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Do two external monitors require both Thunderbolt ports or can a hub be used for two monitors on same Thunderbolt port?
- Thread starter Corpuscle
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I tested out my original question (sort of) on my main computer, an M4 MacMini Pro, and an OWC TB4 hub, driving an Apple 32" Pro XDR and 27" Mac Studio Display.
I know the M4 Pro mini is TB5, but the hub is only TB4, so speeds via the hub will be limited to TB4 numbers.
From MacMini to OWC hub, then from two hub TB4 outputs to both monitors. Both monitors were seen and look fine.
So, there is enough bandwidth from one Mini output to support both monitors via a TB hub. Hopefully this will apply to the MacBook Air M4 that I just ordered. I'll let you know in about a week.
Thanks for all the discussions.
I know the M4 Pro mini is TB5, but the hub is only TB4, so speeds via the hub will be limited to TB4 numbers.
From MacMini to OWC hub, then from two hub TB4 outputs to both monitors. Both monitors were seen and look fine.
So, there is enough bandwidth from one Mini output to support both monitors via a TB hub. Hopefully this will apply to the MacBook Air M4 that I just ordered. I'll let you know in about a week.
Thanks for all the discussions.
FYI, I tried this with at Thunderbolt 3 hub and it just mirrors a single extended display on the two (meaning two total displays including the internal). If I plugged one monitor into each port I had 3 separate displays (including the internal).
I suspect you would need TB4 to support two monitors via one TB cable from computer to TB hub. Can someone confirm?
TB == TB == TB (and All That)
I have two Dell P2715Q displays attached, and working, to one TB4 port on my OWC TB4 Hub (which is connected to one TB4 Port on my M2 Studio).
Two displays working via a TB4->2xDP OWC adapter.
I have also, successfully, directly-attached each to individual ports on my Studio.
I have no other TB-Enabled devices with which I can compare.
Success is what one holds to confirm, at-hand.
[I probably mish-mashed my textual representation, but, so; it's so: two displays -> one-port is truly real]
No such thing as a Thunderbolt 3 hub. What Thunderbolt 3 dock or adapter did you use? Probably something that contains a DisplayPort MST hub, like the HP Thunderbolt Dock G2. All the ports (HDMI, DisplayPort, USB-C, VGA) connected to the same MST hub will be mirrors.
To connect two displays to a Thunderbolt 3 dock, one of the displays needs to be connected to the downstream Thunderbolt port of the dock. If the dock does not have a downstream Thunderbolt port then it means one of the display outputs can be used for a second display.
A Thunderbolt 3 dock or adapter can connect two displays. However, at least one of the displays will not have a Thunderbolt connection. Without a Thunderbolt connection, the downstream USB-C ports of an Apple Studio Display will be limited to USB 2.0 speed (480 Mb/s) instead of USB 3.1 gen 2 speed (10 Gbps).
Only TB4/USB4 and above support hubs/docks with multiple downstream Thunderbolt ports, so in your case - two Studio Displays connecting via Thunderbolt - yes, you'd need a TB4 or TB5 hub/dock.
With displays that connect via DisplayPort, DisplayPort-over-USB-C or HDMI then it's a case of checking the specs of your TB3 dock/adapter very carefully to see if it supports multiple independent displays on a M4 Macbook. Some won't (at all) some use DisplayPort daisy-chaining (which works on PCs but can only mirror displays on MacOS), M1/M2 Airs couldn't support two displays via Thunderbolt full stop and M3s only in clamshell mode... etc.
To a first approximation, TB4 = TB3 + support for multiple downstream TB ports (hubs) + guaranteed support for a minimum of two displays + support for USB 3 "tunnelling".
TB4/USB4 and above hub/dock is needed only if you need USB 10 Gbps from both Studio Displays. A Thunderbolt 3 dock can get you USB 10 Gbps from one display while the other will be limited to USB 480 Mb/s.
