On the one hand, yes others have reported the quick change in temp and cpu usage. It is totally normal for Nehalem and Hyper-threading to quickly change and jump in processor speed for seemingly minor events.
But it should drop just as quickly.
iTunes seems to be the worst culprit and likely needs to be optimized (recompiled) to behave better.
On my PCs that all use Intel "Bloomfield" (part of Nehalem, 4-core/8-threads) it will jump from 2.6GHz up to 3GHz and during idle time drop as low as 1.6GHz.
MacRumors - probably what needs to be said has been, probably in some depth even, and nothing to add.
QuickTime and Flash also can be singled out as offenders, same reasons. Windows 7 has already seen a lot of collaborative work between Intel and MIcrosoft on multi-core threading and optimizing code and my guess is we'll have to wait for Snow Leopard and updates.
I have the same problem with my Mac Pro 2009 2.93Ghz Quad Core running 10.6.1. My CPU averages 35C under normal workload. However, if I play audio through ANY application (iTunes, VLC, Quicktime, Flash, etc) the CPU temperature increases to 60-61C. The BOOSTA fan does not speed up. This problem existed in 10.5.x as well.
I've seen the CPU go as high as 70C when the ambient temperature was higher. It appears this happens regardless of the output (line, headphones, digital) or the sound level. It is not correlated with the CPU's activity level. Very strange.
Unfortunately, it's not just iTunes.
If I play a video file through VLC and disable the audio track (not mute, but actually disable it through the audio menu) my CPU stays around 39C. If I bring the audio track online, it jumps to about 65C. I can barely get CPU temps to 60C running handbrake for an hour. This does not happen on my Macbook Air or my Mac Pro 2006.
Since this affects all audio playback, I'm guessing it's an issue with CoreAudio, maybe the driver for the sound device or something in the I/O kit? This happens with 10.5 and 10.6.
Top, Activity Monitor, iStat all report very little active CPU time while the CPU is running at 65+ degrees. This alone is a very strange situation. Either the temperature returned from the sensors is incorrect or the OS is returning incorrect CPU load information to the monitoring applications.
Very strange situation that wouldn't bother me as much if I hadn't had a couple of kernel panics on this machine. It's frustrating to see the CPU running at 70C and the CPU fan not speeding up.
My guess is developers need to use some radioactive iodine to watch a data stream and threads.
The system is thrashing. Not page outs like in old days, but is unable to efficiently send data to the right core, the right processor, the right cpu caches.
Every little action like open a window (say 8) will trigger a spike in temp of 3-9*C along with a jump in core speed and from idle 12:1 to 21:1, from 1600 MHz to its top rated 2.66MHz. It takes very little and Nehalem will kick out some serious heat. It is common to see 20*C spike in temps, and to run in the 60*C plus range while working hard.
Give a year to untangle the code threads?
I am seeing the EXACT same problem on a 2009 4 Core MacPro Purchased around 9/1/2009.
My system idles at 31(c) and jumps to 60(c) when playing audio? Higher heat = more voltage. For what?
When I Peg All 4 cpus and 4 virtual at 100%... I will hit around 69(c) before boostA increases in speed to bring the temp down to 65(c)..
Why does 1% usage for audio = same heat as 100% system utilization??
I agree. Something is seriously wrong...
Somehow I'm glad you have problems with your Mac Pro too. See also my "Extremely noisy fans" thread. Yours just gets hot. Mine triggers the Boost, Exhaust and Intake fans to run at 4000, 2764 and 3789rpm respectively. That's an entirely different kind of music... And it does so even while 100% idle - and for no particular reason.
Did we buy a bummer?
Yes - It is a bummer that *something somewhere is making our CPU's run out of control while playing sound*.
1) Have you tried resetting the SMC? Shut down. Unplug everything from mac pro for at least 15 seconds. Plug in power.. then mouse/keyboard... then everything else.
2) I had installed FanControl, not SMCFANCONTROL... this screwed with the SMC and made the fans run out of control. It needs to be manually removed.
As I recall, 80s to almost 90 C. And like the rest of you, Activity Monitor show my CPUs doing nothing or practically nothing. Hardware Monitor tells me 95C is the shut down point. That's what should happen, not a destroyed machine. Quicktime can produce some weird spikes too if I remember correctly.
All in all a weird situation. I think the Hatter has the best answers though. And I have to admit for myself, I wonder if it really matters that the temps spike. Maybe Apple is fully aware of this and sees it as no cause for alarm. My fans hardly change either. The one poster whose fans go berserk may have deeper issues in his Mac.
Just stopped by my local apple store and casually spoke with my business rep about the issue. 2 minutes later we had the widget version of istat menu installed and within a short while the temp went from 33(c) to 52(c) and was still climbing.
He couldn't believe what he was seeing. Is going to do some digging and call into apple engineering tomorrow to see what he can find out.