Wonyoung Yang

Effects of room acoustics on the intelligibility of speech in classrooms for young children

This paper reports new measurements of the intelligibility of speech in conditions representative of elementary school classrooms. The speech test material was binaurally recorded in simulated classroom conditions and played back to subjects over headphones. Subjects included grade 1, 3, and 6 students (6, 8, and 11 year olds) as well as adults. Recognizing that reverberation time is not a complete descriptor of room acoustics conditions, simulated conditions included realistic early-to-late arriving sound ratios as well as varied reverberation time. For conditions of constant signal-to-noise ratio, intelligibility scores increased with decreasing reverberation time. However, for conditions including realistic increases in speech level with varied reverberation time for constant noise level, intelligibility scores were near maximum for a range of reverberation times. Young childrens intelligibility scores benefited from added early reflections of speech sounds similar to adult listeners. The effect of varied reverberation time on the intelligibility of speech for young children was much less than the effect of varied signal-to-noise ratio. The results can be used to help to determine ideal conditions for speech communication in classrooms for younger listeners.

Auralization study of optimum reverberation times for speech intelligibility for normal and hearing-impaired listeners in classrooms with diffuse sound fields

Speech-intelligibility tests auralized in a virtual classroom were used to investigate the optimal reverberation times for verbal communication for normal-hearing and hearing-impaired adults. The idealized classroom had simple geometry, uniform surface absorption, and an approximately diffuse sound field. It contained a speech source, a listener at a receiver position, and a noise source located at one of two positions. The relative output levels of the speech and noise sources were varied, along with the surface absorption and the corresponding reverberation time. The binaural impulse responses of the speech and noise sources in each classroom configuration were convolved with Modified Rhyme Test (MRT) and babble-noise signals. The resulting signals were presented to normal-hearing and hearing-impaired adult subjects to identify the configurations that gave the highest speech intelligibilities for the two groups. For both subject groups, when the speech source was closer to the listener than the noise source, the optimal reverberation time was zero. When the noise source was closer to the listener than the speech source, the optimal reverberation time included both zero and nonzero values. The results generally support previous theoretical results.

Ceiling baffles and reflectors for controlling lecture-room sound for speech intelligibility

Reinforcing speech levels and controlling noise and reverberation are the ultimate acoustical goals of lecture-room design to achieve high speech intelligibility. The effects of sound absorption on these factors have opposite consequences for speech intelligibility. Here, novel ceiling baffles and reflectors were evaluated as a sound-control measure, using computer and 1/8-scale models of a lecture room with hard surfaces and excessive reverberation. Parallel ceiling baffles running front to back were investigated. They were expected to absorb reverberation incident on the ceiling from many angles, while leaving speech signals, reflecting from the ceiling to the back of the room, unaffected. Various baffle spacings and absorptions, central and side speaker positions, and receiver positions throughout the room, were considered. Reflective baffles controlled reverberation, with a minimum decrease of sound levels. Absorptive baffles reduced reverberation, but reduced speech levels significantly. Ceiling reflectors, in the form of obstacles of semicircular cross section, suspended below the ceiling, were also tested. These were either 7 m long and in parallel, front-to-back lines, or 0.8 m long and randomly distributed, with flat side up or down, and reflective or absorptive top surfaces. The long reflectors with flat side down and no absorption were somewhat effective; the other configurations were not.

Optimum Reverberation for Speech Intelligibility for Normal and Hearing-Impaired Listeners in Realistic Classrooms Using Auralization

The objective of this study was to use auralization techniques to investigate the optimal reverberation for speech intelligibility for normal-hearing and hearing-impaired adult listeners in classrooms with non-diffuse sound fields. This extended a previous study involving rooms with diffuse sound fields to more realistic rooms. Modified Rhyme Test (MRT) signals were auralized in six virtual classroom configurations with different reverberation times. Each classroom contained a speech source, a listener at a receiver position, and a noise source located between the talker and the listener. Two speech- and noise-source output-level differences (0 and +4 dB) were tested. Subjects performed speech-intelligibility tests in the virtual classrooms to identify the reverberation time that gave the best results in each case. For both normal and hearing-impaired listeners, the optimal reverberation time was generally non-zero, and increased with decreased speech-to-noise level difference. Hearing-impaired subjects apparently required more early energy than normal-hearing subjects. The optimal reverberation time for speech intelligibility in classrooms is not necessarily zero, as is commonly believed. The optimal value is generally non-zero, and varies with the room, the locations of the speech and noise sources and the listener, and the noise level.

An integrated comfort control with cooling, ventilation, and humidification systems for thermal comfort and low energy consumption

Over the past few decades, interest in issues related to the global environment and energy resources have increased in many industries, including the building sector which accounts for nearly 40% of the global energy consumption. Simultaneously, the demand for precise comfort control in buildings has increased because people have acquired a better quality of life and expect more from modern technology. In most cases, air-conditioning and ventilation systems have been installed in residential and commercial buildings. However, these systems can increase energy consumption requirements because of their lack of appropriate control. Such increases can be reduced by integrating the control of available sources of cooling, humidification, ventilation, lighting, and so on. An integrated comfort control strategy that integrates an air-conditioning, a humidifier, and a ventilation system by considering the outdoor environment is proposed for ensuring indoor thermal comfort and energy savings in buildings. The control strategy was evaluated in a virtual test bed with a variable refrigerant flow system, a humidifier, and ventilation fans. The performance of the proposed integrated comfort control was compared to that of conventional individual controls using EnergyPlus in terms of thermal comfort and energy consumption. The results showed that the integrated comfort control improved thermal comfort and lowered energy consumption. The methodology of deriving the integrated comfort control was expected to be useful for designing better control logics for thermal comfort and energy conservation.

