UAL747
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Can Noise Cancelling Technology Work For Airliners

Wed May 21, 2008 4:03 am

The technology has been developed and tested in small GA aircraft, however, I was wondering if you think there might ever be a technology that would work with modern day airliners? As I understand it, the equipment picks up the wavelength and amplitude of the sound and bombards the unwanted sound with opposite flowing waves against the original sound wave.

In my mind the equipment would work by monitoring throttle imputs on the engines and the wind noise in the aircraft. But how would this equipment be dispersed in the aircraft? Do you think it is a good idea?

Personally, I always love a little white noise, but I know that there are tons of people who wish planes would be dead silent, so for the flying public, it might be worth looking into, but possibly cost prohibitive.

UAL
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Yflyer
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RE: Can Noise Cancelling Technology Work For Airliners

Wed May 21, 2008 4:14 am

I believe the Bombardier Q400 already uses some sort of noise canceling technology.
 
Inbound
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RE: Can Noise Cancelling Technology Work For Airliners

Wed May 21, 2008 4:18 am

You beat me to it....

yes, the Dash8 Q300 and Q400 (Q being for Quiet) use an Anti Noise and Vibration System involving noise cancelling technology.
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mestrugo
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RE: Can Noise Cancelling Technology Work For Airliners

Wed May 21, 2008 4:20 am

I've got one of those headphone sets with noise cancelling technology and the stuff, and now I can't travel without them.

I guess it's just a matter of scales; you could probably also install the same thing with huge baffles, but, if somebody accidentally taps or covers the mcrophone the system uses to cancel the noise, prepare to deafen all your passengers with an annoying screech.
 
sstsomeday
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RE: Can Noise Cancelling Technology Work For Airli

Wed May 21, 2008 4:37 am



Quoting Inbound (Reply 2):
yes, the Dash8 Q300 and Q400 (Q being for Quiet) use an Anti Noise and Vibration System involving noise cancelling technology.

There is also technology on (some) A/C which ensures that the turbines spin at exactly the same rate during cruise, is that not correct? This stops the droning sound created when one turbine slightly overtakes the other by a single rotation every few seconds. Is that what you were referring to?

What about noise cancelling technology for the OUTSIDE of the A/C? I recall some elaborate curly structures (forgive my lack of technological expertise) on the back end of 707 engines, which were for noise reduction.

I also understand that certain propellers are now designed with a pronounced curve, which not only make them more effective in terms of thrust but also reduce noise.

I'm sure there has been many gradational improvements in this area. It seems that with certain airports being hit with restrictions and fines largely to do with noise, that reducing the noise footprint an A/C makes in the vicinity of an airport is a major selling point.
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Viscount724
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RE: Can Noise Cancelling Technology Work For Airliners

Wed May 21, 2008 10:15 pm



Quoting Inbound (Reply 2):
yes, the Dash8 Q300 and Q400 (Q being for Quiet) use an Anti Noise and Vibration System involving noise cancelling technology.

The Saab 2000 also has a similar system.
 
pnwtraveler
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RE: Can Noise Cancelling Technology Work For Airliners

Wed May 21, 2008 10:36 pm

I like that throbbing sound when one turbine spins at a slightly different rate than the other. Dead quiet makes the flight to dull. Heck I am hurtling through space at 5x the speed my car will go - I wannahear and feel some of it  tongue . Part of the problem is that air travel has gotten so pedestrian these days some of the romance and excitement is gone.
 
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RE: Can Noise Cancelling Technology Work For Airliners

Wed May 21, 2008 10:50 pm



Quoting Pnwtraveler (Reply 6):
Part of the problem is that air travel has gotten so pedestrian these days some of the romance and excitement is gone.

Only SOME of the romance is gone?  Wink
 
UAL747
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RE: Can Noise Cancelling Technology Work For Airliners

Wed May 21, 2008 11:11 pm



Quoting SSTsomeday (Reply 4):
There is also technology on (some) A/C which ensures that the turbines spin at exactly the same rate during cruise, is that not correct?

I think this is called "Prop Sync."


On my dad's Cessna twin, once you reach your cruising altitude, you flip the switch and you can hear the props start to sync together and the "washing machine, wooosh-wooosh-wooosh" sound goes away.

UAL
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SUPRAZACHAIR
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RE: Can Noise Cancelling Technology Work For Airliners

Thu May 22, 2008 12:06 am



Quoting Inbound (Reply 2):
yes, the Dash8 Q300 and Q400 (Q being for Quiet) use an Anti Noise and Vibration System involving noise cancelling technology.

...and Q200.
 
tdscanuck
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RE: Can Noise Cancelling Technology Work For Airliners

Thu May 22, 2008 5:50 am



Quoting UAL747 (Thread starter):
The technology has been developed and tested in small GA aircraft, however, I was wondering if you think there might ever be a technology that would work with modern day airliners?

