Airborne (or acoustically transmitted) noise is always present in the aircraft. Depending on the type of aircraft, the noise may be so significant that measures must be taken to reduce it. This may be accomplished through better passive attenuation performance of helmet/earcup, but for the low frequency components, this is not an option. Here, the only solution is Active Noise Reduction (ANR).
Terma's ANR is highly adaptable and does support even the noisiest platforms. This is accomplished via detailed analysis of comprehensive data material, collected from various platforms, prior to designing/configuring the system.
Illustration of Active Noise Reduction
The system improves performance on each of the significant issues which arise from severe noise environments, including:
- Reduction of stress
- Reduction of fatigue
- Reduction of hearing damage risk
- Increased speech Intelligibility.
Stress and Fatigue Reduction
The profile under which aviators and aircrews operate has changed from short missions of a few hours to missions of 8 to 10 hours, depending on mission and aircraft type. Under long duration operations, the need for low frequency hearing protection becomes important to lower the level of stress and fatigue.
Speech Intelligibility improvement
Intelligibility is dependent on the ratio between noise and signal. When the noise component is dominant, the signal needs to increase, and thereby, the overall audio level is increased to something that becomes unpleasant or even potentially damaging to the hearing. Lowering the noise (through ANR) improves the signal to noise ratio and the intelligibility and potentially allows the signal level to be decreased, so an overall audio level within the approved limits is obtained.
As shown in this picture, the ANR system is completely embedded in the earcup and requires no special external boxes or aircraft group-A changes.
Termas ANR Reduces Noise below 1 kHz
Terma's ANR performance is tested in various environments, including the F-16 cockpit. As can be seen from the graph below, where the blue columns indicate a passive attenuation and the red columns indicate the combined passive and active attenuation, the contribution from the active part is present over the frequency range below 1 kHz and is optimized to generate the highest A-weighted attenuation.
Total Noise Reduction
A-weighted performance examples of the Terma ANR system are the F-16 and H-60 noise environments, where the total SPL is reduced to below 78 dBA.
Earcups Versus In-Ear
Terma has selected the strategy of supplying an earcup solution as compared to in-ear, based on feedback from the customer. As compared to in-ear, earcup has the advantage of being much more comfortable, offering low maintenance, and providing a high 3D-Audio performance.
Easy In-Flight Evaluation on any Platform
It is possible to predict the performance of the system on alternate platforms, if a calibrated recording of the cockpit noise environment is available. If not, it is still possible to evaluate the performance of the Terma ANR system in many cockpits, without having to make aircraft Group-A changes. Simply install the ANR enabled earcups in a helmet, and attach the ANR Flight Test kit (a small pilot mountable box with batteries and interface electronics) between the aircraft intercom connector (typically) and the headset. During flight, the ANR can be switched on/off to allow an A/B comparison.