Anechoic room is an acoustical experiment room which has walls, ceiling and a floor with high sound absorption coefficient, to realize the acoustically free field. The free field means that like outdoor space, only the direct sound which is radiated from the sound source is observed, without any obstacle for sound propagation. In other words, it is like a white and plain canvas on which we can draw anything with sound.
Therefore, the anechoic room is used for various purposes and the way of using can be expanded infinitely according to the imagination and ideas from engineers or researchers. Historically speaking, the typical usages of the room were to measure the acoustical characteristic of microphone or loudspeaker, to correct the sensitivity of sound level meter, and to measure the sound power level of various kinds of noise sources. Now, in addition to these usages, the purpose of using an anechoic room has been expanded to much wider, like to measure the radiated sound from an automobile or a copying machine, or for the subjective listening test.
We create a complete proposal from design and construction of the anechoic room to the measurement system according to our customer needs.
The specifications of an anechoic room is various, from the panel-made structure to custom-made. The detail of each project is determined after discussion with the customer's objectives and investigation of the environment where the anechoic room will be located. With these processes, we can provide the anechoic room which is suited for the customer's requirements with appropriate cost.
The process of designing is complicated, but the followings are considered as the key points for the specification.
(A) The choice of full-anechoic room or semi-anechoic room
(B) Absorptive layer specification
(A) Full-anechoic room | Semi-anechoic room
There are two types of anechoic room. The first one is "full-anechoic" room, which has the absorptive walls, ceiling and floor. The second one is "semi-anechoic" room, which has the absorptive walls and ceiling, but the floor is reflective.
Generally speaking, the full-anechoic room is mainly used for the acoustical research and development work, the measurement of the acoustical characteristics of the microphones and loudspeakers, and calibration of the measurement system. But the waking floor is grid-shaped, it become harder than semi-anechoic room to setup the measurement object and systems in the room.
On the other hand, as for the semi-anechoic room, it is easy to set up for the measurement because the floor surface is finished hard. But at the time of measurement, we need to pay attention to or take into the account the effect of the floor.
(B) Specifications of the absorptive layer
One of the important performances of the anechoic room is the decay characteristics of the sound pressure level away from the point source. It is widely known as "inverse square law". According to this performance which is required for, the specification of the absorptive layer is determined taking into the consideration of the size of the room, the measurement area and the target frequency. If the lower frequency band is required to measure, the size of room should be large and the absorbing wedge is used generally.
On the contrary, for measuring of relatively high frequency band and the measuring point can be selected closely to the object, we may select the sound absorbing layer without wedge-shaped, taking into the consideration of the cost.
We have made a lot of effort for research and development in the field of measurement and evaluation of acoustic materials, and these results and experiences are used for the interior design of an anechoic room as well.
Full-anechoic room
Semi-Anechoic room
If you are considering the global market, your product should abide by the law or business standard related to noise regulation of the country where you would like to export to. For example, in EU, the EU noise emission directive is become strict year by year.
For example, Germany has an advanced environmental standard called BLUE Angel (DER BLAUE ENGEL). To be certified by BLUE Angel, the office equipment needs to satisfy its sound power level requirements.
As for other equipments, like construction equipment, the evaluation of the sound power level which covers radiated noise from the entire equipment has become more common, than using the conventional sound pressure level measurement.
The measurement of sound power level from a source can be performed in both the full-anechoic room and the semi-anechoic room. But now, the semi-anechoic room is widely used since the measurement in the full-anechoic room is required to place the microphones below the equipment (sometimes it may be under the walking floor). In this case, the microphones are arranged to be surrounded around the machinery, and perform the measurement simultaneously at all measuring point to capture the irregular operating noise. The automatic measurement system using a microphone positioning system can be used to evaluate such noise problem quickly and precisely.
In the industry of electronic manufacturers, the sound quality metrics like loudness, sharpness, etc. which are considered to be included the human auditory characteristics has become popular, adding to the conventional evaluation based on physical characteristics such as sound pressure level, sound power level and so on. The product development become new stage, in which not only "noise" power or sound pressure level reduction physically, but also creating the "sound" which is more comfortable for the customers, taking the auditory perception into the account..
For the similar purpose, in an anechoic room, jury evaluation of operating sound of the product and psychoacoustic listening test are conducted to obtain the relationship between the subjective evaluation and objective characteristics. As well as the anechoic room construction, we provide a consulting service using psychoacoustic listening test with our acoustic listening test system "Shinji".
Recently, the cases which are required to measure or evaluate the very quiet products have been increasing. For example, the following cases are typical ones.
- Noises which AV equipment (like LCD TV) iis operated in silent mode
- Operating noise of the hard drive using iin the PC or AV equipments
- Fundamental research work related to the human auditory
For such case, sometimes ordinary microphone is difficult to use for precise measurement due to its electrical self-noise, therefore the measurement must be made with a special microphone having low self-noise characteristics.
Of course, these anechoic rooms should be designed carefully with excellent sound and vibration proofing structure, and air conditioning system as well. We had an experience to construct the one of nation's best anechoic rooms which is famous for low background noise level less than 0dBA. If you have any problems or questions on such acoustical experiment room, please call us. We can provide you the best service corresponding to your specific needs.
Like the automotive manufacturer needs chassis dynamometer in their anechoic room, the electronic manufacturers need anechoic rooms with special facilities. For example, for an air conditioning manufacturer, the coupled anechoic chamber which can operate and measure both outdoor and indoor unit simultaneously, and the anechoic chamber with special air conditioning system to change the temperature in very short time are required. For such anechoic rooms, many kinds of equipment which produce the serious noise and vibration are usually placed in the surrounding area. To design and build the anechoic chamber in such environment should pay great attention. Even if the request is technically difficult, we offer the anechoic room with high usability, using our company resource and wide network in the industries.
The picture of the anechoic room shows an automatic sliding reflective floor to convert from full-anechoic chamber to semi-anechoic chamber quickly. This purpose is to make an easy set up of the air conditioner system in the room. We can design and set up the customized measurement system and software which can control the testing facilities as well.