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Topic: How Much Quieter Is 350 Compared To 787?
Username: JonssonF
Posted 2013-06-23 09:24:21 and read 25973 times.

How much more quiet is a A350 compared to B787? During the first week the 350 has been dubbed "hushliner". It is ofcource hard to say watching clips but I think 350 is quiterer if I compare youtube clips. When watching landings and takeoffs at airports for example I think 320 is quieter than 737, the A380 is very quiet.
Anyone of you out there having figures regarding 787 and 350?

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: OldAeroGuy
Posted 2013-06-23 09:39:18 and read 25923 times.

Are you talking about community noise or cabin noise?

If it's community noise, since the A350 isn't certified yet, I doubt anyone will have meaningful numbers.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: ER757
Posted 2013-06-23 09:42:47 and read 25855 times.

Quoting OldAeroGuy (Reply 1):
If it's community noise, since the A350 isn't certified yet, I doubt anyone will have meaningful numbers.

People who were at the PAS and watched both the 787 flying display and the A350 flyby might have some input though. Safe to say some sort of comparison could be made

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: OldAeroGuy
Posted 2013-06-23 09:59:55 and read 25611 times.

Quoting ER757 (Reply 2):
People who were at the PAS and watched both the 787 flying display and the A350 flyby might have some input though. Safe to say some sort of comparison could be made

None that would have any validity. Both airplanes would need to be at their certification weights and flying the certification noise profiles. At PAS, I can guarantee that neither were.

Even then, noise measurements require precise instrumentation. Human ears alone just aren't reliable enough to correctly assess a difference of this type.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: lightsaber
Posted 2013-06-23 10:11:43 and read 25489 times.

Quoting ER757 (Reply 2):
People who were at the PAS and watched both the 787 flying display and the A350 flyby might have some input though. Safe to say some sort of comparison could be made

I could understand the RR engines being quieter on the A350, but what is the comparison to the GEnX? Those engines were built to be incredibly quiet.

Also, the A350 at Paris was very light. A light plane makes less noise than a heavy plane. That is not the venue to compare noise...

Lightsaber

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: Roseflyer
Posted 2013-06-23 10:13:01 and read 25455 times.

I would be surprised if there was a huge difference. Boeing and airbus marketing probably both claim they are the best by comparing to older airplanes rather than head to head.

I also would be surprised if airbus and rolls-Royce could make the a350 much quieter with its significantly more powerful engines.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: francoflier
Posted 2013-06-23 10:21:00 and read 25356 times.

Am I the only one who doesn't give a damn about how quiet they are?

This being, quintessentially, a nerd forum, I'd almost expect to see a fight about which is the loudest...

I don't live near an airport, and if I did, I'd acknowledge the intrinsic implications of its near presence before I bought or rented the place. (hint hint, NIMBY)

Non-hushkitted JT-3, anyone?

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: BoeingVista
Posted 2013-06-23 10:23:49 and read 25322 times.

Quoting lightsaber (Reply 4):
Also, the A350 at Paris was very light. A light plane makes less noise than a heavy plane. That is not the venue to compare noise...

The A350 was probaby heavier than the 787's It may not have a cabin but it was loaded with test equipment and enough fuel to continue for a 6 hour series of flight tests.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: PITingres
Posted 2013-06-23 10:36:22 and read 25178 times.

I'd guess that both are more than quiet enough.  


I was recently visiting a friend who lives a few miles off the western end of the RAF Brize-Norton runway. It's quite an experience to listen to one of the (last) VC-10's shriek their way past - and you might as well listen, because you're not hearing anything else while it's overhead! By comparison, a 787 fly-by is a non-event and I'm sure the A350 is similar.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: ER757
Posted 2013-06-23 10:37:50 and read 25178 times.

Quoting lightsaber (Reply 4):
I could understand the RR engines being quieter on the A350, but what is the comparison to the GEnX? Those engines were built to be incredibly quiet.

On the 787, the GenX is definitely quieter than the RR's. I really love the sound of the Trents, prefer them to GE for the geek factor for sure. I'm guessing people under the flight path might disagree though  

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: lightsaber
Posted 2013-06-23 10:57:03 and read 24985 times.

Quoting BoeingVista (Reply 7):
The A350 was probaby heavier than the 787's It may not have a cabin but it was loaded with test equipment and enough fuel to continue for a 6 hour series of flight tests.

As OldAeroguy noted, lets test them per established process and compare. Noise is a test that is too easy to cheat on. As noted:


Quoting OldAeroGuy (Reply 3):
Even then, noise measurements require precise instrumentation. Human ears alone just aren't reliable enough to correctly assess a difference of this type.

   And test to test variation is huge.

I was able to find one chart (table 14.2) which has projections for the XWB with 787 data:
http://www.sydneyairport.com.au/corp...%2014%20-%20noise%20management.pdf

Both the 787 and A350 are close. Per that chart, Airbus looks to be promising a fractionally quieter aircraft. An aircraft quieter than the 737NG and A320 (current). Both should be quieter than the MAX, but slightly noisier than the NEO. (But honestly, the differences will not be determinable accurately by the human ear.)

I find it amusing that, per that chart, a 748, 762, 732, and MD-80 make the same noise in db...

Quoting francoflier (Reply 6):
This being, quintessentially, a nerd forum, I'd almost expect to see a fight about which is the loudest...

I want aviation to grow. To do so, we need to get under 85db. My neighborhood tickets all road vehicles that make over 85db. Every weekend scores of motorcycles receive tickets from the local police (the neighborhood has a nasty reputation for that). Its rather nice sleeping in quiet. While I think NIMBYs are silly complaining buying near an airport, the reality is that air transit must get quieter or growth will be constrained.

Chapter 4 rules are here. No concorde with its 110db will be allowed again. Its time to work on getting below 85db.

