How to Avoid Mobile Phone Interference w/ Speakers

EnzoTen asks: "Everyone has been sitting at their desk rockin, jamming, or groovin to their favorite tunes. You are in a trance, getting work done... then... BZZZPT... BZZTP..BTT.. BZZZZZZZZPTT... the blood curdling noise of your cell phone interferes with your desktop speakers playing 4 times the volume of your music and it takes everything in you not to flip your desk upside down, or throw your mobile phone across the room. Is there anyway to avoid mobile phones interfering with speakers? Are there speakers available that are shielded from this type of interference?"

Re:Never happened...

[Anonymous Coward]

This happens with amplifiers, speakers, and CRT monitors if the phone is near them when the phone is actively sending data/voice.

GSM

[Detritus]

It seems to largely be a problem with GSM handsets, so users of handsets that comply with other standards may not notice a problem. GSM uses TDMA, and has also been noted for interference to hearing aids.

The solution is to properly shield the speakers and speaker wire. The speaker wire behaves like an antenna, coupling the signal into the audio amplifier, where it is detected and amplified. It's behaving like a crystal radio, a primitive type of AM radio receiver.

Re:You've gotta wonder

[Omniscientist]

Preposterous. GSM's data burst frequency is in the range of human hearing. However, the signal isn't strong enough for you to hear, unless the signal is amplified somehow. The speakers and their cables allow the signal to pass through an amplifier, allowing you to hear it. The only way that would hurt us is if we had giant antennas connecting to amplifiers embedded in our ears, and becoming deaf from the loud noises.

Kidding aside, the worry over cellphones is the damage that might result from the RF energy being emitted. However RF energy is non-ionizing radiation, so the frequency is way too low to do any sort of damage to your DNA. I believe it's media fueled hype, but I'm not an expert on the subject.

Either way, the real danger that cell phones present are when someone happens to be using one and driving a car.

Re:Simple

[Hes Nikke]

that doesn't work, my cell phone will drive speakers that are off, unpowered, and unplugged... try again next time!

Re:Never happened...

[dscho]

Slashdot comments at its best. Useless.

If you do not recognize the problem, it just might be that you

a) do not experience it -> cannot help.
b) do not hear it -> cannot help.
c) notice it, but do not want to help!

In every case, it might have been a good idea to wait and see if more
intelligent and/or helpful people chime in, and might provide an answer to
the riddle. And until that time, just shut up. You probably will just look
foolish if you try otherwise .

I actually *understand* the physics behind that phenomenon, and alas, there
is no better solution than what was provided in another response: put your
cell phone at least one foot away from the speakers. The problem is Maxwell:
in order to send a signal successfully to the next station (remember: this
is most likely indoors, as speakers are less usefull outside, and thus, there
is probably a wall, which has to be penetrated by electromagnetic waves) the
cell phone has to "pump up the volume".

The energy is degrading with the second power of the distance to the cell
phone, so: putting it at double distance to the speaker (or the next
station, for that matter) will lower the received energy by 75%. Same is true
for the station, but that is farther away to begin with.

educating people every day,
Dscho

Re:GSM

[Andy Dodd]

Not quite correct.

I'm 90% positive that the protocol for UMTS has no connection to GSM either.

In short, UMTS is an entirely different standard than GSM, the only thing in common is the name, as UMTS is considered "3G GSM". The protocol is different, and so is the underlying modulation. (In the case of changing to CDMA modulation, you have to change the protocol to take full advantage of the new modulation scheme.)

Don't use wireless?

[lpq]

The Original Poster didn't say if his office speakers were wired or wireless.

I've never experienced radiowave interference on my wired speakers, but know my house (neighborhood?) is nasty on radiowave interference. I tried purchasing some FM-speakers, but they couldn't receive a clean signal
across my living room.

How is your network connection? Wired or wireless? Could it be the network signal being messed with before it hits your computer and you computer just amplifies and echo's out the interference?

I strongly doubt it's in the speaker wires. While I remember a friend of mine in college would play tricks on guys living in the next dorm room, he had a ham radio license and foot long antenna. Still he had to be less than a foot to cause the interference you are talking about -- holding the antenna parallel to the speaker wire that ran along the edge of next door room. Any farther, or disorient the antenna (not parallel to speaker
wire) and there was no interference. He only did a few times when they were cranking music too loud -- they thought it was a problem in their setup, so they stopped cranking it so loud...:-)

However, a cellphone, given it's small antenna and the lower power (his ham setup ~10-30W; modern cellphone: max 3W), it would be hard pressed to generate the same interference.

I'd look to other causes than a cellphone for interference in wired speakers.

However, for 1/8th inch connector thin-wire computer audio, most of the wire I see is shielded. RadioShack sells shielded and unshielded audio cable in lengths up to 20-30 feet. It's not that expensive: less than 20 bucks for a 20 foot extension cord last time I bought some.

Good luck.
-l