1. Introduction
Multi-functional lecture halls and comprehensive auditoriums have emerged as pivotal components within contemporary infrastructural developments. Particularly in locales characterized by land scarcity and fiscal prudence, the establishment of expansive facilities endowed with acoustically refined attributes to accommodate large gatherings stands as a judicious choice. This architectural typology finds expression in educational institutions and municipal entities (Liang et al., 2021) [
1], wherein these spaces are meticulously crafted to facilitate a myriad of activities ranging from scholarly discourse and deliberative sessions, to the dissemination of lectures and presentations, alongside provision for multimedia engagement and training endeavors. For instance, the Clifton Court Hall within the precincts of the University of Cincinnati’s College of Arts and Sciences exemplifies a pivotal nexus for scholarly dialogue and communal interaction, fostering an array of communal and collaborative zones alongside dedicated team rooms (Bennett, 2001) [
2].
Against the backdrop of burgeoning higher education pursuits in developing nations, the exigencies placed upon academic lecture halls within university settings have witnessed an augmenting trajectory, both in terms of functional efficacy and spatial magnitude [
3]. In China, in particular, it has been seen that the construction of lecture halls has peaked in the last two decades, and much new research has been generated on how to design these venues [
4,
5]. Budiaková [
6,
7] and Zhao Juan [
8] proposed the optimization design strategy of lecture halls from the perspective of ventilation, Chen Xi [
3] proposed the design guidance for academic lecture halls in universities from the perspective of environmental design, and Huang Hui [
9] kept eyes on the topic of the spatial design of lecture halls. However, in recent years, the number of publications in this field in China has been decreasing year by year and this topic is seemingly getting less attention than before (see
Figure 1 below). In an era of rapidly changing materials and technologies, the reclaiming of the academic lecture hall is an issue that needs to be emphasized by architectural researchers.
Meanwhile, due to the specific use of lecture halls, most countries have comprehensive or specialized codes designed to guide architects in creating the best acoustical environment in these spaces. These guidelines, such as those outlined by the World Health Organization (WHO, 1999) [
10], the Architectural Institute of Japan (Fukuchi & Ueno, 2004) [
11], the Australian/New Zealand Standard [
12], and the German Institute for Standardization [
13], advocate for high levels of acoustic absorption and short reverberation times to enhance speech clarity within lecture halls. China’s current reference model, GB/T50356-2005 “Code for architectural acoustical design of theater, cinema and multi-use auditorium” [
14], emphasizes these principles in the architectural acoustical design of theaters, cinemas, and multi-use auditoriums.
However, despite the existence of acoustic code guidance, numerous academic surveys and reports continue to find discrepancies between expected and actual results in terms of acoustic performance in these venues. They have emphasized that there is a gap between the expected and actual results in these venues, particularly in terms of acoustic performance, which often falls short of expectations. Nassiri [
15] investigated the background noise levels in university classrooms through a study that was largely substandard, revealing deficiencies in acoustics. Escobar [
16] analyzed the acoustic parameters of a university auditorium and multi-functional conference room and proposed improvements accordingly. Pinho [
17] examined the acoustical performance of school buildings in Portugal, elucidating prevalent issues. Sala and Rantala [
18] investigated acoustics and activity noise in school classrooms in Finland, amplifying concerns regarding ambient noise levels. Ricciardi and Buratti [
19] conducted an objective and subjective assessment of acoustic comfort in classrooms, combining perceived and actual conditions to evaluate the acoustic effectiveness of classrooms. In addition, van den Heuij [
20] evaluated the acoustic effectiveness of academic classrooms through existing acoustic reference levels, pointing out where the existing deficiencies lie. Astolfi [
21] provides a summary of recent developments in classroom acoustics and describes the effects of noise on students and lecturers. However, at the same time, the researcher points out that further research is needed for this complex communication scenario.
