Use two Alienware AW3225QF 4K monitors with MBP M4 Pro

[TheClam]

I received a MacBook Pro M4 Pro (48GB) from my employer and a Dell WD19TB dock. If I hook up my two old 27" 4K Dell monitors U2718K (one via HDMI, one via TB), it works fine. When I try to hook up my two new 32" 4K Alienware AW3225QF monitors, only one will display. I can plug in one at a time and set it to 30 Hz, but I can never get both to work. Same exact resolution and cables as the old monitors.

When I plug in my personal MacBook Pro M3 Max, I can have no issues with the driving both AW3225QF monitors.

I have the latest firmware on all devices and running the latest MacOS Sequoia 15.3.1.

Has anyone been able to get these two gaming 4K monitors to work (even at low Hz - don't need that for work), through a dock or directly?

 

[joevt]

If I hook up my two old 27" 4K Dell monitors U2718K (one via HDMI, one via TB), it works fine.

The Dell website does not list a U2718K. Did you mean U2718Q?

The Dell U2718Q is limited to HBR2 x4 connection for 4K60. Two of these cannot exceed the bandwidth limit of Thunderbolt 3 so they usually will work well with a Thunderbolt 3 dock.

The WD19TB dock doesn't have a Thunderbolt port. What ports are you connecting the two Dell U2718Q monitors to?

When I try to hook up my two new 32" 4K Alienware AW3225QF monitors, only one will display.

I can plug in one at a time and set it to 30 Hz, but I can never get both to work. Same exact resolution and cables as the old monitors.

Are you connecting the two 32" displays the same way as the 27" displays - to the same ports of the WD19TB?

The AW3225QF is a HBR3 x4 display supporting 4K up to 240Hz using DSC.

To connect two of these to Thunderbolt 3, you would need to limit link rate to HBR2 x4 which can allow 4K up to 220Hz using DSC@8bpp but maybe the M4 Pro graphics drivers are not smart enough to allow two of these to connect to Thunderbolt 3. You should complain to Apple.

The AW3225QF doesn't appear to have options to select max DisplayPort version or link rate or enable/disable DSC?

One way to limit a display to HBR2 x4 link rate/width is to use a DisplayPort 1.2 MST Hub. It would be interesting to know if a DisplayPort 1.2 MST Hub allows the passthrough of DisplayPort with DSC.

Another way is to connect the display to a USB-C hub that supports USB 3.x data. In this case, the DisplayPort connection will be HBR3 x2 which uses 75% bandwidth of HBR2 x4 which in turn lowers the max resolution using DSC@8bpp to 4K 170Hz.

Some displays have a built-in USB-C hub. The AW3225QF does not (the USB-C port is for data only, not video).

A third way is to use a DisplayPort cable that has one of the lanes disabled. This will force HBR3 x2 link width. I don't think such a

macOS on Intel Macs limits DSC target bits per pixel to 12 but there is a patch to get around that.
I've seen macOS on Apple Silicon Macs use DSC@8bpp for 4K 240Hz mode. I don't know if it will allow DSC@8bpp for other modes or refresh rates.

If macOS were smart enough, it could allow two displays to connect at HBR3 x4 to Thunderbolt 3. Each display would be limited to 20 Gbps which is still enough for 4K240 with DSC@8bpp.

When I plug in my personal MacBook Pro M3 Max, I can have no issues with the driving both AW3225QF monitors.

Is M3 Max more capable than M4 Pro?

Are the two AW3225QF connected directly to the MacBook Pro M3 Max or to the WD19TB?

Did you try connecting the two AW3225QF directly to the Mac Book Pro M4 Pro?

 

[TheClam]

Thanks for the help. This problem is vexing me.

Yes, I meant U2718Q.

Yes, the Alienware AW3227QF can do 240 Hz and has a DP (which I attach to my gaming PC Nvidia 3980) and two HDMI ports. I am trying to use the HDMI ports with the dock to the MBP M4 Pro. This is for work, so I am not doing high speed video or gaming so a 30 Hz refresh is sufficient for my needs.

The WD19TB does have a one thunderbolt port (next to he power ingress) https://dl.dell.com/Manuals/all-pro...ations/dell-wd19tb-dock_Setup-Guide_en-us.pdf

When I connect my work Dell laptop or my personal MacBook Pro M3 Max, both monitors display fine (albeit at a 30 or 60 Hz rate which again is fine for work needs).

The MacBook Pro M4 Pro specs on Apple says it can do two external 4K displays. The MacBook Pro M3 Max specs can do four external displays. The M3 Max is more capable GPU wise than the M4 Pro in terms of video.

I tried multiple variations such as going to the DP rather than HDMI on the monitors. Trying different cables and adaptors. When I try different monitors, it works as expected.

So I am wondering if there is a setting on the MacBook Pro where I can tell it to limit external 4K displays to 30Hz? Perhaps it is trying to use all its bandwidth on a 240Hz monitor.