Ok. That’s using one of the studio displays in DisplayPort-over-usb-c mode which sounds like it does work, although officially it only supports Thunderbolt on Mac (but supports non-TB iPads so go figure). May be some cable issues and not all tb3 docks have extra USB-C ports with video support (do USB-C to DisplayPort cables work “backwards”?)
Is that stated by Apple somewhere? I suppose they only mention Thunderbolt Macs as being compatible but they don't say other Macs are not compatible. Everywhere they mention Thunderbolt, they also mention USB-C (but they don't mention DisplayPort Alt Mode). Basically, their Tech Specs lacks details.
Some USB-C to DisplayPort cables are described as bi-directional so they might work, but then you would be missing the USB features of the display such as camera and audio and brightness control. So you would want a USB-C cable that combines 4 lanes of DisplayPort with USB 2.0 such as those described at https://forums.macrumors.com/threads/alternative-to-the-belkin-vr-cable.2378619/
To answer my own question, the 15" MBA arrived yesterday. And the two monitors were supported with one TB4 cable from the MBA. I'm using the OWC TB4 hub which works perfectly. Connected to the hub are the two monitors, a 27 Studio Display and an NEC 27" 4K display. Multiple USB A devices via a USB A hub which connects to the TB4 hub. Other USB C devices connect to the back of the Studio Display. Then the output from the TB4 hub to the MBA. This leaves one TB4 port on the MBA free. The hub also supplies power to the MBA.
I'm used to a 32 Apple XDR and a 27 Studio Display. The MBA screen is fine. Not as good as the MBP screen, but it's considerably less expensive. Sharpness is great. It is a retina screen.
A great feature is the clamshell functionality. When connected to the external monitor, when the MBA is closed, the menubar, doc, etc automatically go to the external monitor. The MBA screen isn't even seen when the lid is closed.
Please help!
I think I've made a mistake. I bought the Belkin 11 in 1 hub, and thought that it would support two monitors from the MacBook Air. It may, but not two HDMI connected monitors – They just mirror each other.
I have:
- One MacBook Air M4 2025
- Two Dell monitors P2715Q (They have HDMI and Displayport)
- One Belkin 11-in-1 hub. See attached picture.
Questions:
- To attach the second monitor, should I use a USB-C to DisplayPort cable? Will all cable works or does it need to have special specifications?
- Does anybody know if I can put that cable in the USB-C DP-Alt port on the hub?
At the moment it feels like the Belkin hub was one of my worst spent $250 ever...
I think I've made a mistake. I bought the Belkin 11 in 1 hub, and thought that it would support two monitors from the MacBook Air. It may, but not two HDMI connected monitors – They just mirror each other.
I have:
- One MacBook Air M4 2025
- Two Dell monitors P2715Q (They have HDMI and Displayport)
- One Belkin 11-in-1 hub. See attached picture.
Questions:
- To attach the second monitor, should I use a USB-C to DisplayPort cable? Will all cable works or does it need to have special specifications?
- Does anybody know if I can put that cable in the USB-C DP-Alt port on the hub?
At the moment it feels like the Belkin hub was one of my worst spent $250 ever...
MBA M4 support 2x external displays when each display connected to a Thunderbolt USB-C port. You need Thunderbolt hub if you want to connect multiple external displays through a single Thunderbolt USB-C port. Unfortunately, the Belkin hub is USB, not Thunderbolt. Reason multiple external displays work with Belkin hub and Windows is support for Display Alt-Mode, which Macs do not support.
The product web page you link even has a display support matrix. Matrix show hub only support 1x external display for macOS. You choose between connect via USB-C or HDMI. Connect more than one display, displays will mirror, which is what you are experiencing. In short, to support both your external displays w/out mirroring, connect one display through the hub connected to MBA USB-C and the other display directly to 2nd MBA USB-C.
The product web page you link even has a display support matrix. Matrix show hub only support 1x external display for macOS. You choose between connect via USB-C or HDMI. Connect more than one display, displays will mirror, which is what you are experiencing. In short, to support both your external displays w/out mirroring, connect one display through the hub connected to MBA USB-C and the other display directly to 2nd MBA USB-C.