Many Chinese researchers have also studied these deficiencies. For example, as a leading expert in this field, Kang Jian [
22] has conducted a lot of research on acoustics in Chinese venues. Xie Hui [
23] emphasizes the importance of the acoustic environment of lecture halls and puts forward the suggestion of improving the acoustic environment of lecture halls by changing the decorative materials and design on a larger scale. Wang Chao [
24] conducted a time-varying analysis of the acoustic effects of very large spaces, especially public transportation spaces. Yan Xiang [
25] specifically took the renovation of the lecture hall of Tsinghua University as an example to explain the dilemma of multi-functional lecture halls and proposed that architectural acoustic adaptive design should be carried out based on more detailed acoustic functional requirements. These mainly provide guidance for the design and remodeling of lecture halls in the institutions of higher education from the technical level, but these high-investment optimization options are relatively difficult to achieve in many areas, with limited referentiality. That is to say, only by the in-depth consideration of the relationship between building renovation and the conditions and needs of the building can we better improve the acoustic performance of the building and promote the introduction of more applicable and reasonable specifications.
The problems that have been pointed out and still exist in the studies above show that a large number of halls have problems with inaudibility and how to improve it in a simpler way. To this end, the authors conducted a questionnaire survey of the academic lecture hall of the School of Architecture and Planning at Yunnan University. It found that 131 of the 200 students surveyed (more than 65%) indicated that they were dissatisfied with the current acoustic conditions. Only 24 students, representing 12% of the sample size, expressed satisfaction.
Therefore, this study takes this hall as an example, which has similar problems. This research uses a combination of experimental testing and computer software simulation to carry out acoustic environment design research through the use of the acoustic simulation software EASE 4.4 digital modeling of the hall. Testing with the material parameters and environmental noise, it analyzes the data on loudness, speech intelligibility, reverberation time, and other indicators. Later, this research studies their structural characteristics and indicate the problems existing in the acoustic environment design of this kind of college lecture hall. Then, the acoustic environment design transformation program is proposed and verified by software simulation to achieve sound quality optimization so that the academic lecture hall can meet the normal use requirements.
2. Overview and Material Test
2.1. Building Introduction
Yunnan University at college town located in Chenggong New City Area accommodates over 20,000 students and staff, with a total construction area of about 1,029,000 square meters. However, the fact that most of them are located in mountainous areas means that the buildings have to be relatively compact. The multi-functional use of space became inevitable. The academic lecture hall, situated within the School of Architecture and Planning at Yunnan University, on the inside of the college building, surrounded by sloping land, was finalized in 2010.
It was primarily serving as a venue for conferences, academic discourse, and student engagements. It spans approximately 24 m in length, 16.8 m in width, and boasts a net height of 8.1 m in architectural design dimensions. The hall occupies a rectangular footprint encompassing 403.2 square meters, with a volumetric capacity of around 2857.68 cubic meters. It accommodates a total of 302 seats, averaging 9.46 cubic meters per seat. Notably, the hall features a length of 18 m accessible to the audience (of a total of 24 m), with seating arranged in a tiered fashion, comprising 12 rows and 3 columns (13 rows in the central column), each row accommodating 24 seats, incrementally elevated by 0.1 m.
To mitigate potential noise disruptions, the lecture hall strategically aligns with the eastern courtyard of the college, ensuring minimal interference with daily instructional activities. Accessible through the ground floor main entrance of the college, a passageway connects the hall to the college atrium, while a rear entrance facilitates ingress and egress directly to the lecture hall (see
Figure 2c).
Generally, the spatial layout of the auditorium is often in the form of theater architecture (rectangular, polygonal, fan-shaped, curved, etc.). However, the most important prerequisite for the audience layout in the academic lecture hall is to ensure clear vision and clear sound at the same time. Therefore, there are few balcony seats in the academic lecture hall, and the spatial form of the auditorium has some little changes. Different from professional opera houses, etc., due to many constraints such as land scarcity and financial constraints, the use of a relatively simple rectangular plane is the strategy currently widely used in such places. The sound nature of the lecture hall is mainly electro-acoustic (a combination of microphones and speakers), and the sound propagation is optimized based on the internal decoration and the acoustic properties of the materials.
2.2. Software Introduction
We used EASE 4.4 digital modeling software to model the lecture hall. In this software, buildings can be constructed as a 2D surface using line elements firstly. These 2D surfaces can then be extruded to create a 3D model. Additionally, the software allows us to match materials from its library to the corresponding materials in the 3D model. Then, we analyzed the building by EASE (a software developed by Ahnert Feistel Media Group, Berlin, Germany), which is widely used in electro-acoustic simulation. The material library of EASE is complete and can be converted with other software file formats.
The sound effect of the hall is related to the shape of the material, etc., and the basic status quo of the hall can be simulated by EASE to obtain the relevant situation of each acoustic parameter. The basic steps of measurement using the EASE 4.4 are as follows: 3D modeling, inputting acoustic parameters such as sound-absorbing materials, and then outputting acoustic parameters such as speech intelligibility [
26].
