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June 11, 2007

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Weird, Random Interference In Speakers

I've been thinking for a while now that I'd have to replace my clock radio. Every once in a while, in the morning, I'll get a weird series of ticks that I couldn't pin down the source of. Well, I've had the thing since high school, so it's probably just on its last legs. It also works well enough and I don't listen to it for more than a couple minutes at a time, so it's not high on the to-do list.

This weekend I bought new speakers for my computer. After an unrelated failed attempt at getting the bluetooth connection to work so I could download some pictures from my cell phone, the new speakers started doing the exact same ticks.

I noticed something in the speakers I figured I was going to be replacing: The ticks always happened at 17 minutes after the hour. Even weirder, that would also be about the time my clock radio does the same thing, even though it's not even in the same room.

Obviously, there's something going on at x:17 that's causing this interference, but what?

After my hourly dose of "tick tick-ti-tick tick-ti-tick" I finally had enough: I looked online. After some rooting around in Google, someone mentioned that their cellphone did strange things to their radio.

Cell phone. My cell phone's been sitting on the desk near the speakers since I futzed with bluetooth. And that's when the new speakers started ticking. I don't know exactly what the thing's doing every 60 minutes, but if it's close enough to the speakers it manages to induce a current and cause the ticks. Maybe re-registering on the network?

Anyway, it seems the new speakers aren't shielded very well; the phone can mess with them when it's a foot or two away, whereas it has to be within a few inches of the clock radio. (And I have to listen to Elliot In The Morning babble for more than a couple seconds before I hit the snooze bar.) Doesn't surprise me, really... I bought the speakers for their price, not their quality.

Ah. Now that I have an idea what to google for, I find the following:

Your speakers are detecting data bursts from the phone. GSM data bursts are at 217 Hz which is in the range of human hearing.
(http://cellphoneforums.net/ alt-cellular-cingular/ t162446-moto-v551-hourly- interference-computer-speakers.html)

A different phone on a different network, but T-Mobile is GSM (as far as I know) and I doubt the make of phone (Nokia vs. Motorola) means anything. Oddly enough, I never notice this when the phone rings, but that may be because I don't get calls very often.

Solutions include shielding the speaker wires (too expensive and annoying) or keeping the phone away from them. I'll go with option B. That also explains why the clock radio is less affected: It doesn't have external wires so the body of the radio acts as a partial shield.

Edit, 9:00 PM: Experimented with the phone and the clock radio this morning, and the clock radio's as bad as the new speakers. I just rarely listen to morning radio long enough for the re-registration to happen. The old speakers worked just fine, so I'm guessing they were at least semi-shielded, but the power switch was broken, making them kind of tough to use reliably. I'll just have to remember to keep the cell away from the desk.

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This page last updated Jul 19, 2019 3:34:19 PM.