Reverberation room is a room for acoustic experiment which is used to evaluate the sound absorption coefficient and the sound transmission loss of acoustic material. It has reflective walls, floor and ceiling to realize the conditions of the diffuse sound field approximately within limited space. In the reverberation room, the energy of the sound travelling from various directions, the reverberation time is extremely long, and sound pressure level distribution is almost uniform.
The following three points are the major purpose of using a reverberation room. But recently, the reverberation room is sometimes used to evaluate the sound insulation performance of automobiles.
(1) Measurement of the sound absorption coefficient by reverberation room method of the acoustic material
(2) Measurement of the sound transmission loss of the acoustic material
(For this purpose, either the coupled anechoic room and reverberation room, or coupled two reverberation rooms, which has an opening in between two rooms for setting up a test specimen is required.)
(3) Measurement of the sound power level of various machineries
We can offer a comprehensive proposal from the design/construction of the reverberation room to the measurement system.
In ISO 140-1, although the word "reverberation room" or "reverberation chamber" cannot be found, the designing guide to build the experiment room is provided. The summarized important points are followings.
(1) Appropriate room volume related to the target frequency band
(2) Appropriate room shape and diffuse equipment to realize the diffuse sound field
(3) Extremely small averaged sound absorption coefficient of the room
(4) Extremely low background noise level
The important ones among these are the volume and the shape of the room. Generally, lower the required frequency band is a bigger reverberation room is required. As for the shape, a chamber with irregular shape, leaning walls and ceiling has been widely used, but now, a rectangular shaped reverberation room can be designed and used, with appropriate room size ratio, equipping the diffusers to compensate the diffuseness at high frequency, and equipping and low frequency absorbers to eliminate the effect of low frequency room acoustic modes.
We have a lot of experience and achievements from concrete-made ones, to ones made of panels which are light-weight and easy to build even in a place where heavy structures cannot be built on. As well as the anechoic chamber needed for measurement of the sound transmission loss, we are ready to offer you proposals according to the requirements.
Currently, the automotive industry is trying to use materials with appropriate transmission loss and sound absorption coefficient to the proper parts, to provide a comfortable and quiet cabin for their customers. However, the measuring standard of the sound absorption coefficient by reverberation room method such as ISO 354 or JIS A1409, and the sound transmission loss such as JIS A1416, are supposed to evaluate relatively large sample such as the building materials for construction. For example, like automotive interior materials, it is difficult to follow such standards because of the difficulties to produce large samples in the factory. To evaluate small samples, using a small reverberation chamber is the best and makes sense, but without any experiences, many technical problems may be encountered during the measurement including the instability of measurement result.
We have developed various ideas, devices, and techniques to improve the sound field that can be applied for small reverberation room measurement, to evaluate the acoustic performance of small samples as precisely as possible. Furthermore, we have examined the measurement system well and minimized the instability of measurement result that is sometimes observed in a small reverberation room as much as possible.
We have many years of experience in setting up measurement system both the sound absorption coefficient by reverberation room method which is in a reverberation room only, and the sound transmission loss evaluated in coupled reverberation room and anechoic room.
Recently, besides testing the material, a sound insulation performance is evaluated on components assembled from several parts like the door, floor panel or dash panel.
In these cases, a large-scaled coupled reverberation room and anechoic room is required compared to the material test only. Regarding a measurement system, we can make a variety of proposals that includes the automatic measurement of near-field sound intensity using a microphone positioning system, and weak parts or area identification of sound insulation using the sound source visualization system Noise Vision.
Another purpose of using a reverberation room in the automobile industry is to evaluate the sound insulation performance of a vehicle. A special characteristic of a reverberation room is that the sound pressure level inside it is almost uniform. When the vehicle is placed in the reverberation room, the sound pressure level around it would be almost uniform and the weak point of the sound insulation of the vehicle can be identified within a short period of time from the measurement inside it. Using Noise Vision, our sound source identification and visualization system is the most suitable for this measurement.
