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Acoustic Application for Classroom

As teaching methods and contents keep changing, the traditional classroom teaching environment is far from meeting the requirements of modern teaching. In order to increase students' perceptual knowledge, increase the lecture information content, teachers often need to provide colorful pictures, texts, sounds and other information to integrate the students’ vision and hearing. Therefore, the multimedia classroom has become the mainstream in universities construction. However, the creation of sound environment is ignored in the actual construction process, or the effect is not ideal. Sound is a powerful tool, because it is very expressive. Thus, it is necessary to ensure teacher's clear speeches, the fidelity of music and sound effects in the multimedia classroom so as to improve the education quality.

 

The sound environment of college classrooms is crucial to modern education and teaching. It is an effective way to perfectly combine vision and hearing, and help to improve teaching quality and learning efficiency. The sound environment is influenced by many sources, including internal and external sources of noise, interior acoustics, architectural design and sound amplification system that require our long-term and all efforts to create a better sound environment.

 

Interior acoustic factors

According to the indoor acoustics theory, sound sources are transmitted indoors by Direct sound, early reflections and reverberation. The sound transmitted directly by the sound source is direct sound; Early reflections are also called recently reflected. In the sound field, suitable early reflections can enhance the direct sound loudness, improve language clarity. But the sound location will be destroyed so impact speech clearness if there are too much reflection. The reverberation is the sound arrives after the early reflected sound, which is reflected repeatedly by the room interface.

 

Reverberation is the situation that the sound waves keep still when the sound source is stopped due to the presence of reflections. Reverberation occurs where space and obstacles exist. In the classroom, the sound signals from the teacher are reflected by the walls and become strong reverberation. The more reverberation, the more overlapped sound signals, the more difficult for the students to distinguish the sound. Because the reverberation has nothing to do with the classroom environment. So even if the classroom environment is quiet, its impact on the implementation of teaching still exists. Compared to normal people, reverberation adds a further complication on hearing impaired children, making it more difficult to listen and understand. So reverberation processing is an important aspect of classroom acoustics.

 

Appropriate reverberation helps to obtain a sense of space and help to improve the fullness of the sound. While too strong reverberation will destroy the speech clearness. The level of clearness depends mainly on the ratio of the direct sound and the previous reflected sound to the reverberation. For clearer speeches, direct sound and the first two reflections have to be strengthened to be prior to reverberation.

 

When teachers use language to express their teaching content, to ensure the teacher's speech clearness and understandable is the most important. Therefore, the shorter reverberation time is better.

 

In order to build a good sound environment to get the right reverberation time and reduce sound defects, it is an effective method to make use of amplifying system to increase sound pressure and clearness so as to balance the acoustic field. In practical application, reverberation should be modified to adapt to different situation.

 

Sound Insulation Design Code for Civil Buildings GBJ118-2010 Chapter Four made specific requirements for the classroom acoustic indicators

 

Permitted Noise Level


1.1.1    The allowable noise levels of various teaching buildings and teaching aids in school buildings shall comply with the stipulations in the table:

 

Indoor allowed noise level

Indoor allowed noise level.jpg

Note:1. Special quiet requirements room are those for language learning classrooms, recording studios, reading rooms and so on. General classrooms refer to ordinary classrooms for history and geography, science, music, instrument practice, multi media and arts teaching. Rooms without special quiet requirements refers to the gym, dance classrooms, operation  labs, teacher's office and rest rooms.

 

2. When there is a disturbing noise (such as a concert) which will distract the students' attention, the allowable noise level in Table 4.1.1 should be reduced by 5 dB.

Regarding sound insulation and noise reduction design for school buildings near main road, it is better to arrange playground along the main road as a noise isolation belt. And it is supposed to design a sound isolation belt with certain distance between factories and teaching buildings. If the classrooms windows and doors face the playground, the distance between classroom wall and stadium should not be less than 25m.

 

No. 4.3.2 if there is no enough noise reduction measures in teaching buildings, the mechanical equipment that emits strong noise and vibrates is not allowed.

 

No. 4.3.3 Closed corridor in teaching building, hallway and staircase should set the sound absorption coefficient of not less than 0.50 (500 ~ 1000Hz) sound-absorbing material if possible. Or set sound-absorbing material whose sound absorption coefficient not less than 0.30 on the ceiling and wall. The selection of sound-absorbing materials should meet fireproof requirements.

 

No. 4.3.4 Reverberation time of all kinds of classrooms shall comply with the provisions of Table 4.3.4

 Reverberation time of all kinds of classrooms.jpg

Note: 0.1s variation is allowed in the reverberation time table above. 10% variation is allowed for the room volume.

 

No. 4.3.5 Rooms generating noise (music rooms, dance rooms, instrument practice room, gym) shall be divided into special area and treated by noise reduction measures if they are together with other teaching rooms in the same teaching building.

 

 


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