Test chambers and acoustic rooms

Anechoic and hemi-anechoic chambers, reverberation rooms, transmission suites and listening rooms, designed around the test method they have to serve rather than around the room that happens to be available.

• What sets the design is the test method, the interior volume, the working space around the object, the lowest frequency band of interest and the permissible background noise level inside. All five have to be agreed before anything is drawn.
• The low-frequency cut-off of an anechoic chamber is inversely proportional to wedge depth, so choosing a cut-off frequency also chooses how thick every surface of the room becomes.
• High-precision rooms are built as a room within a room, with the inner room on a vibration isolation system calculated for that specific mass and cut-off frequency.
• Wedges are available in foam, fibreglass and perforated metal-faced constructions. The metal-faced type is designed for large facilities that need low-frequency absorption and that have heavy objects moved in and out.
• A fully anechoic chamber normally has a tensioned steel cable floor above the wedge tips with an acoustically transparent catch net beneath it. Where heavy objects have to be supported, a floor grating is used instead.
• Reverberation rooms and transmission suites are the opposite problem: the boundaries have to reflect rather than absorb, and temperature, pressure and humidity have to be controllable.
• A transmission suite is two reverberation rooms back to back with the test specimen in the aperture between them.
• Every one of these is designed for the specific project. There is no catalogue item and no list price.

Where this is specified

• Microphone and sound level meter calibration
• Sound power measurement of machinery for product conformity
• Testing of hearing protectors and audio equipment
• Sound absorption and transmission loss testing of building materials
• Insertion loss measurement of duct silencers
• Hearing research and psycho-acoustic research
• Listening rooms for product sound quality assessment

Standards that define the requirement

• ISO 3744 and ISO 3745 are methods for determining sound power levels in a free field, which is the reason an anechoic chamber is built in the first place.
• ISO 26101 is the method for qualifying acoustic test environments — how a finished room is shown to meet the criteria it was designed to.
• ITU-R BS 1116-1 sets the conditions for listening rooms used to assess small impairments in audio systems.

These are the documents that set the requirement. Naming one is not a claim that a particular supplied item is certified to it; test evidence is issued per project.

Product lines in this family

• Fully anechoic and hemi-anechoic chambers, single and double wall
• Reverberation rooms
• Transmission suites
• Listening rooms for sound quality assessment
• Anechoic wedges in foam, fibreglass and perforated metal-faced constructions
• Isolated floating floor systems, cable floors and floor gratings
• Acoustic doors and windows for test chambers
• Silenced ventilation systems and low-reflection interior lighting
• Refurbishment of existing chambers, including replacement of degraded wedges