Why does a person hear fluctuations in loudness of sound of the aeroplane engine when it travels from one poin

Question

to the other?

If it was Doppler's effect, then the frequency is in question, but here its the amplitude of the sound...

Hence let me know the reason..?

Answer 1

it's due to constructive/destructive interference coming from the fan blades of the engines.

Answer 2

I assume that you are referring to turbojet powered airplanes.

As the aircraft approaches you are hearing the sound of the intake portion of the airflow into the engine, and as it passes you are hearing the sound of the exhaust exiting the engine.

Both sounds are distinctive in nature. While the sound of the intake is less concentrated, the sound of the exhaust ( hence jet ) is much more concentrated and has also been accelerated to tremendous velocities.

Hope this helps.

I am an airline pilot with many years of experience so if you have other questions please feel free to e-mail me.

Answer 3

It's neither of the other answers.

You are hearing both the intake and exhaust. As the aircraft, or any other noise making object, comes toward you, the sound waves are being compressed increasing the frequency and making it sound higher pitched. The amplitude only gets higher because the sound is getting closer . The actual volume only increases as it gets closer. When the object passes you, the sound waves are stretched out and they sound like they are decreasing in both the amplitude and pitch. Next time you see an ambulance coming your way check it out.