Before the data analysis of loudness, reverberation time, speech intelligibility, and other indicators, according to the above design drawings and measured dimensions, first of all, the academic lecture hall were modeled [
27]. We set the main structure of the lecture hall walls, columns, and other structures according to the previous CAD computer-aided design drawings of the plan and section; then the indoor stage and seats were input in further detail; finally, the corresponding materials were given to the lecture hall. Then, the listening surface (bright yellow) was set—featuring blue chairs representing acoustic simulation listening points (receivers), parallelograms delineating listening areas, and red horn patterns symbolizing sound sources within the lecture hall (see
Figure 3).
The model construction entails several other steps (flow chart in
Figure 4):
- (1)
Importing a three-dimensional model into the EASE software 4.4 based on the actual dimensions;
- (2)
Conducting inspections for sound leakage and boundary surface irregularities;
- (3)
Configuring interface absorption coefficients for the model (as detailed in
Table 1, the acoustic absorption index of decoration materials in the academic lecture hall);
- (4)
Implementing stage sound settings corresponding to the lecture theater’s actual BD-H1086 sound usage;
- (5)
Generating sound simulation diagrams.
Figure 4.
EASE software acoustic setting flow chart (taking reverberation time test as an example).
Figure 4.
EASE software acoustic setting flow chart (taking reverberation time test as an example).
Table 1.
Acoustic absorption index of decoration materials in academic lecture hall.
Table 1.
Acoustic absorption index of decoration materials in academic lecture hall.
Name of Material | Frequency/Hz |
125 | 250 | 500 | 1000 | 2000 | 4000 |
1 | Hardwood flooring (WOOD FLR) | 0.20 | 0.15 | 0.10 | 0.08 | 0.08 | 0.05 |
2 | Smooth tile (CORTEGA) | 0.31 | 0.32 | 0.51 | 0.72 | 0.74 | 0.77 |
3 | Empty seats (MTSEAT FAB) | 0.19 | 0.37 | 0.56 | 0.67 | 0.61 | 0.59 |
4 | Audience with thick cushions (PUBLIC TKC) | 0.50 | 0.70 | 0.85 | 0.95 | 0.95 | 0.90 |
5 | A 12.5 mm thick plasterboard with 3 cm backspace (GYP125MM) | 0.30 | 0.20 | 0.05 | 0.02 | 0.02 | 0.02 |
6 | A 90/15 mm wood grid with 6 cm backspace (WOOD GRID1) | 0.10 | 0.36 | 0.99 | 0.99 | 0.50 | 0.35 |
7 | Dual pane glass (WINDOW DP) | 0.25 | 0.10 | 0.07 | 0.06 | 0.04 | 0.02 |
8 | Soundproof solid wood door (DOOR HOLLOW) | 0.15 | 0.10 | 0.06 | 0.08 | 0.10 | 0.05 |
9 | Perforated Plate (PERFPANEL1) | 0.78 | 0.58 | 0.27 | 0.15 | 0.04 | 0.12 |
2.3. Material Acoustic Performance Testing
2.3.1. Introduction to Material Distribution Location
In terms of the overall environmental material settings, the following configuration is adopted (see
Figure 5). The academic lecture hall incorporates a highly sound-absorbing structure on both the back of the stage and the rear wall of the auditorium, effectively reducing sound focus, echo problems, and microphone feedback. This design choice also serves to reduce reverberation time and control unwanted echoes. The use of environmentally friendly E1 fire-rated A1 grooved wood acoustic panels for the stage back wall and rear side walls further enhances sound absorption and propagation efficiency. Using a standardized modular design and slot-and-keel construction, these panels facilitate optimum sound transmission within the hall (shown as ① in
Figure 5).
In order to meet the requirements for floor noise insulation and vibration damping, the academic lecture hall uses a timber floor layout—with a primary frame structure consisting of 50 mm × 50 mm timber keels spaced at 400 mm intervals. In addition, a comprehensive application of burnt carbon slag sound insulation layer further enhances sound transmission attenuation, thereby optimizing audience perception quality (shown as ② in
Figure 5).
