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Connecting Two LG Ultrafine 4k Monitors to M1 MacBook Air

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pcd213

macrumors 6502a
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Jun 24, 2019
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I am trying to connect two LG Ultrafine 4k monitors (24MD4KL-B) to a 2020 M1 MacBook Air.

I have heard that I need a DisplayLink hub but (and pardon the ignorant questions here) the LG monitors are powered by USB C, not HDMI, and all of the DisplayLink hubs that I have seen have two HDMI ports on them.

Which of the two approaches is the correct one?
(A) I need to buy one of these DisplayLink hubs and buy two HDMI to USB C cables, and then plug each of those cables into each USB C monitor?
(B) I only need to buy the DisplayLink hub and one HDMI to USB C cable, plug that cable into one monitor, and daisy chain the two monitors together (with a thunderbolt USB C to USB C cable)?

Thanks for your help. This has been very confusing for me.
 
Last edited:
Hi, thanks. I’m aware of that. I have been told that if I use a display link hub, I can get around this limitation and drive two monitors with the M1 MacBook Air. I’m asking specific questions about that setup here.
 
I have a Pluggable 2x4k@60 Hz adapter and it has 2 HDMI and 2 DisplayPort ports. I imagine that you don't have DisplayLink USB-C outputs to monitors because it can't push USB-C levels of data out. I have not tried using HDMI to USB-C or DisplayPort to USB-C cables to connect to a USB-C monitor and I suspect that my cables aren't bidirectional to try that out. I'd also guess that it's not a common setup because most monitors that I've run into (outside of Apple monitors) have HDMI, Mini DisplayPort and/or DisplayPort available, sometimes in addition to USB-C.
 
pcd213 said:
Hi, thanks. I’m aware of that. I have been told that if I use a display link hub, I can get around this limitation and drive two monitors with the M1 MacBook Air. I’m asking specific questions about that setup here.
Click to expand...
You should know that DisplayLink is not a full replacement for a native display output. Think of DisplayLink as a simple USB-attached framebuffer or GPU, it will light up a display but is neither as efficient nor as performant as a "real" display output. Not saying you shouldn't use one, just be aware of what it is, what it is not, and what its limitations are.
 
I don’t see how a “HDMI to USB-C” cable would work in that direction… the displays support Thunderbolt 3, or USB-C DisplayPort Alt mode. Neither of which, you’re gonna get (or convert) from HDMI. I haven’t seen any DisplayLink adapters that output DisplayPort Alt via USB-C… “Maybe” an adapter from DisplayPort would work? Don’t know.
 
So I guess that the customers who are buying 2 LG Ultrafine 4k or 5k monitors are those who are buying a machine with the higher end M1/M2 chips. I’m going to try to buy a DisplayLink compatible hub and then two HDMI to USB-C cables, and just see what happens.

If it doesn’t work, I guess I’ll be reselling this second monitor. What a shame. I previously had no idea that the M1 MacBook Air couldn’t power two displays. I feel like this limitation has gone under the radar.
 
pcd213 said:
If it doesn’t work, I guess I’ll be reselling this second monitor. What a shame. I previously had no idea that the M1 MacBook Air couldn’t power two displays. I feel like this limitation has gone under the radar.
Click to expand...
It is mentioned on these forums frequently but I suppose if you are used to Intel notebooks it might never occur to you to check. The single external display is to me the only real problem with Apple’s M1 and M2. It’s hard to explain why they have that limitation.
 
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jdb8167 said:
It is mentioned on these forums frequently but I suppose if you are used to Intel notebooks it might never occur to you to check. The single external display is to me the only real problem with Apple’s M1 and M2. It’s hard to explain why they have that limitation.
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No doubt. I honestly don’t read the forum too frequently, but rather the posts on the main website. I’m just surprised (or maybe not) that apple has used this use case as leverage in selling higher end machines and chips. It’s a shame we most something like this moving from Intel to base M chips.
 
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pcd213 said:
M1 MacBook Air couldn’t power two displays. I feel like this limitation has gone under the radar.
Click to expand...
People have complained and its a limitation on the GPU I believe. Its a bummer that you have to find out the hardway
 
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I had thought “would it make economical sense for me to buy a Mac mini and sell my M1 MBA” because I heard, maybe incorrectly, that the M1 Mac mini doesn’t have this problem and doesn’t need any of the DisplayLink workarounds. But after having to buy a keyboard and mouse, it’s not quite break even for what I could sell my MacBook Air for.
 
pcd213 said:
I had thought “would it make economical sense for me to buy a Mac mini and sell my M1 MBA” because I heard, maybe incorrectly, that the M1 Mac mini doesn’t have this problem and doesn’t need any of the DisplayLink workarounds. But after having to buy a keyboard and mouse, it’s not quite break even for what I could sell my MacBook Air for.
Click to expand...
The mini has the same M1 as the M1 MacBook Air. It can only handle 2 displays just like the M1 MBA. The difference is that on the MBA one display is dedicated to the internal display while the mini doesn’t have a built-in display.

Edit: one display is dedicated to the HDMI port though. The other is available via the USB-C port.
 
