Thunderbolt dock that supports two LG 5k displays?

[FergusH]

Hi all,

I've got two 27-inch LG UltraFine 5K displays and I'd like to connect them to my MacBook Pro 14" M1. Has anyone been successful in using two LG 5k displays via a Thunderbolt dock?

I've got the Sonnet Echo 11 Thunderbolt 4 dock and it definitely does not work (despite Sonnet's website saying it should; I'm going to call them tomorrow). If I have one display connected via the dock and one directly via the Mac, both displays work. However, if I connect both displays to the dock, neither display works (despite one appearing in the display control panel).

I'm hoping someone might have had better luck with another brand of dock.

Thanks.

 

[fwmireault]

I’ll repost the answer of @joevt from an other thread here, I think it may help you

An LG UltraFine 5K requires two DisplayPort 1.2 connections over Thunderbolt (two tiles of 2560x2880 at 483.37MHz). Each connection is 14.5 Gbps. There's no way you could connect two of them to a single Thunderbolt port - that would require 58 Gbps but Thunderbolt can only do 40 Gbps.

There exist 5K displays (e.g. iiyama ProLite XB2779QQS-S1) that take a single DisplayPort 1.4 signal at 967.01MHz but only up to 8bpc. Each display requires 23.2 Gbps so two of them cannot be connected to a single Thunderbolt port.

The XDR display uses DSC which compresses the video signal to ≈12bpp so its 1286.01MHz pixels only requires 15.4 Gbps. You can connect two of those to a single Thunderbolt port.

It should be possible to create an adapter that takes a DSC signal like the one used by the XDR and output two DisplayPort signals for a dual tile display like the LG UltraFine 5K (or the Dell UP3218K or the LG 5K2K display or the Acer XV2713K, etc.). With such an adapter, the LG UltraFine 5K would only require 11.6 Gbps. The LG UltraFine 5K is a Thunderbolt display, so the two generated DisplayPort signals need to be converted to Thunderbolt. That can be done with a Thunderbolt 3 add-in card.

The proposed adapter would be like a video wall processor. It takes one input and divides it between multiple displays. However, I haven't seen one that does DisplayPort 1.4 or DSC. https://www.matrox.com/en/video/products/gxm/dualhead2go-series/digital-me
I suppose it could be made with a sufficiently powerful FPGA that can do DisplayPort 1.4 HBR3 + DSC input and dual outputs but I think they're really expensive?

There may exist some display driver boards that can do the job.
https://forums.macrumors.com/threads/diy-5k-monitor-success.2253100/

 

[joevt]

You might be able to connect both LG Ultrafine 5K displays to the dock if you connect them using a 20 Gbps cable instead of a 40 Gbps cable (use a USB-C (not-Thunderbolt cable) or a Thunderbolt 20 Gbps cable).
But the displays would be limited to 4K output (the GPU will scale 5K down to 4K which will be scaled up by the display to 5K). If custom timings can be supported on M1 Macs, then a 5K39 timing could be used (I've only see one person try that on an Intel Mac - I don't know how to make custom timings on M1 Macs).

 

[Alakiha]

How about Caldigit Thunderbolt 4 | USB4 ELEMENT HUB ?

 

[joevt]

How about Caldigit Thunderbolt 4 | USB4 ELEMENT HUB ?

A Thunderbolt device is not going to make a Thunderbolt port of a computer be able to have more than the max 2 DisplayPort connections that a single LG UltraFine 5K requires to do 5K60.

Well, except if you had an Intel Mac, then you could connect a Thunderbolt 4 dock or hub and a Blackmagic eGPU or Sonnet eGPU Breakaway Puck RX 5500XT / 5700.
Then you could connect one LG UltraFine 5K display to the Thunderbolt 4 hub/dock which would be powered by the GPU of the Intel Mac, and connect the second LG UltraFine 5K display to the eGPU.

eGPU's don't work on M1 Macs. The only way that two LG UltraFine 5K's could be connected to a single Thunderbolt port of an M1 Mac and work at 5K is to somehow get a 5K39 timing to work on each. But like I said before, there's no way to make custom timing on M1 Macs (that I know of).

Another option would be to use a magical device (doesn't exist) that could accept a single 4-lane HBR2 + DSC @ 12 to 16 bpp signal from the M1 Mac and produce two 4-lane HBR2 signals over Thunderbolt for the LG UltraFine 5K. An FPGA could do the DisplayPort splitting while a Thunderbolt 3 add-in card can do the DisplayPort conversion to Thunderbolt. The FPGA idea would be super expensive but I don't know how expensive.