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Slight nitpick - the missing tech isn't "Display Port Alt Mode" (Macs support that - it's how any display works off a USB-C 3.x dock, and how you can connect a non-TB display to a TB3/4 port). The problem is Display Port Daisy Chaining via MST (Multi Stream Transport) which MacOS doesn't support.
With any hub/dock offering multiple display connections you really need to check the specs from the manufacturers to be sure that multiple displays will work on Mac. Often these either rely on MST daisy chaining (which won't work on a Mac) or DisplayLink (which will work on a Mac with drivers, but involves compressing the image to transmit it over USB and can introduce lag or artefacts - avoid unless you've exceeded the number of DP/HDMI/TB displays your GPU supports).
On a side note, it’s annoying that macOS doesn’t support MST. A $300 Windows PC with a $40 hub can support 4 screens, but Apple treats multiple display support as a “pro” feature. At least the m4 MacBook Air supports 2 external displays, but it would be better if it didn’t require using both Thunderbolt ports or an expensive hub.
Sure it is annoying, but it is one way Apple defines its low end. It also annoys me at the high end MBP as well. Having only three Thunderbolt ports is too little for the highest end MBP. My 2016 MBP had 4 TB ports.
Isn't the idea of TB to lessen the stress of needing specific, individual portage?
Slight nitpick - DisplayPort Daisy Chaining refers to connecting a secondary DisplayPort display to a primary DisplayPort display. The chain can be one, two, three, or more displays in length.
Both the primary DisplayPort display and the Belkin USB-C dock contain a DisplayPort MST hub internally.
Daisy Chaining refers to a chain of devices connected together. This implies that the device has an upstream port to connect to a previous device in the chain and a single accessible downstream port for connecting another device.
A daisy chainable display must have two downstream DisplayPort ports - one to support its display - and a second one to support a downstream display.
Code:
_____________ _____________ _____________ ____________
| | | | | | | |
GPU ---|-- MST hub --|----|-- MST hub --|----|-- MST hub --|----|-- Display |
| \ | | \ | | \ | | |
| Display | | Display | | Display | | |
|_____________| |_____________| |_____________| |____________|MST hubs are not limited to two ports though. They can have 1 or 3 or 4 or maybe even more ports. So it could be a tree of hubs with multiple branches that each can have multiple branches. A display can be connected to each of the leaf nodes.
Code:
_____________
| --|- Display
| --|- Display
-------|-- MST hub --|- Display
_____________ / | --|- Display
| | / |_____________|
| --|- _____________
---|-- MST hub --|- | |
/ |_____________| \ | --|- Display
/ --------|-- MST hub --|- Display
_____________ / _____________ | --|-
| | / | | |_____________| \
| --|- | --|- Display \ _____________
GPU ---|-- MST hub --|--------|-- MST hub --|- Display \ | |
| --| | --|- Display \ | --|- Display
|_____________| |_____________| -|-- MST hub --|- Display
| --|- Display
|_____________|Thank you guys for the clarifications! I bought the Belkin hub IRL from a retailer and I was in a hurry. If I ever am in that situation again I know I have to look for *Thunderbolt* hub. 😝
Would this cable work for the second Thunderbolt port? (I realize the site is Swedish but the tech specs should be understandable)
Edit: I found the Belkin Pro Thunderbolt Dock which seems to suite my needs; Thunderbolt connection and 2xHDMI.
It has some bad reviews on Amazon, though. Is there a better option?
Would this cable work for the second Thunderbolt port? (I realize the site is Swedish but the tech specs should be understandable)
Edit: I found the Belkin Pro Thunderbolt Dock which seems to suite my needs; Thunderbolt connection and 2xHDMI.
It has some bad reviews on Amazon, though. Is there a better option?