Note: Figure 11.1 here is a better figure, but lacks the 787/A350:
http://www.bne.com.au/sites/all/file...ntent/files/BACMP09_Chapter_11.pdf

I doubt we'll get down to the 40db of a quiet urban neighborhood at night and certainly not the ~25db of rural living at night (e.g., light wind in trees).
http://airinsight.com/2012/06/07/aircraft-noise/

And look at the noise map of LAX. The 'tail' goes all the way to the 110 freeway!
LAX/pdf/lax2q11%20noise%20contour%20map.pdf" target="_blank">http://www.lawa.org/uploadedFiles/LA...ax2q11%20noise%20contour%20map.pdf

Should we not bring that noise contour in a few miles?

Lightsaber

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: speedbird128
Posted 2013-06-23 11:16:09 and read 24780 times.

Quoting lightsaber (Reply 4):
Also, the A350 at Paris was very light. A light plane makes less noise than a heavy plane. That is not the venue to compare noise...

Was it? How do you know?

Its first flight was at 221t... I would bet the 3rd flight was heavier... Given that it went on to complete a 8.5 hour flight...

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: JonssonF
Posted 2013-06-23 11:21:47 and read 24731 times.

Thanks lightsaber for the document!

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: AA777
Posted 2013-06-23 11:37:00 and read 24570 times.

This is both amazing and SAD!

They days of the buzzsaw engine noise are coming to an end....

http://youtu.be/u1NivHkeiJI

vs

http://youtu.be/-QDhVKxsQDk

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: C680
Posted 2013-06-23 11:49:47 and read 24433 times.

Something else to consider:

The pilot has quite a bit of control over how much noise the aircraft makes on departure or arrival. So if John Leahy want's the press to think the A350 is "so quiet they won't know we are here" he could easily coordinate with his flight crew and ask them to fly a quiet profile. Same is true of Boeing and the 787.

Even Concorde had a noise reduction profile they flew out of JFK for years. Still loud as hell, but better than if they did nothing.

In short: listening to airplane on YouTube or at an Airshow has VERY little to do with how loud or quiet they are. But it does make good rumors on a.net

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: affirmative
Posted 2013-06-23 11:58:50 and read 24305 times.

I was at PAS and saw both the A350 and the 787 and I can't really tell much difference between the two. They're both amazingly quiet. Being the first aircraft to make a pass I was astounded by the lack of noise of the A350 but the 787 was equally quiet on the low speed passes.

I'm guessing this was no help to anyone, but I think the conclusion can only be made in a sound chamber..

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: OldAeroGuy
Posted 2013-06-23 12:01:05 and read 24281 times.

Quoting JonssonF (Thread starter):
During the first week the 350 has been dubbed "hushliner".

Ahhh, marketing! Remember that Eastern Airlines once dubbed the 727-100 the "Whisper Jet"

http://www.georgiaencyclopedia.org/nge/Multimedia.jsp?id=m-3576

Note where it falls on the link provided by Lightsaber:

http://www.sydneyairport.com.au/corp...%2014%20-%20noise%20management.pdf

(Page 173)

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: jayunited
Posted 2013-06-23 12:02:02 and read 24283 times.

As far as the 788 goes that aircraft is extremely quiet on take off and landing. Here at ORD we see both the GenX engines (United) and the RR engines (LOT). It amazes me how one can be outside and the plane will fly by on takeoff and you barely hear the engines. Is this scientific absolutely not just my observation that the engines on the 787 both GenX and RR and fairly quiet. AS far as the A350 I can't comment on it because I've only seen videos of the aircraft nothing in person yet.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: par13del
Posted 2013-06-23 12:11:30 and read 24135 times.

I thought both a/c had similar type engine technologies, so other than one airframe requiring additional thrust, I would assume in terms of environment noise they are about the same given their different a/c size.

A better comparison would be between the current versions of the 787, one GENX the other RR.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: KarelXWB
Posted 2013-06-23 12:13:07 and read 24111 times.

Quoting ER757 (Reply 2):
People who were at the PAS and watched both the 787 flying display and the A350 flyby might have some input though. Safe to say some sort of comparison could be made

But both aircraft flew a different flight path, different height, different thrust setting etc.

We need some real numbers before making a comparison.

Quoting lightsaber (Reply 4):
Also, the A350 at Paris was very light. A light plane makes less noise than a heavy plane. That is not the venue to compare noise...

It was full of test equipment, the weight was 215t what is the equivalent of an 300 pax A330 I believe. Not something I would call 'very light'.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: DocLightning
Posted 2013-06-23 12:14:44 and read 24090 times.

Quoting AA777 (Reply 13):
They days of the buzzsaw engine noise are coming to an end....

I remember as a little boy hearing the NW 727s and DC9's take off before the hushkits. It was the loudest roar. Amazing and impressive to my 6-10yo ears. You could hear them on approach even 40 miles from the airport; they sounded like thunder some days.

In college, I remember parking at the lot just off the end of the 28s at SFO when a LH 744 took off and passed right over my head. Every car alarm in the lot went off and it shook me to my bones.

A few months ago, I positioned myself in the same lot when the LH A380 took off. I heard it, but it didn't set off car alarms, nor did it shake me to my bones.

You lose a sense of the sheer power required to make these vast metal contraptions fly, but on the flipside, it is almost eerie how silent they are and it makes them somehow "feel" lighter and airier to the observer.

I do find it interesting that they claim that the 748i makes as much noise as an MD-80/732. I've never heard a 748 take off in person, but the MD-80 is LOUD! Louder than the 744. So how can the 748 be as loud?

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: kmz
Posted 2013-06-23 12:14:45 and read 24089 times.

what i think will be more interesting than the community noise is the cabin noise. Here we will see which OEM has investigated more into basic research concerning CFRP fuselage and noise. A did some measurement flights with a modified A340 which has a CFRP panel on the side, but I have no idea what they learned from it. Is CFRP better or more difficult for noise reduction measures?

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: a380heavy
Posted 2013-06-23 12:28:15 and read 23893 times.

