2009 Mac Pro (Nehalem): Audio causes CPU temperature rise

Posted by Pierre Igot in: Macintosh
January 11th, 2010 • 4:24 pm

I first read about this a few days ago, over at MacInTouch. I was able to confirm this myself, so I thought I should report on it and add to the chorus of voices asking for a fix.

I bought a new Mac Pro (2 x 2.26 GHz Quad-Core Intel Xeon) with a few bells and whistles back in the fall of 2009. I am quite pleased with the machine and haven’t had any significant complaints so far.

But it looks like most, if not all 2009 Mac Pros are affected by a bug relating to audio playback in Mac OS X. There is a thread about it on the MacRumors forums, another one on Apple’s own Discussions forums, and even an article dated Dec. 16 about it at MacNN.

I personally tried the following on my own Mac Pro.

I left the machine running but doing only background tasks (checking for new e-mail, basically) for a couple of hours in the evening. iTunes was open, but not playing anything.

I came back to the machine and checked the temperatures with Temperature Monitor:

CPU A Heatsink: 30 °C / 86 °F
CPU A Temp Diode: 35 °C / 95 °F
CPU B Heatsink: 27 °C / 81 °F
CPU B Temp Diode: 30 °C / 86 °F

Then I simply started playing an MP3 file in iTunes and monitoring the temp values. Within a few minutes, all four values had increased significantly and eventually stabilized around the following values:

CPU A Heatsink: 45 °C / 113 °F
CPU A Temp Diode: 52 °C / 126 °F
CPU B Heatsink: 38 °C / 100 °F
CPU B Temp Diode: 44 °C / 111 °F

While the values are lower than those mentioned by other MacInTouch readers using early 2009 machines, they are still ridiculously high for just playing a song in iTunes. That’s an average increase of approximately 14 °C just for playing an MP3 track in iTunes. Imagine if the temperature of your iPod in your pocket increased by that much (on top of its normal operating temperature) each time you played music with it.

I was also able to verify the following:

A similar temperature increase occurs when I play stuff with audio in Safari (video clips, etc.). The temperatures drop as soon as I stop playing audio.

A similar temperature increase occurs as soon as I launch Logic Pro, even if I don’t open anything in the application and therefore do not use the application for anything at all.

And again a similar increase occurs as soon as I launch Elgato Video Capture, right at the first screen, before I even start configuring or recording anything.

I was also able to replicate the problem when playing a music track in iTunes under Windows XP in a virtual PC environment in VMWare.

The problem is therefore not just with iTunes and not strictly only with audio playback. There’s obviously something about both Logic Pro and Elgato that activates whichever OS component causes the problem as soon as the applications are launched, even before any audio is played by the user.

I did not try to play a music track in iTunes under Windows XP after rebooting under Boot Camp, because I do not have a Boot Camp volume on this Mac Pro. (I have one on another, older Mac Pro.) But other users report not seeing the problem on the same machine under Windows.

It therefore looks like it’s a software problem, albeit one that affects only 2009 Mac Pros, when running Mac OS X. People seem to suspect a faulty kernel extension. This would be good news in that it should be fixable via a software update.

The bad news is that, in spite of the number of reports mentioned above (and presumably numerous direct bug reports to Apple, to which I have added mine), after several months there is still no fix in sight.

To be honest, I hadn’t noticed anything about my machine’s temperatures until I read about this on MacInTouch. I hadn’t installed Temperature Monitor before last week, so I hadn’t noticed these significant temperature variations. As indicated by others, while abnormally high, the values are still within normal range, and I haven’t noticed any audio-related kernel panics in the several months I have been using this new Mac Pro.

I also use Logic Pro on a regular basis and haven’t noticed any issues with that either, even with several other processes running in the background.

But like other people, I am concerned about the durability of my machine and about wasteful power consumption. It just does not seem right that a simple task such as playing back an MP3 file (something that an iPod achieves on what I am sure is a tiny fraction of the power consumption reflected by the temperatures above) should require so much electrical power and generate such an increase in temperature. It definitely makes me feel uncomfortable about running audio-related tasks on my Mac.

I can understand it not being given the highest priority at Apple, but I sure hope that the problem can be addressed soon, especially if it’s been around for a while now.

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