Why did speakers used to make a strange noise when a phone is about to receive a message? Also, why that doesn’t happen as often now (little to no instances)?

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Why did speakers used to make a strange noise when a phone is about to receive a message? Also, why that doesn’t happen as often now (little to no instances)?

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14 Answers

Anonymous 0 Comments

It wasn’t the speakers themselves, but rather the amplifier. First of all, back then the frequency phones used to operate at was different (900MHz) and fixed. That particular signal would interfere with the audio signal the amplifier was, well, amplifying.

Your phone is not constantly emitting a signal. That would drain the battery and keep the bandwidths busy. Instead, once it’s registered with a tower, it stays put until that tower emits a signal seeking your phone. So whenever a text message would be received, your phone would “wake up” and confirm its presence to the network in order to receive the message. Also, the interference was also present during calls, but the text message had a specific pattern. If you held your phone next to an amplifier during a call, you’d hear a constant sound.

Nowadays, phones operate on a multitude of bandwidths. Furthermore, newer audio equipment is shielded against intereference, as older equipment was designed before mobile phones were as popular.

Anonymous 0 Comments

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Anonymous 0 Comments

Any metal wire can act as an antenna and pick up radio signals. It just so happens that older phones used a radio frequency that speaker amplifiers are good at picking up, so they would and so you could hear your phone’s radio data.

Modern phones use different frequencies (due to much higher data speeds) so it’s no longer the correct frequency for speakers to pick up.

Anonymous 0 Comments

Your phone sends out radio waves like a radio station and your wires are acting like an antenna as everyone is saying.

A big reason you don’t hear it anymore is because of shielding like people say and different frequencies, but the major reason you probably don’t notice is that most speakers nowadays have cables that are sending a digital signal. Sending 0’s and 1’s where your minor interference via radio signals gets filtered out.

When a signal is analog the extremely small amount of interference becomes audible

I normally have a USB cable that sends a digital signal to a sound system, I had to switch to using 3.5mm (aux) output for my PC and that cable has a ton of interference with my phone, which gets amplified before being sent to my headphones. The USB digital signal doesn’t have this issue.

TL;DR
The same way your TV doesn’t go out during a snowstorm anymore, technology has changed and interference like that isn’t an issue for modern methods of transmitting data.

Anonymous 0 Comments

Fun fact: if you put your phone on top of a tube amplifier you’ll still get this noise. It’s not as strong as it was say 10 years ago, but it’s still there.

Anonymous 0 Comments

The phenomena occurred during the 2G era. 3G and later phones use spread spectrum technologies (CDMA, OFDM), which distribute energy over a wider band. I.e., the signal before narrowly concentrated its energy in a single band (let’s say over 0.2MHz). This spike was picked up by the amp driving the speakers. Now, the energy is distributed over a fatter channels (let’s say over 20MHz). Instead of a spike, it’s more like a blunt mallet. This leads me to believe the problem isn’t with the oscillator that tunes to the frequency band (after all, 5G reuses 2G bands) but with the distribution of the energy in that band.

Anonymous 0 Comments

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Anonymous 0 Comments

GSM, the old mobile standard, sliced up their channels into time slots such that there were about 1700 of them per second. This allows more than one phone to share a frequency channel. So a phone sending data would be switching its radio on and off at that frequency, which is in the range of human hearing (and thus speakers and amplifiers are designed to work with it). The actual “carrier” radio frequency was much too high to be heard.

Modern mobile phone standards like 3G, 4G, and LTE use different techniques to slice up channels so multiple phones can use them. These techniques don’t include a signal component down in the human hearing band.

Anonymous 0 Comments

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Anonymous 0 Comments

Two elements. (1) the radio transmitters in phones used to be lousier than they are now, splattering a lot more signal in harmonic and subharmonic sidebands — this was exacerbated by the older digital networks needing a stronger signal; and (2) phones in the U.S. used to use something called Time Domain Multiple Access (TDMA) signaling. Each cell tower would allocate a particular slice of time for each phone in contact with that tower, out of every 100-millisecond-or-so block of time. So your phone would negotiate (a) what time it was (this is a big part of why cell phone time is always dead-on the correct time: your phone *had* to know the exact time, to synchronize with the tower and other phones in the general area) and (b) what times your phone was allowed to talk with the tower, and when it had to shut up to let other phones talk. The buzzing from your speakers was the sound of the phone turning its transmitter on and off very rapidly to use the particular time slice that was allocated for it.

Nowadays essentially all phones use Code Domain Multiple Access — everyone transmits all the time, and mixes the signal with a pseudorandom modulation code, which allows the cell tower to pick out each signal even when several phones are broadcasting at once. That solves a bunch of problems with TDMA, one of which is the buzzing (but there are others also). In particular, your phone’s transmitter tends to switch on and stay on when it is talking with the tower. That still affects nearby circuits, but the effects aren’t in the audio band so they’re not as obtrusive.