On this subject of aircraft noise, and in particular engine noise the Trent 1000's on the 787 have a cowling with chevrons cut out which I believe are used for noise suppression.

Is the cowling design Boeing's making this the reason a similar design wasn't used on the Trent XWB's on the A350? If not, why the omission on the A350 if the design makes the aircraft more quiet without presumably being detrimental to fuel burn?

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: mjoelnir
Posted 2013-06-23 13:02:10 and read 23079 times.

Quoting a380heavy (Reply 22):
On this subject of aircraft noise, and in particular engine noise the Trent 1000's on the 787 have a cowling with chevrons cut out which I believe are used for noise suppression.

Is the cowling design Boeing's making this the reason a similar design wasn't used on the Trent XWB's on the A350? If not, why the omission on the A350 if the design makes the aircraft more quiet without presumably being detrimental to fuel burn?

It is detrimental to fuel burn.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: 3rdGen
Posted 2013-06-23 13:02:54 and read 23090 times.

Once saw a 787 taking off from DOH. And I must stress the word 'saw' because had I not been sitting there watching all the departures I would have never known t was there, it was absolutely silent, more so than a 320. These new aircraft are absolutely unbelievable when it comes to noise, you have to pretty close to them to hear anything.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: wjcandee
Posted 2013-06-23 13:10:03 and read 23699 times.

Eastern called the 727 the "Whisper Jet" and the L1011 the "Whisperliner". It's all relative. (Note: I edited this; I got it wrong at first. Uncle was a captain at Eastern, so I have lots of memories, some of them faulty, apparently.)

The answer to the OP's question is, "It's not."

The quiet thing was just typical Leahey. At the first flight, he made a big deal of doing an "Oh, wow! Did you hear how quiet that was?!" Because he knows it's an important issue in Europe. And the media tools just took it down and reported it. Like the "extra wide body" nonsense. Just marketing. Just crap.

[Edited 2013-06-23 13:11:11]

[Edited 2013-06-23 13:36:21]

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: lightsaber
Posted 2013-06-23 13:24:30 and read 23411 times.

85db is when hearing damage starts. That is what aircraft will be held to. That and the 65db noise threshold. For if one looks at the LAX example I gave in post #10, that is what the FAA currently defines as the airports boundary of noise. This is a political will to pull those noise boundaries to within the airport property.

The 787 and A350 will certainly help do so. They are about 5db quieter than a 762. (The 763ER is about 2db louder IIRC due to the higher MTOW/landing weight.) That is noticeable.

But until noise drops below 85db (hearing damage) during the day and 65db at night (maximum for windows and such to keep the bedroom quiet), we will have a push to reduce aircraft noise.

Quoting jayunited (Reply 17):
As far as the 788 goes that aircraft is extremely quiet on take off and landing.

And yet Airbus is promising the A350 will be a hair quieter.

What time of day were you listening? Neighborhoods are easily 20db quieter at night (see my links in post #10).

Quoting OldAeroGuy (Reply 16):
Ahhh, marketing! Remember that Eastern Airlines once dubbed the 727-100 the "Whisper Jet"

     

And you are correct, it was quieter than many, at 100db!    Great marketing by Eastern, FWIW... And since they were able to claim they were advertising cabin noise... They were able to get away with it. Somehow they were able to get the media to twist it to "three quiet engines."

Quoting KarelXWB (Reply 19):
It was full of test equipment, the weight was 215t what is the equivalent of an 300 pax A330 I believe. Not something I would call 'very light'.

Its still not that heavy. Did it take off at MTOW? The noise grows to the 7th power of air velocity. So small increases in MTOW increase noise handily.

Besides, I provided links showing the A350 will be fractionally quieter (if promises are met). All good, but not enough for the human ear to differentiate. So 10% below MTOW is a bit quieter than MTOW. Since the A350 did a sub-10 hour flight afterwards, that means at least 30 tons of fuel wasn't loaded and it was also shy 10t+ in payload versus a typical mission. That, for noise concerns, is very light. Much less thrust required for takeoff... much lower landing speeds are possible.

Quoting DocLightning (Reply 20):
In college, I remember parking at the lot just off the end of the 28s at SFO when a LH 744 took off and passed right over my head. Every car alarm in the lot went off and it shook me to my bones.

I interned at Solar Turbines and every time a 727 landed, all the car alarms went off.

Quoting affirmative (Reply 15):

I was at PAS and saw both the A350 and the 787 and I can't really tell much difference between the two.

You sir, are being honest. 1db is not something one can differentiate unless they are done back to back. That is the noise difference. Very small...

Quoting affirmative (Reply 15):
but I think the conclusion can only be made in a sound chamber..

Actually, its done by multiple touch and gos at a fairly quiet airfield with sensitive sound measuring gear.

Quoting a380heavy (Reply 22):
If not, why the omission on the A350 if the design makes the aircraft more quiet without presumably being detrimental to fuel burn?

Chevrons reduce noise about 2db at a cost of 0.25% in fuel burn. There is a detriment to fuel burn. Why put in the Chevrons when the latest fans are 3db quieter than the fans on the 787. Yes, technology is moving *that fast.* The other change is that RR improved their turbine technology which makes the core noise less (reducing core losses allows a lower velocity jet out of the core). RR finally stopped using shrouded turbines in the XWB which was a much needed and delayed technology shift on their part.

Lightsaber

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: FVTu134
Posted 2013-06-23 13:33:43 and read 23414 times.

Am I the only one who is nostalgic for the roar of classic airlines such as the BAC 1-11, Boeing 727 (with the JT-8's)? Luckily in the last few years I had a few chances to fly the Tu134 which was always great but while the 737's and 320's are great for comfort... I miss the sound which made your intestines tremble (along with everything in a mile radius)...

Now you understand when people talk about the "good old days"  )
Sorry for drifting a bit off topic

FVTu134

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: KarelXWB
Posted 2013-06-23 13:57:23 and read 22817 times.

