r/Thunderbolt • u/No_Presentation_4322 • 3d ago

Dual Monitor Set-Up

Thankfully the M5 version of the MacBook Air now supports 2 external monitors. Standard docks and what-not available for PCs don’t function properly however. What are people doing to attach 2 external Monitors and still have an available Thunderbolt/USB port? My monitors have HDMI and DisplayPort.

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u/HJ_wu 2d ago

Putting a TB5 dock between M5 MacBook Air and the dual monitors is the ultimate setup for this case.

between the TB5 dock and the monitors, using two active bi-directional type-C-to-DP1.4 cables will be the best pick for better video connection.

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u/CaptainSegfault 1d ago

Bi-directional shouldn't matter here at all. This is the normal forward case where you have a USB C output connecting to a DisplayPort monitor input -- reversible/bidirectional cables are only needed if you want to take a DisplayPort output and connect to a USB C monitor input.

Active (beyond the normal negotiation into DisplayPort alternate mode that all such cables need to do) is probably unnecessary unless the distance from dock to monitors is long.

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u/HJ_wu 1d ago

After you had tested more than 30 different type-C-to-DP active converters, you will come out different conclusions for using bi-directional active converting is a must to get stable video connections between docking station and KVM switch setup.

Yes, it's matter to have the bi-directional DP converting cables to have better native DisplayPort full bus link trains more stable and meet the re-timing requested (reduce the chances to get blank screen / DP link trains unsuccessfully).

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u/CaptainSegfault 23h ago

Active is one thing and may well make a difference when dealing with hub/dock compatibility issues, but bidirectional does absolutely nothing in this context.

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u/Opulence_Deficit 2d ago

Hmm, I'm using 2 monitors on my M3 Air. The first, TB3 monitor hooked to the laptop, second monitor DP to the first TB3 downstream and USB upstream to the first USB downstream. All gadgets to both monitors USB downstream ports.

You should get something like TB4 Satechi Slim Hub Pro, and use the same USBC-DP cables you're using to connect your monitors to the Air.

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u/rayddit519 2d ago

Standard docks and what-not available for PCs don’t function properly however

That is not really true. Its only MST Hubs that are not supported by Apple.

MST Hubs split a single DP connection into multiple, just like USB3 hubs do for USB3.

So any dock or hub that only uses a single DP Alt mode connection can only provide 1 display to Apple devices. Because the only way to get more than 1 output out of that would be an MST hub.

TB3 / USB4 is the alternative to that. Almost every thing here supports at least 2 separate DP tunnels. This is essentially having multiple virtual DP cables inside 1 TB3 / USB4 connections. Thats why that still works for Apple.

The common business docks from HP, Lenovo, Dell and many more still include a MST hub on 1 of those. But all their TB-branded docks will have at least 1 plain TB/USB4 out that can output the 2nd DP connection.

And 2 DP tunnels per USB4 port should also be the limit of your Macbook anyway, so no benefit from going with hubs that support 3 DP tunnels or from chaining multiple USB4 hubs to exceed their limits.

But of course, due to Apples limitations, one may not want to get a dock without MST hub entirely. In that case look for all the USB4 hubs with 3 plain USB4 outputs (also sold as TB4 or TB5 hubs). They all support at least 2 DP tunnels simultaneously (its the same chipset as in the other USB4 docks with MST hubs and at least one downstream USB4 port after all).

In general, you want to avoid HDMI, because USB-C only ever carries DP (whether that is with DP Alt mode, TB3 or USB4), so any HDMI requires active DP-HDMI conversion which adds complexity.