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User profile for user: gony22
gony22 Author
User level: Level 1
8 points

problem using two external monitors - experiencing lags and more

i have been using an external monitor for some time and wanted to step further and work in 3 screens simultaneously .


my gear :

MacBook Pro (Retina, 13-inch, Mid 2014)

2 monitors - benq GW2270

2 HDMI to DVI cables

1 1080P HDMI Port Male to 2 Female 1 In 2 Out Splitter Cable Adapter Converter Set https://www.ebay.com


when i connect each monitor seperately , they work fine and i can modify the preferences so the external screen would be an extension of my desktop.


when i connect them together strange things happen .

  • sometimes the external monitors turn black and do not respond , when i eject the cable they do show 'no signal detected' meaning they did receive a signal yet i saw only a black screen.
  • after i turn off the computer and connect them one after the other , i get the extension i am used to have for one external screen - on both . the two external screens are now mirrors of each other.
  • another feature of this state is constant lagging . when the two external screens are on and mirroring eachother , the mouse freezes and also video freezes when displayed .
  • last thing , in preferences->display setting -> arrangement : i can only see one extra monitor even though both are connected and they are displaying a mirror.



in the apple support i saw the following info about my computer :

  • Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 2560 by 1600 pixels on up to two external displays, both at millions of colors


i thought it means i can use two external monitors . was i wrong?


thanks a lot for any advice !

Posted on May 26, 2019 11:35 AM

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User profile for user: Grant Bennet-Alder
Grant Bennet-Alder
User level: Level 10
133,279 points

Posted on May 26, 2019 12:44 PM

It is not an accident that the pictures shown in that ad feature the IDENTICAL picture on each display. Unless you are doing a presentation in a large auditorium requiring two identical screens, I do not see how that could possibly be what you want.


Your Mac has adequate support for those nearly-antique 1080p benq displays:


2nd Display Support: Dual/Mirroring*2nd Max. Resolution:2560x1600 (x2*)

Details:*This model supports a simultaneous maximum resolution up to 2560x1600 on two external displays via Thunderbolt. Alternately, it can support a single display up to 2560x1600 via Thunderbolt and a single 1080p display at up to 60 Hz, 3840x2160 at 30 Hz, or 4096x2160 at 24 Hz via HDMI.


Connect the first display as you expect, directly to the HDMI port on your computer with the HDMI-to-DVI adapter you have.


For the second display, you need either:


• Mini DisplayPort (ThunderBolt subset) to HDMI with the HDMI-to-DVI cable you have. -OR-

• Mini DisplayPort (ThunderBolt subset) to DVI


a Mini DisplayPort adapter has a computer-end the same size as the ThunderBolt port, and it picks up only a subset of the full ThunderBolt signals needed to drive a display or adapter.


Do not get distracted by ThunderBolt-3/USB-C adapters -- they will not fit or work with your computer.

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User profile for user: Grant Bennet-Alder
Grant Bennet-Alder
User level: Level 10
133,279 points

May 26, 2019 12:44 PM in response to gony22

It is not an accident that the pictures shown in that ad feature the IDENTICAL picture on each display. Unless you are doing a presentation in a large auditorium requiring two identical screens, I do not see how that could possibly be what you want.


Your Mac has adequate support for those nearly-antique 1080p benq displays:


2nd Display Support: Dual/Mirroring*2nd Max. Resolution:2560x1600 (x2*)

Details:*This model supports a simultaneous maximum resolution up to 2560x1600 on two external displays via Thunderbolt. Alternately, it can support a single display up to 2560x1600 via Thunderbolt and a single 1080p display at up to 60 Hz, 3840x2160 at 30 Hz, or 4096x2160 at 24 Hz via HDMI.


Connect the first display as you expect, directly to the HDMI port on your computer with the HDMI-to-DVI adapter you have.


For the second display, you need either:


• Mini DisplayPort (ThunderBolt subset) to HDMI with the HDMI-to-DVI cable you have. -OR-

• Mini DisplayPort (ThunderBolt subset) to DVI


a Mini DisplayPort adapter has a computer-end the same size as the ThunderBolt port, and it picks up only a subset of the full ThunderBolt signals needed to drive a display or adapter.


Do not get distracted by ThunderBolt-3/USB-C adapters -- they will not fit or work with your computer.

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problem using two external monitors - experiencing lags and more

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