Three 4k monitors on Sonnet Echo 11 Thunderbolt 4 Dock w/ M1 Max?

[hardwickj]

Sonnet's own compatibility matrix suggests that using three 4k monitors via their dock is possible (with the caveat that you apparently need to use their Thunderbolt 3 to Dual DisplayPort Adapter).

Theoretically that should be possible since 4k60 uses ~12Gbps bandwidth, and hence 36gbps total within TB4's 40Gbps max, although that doesn't leave much room for Ethernet/USB.

Can anyone confirm that this works? Also, even if using just two displays, would they be mirrored due to MacOS's terrible MST support?

 

[joevt]

Sonnet's own compatibility matrix suggests that using three 4k monitors via their dock is possible (with the caveat that you apparently need to use their Thunderbolt 3 to Dual DisplayPort Adapter).

Theoretically that should be possible since 4k60 uses ~12Gbps bandwidth, and hence 36gbps total within TB4's 40Gbps max, although that doesn't leave much room for Ethernet/USB.

Can anyone confirm that this works? Also, even if using just two displays, would they be mirrored due to MacOS's terrible MST support?

I think your interpretation is incorrect. There are 8 groups but each group has multiple rows. I think you are meant to take a single row as a possible setup. Note that all the rows containing "4K+4K" have both other columns with no display.

What a terrible table. What info is it trying to convey? Wouldn't a few sentences be more concise? I'll give it a shot:

• (i) The hub can drive two DisplayPort devices only (this is represented by the table having only two Thunderbolt columns containing display info).
• (ii) If the hub isn't driving any DisplayPort devices, then a downstream Thunderbolt device can drive two DisplayPort devices (this is represented by the 4K+4K rows which all have no other columns with a display). Actually, any Thunderbolt device in the Thunderbolt chain can drive any number of displays depending on the device, host, available bandwidth, and required bandwidth.
• (iii) Some 5K displays count as two DisplayPort devices (this is represented by all the 5K and 6K rows that don't have a second column with a display - such displays include Thunderbolt displays like the LG UltraFine 5K or the 6K Apple Pro Display XDR, and non-Thunderbolt displays like the Dell UP2715K. These are tiled displays, where the left half and right half are driven by separate DisplayPort signals. Actually, exclude the XDR from this point because it can't use tiled mode when there's a Thunderbolt device, such as a hub, between the display and the host - Apple is using some special code (that won't work with a hub they decided) to setup two HBR3 DisplayPort connections to the XDR - the code is special because Thunderbolt usually limits the two DisplayPort connections to HBR2+HBR2 or HBR3+HBR as those are the max combinations of DisplayPort link rates that can fit in 40 Gbps - Apple can set the connections to HBR3+HBR3 because each tile of the XDR requires less than 20 Gbps and Thunderbolt does not transmit the stuffing symbols used to fill up the DisplayPort bandwidth).
• (1) M1 Max/Pro Macs can connect two 6K displays to the hub (this is represented by the M1 Pro/Max group containing two columns with XDR). The Apple Pro Display XDR has a single-tile mode that uses DSC to reduce the required bandwidth so it's possible to connect two of those when the OS, GPU, and driver supports DSC. With DSC, the XDR also gets improved USB bandwidth. This solution should not be limited to just M1 Pro/Max though. Any Thunderbolt chain supporting two displays and where the DisplayPort comes from a GPU that supports DSC (such as AMD Navi or Navi2) should allow two XDRs to be connected at 6K. If it doesn't work then it's a problem with drivers.
• (2) Original M1 Macs can have only one display connected to Thunderbolt (this is represented by the 2nd M1 group where only one column has a display). A tiled display that takes two DisplayPort signals will also work. This means original M1 Macs can support two DisplayPort devices per Thunderbolt port, but the GPU or drivers are made to allow the second DisplayPort connection only for tiled displays.
• (3a) Some Intel Macs support DisplayPort 1.4 + DSC (this is a subset of the Macs in group 3). These have AMD Navi or Navi2 GPUs. If a single 5K single tiled display is connected, it may use HBR3 link rate leaving only HBR link rate for a second 5K display which is not enough. But if the displays are connected to the hub before the hub is connected to the display, then maybe macOS is smart enough to give each HBR2 link rate. But in that case the displays will be limited to 4K unless the refresh rate or bpp of the 5K resolutions is reduced. Shouldn't these tricks work in the M1 Pro/Max case as well?
• (3b) Some Intel Macs support DisplayPort 1.4 without DSC (this is a subset of the Macs in group 3). These have older AMD GPUs (Polaris or Vega) Without DSC, they cannot connect an Apple Pro Display XDR to the hub for full 6K functionality. 4K and 5K support should be the same as with the previous point.
• (4) Some Intel Macs support DisplayPort 1.4 + DSC with limits (this is represented by the fourth group). These have IceLake CPU/GPU. They support DSC but are limited by the total number of pixels that can be output so they can connect a 6K display to the hub but they can't connect two of them (or even two 5K single-tile displays) even though it has enough DisplayPort 1.4 connections.
• (5) Some Macs are limited to DisplayPort 1.2 (this is represented by 5th groups of Macs which have no 6K support). These Macs use the Alpine Ridge Thunderbolt controller chip and/or older Intel graphics. DisplayPort 1.2 means they are limited to HBR2 link rate and don't support DSC. They can do 5K tiled displays though since the tiles only require HBR2 link rate.
• (6) The hub is not supported by macOS Catalina or earlier (this is represented by the macOS 10.15 group). Catalina doesn't have Thunderbolt 4 drivers to enable the hub. It may be possible for the hub to be enabled during boot before macOS starts, but it won't support hot plug.
• (7) macOS sucks for 8K (this is represented by the only row containing 8K being in the Windows group). Actually, macOS (at least on Intel Macs) can do 8K30 (RGB 8bpc) using DisplayPort 1.4, and 8K60 (4:2:0 8bpc) using a DisplayPort 1.4 to HDMI 2.1 adapter - both without DSC. 8K60 4:4:4 10bpc using a DisplayPort 1.4 to HDMI 2.1 adapter that supports DSC has not been achieved yet in macOS.
• (8) The hub is not supported by Thunderbolt 3 PCs (this is represented by the last group). macOS uses its own Connection Manager to deal with Thunderbolt 4 hubs and docks. This Connection Manager works with Thunderbolt 3 hosts. It may even work with Thunderbolt 2 hosts. I'm pretty sure it doesn't work with Thunderbolt 1 hosts. Anyways, Windows depends on the Connection Manager built into the firmware of the host Thunderbolt controller which doesn't know how to deal with Thunderbolt 4 devices. I'm not sure how Linux behaves.

