Dual 21.5-inch LG UltraFine 4K Displays via Single Thunderbolt Cable?

[joshuad11]

Hi all,

I am hoping owners of at least two LG's 21.5-inch UltraFine 4K Displays can help me determine if I could set up dual monitors via a single cable to my laptop (14-inch M1 Max MacBook Pro) with the use of a Thunderbolt 3/4 dock.

I know that the 23.7-inch displays have two Thunderbolt ports built-in for daisy-chaining, but the older 21.5-inch model actually has a higher resolution of 4096 x 2304. Some sources indicate that daisy-chaining two monitors is only possible at resolutions of 3840 x 2160 or less, but I have also seen setups, such as this one, that supposedly feature two monitors connected via a single cable with the use of a dock.

Has anyone here attempted this setup? Does it work? Do both monitors run at full 4096 x 2304 resolution at 60Hz?

Thanks in advance and apologies if this has already been discussed, but I have attempted to search with no luck.

 

[joevt]

I have not tested the LG 21.5 inch UltraFine 4K display with a M1 Mac but I think you should have no problem connecting two LG 21.5 inch 4K displays to a Thunderbolt 3/4 dock. I would use a Thunderbolt 4 dock or hub because they have at least 2 USB-C ports that you can connect the displays to.

4096x2304@60Hz is 605 MHz (CVT-RB), 593.82 MHz in the LG display. That's too much to allow 10bpc, so we'll calculate bandwidth using 8bpc:
593.82MHz * 24bpp = 14.3 Gbps.

3840x2160 is 533.31 MHz (CVT-RB).
533.25MHz * 30bpp = 16 Gbps.

So the LG 21.5 inch 4K display uses less bandwidth at 8bpc than a normal 4K display uses at 10bpc.