 

[joevt]

The WD19TB does have a one thunderbolt port (next to he power ingress) https://dl.dell.com/Manuals/all-pro...ations/dell-wd19tb-dock_Setup-Guide_en-us.pdf

Oh, I see it now. Not sure how I missed it previously. The dock appears to use a 3 port DisplayPort 1.4 MST Hub where the HDMI port and USB-C DisplayPort Alt Mode port (also known as MFDP or Multi-Function DisplayPort port) are switched. It's probably setup to use the HDMI port if it's connected so that the USB-C port can still be used for data.

The HDMI 2.0 port is limited to HDMI bandwidth (14.4 Gbps). That's slightly more than HBR3 x2 (12.96 Gbps) and less than HBR2 x4 (17.28 Gbps).
However, the HDMI 2.0 port comes from the MST hub which may be connecting at HBR3 x4 link rate.

When I connect my work Dell laptop or my personal MacBook Pro M3 Max, both monitors display fine (albeit at a 30 or 60 Hz rate which again is fine for work needs).

Using the dock?

So I am wondering if there is a setting on the MacBook Pro where I can tell it to limit external 4K displays to 30Hz? Perhaps it is trying to use all its bandwidth on a 240Hz monitor.

It shouldn't use all the bandwidth if you are connecting using the HDMI 2.0 port of the dock.

Maybe try connecting one display to Thunderbolt port of dock while the MacBook is powered on. Does it work with one display?
Then after the first display is working, connect the second display.

 

[TheClam]

Oh, I see it now. Not sure how I missed it previously. The dock appears to use a 3 port DisplayPort 1.4 MST Hub where the HDMI port and USB-C DisplayPort Alt Mode port (also known as MFDP or Multi-Function DisplayPort port) are switched. It's probably setup to use the HDMI port if it's connected so that the USB-C port can still be used for data.

The HDMI 2.0 port is limited to HDMI bandwidth (14.4 Gbps). That's slightly more than HBR3 x2 (12.96 Gbps) and less than HBR2 x4 (17.28 Gbps).
However, the HDMI 2.0 port comes from the MST hub which may be connecting at HBR3 x4 link rate.


Using the dock?


It shouldn't use all the bandwidth if you are connecting using the HDMI 2.0 port of the dock.

Maybe try connecting one display to Thunderbolt port of dock while the MacBook is powered on. Does it work with one display?
Then after the first display is working, connect the second display.

Yes, using the dock.

I can plug in the HDMI or the thunderbolt monitor directly to the MacBook Pro port, however, only one of the displays can work at a time. If I plug in the second cable only one monitor displays. So it happens regardless if the dock is used.

 

[joevt]

Yes, using the dock.

I can plug in the HDMI or the thunderbolt monitor directly to the MacBook Pro port, however, only one of the displays can work at a time. If I plug in the second cable only one monitor displays. So it happens regardless if the dock is used.

You don't have a Thunderbolt monitor.

If the Mac can't connect two displays, then it's unlikely you can connect two displays to the same Mac using a Thunderbolt dock.

Do you set the first display to a lower refresh rate before connecting the second display? The tech specs for the MacBook Pro M4 Pro says it can only connect one 4K 240Hz display. If this doesn't work, then you need to send feedback to Apple to tell them to fix their stuff.

 

[TheClam]

I tried plugging in the monitors directly to the HDMI and the Thunderbolt ports on the laptop. I did try to set the rate to 30 Hz before plugging in the second display. I even tried unplugging both and doing it in the reverse.

I am using a HDMI to Thunderbolt cable on one monitor, and an 8K HDMI cable for the other. I also have an HDMI to Thunderbolt dongle and tried plugging each monitor into a separate thunderbolt port directly. All result in the same circumstance of a single monitor displaying only. Despite setting the profile for each monitor to 30Hz, it still not recognizing the monitor (but the monitor detects it is plugged into a computer). This makes me think that there is an issue with the MacBook Pro M4 Pro rather than the dock or the cables (because I can do one or the other monitor). Again, my older personal MacBook Pro M3 Max can drive both monitors.

Perhaps you are on to something. Are these AW3225AQ monitors seen as only 240Hz 4K monitors to MacOS despite being configured for 30Hz rate?

 

[joevt]

No such thing as a HDMI to Thunderbolt cable or dongle. Do you mean a USB-C to HDMI cable? (source of the signal is USB-C, the destination of the signal is the display's HDMI port).
The cable/dongle work if there's no second display connected?

Perhaps you are on to something. Are these AW3225AQ monitors seen as only 240Hz 4K monitors to MacOS despite being configured for 30Hz rate?

It's possible that Apple made macOS that dumb so that you would have to buy a more expensive computer.

A proper OS would let you reduce the refresh rate of a display to allow a second display to work.