Externally, the walls of the auditorium are constructed of dry-hung stone (the facing stone is hung directly onto the external surface of the building structure, leaving a 40–50 mm cavity between the stone and the structure), which increases structural stability and improves acoustic insulation. To ensure balanced sound dispersion, loudspeakers are strategically positioned on either side of the stage wall and along the center of the side walls, promoting an even distribution of sound pressure throughout the venue. This configuration aims to improve the overall listening experience for the audience, providing a comfortable and high-quality listening environment (shown as ③ in
Figure 5).
2.3.2. Sound Absorption Performance Experiment
We selected the decorative materials in the auditorium and determined their sound absorption coefficients in the laboratory. This was followed by a computerized acoustic simulation. EASE’s material editor provides a variety of materials commonly used in rooms, and new sound-absorbing materials can be edited and added as needed. In the simulation, we set the absorption coefficients of the materials according to the specific data measured in the experiment.
The absorption coefficient of acoustic materials is usually determined by the reverberation chamber method or the standing wave tube method [
28,
29]. The aforementioned method is predominantly utilized in engineering measurements; however, owing to its substantial requirement for sample area, the practical sample area frequently falls short of the necessary size, potentially resulting in significant discrepancies in test outcomes. On the contrary, the impedance tube method simplifies the measurement process because it requires a small sample area and the sound wave is incident perpendicularly to the sample surface, and is more suitable for sound absorption coefficient testing in the laboratory [
30]. The sound absorption coefficient tested by this method complies with the national standard [
31] (Acoustics: Measurement of sound absorption in a reverberation room), and is accepted by the EASE software 4.4 material parameter input terminal standard.
In order to determine the absorption coefficient of the auditorium material, we used the AWA62902 standing wave tube equipment set (shown in
Figure 6). For this material testing, we used two sets of tubes to cover the frequency range from 125 to 4000 Hz. Among them, the larger tube specification is Φ96 × 1000 (mm), and the frequency range is 90 Hz~2075 Hz; the smaller tube specification is Φ30 × 350 (mm), and the frequency range is 1500 Hz~6641 Hz.
We first calibrated the sensitivity level using the standard material module to ensure it reads 93.8 dB at 1 kHz. We then installed the samples of different materials (the spatial distribution of the materials is shown in
Figure 7, and the material names are shown in
Table 1) at one end of the standing wave tube, and provided different frequency sound waves in the range of 125 to 4000 Hz to each material through a signal generator. Next, we measured the minimum and maximum values of the sound pressure amplitude in the system, and calculated the absorption coefficient of each material at different frequencies based on the standing wave ratio method. The test results are shown in
Table 1.
2.4. On-Site Measurement Arrangement and Noise Testing
Environmental noise (background noise) is a physical quantity closely related to indoor noise interference. It refers to the sum of environmental noise contributed by other sound sources other than the measured sound source. Conducting this test can test whether the doors, windows, walls, floors, and partitions of the equipment room in the lecture hall have sufficient sound insulation capabilities, and can also test the extent to which the lecture hall is affected by external environmental noise and instrument noise. In this regard, Zhu Peisheng’s [
32] research shows the correlation between reverberation time, background noise and environmental factors, and further strengthens the above view. It is believed that before conducting on-site testing and site acoustic effect simulation, it is necessary to test the indoor acoustic environment, and it is important to understand its impact on the acoustic environment as an irrelevant parameter.
In this paper, the researchers used DT-859B Professional Multi-functional Environmental Test Meter as the measuring instrument, which was newly launched in 2022 to assess the acoustical parameters in the unoccupied condition. We evenly distributed measurement points along one side of the hall at a height of 1.2 m, as illustrated in
Figure 8 (bright yellow schematic surface); the plan and section are shown in
Figure 3. These points were strategically positioned to encompass representative areas such as the front, middle, and back of the audience area, as well as the left, middle, and right sections of the hall. The test results revealed that the highest background noise level recorded at these measurement points in the academic lecture hall was 34.0 dB in pressure level (see
Table 2), aligning with the background noise limits specified in GB/T50356-2005. The acoustic measurement findings affirm compliance with design specifications and the suitability of the venue for its intended use.
Subsequently, the measured average background noise levels were manually inputted into the EASE 4.4, incorporating the background noise sound pressure level for each frequency band.
