After years of scientific research on the performance of commercial aircraft like 777's or A320'S, the cabin noise is still very loud. Modern aircraft have new features like serrated engine nacelles, like on the 747-8 or 787 engines; improved aerodynamics; vortex generators; cabin insulation, etc. So why do aircraft still have so much cabin noise after all these improvements?
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8$\begingroup$ I think the premise here is questionable. Stand outside near a running jet engine, and you'll appreciate just how much the noise IS reduced inside the cabin! $\endgroup$– Ralph J ♦Mar 10, 2016 at 17:17
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1$\begingroup$ Perhaps for essentially the same reason that people in tourist class are packed in like sardines: because they'll tolerate it and it allows the airline to make more money. $\endgroup$– jamesqfMar 10, 2016 at 19:43
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4$\begingroup$ How quiet do you expect that 550mph wind on the other side of the window to be? $\endgroup$– David RicherbyMar 10, 2016 at 21:43
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1$\begingroup$ The quietest jet aircraft I ever flew on was an Air Force C-141. But that was on the flight deck. Having spent a lot of air time in both military and commercial aircraft, I can say that the commercial versions were always quieter in the passenger area. However there are certain zones that will always be the loudest ... the point where you're at about a 45 degree angle to the intake or exhaust. I always prefer sitting in an aisle seat over the wing root, but that's just me. $\endgroup$– Howard MillerMar 10, 2016 at 22:25
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6$\begingroup$ Go fly a glider. You'll be surprised how much wind noise there is. $\endgroup$– timboAug 14, 2016 at 2:21
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1 Answer
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Like everything in aviation its a trade off of a few factors.
Efficiency: A non-running engine is pretty quiet but that's of little use to a pilot who needs thrust to actually go anywhere. Now you can have lots of sound suppression in an engine and alter the airflow and what not but in the end of the day jets work on Newton's third law so you still need to throw a hot mass out the back. Any attempt to baffle this will take a toll on efficiency. (Side note, car exhausts have a similar effect on car engines these days).
Weight: The generally accepted way to reduce noise is to insulate against it. What you are really doing is adding material to absorb the mechanical energy that is the sound wave and dissipate it. Generally this is done with insulation of some kind (there is a variety of styles). But like anything this takes a toll on weight and will reduce what you can carry.
Cost: Insulation does wear out and break down over time (its usually some kind of foam), so the more you have the more you need to replace. Also of importance is the fact that most of it gets removed during check to inspect the airframe so having a lot of insulation will add to your down time during checks (this costs the airline money in terms of hours).
If you take a look at some custom-built private planes you will see some of the things they can do in terms of added noise reduction and what those implementations look like. On the other hand active noise control is becoming a cheaper and more efficient technology in headphones which makes a case for not needing to improve insulation (it will eventually be cheaper to have a pair of ANR headphones for everyone than maintain a lot of insulation). A lot of the GA community has moved to ANR headsets which are much nicer than their traditional counterparts.
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$\begingroup$ I was flying in a friend's twin engine airplane one day and he had a spare headset with ANR. It was like the engines had shut down. $\endgroup$ Mar 10, 2016 at 22:27