 0.41–0.45 s), “Medium RT” (3 schools, mean RT 0.51–0.55 s) and “Long RT” (4 schools, mean RT 0.62–0.73 s). Significant determinants of self-reported noise exposure were a high number of children in the class, young age of the children, and low teacher seniority. “Long RT” classification was of borderline significance. Significant determinants of disturbance attributed to noise from children in the class were teacher seniority and “Long RT” acoustic classification of the school. The associations between work characteristics and noise disturbance measures were attenuated by low self-rated work capacity, suggesting that the consequences of noise and poor acoustics may not be limited to disturbance attributed to noise, but may have a wide negative impact on the perceived working environment.

The effect of reverberation on the performance of cepstral mean subtraction in speaker verification

Speaker verification (SVR) performance is degraded under reverberation conditions. Cepstral mean subtraction (CMS) is often applied to the feature vectors in order to compensate for convolutive effects of transmission channels, which are considered to have a short-duration impulse response. The effect of reverberation on the performance of CMS applied to the feature vectors in SVR is investigated. Although CMS was found effective in reducing the effect of reverberation for short reverberation time (RT), in cases of long RT, it is shown that CMS may degrade SVR performance rather than improve it. Hence, CMS should not to be used in these cases. In addition, the effect of the room volume was tested and found less critical than the effect of long RT.

Simulating, mirroring, morphing, and blurring acoustic space as an extended instrumental technique.

The paradigm for musical performance is the sound of musical instruments in a fixed acoustical space. Ordinarily space does not shift and change during performances. An ideal space for performing classical composers such as Mozart is the Shaffy Theater in Amsterdam with a relatively short reverberation time 1.5 s. Instruments couple to the space, and space is part of the instrument and vice versa. Players develop special relationships with favorite spaces. After experiencing many different types of acoustics this leads to the desire to change the space during performance in order to hear the different qualities that emerge from spatial coupling. Spatial progressions can be made so that rather than moving sound in space, space can be moved around the sound and produce a variety of qualities.

The importance of the direct to reverberant ratio in the perception of distance, localization, clarity, and envelopment, Part one.

The component of hall sound that travels directly from a musician to a listener carries information on both the location and distance of the sound source and is vital to both the clarity of the sound and the emotional involvement of listeners. Experiments in laboratories and a hall show that the human ability to separately perceive the direct sound in a reverberant field depends both on the time delay between the direct sound and the reverberant energy and on the direct‐to‐reverberant ratio (D/R). Threshold data for direct sound perception as a function of time delay and D/R will be presented, and their implications for listening room and hall design will be discussed. In large halls the delay can be long enough that the direct sound is perceptable at D/R values less than −10 dB, but in small halls the threshold becomes as high as 0 dB. Consequences for hall design include: early reflections in the best halls need not be lateral, small halls sound better with fewer early reflections (implying the use of non‐shoebox shapes, absorbent stage houses, and shorter reverberation times), and in small halls electroacoustic enhancement should increase only the late reverberation.

On the Acoustics of the Underground Galleries of Ancient Chavín de Huántar, Peru

Chavín de Huántar is a monumental World Heritage archaeological site in the Peruvian highlands predating Inca society by over 2000 years. The importance of site acoustics is suggested by distinctive architectural features, notably an extensive network of underground galleries used in part for ritual purposes. The labyrinthine galleries are arranged in a series of small rectangular alcoves off narrow corridors. Here we focus on measuring and modeling the acoustics at Chavín to understand the implications of auditory experiences within the galleries as related to the site's role in developing religious authority. Acoustic measurements and models of a site can be used to archive site acoustics, estimate the acoustics of inaccessible or alternative site architectures, and reconstruct original site acoustics; they may also be used to corroborate aspects of rituals suggested by other archaeological data. Preliminary acoustic measurements at Chavín show a short reverberation time, dense and energetic early reflections, and a large lateral energy fraction. The short reverberation time would enable rhythmically articulated group performance using Strombus shell trumpets found onsite. The early reflections would provide strong acoustic reinforcement and consistent resonances for participants in gallery alcoves. The wide soundfield would envelop participants, contributing to the ritual experience.

Opera House Reverberation Times - Design Considerations

The intimacy of many historic European Opera Houses, especially of the traditional Italian style, is highly cherished and many of these halls are considered to be among the best halls acoustically. From an acoustical point of view the generally small dimensions - often combined with a moderate seat count - provide excellent source presence and clarity. On the other hand, the corresponding small volume leads to short reverberation times, and in recent decades higher reverberation times have been preferred and asked for by clients and audiences in many countries. Ideas will be presented on how this apparent dilemma between the preference for small dimensions (for intimacy, source presence and definition) and increased volume (in order to create longer reverberation times) can be addressed.

An adaptive stereo basis method for convolutive blind audio source separation

We consider the problem of convolutive blind source separation of stereo mixtures, where a pair of microphones records mixtures of sound sources that are convolved with the impulse response between each source and sensor. We propose an adaptive stereo basis (ASB) source separation method for such convolutive mixtures, using an adaptive transform basis which is learned from the stereo mixture pair. The stereo basis vector pairs of the transform are grouped according to the estimated relative delay between the left and right channels for each basis, and the sources are then extracted by projecting the transformed signal onto the subspace corresponding to each group of basis vector pairs. The performance of the proposed algorithm is compared with FD-ICA and DUET under different reverberation and noise conditions, using both objective distortion measures and formal listening tests. The results indicate that the proposed stereo coding method is competitive with both these algorithms at short and intermediate reverberation times, and offers significantly improved performance at low noise and short reverberation times.

Measurement of reverberation time of a passenger car utilizing the wavelet filter bank

A few researchers have tried to find the measurement of the reverberation time of a passenger car. However, this has proved to be extremely difficult because the reverberation time of a passenger car is too short to measure using the traditional bandpass filter. If the reverberation time is very short, the product of the reverberation time ( T) and the bandwidth ( B) of the traditional bandpass filter is very small. The low level of the product BT required for the measurement of the reverberation time using the traditional bandpass filter is 16. In order to overcome this problem, the wavelet filter bank has been developed. In the paper, this new wavelet filter is employed to measure the reverberation times of five different classes of passenger car. The low level of the product BT required for the measurement of reverberation time using the wavelet filter is 4. Therefore, it was possible to measure the reverberation times of five passenger cars successfully using the new wavelet filter bank. It is found that the reverberation times measured in most passenger cars are around 0.04. It is a very short reverberation time compared with those of general acoustic rooms like a concert hall.