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It will probably. The product description at https://ca.alogic.co/products/usb-c...ies-4k-60hz-space-grey?variant=51831117316462 says it is bidirectional so it can be used in either direction (either to connect a DisplayPort display to a USB-C host or to connect a USB-C display to a DisplayPort host).
I prefer Thunderbolt docks that have USB-C or DisplayPort so I can choose my own HDMI adapters (in case better HDMI adapters exist now or in the future).
What ports of a dock do you use?
The simplest Thunderbolt device with two display outputs is something like this:
https://eshop.macsales.com/item/OWC/TB3ADP2DPT
There's also versions with HDMI:
https://www.sonnettech.com/product/thunderbolt/display-adapters.html
(avoid DisplayLink unless you can't connect enough displays using Thunderbolt adapters)
You could get a CalDigit Thunderbolt 4 Element Hub. It has USB-C ports that you can connect displays to (up to two). It has extra ports for USB devices.
You could get a Thunderbolt 5 dock or hub. Your MacBook Air only supports Thunderbolt 4 but you might get a newer MacBook in the future that supports Thunderbolt 5.
Thanks for the input – It’s really starting to make sense now!
I need Ethernet and a bunch of USB-A connections also.
However, it may be good to have more Thunderbolt ports in the future (the Belkin is short of them)... Decisions, decisions. 🤪
I have also thoughts about connecting the Dell P2715Q – Is there any difference in performance between HDMI and DisplayPort?
And also – When deciding betwen Display Port Cables – Are there any differences between USB-C to DP and Thunderbolt to DP?
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Unlikely with a vanilla 4k@60Hz display like that. All things being equal I'd choose DisplayPort because any HDMI output you get from a Mac will be coming from a DP to HDMI converter anyway.
A "USB-C to DP" cable/adapter puts the host USB-C port into "DisplayPort alt mode" so it outputs raw DisplayPort data. Works the same whether the port is "just USB-C (with video output)", TB3 or TB4/USB4.
An actual "Thunderbolt to DisplayPort" adapter will only work off a TB port, in Thunderbolt mode, and contains a TB peripheral controller chip that extracts DP signals from the Thunderbolt signal. Probably makes no difference for a single monitor connection - but it can support two DisplayPort displays on a Mac model that suports multiple TB displays. One was mentioned earlier in this thread. E.g. https://www.startech.com/en-eu/disp...uToAG425KY9MpSPRB6JPNAuXj9lYXEdY5-pDUpY3gVi8J
Beware, though, because non-TB "USB-C" devices are often advertised as "Thunderbolt compatible" (because they are) so, again, always read the small print and check with the manufacturer if unsure.
Most Thunderbolt 4 and 5 docks/hubs use a USB Ethernet adapter instead of PCIe. In that case, you could get an external USB Ethernet adapter.
People may prefer PCIe Ethernet adapters. Some Thunderbolt 4 and 5 docks use a PCIe Ethernet adapter.
DisplayPort 1.2 has slightly more bandwidth than HDMI 2.0.
DisplayPort 1.2 can do 4K60 using 10bpc RGB.
HDMI 2.0 can do 4K60 using 8bpc RGB or 4:4:4. It can do 4K60 using 10bpc 4:2:2 chromo sub sampling which reduces the color resolution but not the grayscale resolution.
No such thing as Thunderbolt to DP unless it's Thunderbolt to Dual DisplayPort or Dual HDMI (not using MST).
https://eshop.macsales.com/item/OWC/TB3ADP2DPT
https://www.sonnettech.com/product/thunderbolt/display-adapters.html
USB-C to DP works with Thunderbolt ports because Thunderbolt ports support USB-C DisplayPort Alt Mode.
Some of the Thunderbolt to Dual DisplayPort or Thunderbolt to Dual HDMI adapters can work with non-Thunderbolt USB-C DisplayPort Alt Mode hosts if they use a Thunderbolt 3 Titan Ridge controller or a Thunderbolt 4/5 controller. But they'll only support one display.