Do I need to use a microfilter here?

[#1]

Hi,
I have the Master Socket (which is the newer type with the test socket behind the face plate) into which is pluged an extension cable. The extension cable doesn't have a two socket plug that is plugged into the master socket, but is the single plug type that fits into the master socket and the downstairs telephone plugs into the back of this plug. The extension cable then goes upstairs to another telephone socket in the study (see picture).
This telephone socket in the study which is where I have plugged in the microfilter. The study telephone, sky box and bedroom
telephone are then plugged into the microfilter via a three socket adapter, along with the ASDL cable from the computer.
The question is do I need to put a microfilter on the downstairs telephone?
I am not quite sure because the downstairs telephone is plugged into the back of the extension cable which does have a
microfilter on it (although upstairs in the study). If I add a microfilter between the downstairs telephone before plugging into the master socket (which is via the back of the extension cable plug) would this give two microfilters on the same line?
I know it is best to use the master socket rather than an extension for the ASDL, but the extension is fairly new so the wiring is good and I don't need the maximum speed that my telephone line will support. Also there is no power point near the master socket for the router and the computer is upstairs in the study.
A solution would be to plug a microfilter into the master socket and run another ASDL cable along side the extension telephone cable to the router. But this will require some work. If I took this route what cable would I need? The yellow cable from the computer to the router is quite thick, but the cable from the router to the microfilter is thin (which is what I would need to replace with a longer probably 10m length). Would this be what I would need http://cgi.ebay.co.uk/RJ11-Male-BT-Broadband-Cable-ADSL-Modem-Router-Lead-20m_W0QQitemZ390040667915
Thanks.

[#2]

Quote from: steed

The question is do I need to put a microfilter on the downstairs telephone?

Yes, definitely.

[#3]

To clarify another point and answer you last query, the recommended maximum number of "dangly" filters on a line is 4, but the fewer the better really.  All POTS devices (phones, faxes etc) must be connected via a filter. What you don't want is two filters in series where you are trying to get ADSL out of the second filter. About the only time you may want two filters in series is when connecting some troublesome DECT phones.
At the end of the day, it depends on how much money you want or are prepared to spend. The best solution for your situation, especially if you have a very good line, would be to run a fixed cable from the Master socket to the upstairs extension socket using twisted pair cable to spec CW1308 (this is most important).  You would only need 2-pair cable, of which you'd only use 1 pair, the Blue/white & White/blue connected to terminals 2 & 5 at the rear of the removeable faceplate on the master and at the extension socket. You'd need an IDC insertion tool (krone type) to make the connections. You can get cheap ones for about 40p for one off jobs. The cable is small and neat and cheap (same type of cable as would be used by BT).
If you want to get rid of dangly filters you could use a filtered face plate (that has ADSL fixed wiring connections) at the master, and a filtered extension with an ADSL outlet and a POTS outlet on the socket plate.
Otherwise stick with what you've got.

[#4]

Quote from: Anotherone

About the only time you may want two filters in series is when connecting some troublesome DECT phones.

And Sky boxes. 
So another filter upstairs might be in order....

[#5]

Oh err, now you mention it I remember reading somewhere that some sky boxes give problems,. can't remember where though 

[#6]

Thanks HPsauce and Anotherone for your replies.
I will see what kind of connection and speed I get with the current set up, and then decide if it needs to be changed.

[#7]

Plug a filter into the socket exposed by the extension lead, then plug your downstairs phone into that.
Without the filter, it is likely that your broadband will only sync at around 135k, instead of a reasonable level!
B.