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So I am a huge fan of the A320, and in a less broader sense, the A320 with IAE-V2500 engines. Arguably the greatest engines in the industry with the greatest sound. However though, I've had a question that I just can't seem to have answered so I'll ask here. If you're sitting inside an A320 with IAE-V2500's and you're taxing out to the runway, you here a very distinct humming noise coming from the engines. What I find confusing about this noise is that it sounds very different on the outside as I have spotted the A320 with V2500's in person, and the idle/taxi sound outside of the aircraft sounds very different from the inside. You can find the sound I'm talking about at timeframe 7:42 until takeoff (taxi) in this provided YouTube video:

Thank you all so much! -Niko

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  • $\begingroup$ I couldn't hear anything change much at 7:42 $\endgroup$
    – fooot
    Aug 7 '17 at 16:41
  • $\begingroup$ I'm not exactly sure what noise you're referring to - do you mean the oscillations in loudness? en.m.wikipedia.org/wiki/Beat_(acoustics) (possibly due to N1 and N2 almost syncing up) $\endgroup$
    – Sanchises
    Aug 7 '17 at 16:57
  • $\begingroup$ @Sanchises, the beat is probably not N1 and N2 almost synching up, it's more likely the left and right engines running at slightly different speeds. I hear the beat coming in about 6:42 on the video, so maybe OP just made a typo with 7:42? $\endgroup$
    – Daniel K
    Apr 5 at 11:00
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I don't think there's anything particularly special causing that sound, it's just how the engines sound.

Inside the airplane you're heavily insulated from exterior sounds, so you're not going to hear much of the airflow and fan sounds from the engine. You're mostly hearing engine sound that travels through the airframe itself, the turbines primarily.

Outside, the engine sound is dominated by the airflow and fan noise.

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  • $\begingroup$ You may mention that insulation may filter out some sound frequencies and thus distort sounds $\endgroup$
    – Manu H
    Aug 7 '17 at 16:45
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I think this is the sound of combustion, as for example it is always the first sound that gets higher in frequency when fuel flow is increased (or engine spools up). Furthermore, the sound is more audible when sitting just above the wing, as this part is quite close to the combustion chamber, so combustion can be heard. It also makes sense as combustion to me should have a sound that is closer to humming than the sound of a mechanical whine such as when the fan spools up. Additionally, when an engine starts up, it first spools up using the bleed air until a certain rpm where a rumbling sound starts to be produced and gets higher in frequency until it becomes like the hum we are concerned with here. Apparently thats the sound of combustion being introduced. Not sure though. I’m just trying to make a case here, so don’t take my word.

On a side note, I also like listening to that humming sound, especially when sitting in front of an iae v2500. The cfm56 also has a similar humming sound on both a320 and b737.

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    $\begingroup$ mmmmm... edible sound.... $\endgroup$
    – FreeMan
    Apr 2 at 17:40
  • $\begingroup$ i mean audible* 😂 By the way do you have any idea what that humming sound could be? Cause what I wrote is just me guessing. $\endgroup$ Apr 3 at 9:12

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