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jdb8167 said:
The mini has the same M1 as the M1 MacBook Air. It can only handle 2 displays just like the M1 MBA. The difference is that on the MBA one display is dedicated to the internal display while the mini doesn’t have a built-in display.

Edit: one display is dedicated to the HDMI port though. The other is available via the USB-C port.
Click to expand...
So I couldn’t even run two displays with the Mac mini if I wanted to? Run one on USB C and the other on HDMI (extended view, not mirror)?
 
pcd213 said:
So I couldn’t even run two displays with the Mac mini if I wanted to? Run one on USB C and the other on HDMI (extended view, not mirror)?
Click to expand...
You can run 2 displays on the Mac mini. All M1(not Pro/Max/Ultra chips) and M2 can run 2 displays total, which includes the built in screen on laptops.
You cannot connect 2 of the LG 4k Ultrafine displays because on the Mac mini, one display must be connected to the HDMI port, and the Ultrafine has no HDMI ports.
 
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chrfr said:
You can run 2 displays on the Mac mini. All M1(not Pro/Max/Ultra chips) and M2 can run 2 displays total, which includes the built in screen on laptops.
You cannot connect 2 of the LG 4k Ultrafine displays because on the Mac mini, one display must be connected to the HDMI port, and the Ultrafine has no HDMI ports.
Click to expand...
So a HDMI to USB C cable wouldn’t help me there?
 
pcd213 said:
So a HDMI to USB C cable wouldn’t help me there?
Click to expand...

chrfr said:
Those cables are USB-C to HDMI. They don’t work in the other direction.
Click to expand...

There are some but they're incredibly rare compared to USB-C -> HDMI. I found these two (one, two), can't speak for how well they work, a third I found via Google was out of stock. I think the use case of HDMI -> USB-C just is not very common.

Edit: the third one says it's not compatible with LG UltraFine so that goes out the window anyway. It needs to be specifically one of the UltraFine models that was USB-C and not Thunderbolt 3, of which I don't think there were many.
 
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Thank you, all. Looks like I need to sell this second LG Ultrafine 4k. :/
 
Get DisplayLink to DisplayPort adapter, then connected a Belkin Charge and Sync cable.
 
chrfr said:
That’s just the aforementioned DisplayLink adapter. The issue of the DisplayLink adapters only having HDMI output is the complication with using the LG UltraFine displays.
Click to expand...
Yes, this is correct. The fact that the two displays only have Thunderbolt ports is the problem here.

Last question, if I bought bidirectional ‘DisplayPort to USB C’ cables, and used those in a DisplayLink hub’s DisplayPorts, do you think that might work? Probably not, but thought I’d ask if “bidirectional” is the silver bullet here.
 
chrfr said:
The issue of the DisplayLink adapters only having HDMI output
Click to expand...
There are many DisplayLink products that can support output other than HDMI. In the products-list page, choose USB adapter with DisplayPort output.
https://www.synaptics.com/products/displaylink-graphics/displaylink-products-list

pcd213 said:
Last question, if I bought bidirectional ‘DisplayPort to USB C’ cables, and used those in a DisplayLink hub’s DisplayPorts, do you think that might work? Probably not, but thought I’d ask if “bidirectional” is the silver bullet here.
Click to expand...
Yes, bidirectional USB-C to DisplayPort cable should work as DisplayPort to USB-C. It won't include a USB signal to support the USB features of the display, such as audio, brightness control, camera, USB ports. That's why I would recommend trying a Belkin Charge and Sync cable or Wacom Link Plus or Sunix UPD2018.
 
pcd213 said:
Yes, this is correct. The fact that the two displays only have Thunderbolt ports is the problem here.

Last question, if I bought bidirectional ‘DisplayPort to USB C’ cables, and used those in a DisplayLink hub’s DisplayPorts, do you think that might work? Probably not, but thought I’d ask if “bidirectional” is the silver bullet here.
Click to expand...
USB-C video is “DisplayPort Alt Mode” so - “maybe” a DisplayPort to USB-C could be used in that direction? I’ve never tried. HDMI to USB-C isn’t gonna work, without a BUNCH of electronics that would make it far more cumbersome than is worth making.
 
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pcd213 said:
I am trying to connect two LG Ultrafine 4k monitors (24MD4KL-B) to a 2020 M1 MacBook Air.

I have heard that I need a DisplayLink hub but (and pardon the ignorant questions here) the LG monitors are powered by USB C, not HDMI, and all of the DisplayLink hubs that I have seen have two HDMI ports on them.

Which of the two approaches is the correct one?
(A) I need to buy one of these DisplayLink hubs and buy two HDMI to USB C cables, and then plug each of those cables into each USB C monitor?
(B) I only need to buy the DisplayLink hub and one HDMI to USB C cable, plug that cable into one monitor, and daisy chain the two monitors together (with a thunderbolt USB C to USB C cable)?

Thanks for your help. This has been very confusing for me.
Click to expand...
Check this guide: https://m1displays.com/

You can get a hub or adapter, and you can get DisplayPort.
 
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