What If I Don't Use DSL Filters?

By David Lipscomb

DSL services require filters to prevent interference.
i Chad Baker/Photodisc/Getty Images

Digital Subscriber Line, or DSL, is a popular choice for broadband Internet. Using a phone line to send the digital data into the home or business, DSL requires the use of filters at each phone jack. These filters affect not only the throughput of the broadband Internet, but the quality of the phone service. Since DSL and the landlines in the structure share the same wires, it is critical that these filters be properly placed and in use.

What Is a DSL Filter?

DSL filters are fundamentally designed to prevent the incoming Internet signal from being "confused" and looking at each phone in the structure as though it were the DSL modem. These filters are low-pass in nature, meaning that they block out high-frequency interference from each phone line, preventing static and dropouts.


DSL filters are found in three major iterations. Standard filters prepackaged with DSL modems are small boxes with a DSL connector at one end and a phone line at the other. Micro filters are designed to incorporate the phone and modem connectors together on one unit, useful if a phone is located close to the modem. Still other versions are in wall plate form, incorporating the filter into a convenient low-profile device that mounts between the wall and phone.


DSL filters must be put in place before any device that uses the structure's phone lines, with the exception of the modem itself. Failure to do this results in dropped signals while online, or at minimum, severely slowed connection speeds. At the other end, static and dropped calls plague connections not using DSL filters. Devices that must employ DSL filters include fax machines, answering machines and copiers that employ built-in modems.

Solid Practices

Connect the DSL modem after each DSL filter is connected to each device sharing the phone line. Simply disconnect the device from the wall, insert the DSL filter into the wall and reconnect the device to the filter. Connect the modem directly to the wall after these filters are in place. You should see the requisite indicator lights flashing after the modem boots up, indicating a solid connection. Additionally, so long as your wires are in good shape at your phone box outside, your phone call clarity should be improved.