Quoting lightsaber (Reply 26):
The 787 and A350 will certainly help do so. They are about 5db quieter than a 762. (The 763ER is about 2db louder IIRC due to the higher MTOW/landing weight.) That is noticeable.

Not just noticeable, every 10 dB increase is a doubling of sound.

+20 dB 4x
+10 dB 2.0x
+6 dB 1.52x
+3 dB 1.23x

So 5 dB quieter is pretty much.

I once heard a DC-10 landing here at AMS, thought that was loud  

Quoting lightsaber (Reply 26):
Much less thrust required for takeoff

But they used TOGA for takeoff.

[Edited 2013-06-23 14:03:49]

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: tortugamon
Posted 2013-06-23 14:06:09 and read 22617 times.

Quoting lightsaber (Reply 10):
I was able to find one chart (table 14.2)

This chart is fascinating to me. 787/350s are quieter than today's 737/320s. Both the max and (more so) the neo are making very large improvements. Not sure why the neo is more in the future than the max but that is another story. The 77W is not on this chart so I tried to look it up and came across a Randy's Journal of note regarding the noise levels of an A380 vs a B777:

"Think of this as a trade-off between the level of background noise that might drown out desired noises (a flight attendant being able to hear the passenger’s drink order) versus undesired noises (one passenger being able to hear every other passenger’s drink order).

That’s why some “white noise” can be desirable on an airplane, and even soothing"
http://www.boeingblogs.com/randy/arc...ives/2007/08/sound_of_silence.html

So the A380 is quiet and that is a bad thing and the 777 is noisier and therefore it drowns out other noises and that is a good thing. It sounds odd to say but to a certain extent, I agree. I think the engine hum does put me to sleep faster than if it was just noise on an airplane but this is a tough argument to make and really ignores the effects of noise outside of the plane which is the real pollution.

tortugamon

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: oly720man
Posted 2013-06-23 14:10:52 and read 22460 times.

Quoting KarelXWB (Reply 28):
Not just noticeable, every 10 dB increase is a doubling of sound.

+20 dB 4x
+10 dB 2.0x
+6 dB 1.52x
+3 dB 1.23x

+/-3dB is a doubling/halving of sound power.

10dB is a factor of 10 in sound power.

A reduction of 5dB means sound power is reduced to approx 1/3 of what it was.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: KarelXWB
Posted 2013-06-23 14:14:38 and read 22373 times.

Quoting tortugamon (Reply 29):
So the A380 is quiet and that is a bad thing and the 777 is noisier and therefore it drowns out other noises and that is a good thing.

Keep in mind that Randy is a marketing guy. It's a bit hard to rely on numbers from his blog postings.

Quoting oly720man (Reply 30):
A reduction of 5dB means sound power is reduced to approx 1/3 of what it was.

Thanks. And yes, that is noticeable. I was quite amazed when I heard that DC-10 for the first time (and yes, I'm familiar with the usual A330 / 777 landings).

[Edited 2013-06-23 14:16:38]

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: OldAeroGuy
Posted 2013-06-23 14:17:52 and read 22342 times.

Quoting a380heavy (Reply 22):
Is the cowling design Boeing's making this the reason a similar design wasn't used on the Trent XWB's on the A350?

Boeing does hold the chevrons patent.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: autothrust
Posted 2013-06-23 20:09:33 and read 17813 times.

Quoting a380heavy (Reply 22):
Is the cowling design Boeing's making this the reason a similar design wasn't used on the Trent XWB's on the A350? If not, why the omission on the A350 if the design makes the aircraft more quiet without presumably being detrimental to fuel burn?

Chevrons are a patent of GE/Boeing, however Rolls Royce/Airbus worked out noise reduction improving zero splice technology for engine nacelles.

Quote:
Airbus A350 XWB set to be quietest generation of airliner as manufacturer improves zero splice technology for engine nacelles

Airbus is developing a noise-dampening engine nacelle intake that could become a feature of the new A350 XWB widebody twinjet.

The next-generation reduced acoustic mode scattering engine duct system (RAMSES) is a development of Airbus's "zero splice" intake liner developed for the A380, which is undergoing flight testing on the ultra-large aircraft.
http://www.flightglobal.com/news/art...turer-improves-zero-splice-211641/

[Edited 2013-06-23 20:13:43]

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: LH707330
Posted 2013-06-23 20:12:28 and read 17671 times.

Quoting ER757 (Reply 9):
On the 787, the GenX is definitely quieter than the RR's.

Why is that? Don't they have similar thrust and mass-flow numbers?

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: Stitch
Posted 2013-06-23 20:44:22 and read 17402 times.

Quoting JonssonF (Thread starter):
When watching landings and takeoffs at airports for example I think 320 is quieter than 737,

I'm under the flight path of SEA so I hear plenty of A320s and 737s overhead. Always easy to tell when an A320 is overhead - it's louder.  

(Though not significantly so - and on approach it always make a deep "whooshing" sound I don't notice from the 737s).



Quoting francoflier (Reply 6):
Am I the only one who doesn't give a damn about how quiet they are?

As someone who lives under an airport flight path, I sure do.

I only occasionally get to hear a 787-8 or 747-8 going into PAE, but I appreciate how much quieter they are than the 747-400, 777-200ER or MD-11F into/out of SEA.

I've also heard the A380-800 on approach and it is amazingly quiet (as it is on the inside). I expect the A350 to be no less impressive (at least on the outside - though I find the 787 quiet enough on the inside, which bodes very well for the A350 as I feel Airbus does a better job at sound insulation).



Quoting ER757 (Reply 9):
On the 787, the GenX is definitely quieter than the RR's. I really love the sound of the Trents, prefer them to GE for the geek factor for sure.

That Trent 1000 has the most amazing sound, doesn't it? First time I heard it I was like "what the heck is that?" and I looked up to see ZA001 doing a low-and-slow flyover.



