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Nick Militello, one of our readers emailed us to say he was having problems with Thunderbolt speeds when using an extra monitor in the chain. We investigate.

Everybody knows that Thunderbolt is meant to be quick, so quick, the cable connecting devices together isn't the weakest link or bottleneck anymore. Nick Militello has been having problems with daisy chaining his devices and monitors up, we'll let him take up the story...



Here is a detailed account of what I am finding in regards to Thunderbolt and the 2.3 17" MBP (quad core, 240gb SSD, 16GB RAM)

I have dual 27" thunderbolt displays connected to a Pegasus R6 12TB RAID 5, into a Blackmagic UltraStudio 3D.

Seeing how the Apple website states that this set up is possible, I wanted to give it a try.






Here are the results- These tests were done after a restart with no other apps running in the background. All applications are the latest and greatest along with firmware.

When the MBP is hooked up to just the R6:


When 1 thunderbolt display + R6


When 1 thunderbolt display + R6 + Blackmagic


We see a slight decrease in speed with 1 display, R6 and the Blackmagic.

However when the second display is plugged in, the speed drops considerably. Once the second monitor is added to the daisy chain, I am no longer able to get sync out of the Blackmagic box to my color correction monitor.

Here is the speed test with (2) thunderbolt displays + R6 + Blackmagic (mind you, 4 out of the 6 available devices you can plug into the line)


Here is what the monitor looks like during After Effects and Davinci Resolve playback. Both are unable to sync in 1080p (24p/59.94/29.97 etc...) FCP 7 actually works but only on 1080p 24p mode. 59.94 doesnt work on anything.


I find it very interesting that the second monitor makes all the difference.

The most confusing thing about this whole experience is that after much head scratching, I decided to plug in a 13" MBP 2.7 dual core. 8GB ram. 5400 500GB hard drive, into this exact setup. I was getting 225 mb/sec write speed instead of 165 mb/sec and After Effects could sync to the monitor. It is odd that the speed increase to just 225 mb/sec was enough to allow a proper signal to get through. It is like whatever is in the 13" can actually deal with the thunderbolt, at least a little better.

I also, like a few I have heard of around the net, am experiencing audio static or distortion on both Thunderbolt display's internal speakers any time I access the R6 in the line.

So here is my Thunderbolt finding. Please let me know if anyone has any thoughts or comments.

(other items testing)

-Switched video card to not auto switch. Just use high performance.
-Went to Apple, bought a brand new 17" 2.5, stock. Tested it, same exact results.
-Moved all the items around in the daisy chain to see if one item has to be first. No luck.
-Laptop monitor open and closed, same result.
-Reinstall OS.
-Brand new motherboard.
-New hard drive
-New RAM
No luck again.

Overall, if they can actually get this to work, I really do think that thunderbolt is the future. I feel that my 17" quad core is faster than my 8 core 2.93 Mac Pro. I feel like it handles FCP and AE way better except for this issue.


Many thanks to Nick for supllying the information and doing some serious testing. We are actually amazed that the 17" MBP will drive two 27" monitors and the Blackmagic at all!. Maybe Apple didn't test this extra load on the bus before advertising the two display and capture device idea on their website.

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