8 Replies Latest reply: Feb 6, 2013 6:28 PM by Grant Bennet-Alder
daveemac Level 1 (0 points)

TIA for your help.  I know there are already threads about mulitple monitors, but my specifics are slightly unique...


I currently run a 42" TV from the DVI port using an HDMI adaptor cable.  Works great.


I'd like to add a 20" monitor (Dell Ultrasharp, lots of connectivity options) and a 17" (older, less connectivity options).



I'll never need all three on at the same time.  One of the new monitors would display the same signal the TV gets; the other monitor would be a second screen.


What's the smartest way to do this?  From my reading I figure it will involve a powered splitter of some kind.  Does my 4870  have enough power to drive the two smaller montiors plus the 42" TV? 



(I also have a 2011 MBP I could throw into the mix, but I'd rather just run everything off of the MP if possible.)



A semi-detailed explanation of what products I need and how to use them would be most appreciated.  Looking for the simplest, cheapest solution.



Mac Pro, OS X Mountain Lion (10.8.2), 4.1
  • Grant Bennet-Alder Level 9 (56,679 points)

    I'll never need all three on at the same time.

    The simplest, cheapest solution with the 4870 card (which has one Dual-Link DVI and one Mini DisplayPort) is to swap cables. Done!


    If you did want all three at once, you could upgrade to the 5770 or 5870 card. These work in all Mac Pro models, drivers are in 10.6.5 and later. These two have one Dual-Link DVI-I port that can drive a wider-than-1920 DVI display directly. The other two ports are Mini DisplayPort, same as the 4870.


    To drive one Single-Link DVI display with Mini DisplayPort, an inexpensive adapter will do. All these cards can produce a DVI signal from a MIni DisplayPort with the correct timing. But the signal levels are a bit on the low side, and when you drive two converters, the signal level is too low and the third display drops out.


    The solution to this problem is to use ACTIVE converters, which boost the signal levels up and keep three display operating. For Single-Link DVI (good for up to 1920 wide or 1080p) you can get an ACTIVE adapter for about US$35. For Dual-Link DVI, the adapter usually requires a USB cord for additional power and the prices are close to US$100.

  • daveemac Level 1 (0 points)

    Thank you very much for your helpful reply.


    Swapping cables is simple in one sense...but a bit of a PITA at the same time.  But it's worth considering.


    New card is kind of expensive, and potentially a can of worms.



    I'm guessing that the single-link splitter won't be able to drive the 42" TV and 20" monitor at 1080p, correct?


    So am I right then that I'd need to run one of the small monitors off of the DVI port and then use an active dual-link splitter to send the mini displayport signal to the TV and to the other small monitor?



    Alternatively, is there a relatively simple way to bring the MBP into the equation and avoid using a splitter at all?

  • Grant Bennet-Alder Level 9 (56,679 points)

    Run your big display directly off the DVI port.


    Then you could run:


    Mini DisplayPort to Single-Link DVI adapter to Single-Link DVI "extension" cable to the top of the desk.


    Then plug/unplug:


    Option 1: 20" display with DVI cable

    Option 2: TV with DVI-to-HDMI cable -- 42" TV set is only 1080p ( = 1920 by 1080)




    and then there is THIS for US$60:




    folks say it is slow.

  • daveemac Level 1 (0 points)

    Thanks again.  However, if I want two instances of my main feed and want one of those to be on the bigscreen, then won't I have to split that main feed output?


    Put another way, if I split the microdisplayport signal will it be possible for the two splits signals to output different feeds?  I'm guessing it's not possible, but maybe it is...


    Pardon me if I missed your point; this whole thing makes me a bit dizzy!



    When people say the USB solution is slow, do they mean that the actual video output is slow?


    Lastly, any suggestions for incorporating the MBP?

  • Grant Bennet-Alder Level 9 (56,679 points)

    When you connect multiple displays to a Mac, this pane appears in System preferences > Displays. The presentation as shown is called "Extended Desktop". This diagram will expand to as many as you have connected. You re-arrange the tiny screens until they are in the same orientation as those on your bench.


    You can merge any two displays by dragging the Icon for one on top of another. The screen resolutuion will change to the highest resolutiuon BOTH displays can handle. (So the Icons may change shape to reflect the new resolution.)


    In the special case of exactly two, you can just check the [√] Mirror Displays checkbox.


    Splitters? Foregtaboutit. You have a Macintosh!


    Arrange Window screenshot.png



  • Grant Bennet-Alder Level 9 (56,679 points)

    When people say the USB solution is slow, do they mean that the actual video output is slow?

    They mean that changes are slow to be reflected in the display. If you run the mouse around that display, it will really lag, and that is very frustrating.


    You could use Screen Sharing across an Ethernet connection to incorporate the MacBook Pro. That would allow you to incorporate it as a Mirror of another display.

  • daveemac Level 1 (0 points)

    When I say "splitter" I mean mini displayport adapter which splits to two outputs.



    Is the mac able to provide two different video feeds via the one port (and then split them via the adapter)?




    I would have guessed this is impossible, but from your message I'm inferring that it can be done.


    So it sounds like I just need a passive displayport adapter.  Care to recommend one?


    Thanks again!


  • Grant Bennet-Alder Level 9 (56,679 points)

    Is the mac able to provide two different video feeds via the one port (and then split them via the adapter)?


    No, but it can do the reverse. Provide exactly the same picture out two different ports on command. Then change to Extended Desktop on command when you re-cable.




    Read carefully. they jumble DisplayPort and Mini Displayport, ACTIVE and not: