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Everyone who used early telecommunications services, not to mention the early dial-up Internet services, is familiar with the tones and hissing sounds of a modem establishing a connection. I recall all my home computer modems, from the early 1980s 300 baud units through to the late 1990s 56K units all having speakers to provide this audible status/feedback during dialing and connecting. Indeed, it is one of the strongest memories surrounding telecommunications during those "pioneering" years.

But terminal programs were usually sophisticated enough to provide nice status indications (mainly visual, but possibly audible) about what was going on with the modem while trying to establish a connection. Such terminal UI features certainly seem superior to the horrendous "groaning" and "hissing" from the modem speaker.

So why were modem speakers such a persistent feature, and "fixture" of the time?

Not all modems from back in the day had speakers, for example an early popular modem was the Hayes Micromodem II (available for Apple ][ and S-100 machines) and it did not have a speaker.

But the speaker served a few purposes that I can think of:

1. Early modems were not very good at detecting various states, e.g. busy line, voice pickup, disconnected number notifications, etc. Without the modem supporting the detection of these states, the terminal program wouldn't do a very good job reporting it.


2. You could quickly tell if the line was busy or if someone picked up the phone. Even with later modems, detecting voice was not quick or necessarily accurate.


3. You could detect any dialing errors easier. Obviously, this would be more appropriate for complicated numbers rather than ones in your local area code / exchange.

Personally, I always left the speaker on though perhaps turned down low enough that I could hear the dial and busy tones. If anything, it did give me the ability to whistle a carrier tone by hearing it so many times :-)

So why were modem speakers such a persistent feature, and "fixture" of the time?

Three basic reasons:

1. Adding a simple amplifier and a speaker is the most easy way to handle unexpected situations


2. In many countries/networks having a speaker aktive while establishing a connection was mandatory to make it legal/get a validation


3. Adding it was as well the least cost intensive way to handle complex situations.

Keep in mind, the kind of modems most people used were not for dedicated lines, like todays cable or DSL installations, but operating over regular dial up. To start with, anything could happen - starting from some angry mom picking up the phone were her son has hooked up his BBS, wrong numbers, all the way to signal tones outside the spec the modem was build for (for example ring tones in various countries used different rhythms and frequencies).

So having a speaker was a quite good debugging tool - after all, whatever happened on a phone line would be withing 3000 Hz, clearly noticeable by humans listening.

This is as well the reason why phone regulators/companies required them to be installed as well. They wanted to minimize interruption of third party (due miss handled/directed calls) as well as having the user able to detect special situations on his own, without calling for service. In fact, in many cases it was as well require that each and every Modem had to have a hand set (or a complete phone) connected, so the operator can pick it up and talk to any (unintended) party on the other side to apologize and or first talk to the other side before switching to data. In reality most private users ignored that part (as well).

These are as well the reasons why feeding the speaker, until a valid connection was established, was the default configuration - though, it wasn't really enforced. If you didn't like it, it could be configured away - at least with most modems.

Last but for sure not least: Modem producers liked it as well. After all, with a speaker they didn't have to invest much money in detecting all kinds of situations. Let the user handle it like he was used to do it with a regular phone call.

Much of this has been covered by previous answers, but to try to summarize:

1. Adding a speaker was cheap and easy. The additional parts were standard, reliable, and inexpensive.




2. It provided rich, immediate, understandable feedback on a variety of call-progress milestones.

Click -- modem is responding enough to grab the line.

Dial tone -- phone line is available. No dial tone? Check whether you're plugged in, see if your regular phone has been off-hook long enough for the phone company to give up on it. If you hear a voice, someone else is using the line; try again later.

Touch-tone/click signals -- you're dialing the remote number. If there are too many or two few digits, you'll hear the difference; eventually, you might even learn to recognize the patterns for frequently-called numbers, so you can hear if you've accidentally dialed the wrong one.

Remote ring -- you've successfully reached the remote number. Busy signal, disconnected-line message, "you must first dial 1"? All much easier for a human ear to interpret than for 1980s hardware.

Connect tones -- you've reached a modem at the other end. Voice or recorded message? You haven't reached a modem.

Silence following the previous stages -- the modem thinks you've connected successfully. Continuing connect/handshake tones? You might have a bad line; if it goes on too long, hang up manually and try again.

I suspect it could be a holdover from the days when a modem was a box that connected between your terminal and your phone. The phone handset was used to dial the remote number; when you heard the whistle from the far modem, you'd press the 'online' button on the modem, and then replace the phone handset.

And, of course, if it wasn't a modem whistle you heard, it was either a confused human, or else some telephone-system signal telling you why you hadn't been connected (either tones or voice announcement).

So audible signals were an intrinsic part of knowing where you were in the connection sequence.

The photo is from Handbook of Data Communications, UK Post Office, 1975. The modem's the box under the telephone.

I seem to recall that the PC-board modems could be configured to not enable the speaker, but I for one always left the audio on, for reassurance that things were progressing in the desired manner.

My guess is that's its mainly for easy human understandable notification.

Probably it can be compared a little bit with electrical cars. They do not make sound. Because people are not used to them, it can be dangerous if one suddenly approaches you (especially from a side you cannot see). To prevent this problem, some cars make sounds (like a motor) to 'warn' people there is a car near.

Of course this is more from a safety point of view, but when someone sees a car, it expects to hear one too. Since people were used to hear a sound from a modem, they need to hear the sound; if it is silent they might think it is nonfunctional (even with some terminal program indicating otherwise).

On an older modem, if one tried to dial a number, one of two things would happen:

1. Before a configurable timer expired, the modem received a carrier tone. In this case, it would output "CONNECT" and then start exchanging data with the far end.




2. The timer expired without the modem having received a carrier tone. In this case, the modem would output "NO CARRIER".

Older modems had circuitry to detect the carrier tone, but not to detect anything else that might happen on the line, since a modem had no real reason to care about such things. All the modem cared about is whether the connection succeeded or failed. A human might want to know more, but the simplest way of giving such information to a human was to add a speaker.

BTW, I remember a modem which had a configuration option to mute the speaker as soon as it heard the carrier pilot tone, rather than at the end of negotiation; I don't know why that wasn't a more common option.