How do I connect MacBook Pro M4 to two external monitors?

your dell display U2724DE appears to be a 2560 by 1440 display with HDR (10 bits/color capability) with:

• 1 x DisplayPort 1.4 (DRR for Microsoft Windows) (Supports 2 x QHD 120Hz 8 bit)
• 1 x DisplayPort 1.4 (Out)
• 1 x HDMI (HDCP 1.4)(Supports up to QHD 2560 x 1440 120Hz TMDS, VRR as per specified in HDMI 2.1)
• 1 x ThunderboltTM 4 upstream port (Video + Data). Alternate mode with DisplayPort 1.4, power delivery up to 90W.
• 1 x ThunderboltTM 4 downstream port (15W) for daisy chaining

If you wish to connect with HDMI, that protocol is very sensitive to cable specs. The display-maker says the device uses HDMI 2.1, which is electrically COMPLETELY different from previous versions, and requires Certified cables marked ULTRA performance. (ULTRA cables are backward-compatible to older versions)

if you wish to connect with DisplayPort adapter/cable, that is very sensitive to cable LENGTH, ONE meter or shorter is required for reliable operation.

If you wish to connect with ThunderBolt, that cable must be clearly marked with the Thunderbolt trademark, and version 3, 4, or 5. Because of Higher data rates, those cables generally must be no longer than 0.5 meters for most cables.

cables 'shipped in the box' are rarely adequate for high end displays.

gasface123 wrote:

And yes, been closing the LID as well

I don't believe that closing the lid does anything for you on a M4 MacBook Pro.

The only Apple Silicon Mac notebooks that offer an extra "lid closed" display output are ones that have plain M3 chips. (MacBook Pros with plain M3 chips did not have that feature at first – the hardware was there, but it took the release of macOS 14.6 to bring them up to feature parity with the M3 MacBook Airs.)

It looks to me like it was a transitional feature.

• Plain M1 and M2 chips support two displays, total. Mac notebooks using those chips support at most a single external display.
• Plain M3 chips support two active displays, total. Mac notebooks using those chips also support just a single external display when the lid is open – but can support a second one, with limitations, when the lid is closed.
• Plain M4 chip can drive three displays total, a first for any plain M4-series chip. MacBook Pros with plain M4 chips can drive two displays with the lid open.

Both plain M3 Mac notebooks and plain M4 Mac notebooks can drive two external displays, but the M4 solution (which would have required building an extra display generator into the chip) is a better and more desirable one.

Servant of Cats wrote:

The Dell display would not show up in the Thunderbolt/USB4 section, as it is not a Thunderbolt device.

I just spotted a mistake that I made here. Your Dell UltraSharp U2724DE has several inputs:

• DisplayPort
• HDMI
• Thunderbolt 4

If you are using the DisplayPort input or the HDMI input, it will not show up in the Thunderbolt/USB4 section. If you are using the Thunderbolt input (something that most third-party displays don't have), your display should show up in the Thunderbolt/USB4 section.

In either case, it should show up in the Graphics/Displays section.

ok, that problem looks like it is off the list.

if the display is detected (i.e., shown is displays settings), can you get it to light up if you sharply reduce the resolution, to say, 2560 by 1440 at 60 Hz? (That drops you back to a lower speed category.)

gasface123 wrote:

I'm trying to connect my macbookpro (new m4) to two external monitors. 

I currently have a new studio display and a brand new dell (u2724de)

Studio display is thunderbolt to thunderbolt (supplied cable)

Dell is using HDMI to HDMI- directly to the macbook. I tried to chain through the studio display but its not recognized via thunderbolt. Thunderbolt to thunderbolt the MBP also doesnt work

The Studio Display takes Thunderbolt input – to support its 5K resolution – but the USB-C hub ports on the Studio Display are not Thunderbolt ports. They are single-purpose USB-C (USB) ports that support neither Thunderbolt nor DisplayPort Alt Mode.

The Dell UltraSharp 27 Thunderbolt™ Hub Monitor - U2724DE has two Thunderbolt 4 ports (to allow Thunderbolt daisy-chaining) and two other USB-C ports that do not support Thunderbolt in any way, shape, or form.

