Why is my cell phone causing noise in my speakers?

Question

Why does my cell phone create a sound like static interference when it is laid near the speakers and the monitor on my desk? Off and on all morning I could hear the interference come and go. If I shut the speakers off, the sound stopped, or was that coincidental?

- Carol

Answer

This question was answered on July 31, 2008. Much of the information contained herein may have changed since posting.

With all of the wonderful electronics in our lives, on occasion they clash with each other and what you are experiencing is the clash between your cell phone and your computer’s speakers.

The type of cell phone and the type of computer speakers that you have will both have a dramatic impact on this noisy irritation You may notice (especially after reading this column) that not all cell phones create the crackling, pulsing noise and not all computer speakers will pick up the interference generated by some cell phones.

Let’s start with your computer speakers The job of your speakers is to amplify sound, so any sound that is introduced to the speakers will be amplified Typically, the sound that is to be amplified is supplied to the speakers via the wire that connects into your computer’s audio output

If, however, the speakers and the connecting wires don’t have adequate “shielding”, then various “radio frequencies” (RF) can be picked up and amplified by the speakers Most computer speakers are very inexpensive and rarely have any real level of shielding, so RF interference can easily sneak into the path of amplification

When you shop for speakers and notice that they claim to be shielded, they are referring to the shielding of the magnets inside the speaker, which prevents magnetic interference with your monitor, not shielding against this problem, unfortunately.

The noise you are hearing can be picked up from various connectors and components in your speaker system including the entire length of the wire that connects to the back of your computer (which inadvertently ends up acting like an antenna if the shielding is degraded or non existent).

Now for the differences in cell phones…

Cell phones that use a GSM network (AT&T or T-Mobile are the major carriers that do) use a pulsing radio frequency to communicate with the cell towers, which is what you are hearing through your speakers

GSM phones will create the pulsing interference at different levels for a number of reasons: prior to and during an incoming or outgoing call, sending and receiving text messages, transitioning between coverage areas or just as an ongoing way to register location with the system.

Another issue is the power needed to communicate with the cell towers; if your phone is having to crank up its wattage in order to connect to a weaker signal, it can introduce noise from a farther distance because it is transmitting a more powerful signal.

Cell phones that use the CDMA network, which consist of most phones from Alltel, Sprint/Nextel and Verizon, don’t use the same pulsing radio frequencies as GSM phones, so they don’t usually have this issue near computer speakers.

A possible exception for CDMA based cellular phones are the newer “world phones” that incorporate both CDMA and GSM technology in the same phone, but only when they are communicating with a GSM network.

Generally speaking, moving your phone away from your speakers (and the wires) or turning it off will reduce or eliminate the noise Higher quality speakers can also help, but make sure to perform “the cell phone test” at the store before buying any new speakers!

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Author

Posted by Ken of Data Doctors on July 31, 2008