Effects of indoor temperature and background noise on floor impact noise perception

This study investigates effects of room air temperature and background noise on the perception of floor impact noises in a room. Floor impact noises were recorded in apartment buildings and were presented in an indoor climate chamber with background noise for subjective evaluation. Thirty-two participants were subjected to all combinations of three thermal conditions (20%C, 25%C, 30%C and relative humidity 50%), four background noise types (Babble, Fan, Traffic and Water), three background noise levels (35 dBA, 40 dBA and 45 dBA) and four floor impact noises (Man Jumping, Children Running, Man Running and Chair Scraping). After a 1-h thermal adaptation period for each thermal condition, the participants were asked to evaluate their thermal and acoustic perceptions. Statistically significant effects were found for the room air temperature and background noise level on the perception of the floor impact noises. Noisiness, loudness and complaints of floor impact noise increased with increasing room temperature and background noise level. Annoyance of floor impact noise showed a peak in acceptable thermal environment for general comfort. Room air temperature was a dominant non-auditory factor contributing to floor impact noise annoyance, while the floor impact noise level influenced the floor impact noise loudness and the floor impact noisiness was almost equally affected by the room temperature, background noise level and floor impact noise level. Further investigation is needed to fully understand the combined perception of floor impact noise under various indoor environmental conditions.

Effects of indoor water sounds on intrusive noise perception and speech recognition in rooms

While water sounds have been used for soundscape improvement, little is known about their applicability in indoor environments. In order to investigate the effects of indoor water sounds on noise perception, a simple indoor water fountain system was used to produce water sounds over three different types of indoor intrusive noise (traffic noise, higher frequency dominated noise of a chair scraping the floor above, lower frequency dominated impact noise of a man running on the floor above) and speech in a test laboratory. Intrusive noise perception (annoyance and pleasantness) and speech recognition (KS-MWL-A) were assessed with three water sound levels (40, 50, 60 dBA) at two exposure times (immediate and 50 min) of water sounds by 54 participants. Short-term exposure to indoor water sounds improved the pleasantness of intrusive noise without increasing annoyance except lower frequency dominated impact noise. The increase in exposure time to indoor water sounds did not affect intrusive noise perception and speech recognition. The water to noise ratio significantly affected annoyance and pleasantness of traffic noise only; however, the level of water sounds did not significantly affect intrusive noise perception. Indoor water sounds can be used to improve intrusive noise perception except lower frequency dominated floor impact noise with no adverse effects on speech recognition dependent upon the speech to water sound ratio. Practical application: This simple indoor water fountain can be directly applied to small offices or rooms to improve intrusive noise perception. When the simple fountain produces water sounds in a room, pleasantness of traffic noise throughout window openings or higher frequency dominated noise such as chair scraping noise can be improved without increment of annoyance and decrement of speech recognition. Short-term exposure to indoor water sounds is effective to increase pleasantness of the intrusive noises.

Combined effects of short-term noise exposure and hygrothermal conditions on indoor environmental perceptions

Realistic thermal conditions with various humidity levels have been considered to examine the combined effects of noise and thermal conditions on indoor environmental perceptions. Subjective assessments of temperature, humidity and psychoacoustics were conducted with 26 subjects under combined environments of seven thermal conditions (18℃: RH 30, 60%, 24℃: RH 27, 43, 65%, 30℃: RH 30, 60%), two noise types (fan and babble noises) and five noise levels (45, 50, 55, 60 and 65 dBA). Three-minute moderate noise exposure did not affect temperature or humidity sensations. However, the temperature and humidity levels affected loudness, annoyance and acoustic preferences when noise was presented as babble. Fan noise perceptions were found to be independent of thermal conditions. Gender differences were clearly found in terms of thermal and psychoacoustic perceptions. Men were more sensitive to hot sensations than women, and women were more sensitive to arid sensations than men. Women were more sensitive to noise levels than men. Gender differences were also found in terms of different types of noise. Men were found to be significantly less sensitive to fan noise than women. Even though psychoacoustic parameters were affected by indoor thermal conditions, thermal parameters were not affected by short-term moderate noise. The combined effect of various types of noise and temperature is still unclear, and this will be considered in a future larger cohort study.

Demo: Micro energy efficiency system based on QR code mote

Micro Energy Efficiency System (MEES) provides energy saving while enabling each individual office in a large building to control heating, cooling, and electricity with its own policy. The usage of a decentralized independent control of each office, rather than a centralized one, is common in Korea. MEES provides measuring and controlling points at multiple granularities. An installation became easy and efficient using QR code, and the user configuration through an energy web portal further enhances the energy efficiency.

Auralization study of optimum reverberation for speech intelligibility for normal and hearing‐impaired listeners

Reverberation and signal‐to‐noise level difference are two major factors affecting speech intelligibility. They interact in rooms. Past work has accounted for noise using a constant received background‐noise level. Noise is actually generated by sources, and varies, and affects speech intelligibility differently, throughout the classroom, depending on where the sources are located. Here, a speech‐babble noise source located at different positions in the room was considered. The relative output levels of the speech and noise sources, resulting in different signal‐to‐noise level differences, were controlled, along with the reverberation. The binaural impulse response of a virtual idealized classroom model was convolved with the Modified Rhyme Test (MRT) source and babble‐noise signals in order to find the optimal configuration for speech intelligibility. Speech‐intelligibility tests were performed with normal and hard‐of‐hearing subjects in each of 16 conditions which were combinations of reverberation time...