Internally it could work. Externally, you've got a power problem. To cancel the noise, you need to output the inverse waveform at nearly the same power level. The power level in jet noise is huge, which means you'd need whopping giant amplifiers and speakers to counteract it.

Quoting Yflyer (Reply 1):
I believe the Bombardier Q400 already uses some sort of noise canceling technology.

I believe this is just for internal noise, where the sound pressure is a lot lower.

Tom.
 
Tod
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RE: Can Noise Cancelling Technology Work For Airliners

Thu May 22, 2008 3:08 pm

The problem with using opposite waves to cancel cabin noise is keeping the waves exaclty opposite in varying cabin locations.

This is why it works with headphones. This distance the noise source travels within the headphones to your ears and the distance the cancelling noise travels withing the headphones to your ears can be tightly controlled. That makes keeps the waves in sync possible.

That is not the case when you speard sets of ears throughout the cabin.

Tod
 
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RE: Can Noise Cancelling Technology Work For Airliners

Thu May 22, 2008 3:47 pm



Quoting Tod (Reply 11):
The problem with using opposite waves to cancel cabin noise is keeping the waves exaclty opposite in varying cabin locations.

This is why it works with headphones. This distance the noise source travels within the headphones to your ears and the distance the cancelling noise travels withing the headphones to your ears can be tightly controlled. That makes keeps the waves in sync possible.

That is not the case when you speard sets of ears throughout the cabin.

On the Dash 8 Q, it's not just active noise cancelling. They have active vibration damping too.
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Tod
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RE: Can Noise Cancelling Technology Work For Airliners

Thu May 22, 2008 5:57 pm



Quoting Jetlagged (Reply 12):
On the Dash 8 Q, it's not just active noise cancelling. They have active vibration damping too.

Nice.

Now if someone would step up and try that with a wide body, that would be cool.

Tod
 
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Starlionblue
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RE: Can Noise Cancelling Technology Work For Airliners

Thu May 22, 2008 11:39 pm

Lending out headphones seems like a simpler and cheaper solution on jets.  Wink

Active noise canceling like Bose or (IMHO much better) passive noise canceling like Shure or Etymotic.
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JGPH1A
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RE: Can Noise Cancelling Technology Work For Airliners

Sat May 24, 2008 6:35 pm



Quoting Inbound (Reply 2):
yes, the Dash8 Q300 and Q400 (Q being for Quiet) use an Anti Noise and Vibration System involving noise cancelling technology.

I'm not convinced it works though - those things are still damn loud inside.
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thegreatchecko
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RE: Can Noise Cancelling Technology Work For Airliners

Sat May 24, 2008 6:39 pm



Quoting JGPH1A (Reply 15):

I'm not convinced it works though - those things are still damn loud inside.

It works quite well actually. There is a huge difference that can not only be heard but felt if the system is paused. It's still a prop, so you will have to hear the engines at some level. IMO, its no louder than an ERJ on the inside, especially near the door.

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RE: Can Noise Cancelling Technology Work For Airliners

Sat May 24, 2008 6:45 pm



Quoting Thegreatchecko (Reply 16):
IMO, its no louder than an ERJ on the inside, especially near the door.

Not in my experience, but you're right about sitting near the door on an ERJ, it's LOUD. Why is that ?
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VIflyer
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RE: Can Noise Cancelling Technology Work For Airliners

Sat May 24, 2008 8:01 pm



Quoting Viscount724 (Reply 5):

The Saab 2000 also has a similar system

And The SF340B+ too. How every I know my company decided a while ago to deactivate the system from what i heard was MX reliability problem with them (one of the first gen systems).

Quoting JGPH1A (Reply 17):
Not in my experience, but you're right about sitting near the door on an ERJ, it's LOUD. Why is that ?

It's mainly due to the local airflow coming off of the nose and transitioning to the fuselage. It's worst at lower alts. (10,000 to mid FL200). And it's cold as the dickens up their too. Remember it's basically a turboprop fuselage going almost twice as fast at lower levels.

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cptspeaking
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RE: Can Noise Cancelling Technology Work For Airliners

Sat May 24, 2008 10:47 pm



Quoting UAL747 (Reply 8):
I think this is called "Prop Sync."

Right you are, for larger piston and turboprop twins anyway...Cessna 400 series, King Airs, etc. Jets are a little different...

Citations have a system that will sync either the fan (N1) or the turbine (N2). This is turned off for takeoff and landing...same concept as the prop sync though with a master and slave engine.

We did a little testing when a I flew a Citation and found that the fan sync is better for the pilots and the turbine sync is better for the passengers in the back. We would set the desired N1 and turn the turbine sync on as part of the climb checklist and off in the before landing, unless it was a dead leg...then we'd use the fan sync as there were no passengers to please.

