Active Noise Reduction

Active Noise Reduction

Comparing Headset Technologies. The Two ANR’s – Active Noise Reduction vs Adaptive Noise Reduction

How Noise Cancellation works

ANR systems are affected not only by the type of noise it is trying to cancel but also by the size and type of the anti- noise speaker, which means that not all ANR systems are created equal and some ANR systems on the market may not do nearly as well as a simple good passive earplug (standard non-electronic earplug) with a high dB rating.

 

ACTIVE NOISE REDUCTION

Active Noise Reduction (ANR), also known as Active Noise Control (ANC) has been around since 1934, with its first commercial applications in helicopters and airplanes in the 1950s. Needless to say the technology is old and there are newer technologies, such as Adaptive Noise

Reduction (discussed later), that are more advanced and effective. ANR uses a microphone to pick up a constant noise and then replays that noise inverted (180 degrees) through a speaker, so that the peaks

and valleys of the sound effectively cancel each other out. See FIG.1. This process is called interference and phase cancellation. It is important to note that ANR can only attempt to cancel constant noises without a variable frequency, which means for example that gun shots or wind cannot be affected by the ANR system and that engines that accelerate and decelerate are not effectively cancelled either. ANR is

also is not a full spectrum anti-noise solution and the best systems on the market will only work between 20Hz and 500Hz, whereas human hearing is generally accepted to be 20Hz-20,000Hz, this leaves a large

gap in the frequency spectrum where ANR does nothing. The absolute best ANR on the market provides about 10 decibels (dB) of noise reduction in the low frequencies (20Hz-500Hz). This system is an  earmuff/earcup style headset and not an in- ear style headset. The muff allows for more room to have a larger speaker to produce the inverse anti-noise. A larger speaker with a soft diaphragm produces the best low frequencies and enables a Resonant Frequency (Fo) in the range of ANRs frequency sweet spot (20Hz-500Hz). Fo is the speakers natural resonance.

 

ANR IN PRACTICE

Let’s say that an in-ear headset on the market has a passive noise reduction rating (NRR) of 22dB and this same system also boasts an ANR system. If we infer that that the ANR system produces an extra 6dB of noise reduction, we have a total noise reduction of 28dB, however that will only be 28dB where ANR is effective which is below 500Hz, leaving the rest of the spectrum at 22dB. It is important to note

that NRR ratings are an average and at specific frequency ranges there may be less or more attenuation.

ANR CONS

  • Only works in low frequencies (20hz-500hz) human hearing is 20Hz-20,000Hz, and therefore most of the spectrum is un-protected (potential hearing damage outside ANR spectrum)
  • Hissing sound caused by ANR circuitry
  • Potential dizziness, light headedness or headaches caused by ANR frequency manipulation
  • Large power draw
  • Is a fixed solution and can only process audio in the fashion the circuit was designed (not adaptive)

ANR Pros

  • Can help alleviate fatigue from exposure to low constant noise (originally intended for pilots)
  • Increase dB protection from constant noise in the low frequencies (only 20Hz-500Hz)

ADAPTIVE NOISE REDUCTION

Adaptive Noise Reduction is a true full spectrum noise reduction technique that is managed by an algorithm that adapts to the users environment. This system can only be implemented when there is more than one microphone per side for the talk-through/hear- thru system. Threat4`s Talon has two (2) mics per side for a total of four. In an Adaptive Noise Reduction system one mic is used as the primary mic and the second as a reference mic. In a noisy environment, both microphones receive noise at a similar level, but the primary mic compares that constant noise that the secondary mic hears, and subtracts the noise. This means that most of the unwanted noise is cancelled while the desired sounds (human vocals) are retained. The net effect in this type of system is the removal of noise found anywhere in the spectrum from 20Hz to 20,000Hz while being tuned for human vocals. A good Adaptive Noise Reduction system can remove 12dB of noise in the entire spectrum. When coupled with a good passive earplug, this can greatly reduce all unwanted noises no matter what frequency they fall in. To put this into practice: if a passive earplug provides a 32dB decibel reduction on average, you can add on up to an additional 12dB of hearing protection with Adaptive Noise Reduction on. Since Adaptive Noise Reduction is not using noise to cancel noise, but rather just does not replay the unwanted noise, there is no risk of ill effects on the body, yet the pros of a traditional ANR system remains.

Threat4’s TALON uses Adaptive Noise Reduction in Mode 3. Headset can also be muted so that only passive plugs and radio audio works in Mode 2.

 

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Categories: Headsets, Hearing Protection, Learning Centre, Military

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