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Anechoic room

What is the anechoic room?

Anechoic Room

An anechoic room (sometimes called as anechoic chamber) is an acoustical experiment room with walls, a ceiling, and a floor featuring extensive sound absorptive finish to realize the acoustically free field inside. Like an outdoor space, the free field means only the direct sound radiated from the sound source is observed, excluding any obstacles for sound propagation. Historically, the typical usages of anechoic rooms were for measuring acoustical characteristics of microphones or loudspeakers, for calibrating the sensitivity of sound level meters, and for measuring the sound power level of various products. Today, in addition to these usages, anechoic rooms are used for a wider variety of purposes, including measuring radiated sounds from automobiles or multifunction printers and copier, or for subjective listening tests.
Nihon Onkyo Engineering creates complete proposals--from designing and constructing anechoic rooms to the measurement systems designed to meet specific customer needs.

Anechoic room design

The key points to consider in the specifications of an anechoic room are as follows:
(A) Selection of full-anechoic or semi-anechoic room
(B) Determination of sound absorptive fitting

(A) Selection of full-anechoic or semi-anechoic room

There are two types of anechoic rooms. The first is the "full-anechoic" room, which has absorptive walls, ceiling, and floor. The second is the "semi-anechoic" room, which has absorptive walls and ceiling, but the floor is reflective. Generally, the full-anechoic room is mainly used for acoustical research and development work, for measurement of acoustical characteristics of microphones and loudspeakers, and for calibration of measurement systems. On the other hand, with a semi-anechoic room, the reflective floor means the acoustic effects of the floor must be considered and taken into account during measurement.

(B) Determination of sound absorptive fitting

If measurement of the lower frequency band is required, the size of the room should be larger, and the sound absorptive fitting generally should be sound-absorbing wedge with a high sound absorption coefficient down to the low frequency range. On the contrary, when measuring a relatively high frequency range and when limited to the close measurement with the measuring objects, the absorptive fittings can be simplified.
Nihon Onkyo Engineering has dedicated significant effort on research and development in the field of acoustic material measurement and evaluation. The outcomes of R & D works and our experiences are also being used as references for the interior design of anechoic rooms. The picture shows the anechoic room in our acoustic laboratory, which can be converted from a full-anechoic room to a semi-anechoic room by taking away the sound-absorbing fitting on the floor.

Anechoic rooms for setting up vehicles (Vehicle anechoic room)

Anechoic room for a vehicle

There are two types in the vehicle anechoic rooms, for either vehicle interior or exterior measurements.
The interior measurements is evaluating the engine noise and road noise in the vehicle cabin and can also be used for noise contribution analysis of sound packages, evaluation of the car audio sound quality, for evaluating the voice recognition capability of the system, and so on. Typical exterior measurements are used for simulation of pass-by noise measurement and for evaluation of the door closing sound. Another example for measuring both the interior and exterior of a vehicle is the wind noise measurement in a low-noise wind tunnel.
If the measurement is conducted during the engine operating, installation of an exhaust system with low noise operation is necessary. Nihon Onkyo Engineering has many experiences collaborating with the air-conditioning suppliers and other test facility suppliers including plans for installing a chassis dynamometer in the room to simulate actual driving conditions and plans as part of low-noise wind tunnel.
Our wide-ranging services include suggestions for easy-to-use system software that integrates various measuring instruments as well as consultations for furthering product development by customer.

Anechoic room for evaluating sound insulation performance

Anechoic rooms for evaluating sound insulation performance are located adjacent to a reverberation room and include an opening between these rooms for attaching the specimen to evaluate. Such coupled rooms can be used for the material testing as well as sound insulation performance evaluations of assembled parts (components) like doors, floors, and dash panels with silencer. As for measurement systems, Nihon Onkyo Engineering can propose various systems that include a microphone positioning system for automatic measurement of the near-field sound intensity, the Noise Vision sound source identification and visualization, and other systems to meet customer needs.

The opening for sound insulation measurement / Evaluation of assembled component
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