Are there similar systems in large jets, perhaps integrated with the autothrottles somehow?
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UAL747
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RE: Can Noise Cancelling Technology Work For Airliners

Sun May 25, 2008 10:36 pm



Quoting CptSpeaking (Reply 19):
Cessna 400 series

Well, his is a 335, but it's as large or ever a bit larger than the 414 I think, but nonetheless, you can tell when the prop sync is turned off or on. Makes a big difference on the ear.

UAL
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ContnlEliteCMH
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RE: Can Noise Cancelling Technology Work For Airliners

Mon May 26, 2008 8:21 pm

I think the problem is more difficult than this discussion indicates. Noise cancelling headphones work becaue the microphone is very near the ears for which the cancelling is intended, and the cancelling sound can be applied directly to those ears. This is why those headphones work well for nearly every environment.

In a jetliner, things are a lot different. It will have at least several major regions of sound inside. What cancels noise in one region could make flight nearly intolerable in another section of the airplane. You'd need to target the sound you're trying to quiet for the location in which you're trying to quiet it. In a turboprop, you're trying to cancel out the prop vibrations. These vibrations have high amplitude and a (more or less) a uniform frequency regardless of where they're heard. So the noise reduction system in the Q400 can be relatively simple. I'm not so sure for a large jetliner.

I am no sound expert. But while attaining my degree I recall a poster hanging in one of the labs. It caughy my attention because it had a cutaway of a jetliner -- an MD80 to be exact. (I think it was a SAS aircraft.) The cutaway showed a mapping of how sound flowed through the cabin though I can't recall any more specifics, such as frequency. The vectors varied in direction and size. What I took away from that poster was that it confirmed something my ears told me every time I flew: the sound in the cabin can be varied from one place to another. Cancelling it well seems like a very difficult problem.
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gopal
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RE: Can Noise Cancelling Technology Work For Airliners

Tue May 27, 2008 9:05 pm

Instead of cancelling the noise generated by the turbines , why not harness some of it and use it for some of the aircraft systems ? Are there machines that can convert sound energy to electricity efficiently ?
 
DaBuzzard
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RE: Can Noise Cancelling Technology Work For Airliners

Wed May 28, 2008 12:01 am



Quoting Tdscanuck (Reply 10):
The power level in jet noise is huge, which means you'd need whopping giant amplifiers and speakers to counteract it

Don't tell the kids in my old neighborhood that....I suspect some of them had enough wattage in their cars to do the job....as long as the frequencies are below about 50hz  Wink Ever see a rear window explode...boom boom booom BOOOOM  crazy 
Seriously though, there are other issues which make this impractical. The external noise from an aircraft is generated from various locations on the aircraft, you would need a counter noise generator at each location (engines, flaps, landing gear openings, etc) to keep the cancelling waves 180 degrees out of phase to get effective cancellation for ground based listeners.

Quoting Gopal (Reply 22):
Are there machines that can convert sound energy to electricity efficiently


The real issue is that it takes energy to create the sound in the first place. If you can build it so it operates more quietly without external means of sound control, it will (all other things being equal) be more efficient. Better not to make the noise in the first place if you can.
 
roseflyer
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RE: Can Noise Cancelling Technology Work For Airliners

Wed May 28, 2008 12:45 am

I got to tour Boeing's noise analysis facility to see how hard they are working on getting interior noise down on the 787. They have very sophisticated sound laboratories.

One difficulty with noise cancelling technology on a large jet is that the largest source of noise is wind noise. Wind noise is either external to the airplane or interior from the cabin air system. It is difficult to cancel this noise since it isn't given off of a solid object vibrating. There is no natural frequency of air which can be cancelled out. The noise comes from a broad wavelength. You have to cancel out quite a wide spectrum in order to keep out wind noise. Current systems don't really work for this inside a plane. You would get some noise cancelling, but not enough probably to make it worth the cost and weight.

Noise cancelling for a propeller is much easier since it is vibrating at a very specific frequency.

Quoting Viscount724 (Reply 5):
The Saab 2000 also has a similar system.

Same as the new ATRs.
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Dalmd88
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RE: Can Noise Cancelling Technology Work For Airliners

Wed May 28, 2008 2:33 pm

I've heard there are some accidents in GA that have been attributed to the pilot wearing noise cancelling headsets. They did such a good job that the pilot never heard the gear warning horn.
 
bio15
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RE: Can Noise Cancelling Technology Work For Airliners

Wed Jun 25, 2008 7:44 pm

Prop Sync usually refers to the propeller synchronizer system, which fine tunes the propellers' RPMs so they match, reducing the frequency beats.

On the other hand theres the propeller synchrophaser system which, in addition to the synching of RPMs, controls the phase, or angle of rotation, of each propeller. It shifts one propeller out of phase from the other, and maintains this constant phase angle so the propeller blade tips are not in the same position. This reduces the impact of blade tip shock waves hitting the fuselage at the same time, further reducing cabin noise.

The Dash-8 and other similar aircraft have synchrophase.


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