Quoting wjcandee (Reply 25):
Eastern called the 727 the "Whisper Jet" and the L1011 the "Whisperliner".

I can vouch for the L-1011. It was significantly quieter on the inside then the 747-200 or 767-200ER.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: HH65MAN
Posted 2013-06-23 20:54:23 and read 17150 times.

When a jet engine is making noise one never has to worry, it's when it's not making any noise you need be concerned....   

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: tortugamon
Posted 2013-06-23 21:28:36 and read 16832 times.

Quoting Stitch (Reply 35):
Always easy to tell when an A320 is overhead - it's louder.

Lightsaber posted a link to a Sydney report that showed each aircraft by DB and A320 was slightly quieter than a B737-800. In my experience they just sound different but I never could tell which is louder. Its amazing what is going to happen with the upcoming generation.

tortugamon

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: Stitch
Posted 2013-06-23 22:38:43 and read 16147 times.

Quoting tortugamon (Reply 37):
Lightsaber posted a link to a Sydney report that showed each aircraft by DB and A320 was slightly quieter than a B737-800.

I don't have a decibel meter in my head so I cannot make an empirical judgement, only subjective.   I just notice that A320s sound a bit louder than 737NGs when they're on approach and departure.

Occasionally we'll get new 737NGs out of Renton / Boeing Field on test flights and they fly a fair bit closer to the ground (to stay under the SEA approach and departure paths) and are therefore a fair bit louder, as well.

I'm just glad AS retired their MD-80s. Those things were really loud.  

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: DocLightning
Posted 2013-06-23 23:18:34 and read 15675 times.

Quoting Stitch (Reply 38):
I don't have a decibel meter in my head so I cannot make an empirical judgement, only subjective.  I just notice that A320s sound a bit louder than 737NGs when they're on approach and departure.

They may produce a higher pitch, which is often perceived as louder.

I think we will rapidly reach a point at which aircraft will be all but inaudible beyond the boundaries of the airport. Already, I live only a couple of miles from OAK and the 73G/A320 aircraft departing are audible, but not a nuisance. The FX MD-10s sure make an old-fashioned buzz, though. I bet once the NEO/MAX comes out, you will really have to listen for the sound to notice it.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: masi1157
Posted 2013-06-23 23:38:08 and read 15382 times.

Quoting KarelXWB (Reply 28):
Not just noticeable, every 10 dB increase is a doubling of sound.

+20 dB 4x
+10 dB 2.0x
+6 dB 1.52x
+3 dB 1.23x

So 5 dB quieter is pretty much.

What you are describing is a very rough estimate for the perception of loudness. A noise level 10 dB higher would be perceived as roughly "twice as loud". But that is about it, even a "2.0x" is far beyound the accuracy of that estimate.

When talking about sound power, your numbers would mean +20 dB -> 100x, +10 dB -> 10x, +6 dB -> 4x, +3 dB -> 2x. And for sound pressure it would read +20 dB -> 10x, +10 dB -> 3.2x, +6 dB -> 2x, +3 dB -> 1.4x. Although these numbers would be correct, they don't reflect the human loudness perception.


Gruß, masi1157

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: BestWestern
Posted 2013-06-23 23:50:22 and read 15254 times.

From the Sydney report, amazing how quiet the 320 NEO is planned to be.

Quoting lightsaber (Reply 10):
I was able to find one chart (table 14.2) which has projections for the XWB with 787 data:
http://www.sydneyairport.com.au/corp...%2014%20-%20noise%20management.pdf

Both the 787 and A350 are close. Per that chart, Airbus looks to be promising a fractionally quieter aircraft. An aircraft quieter than the 737NG and A320 (current). Both should be quieter than the MAX, but slightly noisier than the NEO. (But honestly, the differences will not be determinable accurately by the human ear.)

3db drop in an equivalent in halving of noise energy.... never realized that..

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: garpd
Posted 2013-06-24 00:05:22 and read 15068 times.

I must admit, I chuckled at the thread title. It pre-supposes that the A350 IS in actual fact quieter. (As if it would be in some meaningful manner that will lead to superiority of one over the other?)

Both aircraft are using the same generation engines, give or take. They'll likely be indistinguishable to the naked ear. And a difference in DB will be so minimal, it will not affect sales in any way, shape or form.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: kmz
Posted 2013-06-24 00:09:33 and read 14980 times.

Quoting tortugamon (Reply 29):
I think the engine hum does put me to sleep faster than if it was just noise on an airplane but this is a tough argument to make and really ignores the effects of noise outside of the plane which is the real pollution.

It's not only the engine hum, in flight its aerodynamic noise and air conditioning which make the difference...I flew a SIA B777 in B/C once and the air conditioning was extremely loud compared to the rest of the noises....

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: masi1157
Posted 2013-06-24 00:22:02 and read 14780 times.

Don't forget, that the usual numbers given for community noise are "cumulated", they simply add the numbers for takeoff, approach and sideline. A few dB difference in these cumulated numbers might mean just 1 dB per measurement. 1 dB is about the smallest difference one can distinguish in a back-to-back test. No way one can tell a difference between 2 different aircraft. And add to that the fact, that dB(A) scale has not much to do with loudness perception.

The engines btw are a major noise contributor for takeoff, but on approach they can almost be neglected. "Airframe noise" (=flow noise) is dominant there.


Gruß, masi1157

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: Aviaponcho
Posted 2013-06-24 01:07:34 and read 14242 times.

From March 2013 Airbus Presentation :

Vs Stage4 :

A350-800 248 t : -16 dB
A350-800 259 t : -14.7 dB
A350-900 268 t : -13.7 dB
A350-1000 308 t : -10 dB

Calculated from EASA noise certification (cumulative margin - 10 dB = stage 4 noise margin)

7887-8 T1000A : 17.6 dB
787-8 T1000A/01 : 14.3 dB
787-8 GenX 1B64G03 : 14.5 dB
787-8 GenX 1B64G04 : 11.5 dB
That's not for the last engine (P1/G01 for Genx now)

looks for now that initial engines (both RR and GE) were quieter, and that thrust increase requirement lead to increase noise levels


Be careful, ICAO noise limits seems to be set for every MTOW so a great margin don't necessery imply less "real" noise.

