Why Your Old Phone Sounded The Way It Did

The mobile phone may be sweeping away the traditional wired phone, but that doesn’t change the fascinating history and technology of the older device. At [This Museum Is Not Obsolete] they have a fully functional mechanical telephone exchange as one of their exhibits, and they’ve published a video examining the various sounds it’s capable of making.

When a voice synthesiser was the stuff of science fiction, exchange status couldn’t be communicated by anything but a set of different tones. If you’ve ever encountered a mechanical exchange you’ll recognise the harsh-sounding low-frequency dial tone, and the various sets of beeps denoting different call status. These were produced with a set of oscillators being switched in and out by shaped cams, and the bank of these on their exchange is most of the subject of this video. The common ones such as the engaged tone and the dial tone are explained, but also some we’d never heard such as the one signifying the exchange as out of capacity.

We may never own a mechanical exchange of our own, but we’re glad that someone does and is sharing it with us. You can see the video below the break.


25 thoughts on “Why Your Old Phone Sounded The Way It Did

  1. I used to be in charge of the so called Ruf- und Signalmaschine in the early ’90. They came as a couple and got switched over daily, as it turned out if you use a main one and one just for backup, the backup would fail right away quite often too, which got called “kaputtgepflegt”, maintained to death.

    1. I’ve heard the same about spinning metal hard disk drives. when used with a raid controller, it is common for the mirrored drive to fail within a week of the first drive to fail, usually before the backup is finished downloading. This is because they both have the same wear. I don’t know what the mitigation strategies are, if i had to guess maybe to use an older drive paired with a younger drive so that it’s more likely to fail in a recoverable way.

      1. Mirroring was always a joke as yes you are putting an identical stress load on both drives that at best were the same age type and technology. That goes for both mechanical and ssd

        1. Just because there is some manageable risk for one type of failure doesn’t mean it’s a joke in general. Plus, if your time for copying pairs of drives is that long, seems like it’d take you a very long time to restore the contents of the array from backups if something ever caused a full restore to be necessary, and in that case maybe what you need is to think about availability and whether you can adjust things to be a bit faster to recover in general rather than worrying about solely drive failures.

  2. The Nottingham industrial museum has a working exchange too. It is funny seeing people trying to work out how to use a rotary dial phone who haven’t seen one before! I was involved in a substation refurbishment in Birmingham a few years ago. One of the parts of the building which was needed for operational equipment was the long defunct Midlands Electricity Board’s telephone exchange. It was heartbreaking to know that it would end up as scrap.

    1. I have a typewriter, always fun to see young people type on that. The typing usually sort-of works (until they get their fingers between keys) but inserting a sheet of paper straight and aligned is a whole other problem.

      1. That’s not funny to watch, that’s just painful. Almost as bad as watching old people forget how to read as soon as the words are displayed on a screen instead of a piece of paper. “It says click here to continue, what do I do?! Do I press enter?”

    2. Those rotary dials were invented as a way to torture people I think.
      They require sooooo much goddamn patience and then one of the numbers goes wrong and you have to start over. Horrible interface.
      To think that somebody designed that complex mess and then said “yep, this’ll do fine”

      1. To think that some one designed something that could be made with the available tools and technologies and used by anyone of normal intelligence.


      2. “…Those rotary dials were invented as a way to torture people I think…”

        I’ve no intent to be contrary, but I literally have no idea why you’d feel this way. I don’t remember ever being frustrated by them. Phone dials are an incredibly elegant solution to a very specific design problem… which is why they remained in service as long as they did.

        “…One of the numbers goes wrong and you have to start over. Horrible interface…”

        How is that any different from the touch tone pads that followed? “Starting over” is a feature of the old network, not the dial.

        By the way, I find touch screens annoying. Sometimes hard to trigger when/where you want, easily triggered where/when you don’t, no hapic feedback, easily damaged and, regrettably, an elegant solution to a totally different set of design problems.

        1. The difference is that you could have a digit that takes several damn seconds it seems to finally rotate back, after you first rotate it 300 degrees with your finger in a small shallow hole against a spring.
          And with a 9 to 10 digit number you would have to do it all over again from start, 9 or 10 times.

          And yes it was deliberately slow I’m told because the phone exchange system had a speed limit, but you know even with pretty old tech you could have latched and just have the people wait instead of forcing people to do each step slow. At least you could have done so soon after its release and have replaced it much sooner before a trillion of the annoying things were in the field.

          Mind you I never used a rotary dial as a daily item like people of the era did, but the times I did use it I just could not imagine getting used to it at any point even if I had used it extensively.

          I did at one point got a very cheap slow button phone temporarily that had no memory or latching at all and that was frustrating as hell too, you had to push a digit, wait half a sec, push the next digit andsoforth, and doing it at a normal speed would make it miss digits and you had to start over. I did not use that one long I can tell you.

          The whole thing reminds me of the first bicycles with that ridiculously large wheel and the tiny one, that was not ‘ingenious’ either but rather was ‘not thinking things through before release’.
          I’m quite amazed that it didn’t kill the bicycle concept but was rather popular at the time I’m told.
          People be goofy.