 

[Alakiha]

A Thunderbolt device is not going to make a Thunderbolt port of a computer be able to have more than the max 2 DisplayPort connections that a single LG UltraFine 5K requires to do 5K60.

Well, except if you had an Intel Mac, then you could connect a Thunderbolt 4 dock or hub and a Blackmagic eGPU or Sonnet eGPU Breakaway Puck RX 5500XT / 5700.
Then you could connect one LG UltraFine 5K display to the Thunderbolt 4 hub/dock which would be powered by the GPU of the Intel Mac, and connect the second LG UltraFine 5K display to the eGPU.

eGPU's don't work on M1 Macs. The only way that two LG UltraFine 5K's could be connected to a single Thunderbolt port of an M1 Mac and work at 5K is to somehow get a 5K39 timing to work on each. But like I said before, there's no way to make custom timing on M1 Macs (that I know of).

Another option would be to use a magical device (doesn't exist) that could accept a single 4-lane HBR2 + DSC @ 12 to 16 bpp signal from the M1 Mac and produce two 4-lane HBR2 signals over Thunderbolt for the LG UltraFine 5K. An FPGA could do the DisplayPort splitting while a Thunderbolt 3 add-in card can do the DisplayPort conversion to Thunderbolt. The FPGA idea would be super expensive but I don't know how expensive.

Good to know, thanks for describing!

 

[currocj]

Has anyone tried the Sonnettech Echo 11 tb4 dock? I know the DisplayPort 1.2 limitation still says this is an impossibility but I’m just curious if anyone attempted the dual lg 5K with it

 

[xraydoc]

I think the 5K Studio Display supports DSC, as the documentation for Caldigit TB4 hub states two Studio Displays are supported but not two 5K Ultrafine (which I'm presuming does not support DSC).

 

[Amethyst1]

I think the 5K Studio Display supports DSC, […]

It does. The LG UltraFine 5K does not.

 

[joevt]

I think the 5K Studio Display supports DSC, as the documentation for Caldigit TB4 hub states two Studio Displays are supported but not two 5K Ultrafine (which I'm presuming does not support DSC).
View attachment 2037160

Not sure why Intel Macs and PCs don't also show support for dual 6K60 and 5K60 Apple Displays since they can also support DSC (but not all Intel Macs and PCs support DSC - only some of them).

And it seems to me that in the PC case, 6K60 must use DSC since PCs (running Windows) don't have the software to support dual HBR3 over Thunderbolt to support 6K60 without DSC.

 

[joevt]

The problem with the chart is that it does not include info about GPUs. Some GPUs support DSC. Some do not. Maybe Intel GPUs that support DSC can't support multiple hires displays but can support multiple lower resolution displays? Still, a PC can have aa Thunderbolt 3 or Thunderbolt 4 add-in card connected to any GPU the user chooses.

 

[xraydoc]

Not sure why Intel Macs and PCs don't also show support for dual 6K60 and 5K60 Apple Displays since they can also support DSC (but not all Intel Macs and PCs support DSC - only some of them).

And it seems to me that in the PC case, 6K60 must use DSC since PCs (running Windows) don't have the software to support dual HBR3 over Thunderbolt to support 6K60 without DSC.

Also has something to do with how the PCI/TB lanes are organized on the TB ports on Intel Macs. I recall that on some (all?), one had to plug one monitor into one of the ports on the left side of the machine and one into a port on the right side of the machine. The M-series Macs don't have this limitation.

 

[joevt]

Also has something to do with how the PCI/TB lanes are organized on the TB ports on Intel Macs. I recall that on some (all?), one had to plug one monitor into one of the ports on the left side of the machine and one into a port on the right side of the machine. The M-series Macs don't have this limitation.

This limitation is with dual link SST displays such as the LG UltraFine 5K. An LG UltraFine 5K requires two DisplayPort connections to achieve 5K60 10bpc.
Intel Thunderbolt controllers (a Thunderbolt bus) have two DisplayPort inputs from the GPU and two Thunderbolt outputs.

An Intel MacBook Pro has two Thunderbolt controllers (Thunderbolt buses), one on each side of the laptop.

If you connect a dual link SST display to a Thunderbolt port on one side of an Intel MacBook Pro, then additional displays can only be connected to the other side of the laptop since both DisplayPort connections on the first side of the laptop will be used by the dual link SST display.

Apple Studio Display and Apple Pro Display XDR have dual link SST modes for GPUs that don't support DSC, but they also have single link SST modes for GPUs that do support DSC. They can be forced into single link SST mode with or without DSC if they are connected using DisplayPort instead of Thunderbolt. If they are connected as single link SST, then you can connect two of them to a Thunderbolt bus (if the Mac supports more than one display from Thunderbolt).