Definitions

• Thunderbolt chain - all the Thunderbolt devices connected to a single host Thunderbolt port. With Thunderbolt 4 docks/hubs, this can be a tree.
• DisplayPort device - anything that a display can be connected to. VGA, DVI, and HDMI in a Thunderbolt chain will be provided by a DisplayPort adapter. An MST Hub is a single DisplayPort device that can connect multiple displays - the max number of displays depends on the OS, GPU, drivers, bandwidth, resolution, bits per pixel, and refresh rate. MacOS doesn't support MST for multiple displays but can use other features of the MST hub.

General Thunderbolt notes:

• Thunderbolt 3/4 docks/devices/adapters/displays can drive a max of two DisplayPort devices.
• Thunderbolt 1/2 docks/devices/displays can drive a max of one DisplayPort device.
• Thunderbolt 3 Alpine Ridge supports DisplayPort 1.2.
• Thunderbolt 3 Titan Ridge supports DisplayPort 1.4.
• Thunderbolt 4 Goshen Ridge supports DisplayPort 1.4.
• The total number of DisplayPort devices that can be driven in a Thunderbolt chain depends on the number of DisplayPort inputs that the Thunderbolt host controller has. This is usually two. Some PCs only have one DisplayPort input to their Thunderbolt controller. I wonder if an eGPU like the Blackmagic eGPU or Sonnet eGPU Breakaway Puck 5500 XT/5700 can add additional tunnelled DisplayPort connections to a Thunderbolt chain since they have GPUs with outputs connected to the inputs of their Thunderbolt controllers.

Ok, maybe I fail at concise but at least there's some explanation.

 

[hardwickj]

@joevt you are an absolute wealth of information. Thank you!

As I repeatedly re-read that chart I started to come to the same conclusion you did, both that the chart sucks and that regardless if it's 2 displays connected via one TB port or if its 2 displays connected on separate ports, the maximum is 2 displays. Unless you somehow luck out with some mystical graphics card that supports >2 DisplayPort inputs on a single controller, which I'm pretty sure the M1 Max's are not.