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I'm flying this Friday again and can't find my two-to-one 3.5 mm jack adapter and I was wondering why did they decided to go this way?

One like this:

I'm talking about these

I know why they were using the two prongs, to avoid of theft of the airline distributed headphones. But why not use two regular jacks and just switch the channels on the second one? This way everybody could use his own headphones.

JonathanReez
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TS.
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    Two questions. You might want to split them up. – MastaBaba Sep 20 '15 at 19:32
  • "But why not use two regular jacks and just switch the channels on the second one?" I am not sure I completely understand what you are suggesting by this. But depending on how it was done, it might have meant that someone could use stolen airline headphones with regular equipment just by cutting off one of the two prongs. – Nate Eldredge Sep 20 '15 at 19:36
  • I'm afraid the answer is actually a lot simpler - the double - jack is a relic of the past, from a time where most people did not own headphones. There was no motivation to standardize it. – Benjamin Gruenbaum Sep 20 '15 at 20:25
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    It's mostly historical I suppose because I see fewer and fewer of these. Most my recent flights (80% at least) had standard jacks. – Itai Sep 20 '15 at 23:36
  • @BenjaminGruenbaum: That's almost an answer. However, I does seem to me that this was very much standardized, considering it used to be the standard on airlines. – MastaBaba Sep 21 '15 at 00:05
  • @MastaBaba I've heard it from a person deeply involved in the aircraft industry but don't have a solid reference so I didn't want to post an answer without providing a solid reference. – Benjamin Gruenbaum Sep 21 '15 at 07:19
  • @BenjaminGruenbaum Up to you. :) But, this is not Wikipedia. Personal expertise is valued :) – MastaBaba Sep 21 '15 at 13:38
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    See also http://aviation.stackexchange.com/questions/13154/why-do-entertainment-system-headphones-on-aircraft-have-two-pins – Relaxed Sep 21 '15 at 21:10
  • The bigger question is why would a person owning a set of headphones wouldn't also own an MP3 player or a phone :) – JonathanReez Apr 24 '16 at 12:04
  • @JonathanReez I mostly use the headphone jacks on airplanes for watching movies on the IFE. I rarely use them for music unless there's something really loud (a crying kid, for example) that I need to drown out. – reirab Aug 25 '16 at 21:53
  • I have removed the second part of your question. None of the answers addressed it, and it's really a separate question, so it's better to ask it separately. That way you'll have a good chance at getting some new answers, too. – Fiksdal Aug 26 '16 at 15:44
  • By the way, I flew on Boeing 787 Dreamliner a couple of weeks ago (July 2017) - and the headphone connection was the two-prong type. – Aleks G Jul 27 '17 at 20:09

5 Answers5

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I'll speculate on your main question: Not only did the non-standard jacks mean that the airline's equipment would be useless outside of the airplane, it also meant you had to use their equipment if you wanted to listen to audio. Meaning, the airline could also charge you for it.

MastaBaba
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  • I totally forgot that this was the case back in the days... I guess that was the reason. Thanks – TS. Sep 22 '15 at 11:34
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I can only assume it was to prevent people from stealing their headphones. In response to your second question, I have often used my own headphones on planes that have the two jacks, with mixed results.

Most of the time you only get one audio channel when you do (as you might expect), which means you only hear out of one ear. This typically does not bother me.

Other times, if you pull out the jack slightly, you can get sound out of both ears. Its nice when this happens, although its sometimes a little tricky to keep the jack out slightly (it tends to fall out).

Mark Mayo
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pocketfullofcheese
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The reason was compatibility with piped sound sockets in older planes.

During the transition from piped to wired sound, the spacing between left and right channels was maintained as it suited the metal template in the individual passengers consoles

Karl
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Well, as for "why", others have answered nicely. If you wanted to get around it without using their equipment, you could get a Y-cable in configuration 3.5 TRS F -- 2x3.5 TS M. I tried looking for it online, it seems to be uncommon, so you can either use two cables/adaptors that are available in the music stores (for instance 3.5 TRS M -- 2x3.5 TS M and 3.5 TRS F -- 3.5 TRS F), or solder one yourself.

Explanation to the vocabulary:

Your headphones have a stereo male jack, which is 3.5 TRS M. It fits into a female 3.5 TRS F. The mount in the place is two mono female outlets, which is 2x3.5 TS F, and 2x3.5 TS M fits in them. So, you need a cable with 3.5 TRS F -- 2x3.5 TS M, or a combination of cables that give you this configuration. This is exactly what you show in the picture, however, there the two mono jacks are in a fixed distance, if you use cables, you get variable distance, hence less troubles.

yo'
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0

On some aircraft the second jack is used to provide electrical power for noise cancelling headphones. On most of the aircraft I've been on recently, the 3.5 mm jack is the norm. The two pronged configuration, with one prong for each stereo channel, is becoming uncommon in Europe and North/South America.

Calchas
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