What is Active Noise Reduction?

ANR is an electronic means of attenuating lower frequency noise (applicable where passive techniques alone are inadequate) using the principle of anti-noise. Due to ‘the physics’, ANR is most effective below a frequency of 1kHz. It  works best in confined acoustic environments and thus ideally suited for use in a headset earshell. ANR is based on closed loop feedback, whereby a small sense microphone, located in the earshell, detects noise appearing at the ear. The signal is filtered and amplified before being fed back to the earphone to generate an identical acoustic signal that is in anti-phase. This has the effect of cancelling the noise, thereby improving the audio signal. The circuit incorporates a pre-amplifier, feedback filter and drive amplifier. A stability control mechanism is essential for the correct operation of the ANR system in a dynamic environment, for example, soldiers in vehicles moving quickly over rough terrain. 

There are two basic implementations:

• First: a baffle across the earshell that creates a front and a back cavity.,
• Second: the self-contained ANR Module approach.

The module approach benefits by preserving a greater amount of the volume within the earshell, which, in turn, enables a higher level of passive noise reduction to be achieved. Additionally, a module is easier to retrofit to passive earshells on an upgrade or OEM basis.