I don't want to do the rewiring required to put a splitter at the demarcation point, but we don't have DSL micro filters available here. Can I use two splitters as filters for the modem and the phone?


I think the Wikipedia article clearly answers this question:

Typical installation for an existing home involves installing DSL filters on every telephone, fax machine, voiceband modem, and other voiceband device in the home, leaving the DSL modem as the only unfiltered device.

3 Answers 3


As far as I know, you need a filter for your phones, one way or another. Given that those filters are hard to find for you, I would see two choices:

Get a single filter, in line before the entire house wiring. Split the phone line BEFORE the filter, and connect your modem. You should be able to order such filters, even if they would have to come from remote locations. There are some that will connect to a phone jack, and provide two connections out. One that is unfiltered, and one that is filtered. I got one of those when I switched back to ADSL technology.

Use your modem on and off, and use the phone only when the modem is not in operation. The noise that is filtered out is what the filter is for. If you do not use your modem, your phones will operate just fine without any filter.

  • 2
    After some reading on the topic I think that in my situation (I have 1 phone in one room and the modem is in another room) it should suffice to use a splitter to separate the phone from the line and for the modem no filtering is required, because, as far as I understand from what I've filtering is only done for the phone so a splitter is just one filter for the done and the DSL output on splitters is not filtered in any way.
    – axk
    Apr 30, 2010 at 14:23

I think this would probably give you a better overview of your options and the correct use of filters vs. splitters: http://www.cisco.com/en/US/tech/tk175/tk15/technologies_tech_note09186a0080094a17.shtml Put briefly, in your situation you should use two splitters, not one. Cheers, Chris

  • 2
    Addition: from the link provided above: "The splitter routes the high-frequency and low-frequency signals on the telephone line to the correct device. Signals intended for the router disrupt voice calls. Signals intended for voice calls affect router operation." In other words, you need a splitter to protect both kinds of devices (voice and ADSL) from affecting each other.
    – Chris
    Sep 13, 2010 at 8:59

If I understand your question, you want a whole-house filter for voice and a raw line to your DSL modem? I have done this using one of the DSL filters typically used for a single phone to filter the voice side of a split feed into the house, and run the other leg of the split, raw, directly from the network interface to the modem. I don't know how the number of telephone extensions, the number of extensions in use at the same time, or the total lengths of extension wiring segments might affect this. Maybe I was just lucky that day, but it's worth a try. Another thing to consider is whether you have an alarm system that needs to seize the phone line and how doing this might affect its operation. Best to check that with your alarm company.

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