Exactly how does my cell phone affect my computer speakers?

[KarlGauss]

Just curious.

If I use my cellphone within a yard or two from my computer, the speakers begin to make various sounds (noise, really). Note that the speakers are wired to the computer (not a wireless set-up).

If pressed for an explanation, I would wave my hands a lot and say something to the effect that cellphone was inducing a current in the speakers. In truth, I don't have a clue. What is going on, though? (I'm afraid that one day my daughter's gonna ask me about this and I would never want her to think there's something that Dad didn't know )

[friedo]

Originally Posted by KarlGauss

If pressed for an explanation, I would wave my hands a lot and say something to the effect that cellphone was inducing a current in the speakers.

That explanation is exactly right! Your speakers are acting as an antenna, and the broadcast from the cellphone is being picked up by the circuitry inside, amplified, and turned into sound. Good speakers, like the kind you'd get for a stereo system, have shielded components so they won't pick up outside radio signals. But computer speakers are of notoriously crappy construction.

[Fridgemagnet]

Pretty good guess. There's not enough power in a cellphone transmission to induce enough energy in a speaker so that it's audible, but the signal path electronics are much more sensitive, and though they are designed to be immune to a certain amount of noise, too much will often have a noticable effect.

I've heard plenty of CD players, radios etc. pick up interference from mobile phones; even when in standby they periodically communicate with the base transceiver. The transmitted frequency is itself too high to be picked up directly as an audio signal, but any semiconductor junction can act as a radio frequency demodulator that turns RF into a lower frequency audio signal.

[BlakeTyner]

I live about 50 yards from a major highway, and every once in a while my computer speakers will pick up and amplify truckers on their CBs. It's quite strange to start hearing voices from across the room, let me tell you.

[teela brown]

So what's happening when my radio (either bedside or car) starts sounding like it's receiving Morse code transmissions when a cell phone is near?

[tanstaafl]

My understanding is that that is just the "handshake" between the cell phone and the nearest cell tower. Cell phones have to notify the system of their position periodically so that the system knows which tower to route a call to when one comes in and that is what you are hearing. That's the explanation I got anyway.

[gotpasswords]

Pretty much so - cell phones are communicating via digital signals, so you're hearing pulses in the speakers.

What's a bit amusing is when you hear these enough that you can tell what's interfering with the speakers or a desk phone headset / speakerphone.

Cingular's TDMA signalling comes across as erratic bursts - chikchik chak chik

Nextel sounds like a helicopter - tukka tukka tukka tukka...

[gotpasswords]

Pretty much so - cell phones are communicating via digital signals, so you're hearing pulses in the speakers.

What's a bit amusing is when you hear these enough that you can tell what's interfering with the speakers or a desk phone headset / speakerphone.

Cingular's TDMA signalling comes across as erratic bursts - chikchik chak chik

Nextel sounds like a helicopter - tukka tukka tukka tukka...

[KarlGauss]

Excellent! My thanks to all of you.

[MsRobyn]

Originally Posted by friedo

Good speakers, like the kind you'd get for a stereo system, have shielded components so they won't pick up outside radio signals. But computer speakers are of notoriously crappy construction.

Not necessarily. I work with good speakers attached to audio production equipment and I get the cell-phone noise all the time. I have to keep my phone a few feet away so the speakers don't pick up the noise while I'm actually working. OTOH, the noise isn't picked up by the recording software.

Robin

[garygnu]

Wonderful descriptions of the noise.
I hear it more than just about anyone else, as the interference from up to 54 cellphones and Blackberries goes into speaker wires we have mounted in the first six rows of tables at the conference facility I work in. Specificaly, I work the audio control board. I listen to that combined microphone feed at nearly full unity in my headset for 20 to 40+ hours a week. (I've just started using the compressor function in the board to make the noise not so deafening, but it still makes my job a pain.)

[snailboy]

My stepbrother used to occasionally leave his cell phone next to my computer, and a full second or two before it would ring, the speakers would pop a few times. I was wondering what signal would cause this. What would the phone communicate back to the tower at least a full second before it even started ringing?

[mks57]

Originally Posted by snailboy

My stepbrother used to occasionally leave his cell phone next to my computer, and a full second or two before it would ring, the speakers would pop a few times. I was wondering what signal would cause this. What would the phone communicate back to the tower at least a full second before it even started ringing?

The cellular network is verifying the location of the phone before trying to complete the call. The phone may have been turned off or moved to a different cell.

[gotpasswords]

Originally Posted by snailboy

My stepbrother used to occasionally leave his cell phone next to my computer, and a full second or two before it would ring, the speakers would pop a few times. I was wondering what signal would cause this. What would the phone communicate back to the tower at least a full second before it even started ringing?

It's basically telling the network "Yep, I'm over here and ready to take a call!"