How to run 4 external displays?

Discussion in 'MacBook Pro' started by snowmirage, Mar 13, 2017.

  1. snowmirage macrumors newbie

    Mar 13, 2017
    I have a Mid 2015 MacBook Pro Retina 15-inch running OSX Sierra 10.12.3 which uses the AMD Radeon R9 M370X GPU and Intel Iris Pro Graphics

    I'm experiencing an odd behavior I can not explain.

    To the hdmi port on the right side I connect a 1920x1080 hdmi monitor.

    To the front most thunderbolt port I connect a Monoprice Thunderbolt to HDMI active adapter which connects to another 1920x1080 hdmi monitor.

    To the back most thunderbolt port I cannect a LG 34UM95 via thunderbolt cable (3440x1440 resolution)

    This all works great!

    I am trying to add a 2nd LG 34UM95. If I unplug everything then

    To the back most thunderbolt port connect via a thunderbolt chain both LG 34UM95 monitors they both work!

    Plugging in the HDMI monitor on the right side port also works.

    But when I plug the Monoprice Thunderbolt to HDMI active adapter back into the front most thunderbolt port I get no display on that monitor.

    But if I disconnect the 2nd thunderbolt monitor at the end of the chain that monoprice adapter starts working again.

    Why is this?

    The only two solutions I can come up with are

    1) use the Monoprice thunderbolt adapter at the end of the thunderbolt chain, but to do this I would need a $200+ intermediary thunderbolt device.

    2) Use a usb > hdmi adapter instead. But I have seen a couple that are claiming they wont work with OSX Sierra?

    I'm at whits end here and I'd certainly appreciate some expert insight into this little conundrum.
  2. DeltaMac, Mar 13, 2017
    Last edited: Mar 13, 2017

    DeltaMac macrumors G3


    Jul 30, 2003
    You are running into a limitation of the hardware.
    You have three video device outputs, 2 on thunderbolt, and one HDMI.
    You can chain two thunderbolt devices (or one TB in each port) and add the third to HDMI, then you get no video from a 4th device plugged into the 2nd TB port, or add a third display to the 2nd TB port first, then HDMI won't light up a 4th display.
    Adding a 4th device will remain black. You may be able to count the internal display as the #4 display (I think), but 4 externals won't work.
    (Wait for it - someone will prove me wrong with a picture of 4 external displays running on a rMBP)
  3. snowmirage thread starter macrumors newbie

    Mar 13, 2017
    Hmm that might be true, but Each thunderbolt port is capable of multiple monitors. I know that works I can run 2 thunderbolt displays (chained) off one port.

    I'd have to wait until I'm back in the office to test it, but I'm guessing if I connected another 2 thunder bolt monitors to the 2nd thunderbolt port (or maybe even just added more to the 1st chain) it would work, up to a point.

    Seems like option 1 I mentioned in my post might be my only solution. This seems like it might work but man they are expensive.

    something here just doesn't make sense
  4. DeltaMac macrumors G3


    Jul 30, 2003
    Yes, but notice that El Gato takes the place of using a daisy chain connection, when the display the you want to use has none.

    Anyway, your MBPro has two TB connections, so you can connect two TB displays. Note that you could connect the two displays to a single TB port, assuming the display has a second TB port to allow daisy-chaining.
    If you do THAT, you can (I think) attach a third display to the MBPro second port.
    No daisy chaining on THAT display to add a 4th display, even if it has the extra port.
    It's a 4th display, and the hardware won't support it.

    Use both TB ports, one display each, add an HDMI display. Works.
    Daisy chain two displays from one TB port, add HDMI, Works. Add another display to 2TB port. Won't work.
    You have 3 external video outputs, which can be configured in several different ways, maximum of 3 displays.
    You can have two attached as daisy-chain, then add the El Gato hub, and use THAT with a single display.
    Your MBPro would then have a total of three displays. The El Gato has capability of two displays, but the Mac won't supply video to the second display if you already have 2 displays in use (the thunderbolt bus is supplying all the video outputs possible) Add a third through HDMI (on the MBPro, not the El Gato)
    Get the picture? No 4th external display on your MacBook Pro, even with accessory docks.
  5. Sanpete macrumors 68020

    Nov 17, 2016
    To run four external monitors with a MBP:

    1. Go to the Apple Store.
    2. Buy a 2016 15" MBP.
    3. Connect a monitor to each port. Or daisy-chain.
  6. Samuelsan2001 macrumors 604

    Oct 24, 2013

    No connundrum the MacBook Pro you have supports a maximum of three external displays. its a limitation of the hardware, you are trying to do something the computer just won't do.
  7. campyguy macrumors 68040

    Mar 21, 2014
    Portland / Seattle
    OP, agreed with others here about the limit of number of displays. The rMBP doesn't have enough graphics power to drive all of those displays. Additionally, the limitation of TB relative to throughput - TB cables and adapters with TB cabling, by design are limited to DP 1.1a - we never use TB cables to drive displays in my offices, only DP 1.2 cables that are 2160p-rated. Introducing TB cabling into any display-related chain IMO will only gimp the performance of any display; please refer to the DisplayPort Wiki for more on this. Devices like Matrox's desktop extenders don't work (according to Matrox) with the newer rMBPs that have AMD dGPUs, only the iGPU and the results are limited to 768p (ugh).

    The only solution I can think of is to look into a eGPU set up, which I do employ for some of my Windows laptops in one of my offices but not for any of my Macs. eGPUs for Macs aren't on my radar and there's others in these Forums that have the capability to advise you about these graphics boxes. Good luck.
  8. rutrack, Mar 14, 2017
    Last edited: Mar 14, 2017

    rutrack macrumors regular

    Jan 5, 2017

    With 2015 15" You can run at least 5 displays simultaneously:
    1: Internal
    2: Display Port
    3: Display Port
    4: HDMI
    5: AppleTV

    I haven't tried it, but I guess you can also connect your iPad through "Duet" as external display, which would make it 6.
    You can also try this adapter, should add another monitor:

    Attached Files:

  9. DeltaMac macrumors G3


    Jul 30, 2003
    Ah, good catch! I didn't think about the AppleTV.

    The OP wanted 4 external displays simultaneously, so I guess that does it with the AppleTV
    Is there any lag on the video through the AppleTV (compared to the other displays?)

    The USB-HDMI adapter that you linked is not compatible with Sierra.
  10. rutrack macrumors regular

    Jan 5, 2017
    There is a lag, of course , but it looks usable for text , not sure how the op wants to use it. And I guess you don't have to run Sierra if your use case is not supported, but i don't think the adapter will be more usable than Apple TV anyway.

Share This Page

9 March 13, 2017