787-8 227 t limit 100.9 / 98 / 104.3
A350-800 248 t 101.2/98.5/104.6 if the same as 777 limits (+1.1 dB cumulative limit)
A350-900 268 t 101.5/98.9/104.8 if the same as 777 limits (+2.0 dB cumulative limit)
A350-1000 298 t 101.9/99.5/105
A350-1000 308 t 102/99.7/105 it's +0.3 dB cumulative limit vs 298 t version and +3.5 dB vs 787-8


A350 seems quieter with A350-900 similar as 787-8 GenX1B64-G04 in cumulated noise

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: autothrust
Posted 2013-06-24 01:32:04 and read 13973 times.

Quoting garpd (Reply 42):
Both aircraft are using the same generation engines, give or take.

That is not correct. Trent XWB is not the same generation as the Trent 1000. There are differences in both engines as you can see from the presentation below.

http://www.win.tue.nl/ceas-asc/Works.../CEAS-ASC_XNoise-EV_K1_Kempton.pdf

Here a presentation of Boeing QTD2 Quiet Technology Demonstrator:

http://www.techtransfer.berkeley.edu/aviation06downloads/herkes.pdf

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: Aviaponcho
Posted 2013-06-24 01:36:06 and read 13907 times.

Hum hum

There's a new type certificate for noise on the 787 (14th june) with a massive improvement due to a new main landing gear plug : 7.4 / 7.6 dB gain !

http://www.easa.europa.eu/certificat...28IM%29_Boeing_787-07-14062013.pdf

So let's forget things like : A350 is quiter for now ....
But Trent 1000 is better for noise on 787 i guess ...

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: NeutronStar73
Posted 2013-06-24 05:36:04 and read 11346 times.

Quoting garpd (Reply 42):
I must admit, I chuckled at the thread title. It pre-supposes that the A350 IS in actual fact quieter. (As if it would be in some meaningful manner that will lead to superiority of one over the other?)

I agree with you 100%. The thread title made me laugh, because it already assumes as fact that the A350 is quieter, even though there is no data (as far as we know) that supports that "fact".

Very funny.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: visakow
Posted 2013-06-24 05:43:22 and read 11243 times.

I want the old days back with a Boeing 727 shaki'n the dishes off the rack 6+ miles after takeoff!!

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: lightsaber
Posted 2013-06-24 05:57:34 and read 11059 times.

Quoting LH707330 (Reply 34):
Quoting ER757 (Reply 9):
On the 787, the GenX is definitely quieter than the RR's.

Why is that? Don't they have similar thrust and mass-flow numbers?

That gets down to details. For example, the better the fan pattern factor, the less noise. Chevrons, at a tiny sacrifice in fuel burn, also cut noise.

Quoting Stitch (Reply 38):
I'm just glad AS retired their MD-80s. Those things were really loud.

And that is only about 3dB difference. There will be a slightly greater difference A320 CEO to NEO.

Quoting DocLightning (Reply 39):
Quoting Stitch (Reply 38):
I don't have a decibel meter in my head so I cannot make an empirical judgement, only subjective.  I just notice that A320s sound a bit louder than 737NGs when they're on approach and departure.

They may produce a higher pitch, which is often perceived as louder.

   But the higher pitch also dissipates quicker. Hence why the testing must be done at multiple distances.

Quoting DocLightning (Reply 39):
I think we will rapidly reach a point at which aircraft will be all but inaudible beyond the boundaries of the airport.

That will take another 15 years... but we're getting there.

Quoting Aviaponcho (Reply 45):
and that thrust increase requirement lead to increase noise levels

Noise energy goes as the 7th power of velocity.

Quoting Aviaponcho (Reply 45):
Be careful, ICAO noise limits seems to be set for every MTOW so a great margin don't necessery imply less "real" noise.

   There is a MTOW component.

Quoting Aviaponcho (Reply 47):
There's a new type certificate for noise on the 787 (14th june) with a massive improvement due to a new main landing gear plug : 7.4 / 7.6 dB gain !

Thank you. I didn't see 7.4db change, but the number certainly improved. I guess the gear was whistling...

Quoting Aviaponcho (Reply 47):
But Trent 1000 is better for noise on 787 i guess ...

I'm curious what changed. They now have a 0.8db advantage.


Lightsaber

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: Aviaponcho
Posted 2013-06-24 06:07:02 and read 10905 times.

Lightsaber,

RR has a 3dB leading noise vs Genx (comparing Trent 1000A/01 vs Genx1b64P01/t01 !
it's quite important !

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: KPDX
Posted 2013-06-24 06:15:27 and read 10868 times.

I'm not sure, but I just saw a 787-8 land up close for the first time yesterday. Let's just say I wasn't buying the hype that it was that quiet... Boy was I wrong. It was stunningly quiet.. I took a video from the same spot of a Citation landing right before it. To my ears, that actually seemed louder.  Wow!http://www.youtube.com/watch?v=9aPYz3DJ0jw

To sum it up, anything quieter than the A380/787 is a moot point.. They're already dramatically quieter than other airliners in service today.. Besides, I can't be the only one here that loves a good noisy engine. Loved watching all the American MD-80s at DFW the other day.  cloudnine 

[Edited 2013-06-24 06:17:07]

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: lightsaber
Posted 2013-06-24 07:58:09 and read 9446 times.

Quoting Aviaponcho (Reply 51):
RR has a 3dB leading noise vs Genx (comparing Trent 1000A/01 vs Genx1b64P01/t01 !

Which point? I picked the loudest point and there there was only 0.8db difference from your link.

