Anechoic chamber

A (sound ) Anechoic chamber ( colloquially anechoic chamber ) is a special acoustic laboratory space, the room surfaces are such that it is almost no sound is reflected.

Because of the resulting special properties of the sound field enables or facilitates such a space different acoustic investigations and certain sound recordings.

Anechoic room surfaces

The minimization of the sound reflected from the walls and the ceiling is achieved by covering with absorbent material, usually glass or mineral wool is used. In these materials, the energy of the impinging sound energy is converted into heat. The withdrawal of energy can take place only by the friction of moving air. This means that the particle velocity must be greater than zero. This is, depending on the frequency, in a certain distance from the concrete wall of the chamber at a maximum. To porous material must then be located at this point, to dampen the corresponding frequency optimal. To achieve very complete sound absorption, has a wide frequency range as possible correspond to the acoustic impedance to that of the air. The purpose of the construction of the lining of individual wedges of absorber material. Depending on the intended deepest absorbing frequency, such a lining with wedges considerable depths (eg 1.50. M) reach. To prevent sound reflections to the floor, and the lower chamber boundary surface must be designed sound absorbing. Thus, the space is still well accessible, a grid floor or a strong toughened wire mesh is installed in such a space, for example. To minimize effects due to interference noise from the surroundings of the room, the walls are often additionally provided with a sound insulation or built the space for vibration isolation even on a separate foundation as a " house within a house ".

Sound field

The absence of reflections on the walls, the ceiling and the floor, the sound field corresponds to the outdoors at a great height above the ground (free field). It is the law of distance and thus a fixed relationship between the sound power of a noise source, and the effective value of the sound pressure at a certain place at a known distance. In addition, the light emitted from a sound source sound pressure signal from the space -time is not affected. These two properties of the sound field allow the use of space for various acoustic tests and recording.

Areas of application

One application of anechoic rooms is the determination of the sound power level of equipment, machinery and vehicles. This is determined from measurements of the sound pressure level of an envelope surface around the sound source, the sound power. In addition, such spaces for the calibration of measurement microphones and other electro-acoustic transducers are used. In this case, inter alia, the transfer function and the directional characteristics of such transducers can be determined. An anechoic chamber is also necessary for measuring head-related transfer functions HRTFs. Through the establishment of a number of speakers in an anechoic chamber to a Abhörpostion around sound fields can be generated artificially. For both experiments for sound perception are possible, as well as the acoustic perceptibility eg concert halls, called auralization.

Another application area of such rooms are sound recordings for radio plays, features and film synchronization, in which the action takes place outside. Therefore, a low-reflection Studio is part of the usual space of a radio play complex. To achieve each matching sound impressions, also accessible areas with wood flooring, gravel or leaves are present in such spaces. Anechoic rooms for sound recordings are visually appealing design rule than the aforementioned rooms for acoustic measurements.