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As far as reducing hearing loss, ANR does not help as the wave lengths of noise are still hitting your eardrum but the anr system transmits the opposite wavelength thus you brain does not register a "new" noise.

 

Sorry Skully, I was with you right up until here. ANR reduces hearing loss exactly because of the phenomenon you describe (initially): the system generates an opposite signal which cancels (to the best of its ability) the original noise by destructive interference. It's not a case of the system doubling the amount of sound waves coming in, just in a clever way that tricks your brain... the system is physically reducing the strength/amplitude of the incoming sound the same way that 2 wave patterns crossing in water will produce flat spots where they oppose.

 

I expect the reason it doesn't work for some people, or seems to make things worse even, is that the system is not perfect and/or is not applied properly. It boil down to a microphone picking up all the noises coming in and then a computer chip decided which noises to cancel and how, so it obviously won't work with sudden or randomly fluctuating noises. But that's why it works so well with steady noises like airline cabins etc, though I can't account for the difficulty with turbines... maybe you're right and the frequency is just too high for the system to a) pick up, or B) produce a low enough tone to effectively cancel.

 

Anyway, that's just me armchair-scientisting... I could have forgotten a thing or two since 1st year physics hahaha.

 

I'm going to be lazy and cite wikipedia:

 

http://en.wikipedia.org/wiki/Active_noise_control

"A noise-cancellation speaker emits a sound wave with the same amplitude but with inverted phase (also known as antiphase) to the original sound. The waves combine to form a new wave, in a process called interference, and effectively cancel each other out - an effect which is called phase cancellation.

Modern active noise control is generally achieved through the use of analog circuits or digital signal processing. Adaptive algorithms are designed to analyze the waveform of the background auralor nonaural noise, then based on the specific algorithm generate a signal that will either phase shift or invert the polarity of the original signal. This inverted signal (in antiphase) is then amplified and a transducer creates a sound wave directly proportional to the amplitude of the original waveform, creating destructive interference. This effectively reduces the volume of the perceivable noise."

But Iceman's link covers it well too

 

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I would depend upon the type of helicopter you are flying as to whether or not it makes sense to purchase. The anr systems work wonderfully for piston engines. The do not work so well with high freq

ANR actually Does prevent hearing loss. It's not the best if you hang your head out all day, otherwise it's worth every penny.   Occupational Health and Safety article http://ohsonline.com/Articles

Here's a picture of the compressor...i suspect there was a sound when this happened.

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I can't account for the difficulty with turbines... maybe you're right and the frequency is just too high for the system to a) pick up, or B) produce a low enough tone to effectively cancel.

 

 

Going to correct myself here. High frequency sound is not cancelled out by low frequency sound. But, quoting wikipedia again:

"Active noise canceling is best suited for low frequencies. For higher frequencies, the spacing requirements for free space and zone of silence techniques become prohibitive. In acoustic cavity and duct based systems, the number of modes grows rapidly with increasing frequency, which quickly makes active noise control techniques unmanageable. Passive treatments become more effective at higher frequencies and often provide an adequate solution without the need for active control."

 

... whatever that means :P

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Oh totally. Each person will make their own decision based on their personal assessment of risk of hearing loss vs risk of not hearing an impending failure. Just like every pilot will make his own choice to wear a helmet or not, or a flight suit, or what have you...

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Ya we are getting old Freewheel haha. I wouldn't be so quick to shun ANR though especially like the Bose A20 I use. My hearing has improved in the 2 months I've had it (dont have to crank the TV volume so high) and I am only half as tired as I used to be at the end of da day.

 

As far as hearing the compressor that is still the dominant sound with my ANR (nailed it RE C20R). Next would be the 2 per rev and swish from the blades. I'm certain I would hear a bang from the compressor. I still jump when a pass drops something on the floor behind me. Pretty sure the N1 would drop fairly rapid as a warning, bang or not.

 

Like mentioned earlier the best is to borrow a set and give it a try you might be surprised.

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Oh totally. Each person will make their own decision based on their personal assessment of risk of hearing loss vs risk of not hearing an impending failure. Just like every pilot will make his own choice to wear a helmet or not, or a flight suit, or what have you...

 

Exactly

 

Ya we are getting old Freewheel haha. I wouldn't be so quick to shun ANR though especially like the Bose A20 I use. My hearing has improved in the 2 months I've had it (dont have to crank the TV volume so high) and I am only half as tired as I used to be at the end of da day.

As far as hearing the compressor that is still the dominant sound with my ANR (nailed it RE C20R). Next would be the 2 per rev and swish from the blades. I'm certain I would hear a bang from the compressor. I still jump when a pass drops something on the floor behind me. Pretty sure the N1 would drop fairly rapid as a warning, bang or not.

Like mentioned earlier the best is to borrow a set and give it a try you might be surprised.

To be clear I wasn't shunning ANR; as stated I own a Bose. I just think my point is something that should be considered. I have seen the ANR conversation pop up several times over the years, and it's rarely discussed.

 

The sound of a fire extinguisher hitting the floor (inside the cabin) is something you literally feel through your body. There are many sounds outside the cabin you may not hear. Not all sounds that could indicate an impending failure are a loud bang.

 

FYI I'm not that old...I haven't noticed any significant hearing loss yet :)

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hmm, you don't seem to listen to well so maybe get it checked! Ha ha.

If you ask my wife (or TC Ontario Region for that matter), she'll likely agree with ya... over the years of listening to nonsense I have learned to ignore it...kinda like my own personal built in ANR :).

There is a big difference between "Hearing" and "Listening"

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