Classroom acoustic design scheme

Classroom acoustic design is an extremely important part of the educational environment, which directly affects the learning effectiveness of students and the teaching quality of teachers.

A good acoustic design scheme can effectively improve the acoustic environment of the classroom, enhance the listening effect and focus of students, and also enhance the sound transmission effect of teachers, making teaching more vivid and effective.

Firstly, there are many factors that need to be considered in classroom acoustic design, including the size, shape, materials, and furniture placement of the classroom.

When designing a classroom acoustic scheme, it is necessary to fully consider these factors to ensure the effectiveness and feasibility of the acoustic design scheme.

In addition, it is necessary to consider the functional requirements of the classroom, such as the need for multimedia teaching, music performances, etc., which will have an impact on the acoustic design scheme.

Common acoustic defects in classrooms

（1） Excessive reverberation time

Reverberation time is the most important factor affecting the classroom sound environment, and appropriate reverberation time can make the information received by students clear and accurate,

Excessive reverberation time reduces language clarity, affects students' reception and understanding of information, leads to distraction, and reduces learning efficiency.

At present, the walls and ceilings of most classrooms have a large white surface, and the floor is covered with ceramic tiles. These types of walls are relatively hard, with strong sound reflection, and their sound absorption coefficient is generally only 0.01-0.05.

The curtains are ordinary fabric curtains with a low sound absorption coefficient. Large space and strong reflection result in a long reverberation time, usually above 1.3 seconds.

As shown in Table 1, the volumes given by different countries in 200m ³ The recommended values for indoor reverberation time in the following classrooms are:

教室作为语言交流场所，其听闻环境最直接的评价参量是语言清晰度。

结果表明：在高信噪比条件下，体积不超过200m³的教室中频混响时间控制在0.6s左右室内听闻效果最佳。

Secondly, the acoustic design scheme needs to consider the propagation of sound at different frequencies in the classroom.

Generally speaking, low-frequency sound is prone to resonate in the classroom, while high-frequency sound is prone to reflection.

Therefore, corresponding measures need to be taken in acoustic design schemes, such as using sound-absorbing materials to reduce resonance, using acoustic panels to reduce reflection, etc., to ensure that the acoustic environment in the classroom meets the requirements of learning and teaching.

In addition, the classroom acoustic design scheme also needs to consider the noise control inside the classroom.

In modern society, noise pollution has become a serious problem, and classrooms, as places for learning and teaching, need to maintain a relatively quiet environment.

Therefore, in acoustic design schemes, it is necessary to consider how to reduce external and internal noise, such as using soundproofing materials, installing soundproofing windows, etc., to ensure a quiet environment in the classroom.

Acoustic design basis

Design and testing methods and technical standards:

a. GB/T 50121-2005 "Evaluation Standard for Building Sound Insulation"

b. GB/50118-2010 "Code for Design of Sound Insulation in Civil Buildings"

c. GB/50352-2005 General Principles for Design of Civil Buildings

d. GB/T 50356-2005 "Code for acoustic design of theaters, cinemas, and multi-purpose halls"

e. GB/T19889.5-2005 "Acoustics - Measurement of sound insulation in buildings and building components - Part 5: On site measurement of air sound insulation in exterior wall components"

f. GB/T19889.4-2005 "Acoustics - Measurement of sound insulation in buildings and building components - Part 4: Field measurement of airborne sound insulation between rooms"

The definition of acoustics referred to here is:

• Noise control (sound insulation)

Vibration control (isolation)

Indoor sound field (Jiansheng)

Classroom acoustic design scheme

1、 Indoor Sound Field Design

To ensure sufficient sound level and appropriate reverberation time in the classroom (around 0.6 seconds for small classrooms and 1 second for classrooms with 500 people), the volume of each classroom and lecture hall should not exceed 3-3.5 meters ³。 Focus on designing the following indicators:

1. Appropriate reverberation time

2. Sufficient loudness to ensure that a moderate amount of sound can be heard at various locations indoors

3. The indoor sound field should be uniform, and the unevenness of the sound field should be within ± 4dB.

4. No obvious acoustic defects.

（1） Reverberation time control

The classroom is an acoustic space mainly focused on language, so the clarity of language is very important.

The clarity of language is related to the length of reverberation time and the magnitude of loudness. When the loudness is constant, the shorter the reverberation time, the higher the clarity.

But the reverberation time is too short and the sound lacks fullness, so generally speaking, we control the mid frequency reverberation time of small and medium-sized classrooms to about 0.6 seconds.

Reverberation time of 500Hz-1000Hz in various classroom empty spaces

When the volume is constant, the length of reverberation time is inversely proportional to the total indoor sound absorption. So we need to increase the total indoor sound absorption to achieve the goal of reducing reverberation time.

A typical classroom can use sound-absorbing materials such as wooden perforated sound-absorbing boards, polyester fiber sound-absorbing boards, and perforated gypsum boards. At the same time, materials such as sound-absorbing curtains, sound-absorbing decorative paintings, and sound-absorbing pendants can be used to increase sound absorption.

For staircase classrooms, strong sound-absorbing materials such as AGG sand absorbing boards, fiberglass boards, or wood fiber boards can be used at the back end to avoid acoustic defects.