Each Thunderbolt port of an M series Mac belongs to a separate Thunderbolt controller/bus. Each bus has two DisplayPort connections, just like for Intel Macs. However, for M1 and M2 Macs (not Max or Pro or Ultra), the second DisplayPort connection can only be used by a dual link SST display since those Macs only support one display from Thunderbolt.

 

[xraydoc]

This limitation is with dual link SST displays such as the LG UltraFine 5K. An LG UltraFine 5K requires two DisplayPort connections to achieve 5K60 10bpc.
Intel Thunderbolt controllers (a Thunderbolt bus) have two DisplayPort inputs from the GPU and two Thunderbolt outputs.

An Intel MacBook Pro has two Thunderbolt controllers (Thunderbolt buses), one on each side of the laptop.

If you connect a dual link SST display to a Thunderbolt port on one side of an Intel MacBook Pro, then additional displays can only be connected to the other side of the laptop since both DisplayPort connections on the first side of the laptop will be used by the dual link SST display.

Apple Studio Display and Apple Pro Display XDR have dual link SST modes for GPUs that don't support DSC, but they also have single link SST modes for GPUs that do support DSC. They can be forced into single link SST mode with or without DSC if they are connected using DisplayPort instead of Thunderbolt. If they are connected as single link SST, then you can connect two of them to a Thunderbolt bus (if the Mac supports more than one display from Thunderbolt).

Each Thunderbolt port of an M series Mac belongs to a separate Thunderbolt controller/bus. Each bus has two DisplayPort connections, just like for Intel Macs. However, for M1 and M2 Macs (not Max or Pro or Ultra), the second DisplayPort connection can only be used by a dual link SST display since those Macs only support one display from Thunderbolt.

Thanks for the technical details.

 

[fctx]

I’ll repost the answer of @joevt from an other thread here, I think it may help you

Sorry but, technically, if it holds up (perhaps) .. it's still DIY .. like PC world isn't it?

The most rational and efficient solution is (perhaps) a dongle which clips all the connectors on the side of the MBP in one operation.

Because the M1 Max (the one I have) handles two 5K displays very well.
This was my conclusion after looking at and testing the most powerful TB4 hubs available today:
There is no concrete and effective solution.
Always open to move forward because when you agree to pay for a full option M1 Max with 2 LG 27' IPS 5K monitors, you don't have to (clearly!) it's not to start fiddling with adapters (btw I tested with a TB4-Display port adapter and it doesn't work) and external solutions etc. please ;-)

As said above, the MBP manages this very well.

On my side, I'm looking for a solution where when I put my MBP on the table, I have one (1!) connector, one (1!) manipulation and the whole chain is connected (Screens, power and wired network).
Even more need for USB-C port, they are behind my two screens.

Can't wait to read you soon to find a (real) solution
FRED•ERIC

 

[currocj]

I’ll repost the answer of @joevt from an other thread here, I think it may help you

so you're saying there's hope one day in thunderbolt 5 (80 gbps)?

 

[currocj]

Seems like LG needs to update the 27MD5KL-B to a version that's DP1.4 with DSC/HBR3
Heck, why not even sell a motherboard upgrade option to existing owners???

Why wouldn't they? While they're at it drop the price to $999 to undercut the ASD and the upcoming Samsung Viewfinity S9 5K monitor...

 

[joevt]

so you're saying there's hope one day in thunderbolt 5 (80 gbps)?

Only if the Thunderbolt 5 host controllers double their DisplayPort inputs from two (supports one LG UltraFine 5K display) to four (supports two LG UltraFine 5K displays). I don't think that's likely.

You can connect two LG UltraFine 5K displays if they're connected using DisplayPort instead of Thunderbolt but then they'll be limited to 4K60 (or 5K39 with a custom EDID).

 

[joevt]

Only if the Thunderbolt 5 host controllers double their DisplayPort inputs from two (supports one LG UltraFine 5K display) to four (supports two LG UltraFine 5K displays). I don't think that's likely.

I should say it's not likely for discrete Thunderbolt controllers. But what about integrated Thunderbolt controllers? I suppose since Apple makes their own GPUs and Thunderbolt controllers integrated inside Apple Silicon, they could make their Thunderbolt controllers have as many DisplayPort Input Adapters as they like. A Thunderbolt controller can have 64 adapters. Goshen Ridge uses less than 20 adapters. MapleRidge only uses 11.

Thunderbolt 5 is 80 Gbps in each direction but it also has an asymmetric mode: 120Gbps transmit, 40 Gbps receive. In that case it could connect four LG UltraFine 5K displays (if it had eight DP In Adapters). All the displays would need to be connected to one or two Thunderbolt 5 hubs though.