Report Slow Dl Speed Through Sbc Dsl - - Looking For Help! in General Discussion Posted August 14, 2010 · Edited August 14, 2010 by zalternate Those little 'filters for the phone' can fail sometimes and cause issues. So your modem set itself to operate at the best stable speed it could, due to the bad filter for the phone. I have a POTS(plain old telephone service) splitter in my Demarc(gray box for service from pole) where the lines come into the house. So I don't need filters on every phone. And if there is any issues, I can plug in outside and it bypasses all the phone lines in the house to automatically rule out any house wiring issues.