Performance, Power, Temperature, & Noise

Because the 7950B is not strictly a new SKU, and because the performance of the 7950B isn’t very far ahead of the 7950, we’re going to keep our look at the 7950B’s performance relatively short. As always, if you want a complete breakdown of performance please see Bench, which has our complete results for the 7950B and over two dozen other cards.

Kicking things off, we wanted to start with a quick look at clockspeeds. Unfortunately AMD still hasn’t come through on their promise to expose the precise clockspeeds of their Southern Islands cards, which means we’re stuck looking at clockspeeds in a halfway blind manner. We cannot tell when PowerTune throttling has kicked in to push clockspeeds below 850MHz, and at the other end of the spectrum we cannot tell what PT Boost is doing when it’s boosting. As a result we can only see two card states, the base state of 850MHz when the 7950B is operating at or below 850MHz, and the PT Boost state of 925MHz when the 7950B is operating at between 851MHz and 925MHz. Still, this is just enough information to piece something together.

The above is a graph of clockspeeds when running Metro 2033 at 1920x1200, and it’s virtually identical to what we see with other games. The 7950B fluctuates wildly between its base state and its boost state. This is not the kind of behavior we see from the 7970GE or for that matter NVIDIA’s GTX 600 cards. This fluctuating behavior is unique to the 7950B.

So what’s going on? As near as we can tell, the power requirements for boosting are so high that the 7950B simply cannot maintain that boost for any significant period of time. Almost as soon as the 7950B boosts needs to go back to its base state in order to keep power consumption in check. The culprit here appears to be the 7950B’s very high boost voltage of 1.25v, which at 0.125v over the card’s base voltage makes the boost state very expensive from a power standpoint. If our theory is correct then this means that the 7950B never gets very far past its base clockspeed, and compared to the 7970GE, PT Boost is almost entirely wasted here.

Looking at our performance charts, what we’re seeing would seem to confirm our theory. Keeping in mind that the base clockspeed of the 7950B is 6.25% higher than the 7950, the only time we see a significant jump in performance beyond that is with Civilization 5, where performance increases by 9%. Otherwise performance increases by merely 4% in Crysis, up to 7% in Battlefield 3. Not counting Skyrim (which is CPU limited), we’re looking at an average performance gain of just over 6%, which is very close to the increase in the base clockspeed relative to the 7950.

As we’ve stated before this is free performance and we’re happy to take it, but at the end of the day 6% is not nearly enough to matter with the current competition. Until such a time where the competitive landscape changes, the 7950 will continue to be well behind its next-closest competitor, GTX 670.

Power, Temperature, & Noise

Bringing things to a close, we quickly wanted to break out power, temperature, and noise. As we’ve stated earlier, AMD is making a clear set of tradeoffs with the 7970GE and 7950B, forgoing power efficiency in the name of performance. We’ve seen the 6% performance boost the 7950B offers, but what exactly has the cost been?

Radeon HD 7950 Series Voltages
Ref 7970B Base Voltage Ref 7950B Boost Voltage Ref 7950 Base Voltage
1.125v 1.25v 1.093v

Starting as always with load power, we see that relative to the 7950, the 7950B’s power consumption at the wall is 20W higher in both tests. This fits well with AMD’s official specs, which have the TDP of the 7950B at 225W, versus 200W for the 7950. As a result of this power increase the 7950B draws more power than even the GTX 680 when it comes to Metro, though thanks to AMD’s more rigorous throttling their power consumption still comes in below the GTX 680 under OCCT.

Moving on to load temperatures, it comes as no great surprise that with an increase in power consumption comes an increase in load temperatures. The 7950B still fares well here, staying below 80C in both tests, but the 4C jump in Metro is a bit more than we would have expected for only a 20W increase in power consumption.

Last but not least we have our look at noise under load. Unfortunately the 7950B looks especially bad here, thanks to the more aggressive fan curve we typically see on 7950 cards. With both Metro and OCCT the 7950B is pushing 58dbA+, which is louder than even the better performing 7970. In fact all things considered this is quite a ridiculous amount of noise, the same problem the 7970GE had.

The good news is that the reference 7950 is rarely sold these days, but we have every reason to believe that aftermarket cards will see a similar jump in noise.  There’s no getting around the fact that 225W is a lot of heat to dissipate, especially for designs that weren’t necessarily optimized around that level.

Wrapping things up, it’s difficult to hold a favorable opinion of the 7950B given what we’ve seen so far. AMD may be putting all of their focus into performance-per-dollar, but that doesn’t mean that performance-per-watt has suddenly stopped mattering. The 7950B’s performance boost is free from a price perspective, but the tradeoff that comes with it is anything but. A 6% jump performance for a 10% increase in power consumption and notable rise in load noise will certainly be acceptable to some users, but it’s difficult to argue that this is a good tradeoff overall.

Launch Details
POST A COMMENT

58 Comments

View All Comments

  • gobaers - Tuesday, August 14, 2012 - link

    Dismayed to see the power and noise go out the window with this card. Yes, it's not as tangible as framerate charts, but for me, a card has to be quiet for me to buy.

    I just replaced my aging 8800GT SLI setup with a single GTX 560, and am amazed at how quietly the entire rig runs. It's breathing some new life into the old Sonata Plus.
    Reply
  • rarson - Tuesday, August 14, 2012 - link

    The 560 is a ~$120 card. This is $300+. So clearly you weren't in the market for one of these anyway. Reply
  • JlHADJOE - Thursday, August 16, 2012 - link

    His 8800GT SLI setup was considered top-end and cost at least $500 when it was new. I think he could easily be in the market for HD7950 or GTX670 if and when he chooses to do a full upgrade or new build. Reply
  • CeriseCogburn - Wednesday, August 29, 2012 - link

    He said it has to be quiet so forget 7970 and 7950 and 6970 and 6950. Reply
  • haukionkannel - Tuesday, August 14, 2012 - link

    It seema, that it would be better to reduce the boost voltage to 1.2 or even less. Then with good chip you would get the same performance as in here and would not hit the head to the top ceiling so hard...
    Allso there can be guite huge differencess between 7950 vs 7950 where one can keep running at the 925MHz longer than another.
    Reply
  • ratbert1 - Tuesday, August 14, 2012 - link

    " AMD is announcing that they will be releasing a new Radeon HD 7950 with higher clockspeeds. The new 7950, to be called the Radeon HD 7950"

    Did I miss something?
    Reply
  • silverblue - Tuesday, August 14, 2012 - link

    They probably should've called it the 7950 XT. Reply
  • MrSpadge - Thursday, August 16, 2012 - link

    No, you didn't. Ryan is just showing you how ridiculous it is not to give the new card a new name. HD7955 would have been perfect, given the usual meaning of their numbers. Reply
  • redeemer777 - Tuesday, August 14, 2012 - link

    You guys realize that a 7950 which easily overclocks to 1.1Ghz matches a 680 7970? Reply
  • Sufo - Wednesday, August 15, 2012 - link

    er... more like "Com'on really" people are still doing the old "overclocked card X can match stock clocked card Y" routine.

    Are you retarded? Do you think the high end cards do not overclock at all? People have been blowing past 1.3ghz with their reference 680s.

    I can't fathom the point you were trying to make with this point.
    Reply

Log in

Don't have an account? Sign up now