That said, I would not expect plugging a Dell U2724DE into the Mac, and connecting an Apple Studio Display to the Dell's Thunderbolt daisy-chaining port, to work. Macs can send two Thunderbolt-encapsulated DisplayPort signals over one physical Thunderbolt connection. The Studio Display has a high enough resolution that it expects for both of those signals to support it – each carrying data to refresh one half of the 5K display.

So there aren't enough resources to go around between both monitors if you put them on the same chain.

Maybe the rules would be different if you had a M4 {Pro/Max} MacBook Pro with Thunderbolt 5 ports and were also using a Thunderbolt 5 dock. Thunderbolt 5 theoretically provides much more bandwidth than Thunderbolt 3 and 4 for transmitting video. But in this situation, I think the Thunderbolt 3/4 rules apply.

You're just going to need to hang the monitors off different MacBook Pro host ports.

On many Intel-based Macs that had four Thunderbolt ports, there was only one Thunderbolt bus controller for every pair of ports. I though that had changed with Apple Silicon Mac notebooks that had three Thunderbolt ports; that each port had its own bus controller.

Experiment:

• Leave one display plugged into the same Thunderbolt port that you used before. Move the other display to a different Thunderbolt port.
• Does this make a difference? If so, it could be that two of your three Thunderbolt ports share one controller, and that the 5K display is consuming all of some resource shared between both ports. Moving the cable will have lined the displays up with different controllers, thus fixing the problem. If it doesn't make a difference – then likely that isn't the issue, but the experiment won't have hurt anything, and would have been worth a try.

System Information (Option- > System Information…) might also give clues as to whether two of the ports on your M4 MacBook Pro share the same Thunderbolt controller. (I'm not certain.)

It sounds to me like it should work at the same time as the Studio Display if you use any of:

• HDMI to HDMI
• Thunderbolt to Thunderbolt
• USB-C to DisplayPort adapter or adapter cable
• USB-C to HDMI adapter or adapter cable

HDMI to HDMI might be the only method that supports a 120 Hz refresh rate. It looks like the monitor supports 2560 x 1440 @ 59.951 Hz (see page of the User Guide), so if the Mac was only willing to go up to 60 Hz when sending a signal over USB-C or Thunderbolt, I would hope that the two would settle on the use of that.

Dell – Dell UltraSharp 27 ThunderboltTM Hub Monitor – U2724DE User’s Guide

This is a head-scratcher. I'm not sure what you can do at this point, other than to take notes and to keep talking with Apple Support and/or Dell Support.

M4 PRO processor supports up to Two fully hardware-accelerated external displays. (three for Mac mini)

gasface123 wrote:

The interesting thing is the system info panel doesn't recognize the dell (even when its on and working properly).

The Dell display would not show up in the Thunderbolt/USB4 section, as it is not a Thunderbolt device. It should show up in the Graphics/Displays section, like this:

This is from the Ventura version of System Information. Note that while System Information provides useful information regarding the Displays Settings resolution, and the resolution of the internal drawing canvas, it doesn't show the actual resolution of the display!

You should be seeing something like this for the Dell U2724DE.

If you aren't, that might suggest that the display is not being completely recognized, even if it does show up in the Displays Settings panel.

occasionally, when switching things around, you run into this issue, which messes up your experiments:

The Mac does not rely on windows-like side-loaded "Drivers" which are actually packages of resolutions and settings for a specific display. Instead, it goes straight to the immutable source -- it asks the display itself.

To get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display. "No signal detected" is generated by the DISPLAY, not by the Mac.

This query is only sent at certain times:

• at startup

• at wake from sleep — so momentarily sleeping and waking your Mac may work

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• hold the Option key while you click on the (Detect Display) button that will appear in Displays preferences (from another display)

so try doing some of those things and see if the display comes alive.

You cannot daisy-chain the monitors. It won’t work.

You also cannot connect both to the same Thunderbolt 3 or 4 dock. It won’t work.

You need to plug them in via different ports on the MacBook because the 5K display will consume ALL of the display signals available on a single Thunderbolt port.