Anechoic Chamber

An anechoic chamber is a specialized acoustical space designed to provide a free-field environment, where sound waves propagate without reflections or external noise interference. Functioning much like a precision acoustic measurement instrument, it allows for accurate testing of sound sources and receivers under highly controlled conditions.

Free-Field Conditions

In an ideal free-field, the inverse square law applies perfectly:

Sound pressure level decreases by 6 dB for every doubling of distance from a point source.

To achieve this, all surfaces must exhibit near-perfect sound absorption, with an absorption coefficient close to 1.0 at all angles of incidence. While a true free-field is physically idealized, well-designed anechoic chambers approach this standard with minimal deviation.

Construction Considerations

Creating a high-performance anechoic chamber involves careful design across acoustic, mechanical, structural, and electrical domains. Key elements include:

• Anechoic Wedge Design & Treatment Selection

• Defined Cut-Off Frequency based on wedge depth

• Ultra-Low Internal Ambient Noise

• Noise Isolation from external environment

• Vibration Control & Mechanical Decoupling

• Silenced Ventilation Systems

• RF Shielding (if electromagnetic compatibility is required)

• Specialized Acoustic Doors & Cable Routing

• Floating Floors or Walkways with Gratings

• Dedicated Lighting & Power Systems

For optimal performance, anechoic chambers are often constructed as standalone structures, isolated from host building walls and foundations to eliminate structure-borne noise transmission.

Noise & Vibration Isolation

One of the critical features of a functional chamber is its ability to block external noise effectively. This typically requires:

• Single or Double-Wall Construction

• Specialized Vibration-Isolated Mounting Systems

• Decoupling Elements to prevent structure-borne transmission

Such isolation ensures that internal background noise remains below testing thresholds, preserving measurement accuracy.

Anechoic Wedges

A practical and widely used method to simulate a free-field is to apply wedge-shaped acoustic absorbers to interior surfaces. These wedges:

• Gradually change acoustic impedance, allowing sound waves to enter and be absorbed

• Prevent reflections by eliminating hard surface boundaries

• Determine the lowest effective frequency (cut-off), which is inversely related to wedge depth

To maintain consistency, tight statistical quality control is implemented during manufacturing, ensuring that all wedges meet acoustic performance standards.

Applications of Anechoic Chambers

• Acoustic testing of loudspeakers, microphones, and transducers

• Measurement of noise emissions from mechanical or electronic devices

• Psychoacoustic experiments and product sound design

• Research and development in automotive, aerospace, and consumer electronics industries