View Full Version : Cell phone ring causes speaker buzz: why?
07-30-2003, 01:04 PM
I've noticed this while driving: When my cell phone rings, starting just beforehand, a loud buzzing comes out of the stereo speakers and continues until the phone is either answered or the caller goes to voicemail. What causes this? Is it bad for my speakers? I noticed it just happened here, too - I'm sitting in a radio station production booth, and I called my cell phone to retrieve a message. The phone was set to "silent," but the speakers above me buzzed loudly, as well as the speaker in the handset.
07-30-2003, 01:18 PM
I'm not sure why either, but I have the same problem. Presumably the speaker wire is not sufficiently shielded to prevent it from picking up the cel phone signal and reading it as noise. I don't think this can really be bad for your speakers....it's been going on at my house (in my car, and with the speakers on my computer) for about a year now, and the speaker seem to work fine otherwise.
07-30-2003, 01:39 PM
As part of the process of ringing, your cell phone is transmitting some relatively high-power RF to the local cell site to tell the system "I'm on and ringing" and to negotiate how much radio power is needed.
My plain ol' Nokia creates a blast of noise in my office phone headset when it receives a call. Every now and then, I'll get a quick "ft-ft" noise, presumably from the phone reminding the system of its availbility.
Nextel phones cause a strange helicopter thup-thup-thup-thup noise when they're in use.
07-30-2003, 01:40 PM
This is caused by the acknowledgement signal your phone sends out in response to an "incoming call" signal from the cell network. Most PC speakers are insufficiently shielded to prevent a relatively strong RF signal from causing interference, and this is what you are hearing. It's harmless to the speakers, if a bit annoying to you.
07-30-2003, 02:01 PM
Thanks, guys. This is a Nokia causing the problems. It's interesting you mentioned insufficient shielding on the part of the speakers - the ones here in the studio are professional, seemingly (Alesis M1 Active Mk2, if that means anything). I thought they might be made of stronger stuff.
I had a Nokia that also did this. I always knew when it was going to ring because my the speaker on my desk phone would make a noise before the cell phone rang.
07-30-2003, 05:22 PM
It's not so much the speakers as the line-level cables and amplifiers. This applies to $19 amplified PC speakers equally well as a $1900 studio amp. It only takes one corroded bit in a connector or a cold solder joint to act as a rectifier and turn RF into an audio-band signal. RF has also been known to sneak into amplifiers via the generally unshielded speaker connections - some amp's internal feedback circuitry is more susceptible to this than others.
If a phone or any other sort of transmitter was putting out so much RF to make noise in speakers on its own, I'd flee the area before I got cooked.
07-30-2003, 09:50 PM
Same phenomenon observed here...
I get home, put my phone on the desk and check my email. When my wife calls for the ride home, BOTH of my imacs buzz and twitter BEFORE the phone rings. I usually answer it before it rings, since I know there's a call coming in.
07-30-2003, 10:37 PM
Originally posted by gotpasswords
If a phone or any other sort of transmitter was putting out so much RF to make noise in speakers on its own, I'd flee the area before I got cooked. Will RF really "cook" me? Is this why people have been blaming cell phones for brain tumors?
07-30-2003, 10:42 PM
Originally posted by SanibelMan
Will RF really "cook" me? Is this why people have been blaming cell phones for brain tumors? Relax. it takes hundreds of watts of RF power to cook anything. Your phone is emitting about .1 watt, typically. No reputable study has ever found a statistically significant risk of brain cancer from linked cell phone use. Gotpasswords was merely making the point that it would take a LOT of RF power to cause noise in the spaker cone itself, rather than trhough the attached amplifiers.
07-30-2003, 11:22 PM
Ah, thank you. I didn't want to die from sitting in a windowless, foam-covered room and being buzzed at.
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