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I noticed that the cabin chimes on the Boeing 747-400 overall sound one semitone lower than on other aircraft, including the 737, 777, Airbus A320, and even the 747-8. The same semitone-lower chimes are used on the Bombardier Q400, but that was built later.

Notice here that with the exception of some Qatar Airways planes using the "high" chime instead of the "low" chime for the seat belt sign, all the "low" chimes sound the same, with the exception of the Bombardier Q400. That chime is the same as the one on the Boeing 747-400.

Why is this the case?

Update: I noticed that this question was marked as being primarily based on opinions. However, it's not based on opinions. If you looked at the video links I supplied above, it is a fact that the cabin chimes on the 747-400 are lower-pitched than most other planes. All of the planes in the compilation video, except one, are at the same higher pitch. It's not just my opinion that they're lower-pitched. Also, if the answer is that "the chime manufacturer simply built it that way", that should be an answer. Questions shouldn't be closed based on the answer, the merits of the question alone should be judged.

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    $\begingroup$ You realize that there is no standardization for these tones and they can differ by manufacturer and model. They can even differ by operator... $\endgroup$ – Ron Beyer Oct 29 '18 at 4:27
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    $\begingroup$ Obligatory Fawlty Towers: "the fire bell is a different; it's a semitone higher" $\endgroup$ – Zach Lipton Oct 29 '18 at 5:20
  • $\begingroup$ A born skill known as a "perfect pitch" is required to hear a semitone difference for the single, randomly sounded tone. Not even every professional musician can do. Most people can only tell the difference between the two that sounded very recently. $\endgroup$ – h22 Oct 29 '18 at 9:35
  • $\begingroup$ I work for a company that makes such a chime and I can tell you that manufacturing tolerances amongst components in the circuit play a part. I don't think there is a rigid specification for this either. $\endgroup$ – Michael Hall Oct 29 '18 at 16:36
  • $\begingroup$ In the compilation video, the chimes are all the same note except for the dash 8 Q400, which is a minor second below the rest, and the 787-800, which is a minor third above the rest. However, the video for the 747-400 is from a flight simulator, which should not be considered definitive. $\endgroup$ – Wayne Conrad Nov 13 '18 at 10:07