          1. Most people avoided 10 digit calls, which cost more. Long past the introduction of touch dialing and until cell phones took over, you made primarily local calls to people and businesses in your area. You didn’t need the area code for those and so they were 7 digits. When you made a 10 digit call you may have been more deliberate and less hurried; maybe you were calling family across the country after a certain time of day so as to get the cheaper rates. And you could hear the distance in the effects on the call quality and latency compared to the local calls….

            Before that, numbers were even shorter. But either way, since the phone system accepted about 10 pulses per second (plus or minus a few), and digits had between 1 and 10 pulses, the average 7 digit call should involve less than 4 cumulative seconds of waiting for the dial to spin back.

      3. Try tapping the hook switch in the right cadence a series of Morse e’s to “dial” a number. We did it as kids on numbers with lower digits. Our 2 biggest prefix were 742 and 743 which from ’58 to ’86 only needed 2 digits, 42 or 43 if you knew that trick. 6 digit numbers! I have the ’58 and ’59 phone books and what a difference. 58 has the most boring cover with a hand holding the greatest handset ever made the Bell standard, and every number was 5 digits. In ’59 color and teenagers talking on phones also in color, and the familiar 7 digit numbers. Welcome to the space age.

      4. Back when they had been invented, though, phone numbers were quite short.
        My grandparents phone number had just 5 digits, for example.
        That’s still manageable, considering how seldomly the phone was being used.

        1. Bah… my great grandfather’s butcher shop had phone number “2” in his town. I haven’t yet figured out who had “1”, and whether or not they ever called to order beef.

          (My great grandfather was a bit of a forward thinker. He was on the committee that brought the first dynamo to that town also. I’ve seen some of his old high school physics exams, and they put me — a college physics major — to absolute shame).

          1. Somewhere I have a metal screwdriver. It has the phone number of a plumber in the town I grew up in. It is a 3 digit number.

      5. I mean. It is easier than walking to the neighbor’s house to talk to them. Or taking a horse across the village to talk to someone. Or a steam locomotive, or a ocean liner. ps I’m a somewhat active CW operator, so take that for what it’s worth haha

      6. I mean, it’s slower, but if you put your finger in the wrong hole somehow you could just take it back out; the phone system doesn’t know anything happened until you have released it to spin back into place. If you hold down a button on a touch interface, you may get more and more of that number depending how long you touched it. Or if you’re prone to missing the number you want, you’ll probably do it a lot with buttons or especially touchscreens.

  3. “such as the one signifying the exchange as out of capacity.”

    I’ve run into that one, in Germany in about 1992. It had a voice recording instead of a signal tone.

    I knew someone who lived in a small village. I tried to call her one evening, and got a voice announcing that the local exchange was over loaded – there were no available connections to that exchange.

    I hung up and tried again. This time the call went through. The girl I called said she had just been talking on the phone to a girlfriend in another village. She hung up just before I called the second time.

    The line she had been using was the last available connection to or from her village. Nobody could call into or out of the village until she (or someone on one of the other lines) hung up.

    1. The early 90s were still a challenge. Even bigger cities had capacity issues.
      There are multiple reasons for this.
      a) too few landlines had been deployed over years.
      b) the growth of population of citizens wasn’t being taken into account.
      c) the fibre network hasn’t happened.
      In the 1970s, our postal minister foresaw the need for a modern,
      fibre-based communications network,
      but the money went into building the cable TV network (yuck!).
      Because, what’s possibly more important? Communications among people or soap operas, senior programs (schlager music) and football on TV?
      d) re-union of both Germanies.
      The East German telephone network was in poor condition (the former East Germans may disagree, but it really was) and the Deutsche Bundespost/Telekom was busy repairing it.
      e) switch over to digital network, which also included building an ISDN infrastructure. Twice, actually. There was the older national ISDN (1TR6) and Euro-ISDN (DSS1).
      The national version had semi-permanent connection feature and was more sought after.

  4. We were on a party line during the early to mid 60’s. You had to listen on the line first to see if someone was using it before you dialed the number you wanted or the call didn’t go through.

  5. My Mom was the local night operator for the phone exchange in my home town before they changed over to the automatic exchange. It was a plug board system where you jiggled the line and then asked for a specific number from the operator. The local small towns resisted the automatic exchanges as long as they could because the night operator also acted as the contact for the fire department and police, and would be paid by the phone company instead of out of the city budget.

  6. Those rotary dial tone generators were still operational well into the 2000’s in a lot of exchanges although how much of the equipment was actually still wired to them is open to debate as all the POTS exchange equipment was digital by then, but there was a lot of legacy private wire and other analogue gear that may well have still been relying on them.

    Almost any exchange you walked in you could hear one of these whirring away in the bottom of a rack somewhere.

  7. When I was a kid in the 70’s we only dialed 4 digits.
    We were hi-tech when the touch-tone phones came out!! :)

    I did some PBX work ~10 years ago and many motels/hotels were
    still using T1 lines to the PBX.

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