4. Results and Retrofit Solution
Due to the problem that different types of sound-absorbing materials have different sound absorption coefficients and the update speed of sound-absorbing materials changes with each passing day, this study did not compare the different types of sound-absorbing materials. Instead, computer simulation methods are used to predict the appropriate locations for using sound-absorbing materials and imported into the architectural acoustics software EASE. The acoustic performances are then calculated based on different acoustic parameters such as material and location, to predict the impact on speech metrics where sound-absorbing materials should be placed in the room. From the aspect of reducing the quantity of sound-absorbing materials and thus the proper placing of building materials, a feasible renovation plan is proposed for the indoor acoustic environment of the existing lecture hall.
Kawata [
43] suggested that acoustic materials should be distributed over at least two surfaces of a room to achieve acceptable acoustic conditions for speech intelligibility. Based on previous studies [
44], this experiment applied acoustic materials to the acoustic performance of the rear wall, front ceiling, and rear ceiling. The acoustic absorbing materials were placed and tested in three steps as shown in the following figure (
Figure 13).
Step 1: Sound-absorbing materials with an area of 88.2 m2 were applied to the rear wall (RW), front ceiling (FC), middle ceiling (CC), and rear ceiling (RC) to compare their acoustic performance.
Step 2: Based on the results of step 1, we set the sound-absorbing material on the RW. And 88.2 m2 of sound-absorbing material was applied to FC, CC, and RC, respectively, and the acoustic performance of the three spatial combinations of RW + FC, RW + CC, and RW + RC was compared.
Step 3: Based on the results of step B, we applied sound-absorbing material to RW and CC. Then, we set 88.2 m2 of sound-absorbing material on FC and RC, respectively. We compared the acoustic performance of RW + CC + FC, RW + CC + RC, and the ceiling part (AC = FC + CC + RC).
Through calculation, we found that in step 1, the shortest reverberation time was obtained at RW. In step 2, the method RW + CC obtained the shortest reverberation time. In step 3, the method RW + CC + FC obtained the shortest reverberation time. The current measured values on-site (MEAS) are also shown in
Figure 14.
In summary, we found that the best sound absorption effect is obtained when the sound-absorbing material is applied to the rear wall, followed by the center, front, and rear of the ceiling. Therefore, when limited material updates are being made, the lecture hall should prioritize the use of sound-absorbing materials on the back wall to obtain higher clarity. In terms of multi-position combination arrangements, the combination of rear wall + ceiling center + ceiling front (RW + CC + FC) is the most efficient, exceeding the traditional combination of full ceiling (AC) and full rear (RW + CC + RC). This idea deserves more trials and field research.
5. Conclusions and Discussion
A multi-purpose lecture hall known for its space-saving features faced a flood of feedback about poor acoustic performance. This study takes the lecture hall of the School of Architecture and Planning of Yunnan University as an example to explore the possibility of improving the acoustic environment performance through spatial layout optimization from the perspective of architectural design. Through a combination of experimental testing and computer software simulation, the research deeply explored three key objective parameters for evaluating the sound quality of academic lecture halls: speech intelligibility, loudness, and reverberation time, and summarized the acoustic environment of the academic lecture hall in design problems. According to this, it was found that the main obstacle to the unclear hearing problem reported by students lies in the design and control of reverberation time. Software simulation is then used to determine the optimal location for sound-absorbing material placement, and the reverberation time can be controlled within the range required by the specification while using the better spatial distribution of sound-absorbing materials. At the same time, in conjunction with other optimization methods, strategies to optimize the acoustic environment of the academic lecture hall are proposed to better meet the needs of use.
Nonetheless, there are still several domains that necessitate further refinement. Firstly, despite numerous studies indicating that computer simulations can precisely undertake architectural acoustic investigations, an on-site comparative experiment would constitute a valuable adjunct. However, the implementation of the upgrade project, based on the findings of this study, will require a considerable duration to finalize, thus postponing the before–after comparison until its completion, which constitutes a significant limitation of this research.
Secondly, the activation of numerous electronic devices (e.g., air conditioning and lighting systems) complicates the actual conditions of the venue beyond the ideal scenario. The human body, acting as a sound absorber, and the low murmur of crowds have the potential to skew the actual audience effects derived from the research. It is noteworthy that the volunteers engaged in this study were young students, possibly introducing variations in auditory perception across different demographic groups.
In conclusion, the findings of this study, alongside the results of future investigations conducted within these constraints, are anticipated to serve as a reference for the establishment of regional standards in campus hall acoustic environment design.