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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As a record store manager it’s frequency changes that the amplifier cant give a good sound to doesnt happen nowadays due to technology advancements
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inexplainlikeimfive
GSM phones (AT&T and TMO in the U.S.A) use a type of communication where each phone is allowed to talk for a short period of time. (like old mainfraim computers, time sharing) In this brief amount of time the phone sends out large amounts of radio waves. When your phone’s transmit time is over the next phone gets to transmit. (Your phones get to transmit about every 4.3 milliseconds) This is how a cell phone tower is able to talk to multiple phones at once.
Your speakers most likely have an amplifier in them and one or more of the short copper wires on the circuit board are acting as an antenna. This antenna is picking up the short, but powerful, transmissions from your phone. (Happens at about 217Hz)
Source: I design speaker systems for iPhones and we make sure (so does Apple) that you can’t hear the noise.
for those older than 5 check out this link for more in depth sources: (http://www.google.com/search?gcx=w&ix=c2&sourceid=chrome&ie=UTF-8&q=TDMA+217+Hz)
It was your [phone yelling back at the tower, ](https://youtu.be/Du8yQeQdMBk?t=523)louder and louder until the tower can hear it properly.
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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.
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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.
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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.
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.
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