Anechoic room is an acoustical experiment room which has walls, ceiling and a floor with high sound absorption coefficient, to realize an acoustically free field. The free field means like an 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 it 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 a microphone or loudspeaker, to correct the sensitivity of the 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 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 an anechoic room to the measurement system according to our customer needs.
The specifications of an anechoic room various, from a 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 an 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 absorptive walls, ceiling and floor. The second one is "semi-anechoic" room, which has absorptive walls and ceiling, but the floor is reflective. Generally speaking, the full-anechoic room is mainly used for acoustical research and development work, the measurement of the acoustical characteristics of the microphones and loudspeakers, and calibration of the measurement system. But the walking floor is grid-shaped becomes harder than a 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 the measurement because the floor surface is a hard finished. But at the time of measurement, we need to pay attention to or take into the account the effect of the floor.
(B) Specification of sound 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. The picture is shown the anechoic room in our acoustic laboratory. The room can be converted from a full-anechoic room to a semi-anechoic room, by removing the sound absorbing structure on the floor.
Full Anechoic Room
Semi Anechoic Room
Setting up an anechoic room for a vehicle and the focus is measuring the interior and exterior of the vehicle.
For noise measurement in a vehicle cabin the engine sound, the road noise can be measured and evaluated. Also, the noise contribution analysis of the interior, evaluating the car audio sound quality, examining the voice recognition capability of the GPS car navigational system, etc can be performed. Typical measuring the exterior of a vehicle is the simulated pass-by noise measurement and the door closing sound. Moreover, for example, measuring both the interior and exterior of a vehicle, the experiment of putting the vehicle into a low-noise wind tunnel (the interior specification of such wind-tunnel is similar to the semi-anechoic chamber) to evaluate the wind noise is conducted. Based on a premise, when starting up an engine, it's necessary to install an engine exhaust extraction system and its silencer. We have many experiences of collaboration with other industrial facility suppliers like chassis dynamometer for simulating actual driving and so on. Moreover, we propose beneficial and convenient system software to integrate various measurement instruments. We provide a comprehensive service and consulting for product development for our customers.
During the stage of developing an engine, the engine noise measurement at a test rig is conducted. The typical configuration of an anechoic chamber for measuring the noise from the engine and transmission is semi-anechoic chamber, which as the metallic surface plate for stable setup of the work and has the driving facility for them.
The great care for architectural design is required to avoid the effect of the vibration and the noise from such driving facilities, even if a vast room or excessive absorbing structure on the wall or ceiling may not be required. The proposal to combine the system products of our company such as a noise source identification and visualization system (Noise Vision) is possible.
An anechoic room to evaluate sound insulation performance is located by a Reverberation Room and having an opening to install the specimen between two rooms. In such combined rooms, it is possible to examine the sound insulation performances of assembled parts (components) like doors or floor panels. We can provide a wide ranged proposal including automatic sound intensity measuring system using a microphone traverse equipments (MT series), sound source identification and visualization system (Noise Vision) and so on.