Either way, RR is quieter and that is a good thing.

Quoting KPDX (Reply 52):
To sum it up, anything quieter than the A380/787 is a moot point.. They're already dramatically quieter than other airliners in service today.

That I disagree. Have the same landing happen at 10pm and you wouldn't be saying either is quiet. And the A380 isn't quiet. I've been on the 405 as one went into LAX over head. I was glad to have my windows closed. Although, a 767 is *far louder*. So is an MD-80...

Noise needs to be further reduced. And it shall be. For example, the 3.5:1 gear ratio GTFs will be notably quieter than the soon to enter service 3:1 GTFs.

Lightsaber

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: Aviaponcho
Posted 2013-06-24 08:05:14 and read 9336 times.

Lightsaber I was talking cumulative noise that's why !

So we Agree !
And RR is quieter without chevrons ! nice catch

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: BestWestern
Posted 2013-06-24 08:14:23 and read 9176 times.

Quoting lightsaber (Reply 50):
Noise energy goes as the 7th power of velocity.

If you have time, Please explain.....

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: Aviaponcho
Posted 2013-06-24 08:18:08 and read 9122 times.

By the way, I'd like to see A320NEO noise certification just to compare GTF and Direct Drive !
Can Direct drive compete ? really ?

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: brilondon
Posted 2013-06-24 08:22:13 and read 9071 times.

Quoting francoflier (Reply 6):
Am I the only one who doesn't give a damn about how quiet they are?

No way. I am with you all the way.

Quoting francoflier (Reply 6):
Non-hushkitted JT-3, anyone?

I am with you. Today aircraft are quiet and really don't have to worry about noise like the G.O.Ds. I would like to hear the roar of a 707 or 727 and the smoke that use to spew out the engines of those aircraft on takeoff. I loved the Convair 880 and 990 the way those aircraft would leave their mark on the sky. It was what first brought me into aviation as an enthusiast in the first place.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: Stitch
Posted 2013-06-24 08:27:04 and read 9034 times.

Quoting brilondon (Reply 57):
I would like to hear the roar of a 707 or 727 and the smoke that use to spew out the engines of those aircraft on takeoff.

To each their own, of course, but having watched and listened to an E-3A leave PAE darkening the sky with black smoke and sounding like the Apocalypse itself was on hand, I will gladly take the current generation of commercial airliners and greatly welcome the quiet the A380, 787 and A350 will bring.  

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: oly720man
Posted 2013-06-24 08:57:11 and read 8644 times.

Quoting BestWestern (Reply 55):

Quoting lightsaber (Reply 50):
Noise energy goes as the 7th power of velocity.

If you have time, Please explain.....

Google "Eighth Power Law of Jet Noise"

The noise (or acoustic) power is proportional to the jet exit velocity to the 8th power.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: lightsaber
Posted 2013-06-24 09:59:57 and read 7962 times.

Quoting Aviaponcho (Reply 56):
By the way, I'd like to see A320NEO noise certification just to compare GTF and Direct Drive !

I would like to see that too. But they have similar bypass ratios (ok, GTF is slightly better), and the direct drive will have Chevrons. Both expand the turbine more to cut noise and do so in ways that preserve turbine performance.

I want to see the LEAP-X make weight... Yes, the CMC turbines will help cut weight nicely, but I'm confused as to how that many stages of low turbine could weigh that little...

Quoting oly720man (Reply 59):
Google "Eighth Power Law of Jet Noise"

   But due to absorption of noise by the nacelle (just metal, before noise dampening), the 7th power works better for correlating high bypass engine noise.


Lightsaber

Quoting BestWestern (Reply 55):
Quoting lightsaber (Reply 50):
Noise energy goes as the 7th power of velocity.

If you have time, Please explain.....

Dig in.   You just opened Pandora's box. Its not an easy topic to get one's mind around.
http://adg.stanford.edu/aa241/noise/noise.html

Quoting Stitch (Reply 58):
To each their own, of course, but having watched and listened to an E-3A leave PAE darkening the sky with black smoke and sounding like the Apocalypse itself was on hand, I will gladly take the current generation of commercial airliners and greatly welcome the quiet the A380, 787 and A350 will bring.

paaa... nothing to a full augmented takeoff of a PW100-229 powered F-16. Now there is noise!


Noise I don't want to live under the flight path...  

Lightsaber

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: masi1157
Posted 2013-06-24 10:05:17 and read 7901 times.

Quoting oly720man (Reply 59):
Google "Eighth Power Law of Jet Noise"

The noise (or acoustic) power is proportional to the jet exit velocity to the 8th power.

That is only half the truth, because it only holds for jet noise, i.e. noise generated by turbulence interacting with itself, so to say. While this noise rises very steeply, it has a very low efficiency. In almost any other flow noise problem other than pure jet noise, when turbulence interacts with solid surfaces, the generated sound power is approx. proportional to the 6th power of the flow velocity. That is true for flow in ducts, flow around obstacles (like aircraft structures) and for many but not all of the noise generating mechanisms inside the engine. And it is only true for broadband noise, but not for tones. While the slope is less steep (6th vs. 8th power), it is generated much more efficiently and therefore very often dominates.

In reality it is not exactly the 6th power, but rather the 5th for low frequency through the 7th for high frequency. And since noise levels are always expressed in dB, the proportionality becomes delta-L = 10*LOG10((v2/v1)^6) = 60*LOG10(v2/v1).


Gruß, masi1157

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: TVNWZ
Posted 2013-06-24 10:20:38 and read 7843 times.

Just took the 787 from DEN to EWR a couple of weeke ago. It was the quietest plane I have ever been on. I don't know how the A350 can be quieter.

But, frankly, I was most impressed with the window tinting. Very cool.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: bikerthai
Posted 2013-06-24 10:45:52 and read 7707 times.

Quoting lightsaber (Reply 60):
paaa... nothing to a full augmented takeoff of a PW100-229 powered F-16. Now there is noise!

