Dual monitor (total 3) docking system for iMac

pattara1988 wrote:

Thank you so much, do you have the name of the product “stunt box” and name of the software you mentioned?

There are many "stunt box" hubs and adapters. "Stunt box" is a description of what the things do – not a brand name.

The J5 product you bought is one such product. It uses workaround technology from MCT. (MCT may stand for Magic Control Technology – I'm not sure.)

Other "stunt boxes" use DisplayLink. If you get products based on DisplayLink, you probably will be told to go to the Synaptics site for drivers and technical support.

Synaptics – DisplayLink Graphics

DisplayLink – Troubleshooting: macOS

Other World Computing – OWC USB-C Dual HDMI 4K Display Adapter with DisplayLink

SonnetTech – DisplayLink Dual HDMI Adapter for M Series Macs

SonnetTech – DisplayLink Dual DisplayPort Adapter for M-Series Macs

(many more from other vendors – any time you see a non-Thunderbolt device claim that it lets you attach multiple monitors to a Mac, you have to suspect that DisplayLink or some other workaround is involved)

Note that these are not recommendations or guarantees of compatibility – just examples.

Your 24" M3 iMac only supports one external display.

There are workaround products (based on DisplayLink and similar technologies) that will let you drive more displays in a second-class way, but they may involve significant compromises. To make any of them work, you need to have both the external "stunt box", and matching software on your Mac to drive the external "stunt box."

amalia2345 wrote:

For adding two extra monitors to your iMac M3, consider docking systems like the CalDigit TS3 Plus, OWC Thunderbolt Hub, Anker PowerExpand Elite, or Belkin Thunderbolt 3 Dock Pro.

None of those docks will support adding two external monitors to a 24" M3 iMac. They are Thunderbolt docks, and a Thunderbolt dock can carry video signals from a Mac to two monitors with resolutions of 4K or less - but that assumes that the Mac in question can provide two (or more) video signals for external displays.

The OP's 24" M3 iMac can only provide one signal for an external display, and so these docks will only support one external display when attached to it.

pattara1988 wrote:

I bought j5 (JCD381) and it didn't work with my iMac M3, OS Sonoma 14.5

https://en.j5create.com/products/jcd381

The product description claims the device is macOS-compatible, but can drive two monitors over a plain USB-C connection. Macs don't support driving two displays over one host port unless Thunderbolt is involved and this device clearly is not a Thunderbolt device, so some sort of second-class workaround must be involved.

There's also a little logo – "Powered by MCT" and nearby text "Multi Display Technology Patent / MCT is a patent owner of USB™* Multi Display Technology."

So where a lot of workaround products use the DisplayLink workaround technology from Synaptics, this one uses the USB Multi Display [workaround[ Technology from MCT.

The downloads page has two different macOS drivers. There is one for macOS 11 (Big Sur) and later.

https://en.j5create.com/pages/drivers/#jcd381-show

The vendor wants you to read this page before downloading and installing it. It mentions known issues on macOS 11 (Big Sur), 12 (Monterey), and 13 (Ventura), but makes no mention of macOS 14 (Sonoma).

https://en.j5create.com/pages/big-sur-monterey-support

For adding two extra monitors to your iMac M3, consider docking systems like the CalDigit TS3 Plus, OWC Thunderbolt Hub, Anker PowerExpand Elite, or Belkin Thunderbolt 3 Dock Pro. These options support dual monitor setups and are compatible with macOS Sonoma 14.5. Since your j5 (JCD381) didn’t work, these alternatives are known for better compatibility with macOS and should meet your needs.

Remember … driving external monitors is more complex than just “plumbing them together.”

Your computer must calculate the exact position of each and every pixel on each and every screen.

Unfortunately — and as Servant has posted — your computer only has the ability to do this for ONE extra / external screen.

Thanks for the report, great work! :)👍