Noise Attenuating Headsets

[Farrell]

I know one of you will be able to clear this up for me.

I have a pair of Bose X nopise attentuating headsets - and they are great at cancelling out all the unwanted noise in the cockpit - especially on props.

However, my question is this - and it probably stems from my lack of knowledge of how the whole system works - Does the gadgetry in the headphones actually reduce the sound, and therefore the potential damage to my hearing......or does it just alter the sound so that i can't hear it.....i can't really word what i'm saying, but hopefully one of you will know what I mean!

[effortless]

If you want to demonstrate how they work, face your hi fi speakers to each other and play summat bassy. Then reverse the connections on one of the speakers. The bass should be considerably attenuated. This is because the speakers are 180 degrees out of phase. That is, when one speaker is moving out the other is moving in, thus the sounds cancel each other out to some extent. Cancelling earphones do something similar in as much as they pick up outside noise and play it out of phase through the speakers. Hence noise cancelling headset. :ok: Of course I may have someone tell me I'm wrong but what the hell. :}

[welliewanger]

Effortless is right. The hifi demonstration is good, although, you'll find that the effect differs depending on where you are in the room. The lower the bass, the longer the wavelength, therefore larger "patches" of destructive interference.

Another example is ripples on a pond. Drop two stones into a pond and when the waves collide they add to each other. Two peaks colliding makes a really big wave (at that point) two troughs make a really deep trough (at that point). ANR tries to guess where your ear is and what the sound wave will be at that point (peak or trough) then it adds the opposite sound.

Oh dear! I'm making it even more complicated!!

Short answer: Yes, ANR does remove the sound around your ears. It's not masking it.