Anechoic
Definition
Anechoic
Anechoic describes an environment or condition with no sound reflections, creating a free-field where sound propagates as if in infinite open space. Anechoic chambers use deep wedge absorbers on all surfaces to eliminate reflections above a cutoff frequency, enabling precise acoustic measurements without room influence.
An anechoic environment is the gold standard for acoustic measurements because it isolates the direct sound from any room contribution. In a true anechoic chamber, all six surfaces (walls, floor, ceiling) are lined with deep absorptive wedges, typically fiberglass or foam, that absorb over 99% of incident sound energy above the chamber's cutoff frequency.
The cutoff frequency depends on wedge depth. A chamber with one-metre wedges provides free-field conditions above approximately 80 Hz. Below this frequency, the wedges are too short relative to the wavelength to absorb effectively, and the room begins to influence measurements.
Professional speaker manufacturers test frequency response, sensitivity, and directivity in anechoic chambers to obtain data free from room artifacts. These measurements form the baseline specifications published in datasheets. When you measure the same speaker in a real room, reflections add peaks and dips that deviate from the anechoic response.
For field measurements where an anechoic chamber is not available, techniques like windowed impulse response (gating) can approximate anechoic results. By capturing the impulse response and time-windowing before the first reflection arrives, you isolate the direct sound. SonaVyx uses this approach in its impulse response tool, allowing you to examine the quasi-anechoic frequency response of a system in any room.
Hemi-anechoic chambers have absorptive treatment on five surfaces with a reflective floor, simulating outdoor ground-plane conditions. These are common for automotive and industrial noise testing.
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