Well, how about a flight of Blue Angles taking off for their practice runs. Whether on game day or just a practice run, they do make it very dramatic!!! True professionals all the way.

We will miss them this year at Sea Fair.  


bt

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: ER757
Posted 2013-06-24 12:25:11 and read 7443 times.

Quoting Stitch (Reply 35):
That Trent 1000 has the most amazing sound, doesn't it? First time I heard it I was like "what the heck is that?" and I looked up to see ZA001 doing a low-and-slow flyover.

Yeah, it sure has! I miss the days of the flight test program and even when NH was flying into SEA with the 787, I'm about three miles southeast of the airport but could always tell when it was departing by that unique sound - I'd look up from whatever I was doing and there she was. Hope NH comes back, not sure if they will though.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: LH707330
Posted 2013-06-24 13:20:27 and read 7230 times.

Quoting DocLightning (Reply 39):
Quoting Stitch (Reply 38):
I don't have a decibel meter in my head so I cannot make an empirical judgement, only subjective. I just notice that A320s sound a bit louder than 737NGs when they're on approach and departure.

They may produce a higher pitch, which is often perceived as louder.

I live under the SEA approach too (Cap Hill), and the A320s are easy to spot by their characteristic howl, but I think this is due to the fact that the noise is more distinctive. The 737 noise blends in better with other urban noise IMHO.

Quoting Stitch (Reply 58):
To each their own, of course, but having watched and listened to an E-3A leave PAE darkening the sky with black smoke and sounding like the Apocalypse itself was on hand, I will gladly take the current generation of commercial airliners and greatly welcome the quiet the A380, 787 and A350 will bring.

There was one down at BFI about a year ago near my office that was hellishly loud, fun once or twice, but annoying long term.

Quoting bikerthai (Reply 63):
We will miss them this year at Sea Fair.

Indeed we shall, maybe a Vancouver road trip will be in the cards instead....

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: SoJo
Posted 2013-06-24 13:34:21 and read 7156 times.

If only they could have built a bigger, noisier version of the Vulcan bomber as a passenger jet. The noisier the better IMO. I was at Fairford when Concorde was still a prototype. Now that was noisy. Wonderful. Bring back noise   

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: DocLightning
Posted 2013-06-24 13:38:50 and read 7137 times.

Quoting LH707330 (Reply 65):
I live under the SEA approach too (Cap Hill), and the A320s are easy to spot by their characteristic howl, but I think this is due to the fact that the noise is more distinctive. The 737 noise blends in better with other urban noise IMHO.

The A320 also makes that weird "flying saucer" whine that I think we determined are made by the landing lights being extended.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: LH707330
Posted 2013-06-26 13:39:03 and read 6261 times.

Quoting DocLightning (Reply 67):
The A320 also makes that weird "flying saucer" whine that I think we determined are made by the landing lights being extended.

Are you sure that's not a doppler effect due to sound refraction? I sometimes hear silence, then a high pitched, rapidly descending tone, followed by the normal A320 howl, but I've heard it with 737s too (stabilizing to their lower rumble) on certain occasions.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: masi1157
Posted 2013-06-26 14:45:22 and read 6029 times.

Quoting LH707330 (Reply 68):
Are you sure that's not a doppler effect due to sound refraction?

Are you sure the Doppler effect has anything to do with sound refraction?


Gruß, masi1157

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: LH707330
Posted 2013-06-27 00:39:05 and read 5726 times.

Quoting masi1157 (Reply 69):
Are you sure the Doppler effect has anything to do with sound refraction?

Good point, I'm mixing up language, what I meant to write was a sound refraction that delays waves and lets them stack up to give the whooshing sound. To an extent this is doppler (plane moving towards observer) combined with refraction (waves get bent and arrive at closer intervals) to give the sound.

Gruß,
M

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: masi1157
Posted 2013-06-27 09:56:18 and read 5415 times.

Quoting LH707330 (Reply 70):
Good point, I'm mixing up language, what I meant to write was a sound refraction that delays waves and lets them stack up to give the whooshing sound. To an extent this is doppler (plane moving towards observer) combined with refraction (waves get bent and arrive at closer intervals) to give the sound.

Why should there be any refraction, when the aircraft is flying rather low? The air temperature will be rather constant, and that is about the only reason for a variation in the speed of sound (which would be necessary for refraction), that I can think of. And even more, why should that effect vary with frequency? I would simply book it under "directivity". But I am not quite sure, what "whooshing" sound you are talking about.


Gruß, masi1157

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: LH707330
Posted 2013-06-27 17:48:29 and read 5133 times.

Quoting masi1157 (Reply 71):
Why should there be any refraction, when the aircraft is flying rather low? The air temperature will be rather constant, and that is about the only reason for a variation in the speed of sound (which would be necessary for refraction), that I can think of. And even more, why should that effect vary with frequency? I would simply book it under "directivity". But I am not quite sure, what "whooshing" sound you are talking about.

this:

Quoting LH707330 (Reply 68):
I sometimes hear silence, then a high pitched, rapidly descending tone, followed by the normal A320 howl

Refraction accounts for the nothing, then rapidly descending frequency, then normal noise. It could also be a weakening headwind that the plane is flying in to. If you have another explanation, I'm all ears.

Topic: RE: How Much Quieter Is 350 Compared To 787?
Username: masi1157
Posted 2013-07-01 14:52:07 and read 4578 times.

Quoting LH707330 (Reply 72):
Refraction accounts for the nothing, then rapidly descending frequency, then normal noise. It could also be a weakening headwind that the plane is flying in to. If you have another explanation, I'm all ears.

As I said, I would book all that under "directivity". Wind may have an effect, that is true. But I am an interior noise guy and don't know too much about all the strange phenomena related to exterior noise. However, what you are describing, sounds to me like not being "refraction" but rather "dispersion" (speed of sound depending on frequency).

Gruß, masi1157


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