（2） Design of Sound Field Uniformity

1. The main issue with classroom sound field uniformity is the difference in sound pressure levels between the front and rear rows. It is necessary to fully utilize the early reflected sound transmitted from the ceiling and side walls to improve the rear row loudness, and improve uniformity through diffusion reflection processing.

Tilting the ceiling above the podium and both sides of the podium can effectively reflect the teacher's voice into the classroom and back seats. Using geometric acoustics, the tilt angle of the reflection surface can be determined.

2. Reasonable use of sound reinforcement equipment can also greatly solve the problem of uneven sound field. In the classroom, the speaker can be aimed at the student area, and it should be avoided to install the speaker in the corner area.

3. When the classroom area is large, a fan-shaped classroom is generally used for short visual distance, good perspective, and direct sound transmission, which is commonly known as a stepped classroom.

Due to the large number of seats in a fan-shaped classroom, the length is generally greater than 10m. It is best to raise the seats and create a stepped shape to avoid absorption of direct sound by students in the front and middle rows, and to increase the power of direct sound in the rear.

As shown in the figure, the way to slope is to make the floor into a stepped staircase, and a large slope is beneficial for improving both the acoustic and visual environment.

（3） Acoustic defect treatment

Acoustic defects and solutions:

1. Echo: When the time difference between direct sound and reflected sound exceeds 50ms, it is called echo. If a wall surface exceeds 8.5m, it may produce echo.

The method to eliminate echoes is to apply sound-absorbing treatment to the narrower wall of the room or create a undulating (diffuse) pattern on the surface of this wall.

2. Trembling echo: Trembling sound is caused by multiple reflections between parallel walls, which causes the afternotes of the sound to sound somewhat trembling.

The solution is to first avoid using strong reflective materials on both sides of the parallel wall or creating a diffuse reflection on one side of the wall. Alternatively, one side of the wall can be tilted at a certain angle to change the parallel propagation path.

3. Resonance (standing wave): In building sound, standing waves in a room always exist. The simplest way to eliminate standing waves in a room is through the irregularity of the room, which means that the four walls do not exhibit strict proportions and parallelism, which is difficult to achieve in school classrooms.

Adding irregular items such as wall decorations or bookshelves and tilting the rear blackboard at a certain angle can change the reflection characteristics, reduce standing waves, and also help suppress vibration echoes.

二、 Classroom sound insulation

Noise interference is a prominent problem in certain classrooms near noise sources, and continuous or sudden noise interference can affect the pace of teacher lectures and affect student attention.

The most common sources of noise encountered in classrooms are traffic noise near schools, sudden honking or mechanical vibrations, noise from playground activities, footsteps and conversations in corridors, and noise from adjacent classes.

According to the Code for Design of Sound Insulation in Civil Buildings, the allowable noise level limit in ordinary classrooms is ≤ 45dB, and the weighted sound insulation between classrooms is ≥ 40dB.

For noise control, there are two methods: controlling the noise source and cutting off the propagation path.

（1） Noise source control

1. Corridor noise: Lay elastic flooring in the corridor to reduce the noise generated by footsteps; Install thin plate resonance sound-absorbing structures or polyester fiber sound-absorbing boards in the corridor, combined with mineral wool board sound-absorbing ceilings to reduce noise.

2. Noise from mechanical equipment such as fans: Mechanical equipment that generates significant noise and vibration is subjected to vibration reduction and vibration reduction treatment, and vibration propagation is reduced through decoupling with shock absorbers; Reduce the airborne transmission of noise through sound barriers or soundproof rooms.

（2） Control of noise propagation pathways

For noise that cannot be controlled from the source, the impact of noise on teaching can only be controlled by increasing the sound insulation of the classroom itself to cut off the transmission path.

1. Sound insulation of doors and windows: The reason why doors and windows have poor sound insulation is because they belong to lightweight components, and their surface density is generally much smaller than that of walls.

At the same time, the gaps around doors and windows are also an important way for sound transmission. Therefore, the key to improving the sound insulation of doors and windows is the material of the doors and windows themselves and the treatment of the gaps around them. Replacing professional soundproof doors and windows can solve the problem once and for all.

According to the law of mass, doubling the surface density of components increases the sound insulation by 6dB. The design of soundproof doors should use materials of different materials stacked together, which is beneficial for reducing resonance frequency and improving sound insulation;

The door joint treatment should ensure close contact between the door and the frame, as well as between the door and the ground, without forming any gaps.

The sound insulation of windows mainly depends on the number and thickness of glass layers, as well as the sealing degree between window sashes and frames.

The more layers and thickness of glass, the larger the cavity between the glass, the higher the sound insulation, and the better the insulation performance.

Elastic material pads can be used around glass gaps to reduce vibration and noise transmission.

In summary, the acoustic design scheme of the classroom is an extremely important part of the educational environment, which directly affects the learning effectiveness of students and the teaching quality of teachers.

A good acoustic design scheme can effectively improve the acoustic environment of the classroom, enhance the listening effect and focus of students, and also enhance the sound transmission effect of teachers, making teaching more vivid and effective.

Therefore, in the implementation of classroom acoustic design schemes, it is necessary to fully consider the characteristics and functional requirements of the classroom, and take corresponding measures to improve the acoustic environment of the classroom to ensure smooth learning and teaching in the classroom.