# Does it matter which way you plug an ADSL filter? **URL:** \ **Category:** Factual Questions\ **Created:** [September 4, 2012, 5:06pm UTC](https://boards.straightdope.com/t/does-it-matter-which-way-you-plug-an-adsl-filter/633652 "2012-09-04T17:06:02Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\ **Post date:** [September 4, 2012, 5:06pm UTC](https://boards.straightdope.com/t/does-it-matter-which-way-you-plug-an-adsl-filter/633652/1 "2012-09-04T17:06:02Z")
ADSL filters are usually marked. One port goes to the wall plug and the other to the telephone. However I have plugged them the other way round and didn’t notice any difference. Does it matter how you plug them? ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [September 4, 2012, 5:15pm UTC](https://boards.straightdope.com/t/does-it-matter-which-way-you-plug-an-adsl-filter/633652/2 "2012-09-04T17:15:41Z")
It always has for me. phone doesn’t work if its backwards. The filter removes the high pitch squeal from dsl. I used a wall phone for awhile without a filter and put up with the noise. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [September 5, 2012, 3:16am UTC](https://boards.straightdope.com/t/does-it-matter-which-way-you-plug-an-adsl-filter/633652/3 "2012-09-05T03:16:29Z")
When I got my VERY FIRST DSL modem a few years ago, the first thing I did was plug in the ADSL filter backwards. The DSL reception that I got at the modem was awful. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [September 5, 2012, 7:01am UTC](https://boards.straightdope.com/t/does-it-matter-which-way-you-plug-an-adsl-filter/633652/4 "2012-09-05T07:01:40Z")
The “modem” port is unfiltered, the “telephone” port has the filter. If you plug it the wrong way round, I think the modem won’t work. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [September 5, 2012, 12:33pm UTC](https://boards.straightdope.com/t/does-it-matter-which-way-you-plug-an-adsl-filter/633652/5 "2012-09-05T12:33:06Z")
> [@AaronX](#): > > The “modem” port is unfiltered, the “telephone” port has the filter. If you plug it the wrong way round, I think the modem won’t work. That’s right. Filter backwards in the line from the wall socket to the telephone, but the modem couldn’t connect to the outside world. IIRC, it did connect but only very sporadically. Go figure. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 5, 2012, 4:52pm UTC](https://boards.straightdope.com/t/does-it-matter-which-way-you-plug-an-adsl-filter/633652/6 "2012-09-05T16:52:05Z")
I’m surprised by these answers. Our DSL came with one splitter, that plugs into the wall, the modem, and a phone, and obviously that one needs to be connected correctly. Apart from that, we got several filters, that just filter the DSL part of the signal from the phone part of the signal. These are used for any other phones in the house. Those have to transmit the phone signal both ways for the phone to work, and I’d expect the attenuation of the DSL signal would be the same both directions as well. Are people here mixing up the splitter and the filters? ---
**Author:** ![Blakeyrat](https://avatars.discourse-cdn.com/v4/letter/b/ecd19e/32.png) [@Blakeyrat](https://boards.straightdope.com/u/Blakeyrat)\ **Post date:** [September 5, 2012, 5:39pm UTC](https://boards.straightdope.com/t/does-it-matter-which-way-you-plug-an-adsl-filter/633652/7 "2012-09-05T17:39:20Z")
> [@aceplace57](#): > > The filter removes the high pitch squeal from dsl. I used a wall phone for awhile without a filter and put up with the noise. Except if you talk into it, your DSL will disconnect. The filter prevents the DSL noise from annoying you on the phone, but it also prevents your talking from screwing up the DSL signal. Both voice and data need the filter in place to work correctly.