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About mcvan

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  1. Thanks for all the details about your new testbed, Eugene. Obviously a great system now even better. There is only one disappointment for me: Acoustic measurement distance changed from 18mm to 3mm. I know this is to allow readings with an SLM that is not sensitive enough to go farther back, possibly in an environment that is not quiet enough. But such close distance is completely at odds with all known & accepted SPL measurement practices. The main issue here is boundary / coupling effects which boost readings, particularly at the lower frequencies. You can hear this any morning while driving to work. The typical radio announcer/DJ speaks with his mouth close enough to the mic so that his voice is unnaturally chesty & deep sounding. This is caused by boundary / coupling effects. The very same effect applies to a mic placed so close to any noise source -- like a HDD. I hear it in audio recordings in my lab when HDDs and fans are placed too close to the mic. An acoustics prof at the Univ of BC recommended I avoid getting any closer than about 1/2 meter when taking SPL measurements. (And also to stay at least a meter away from walls, especially corners where audio reflections reinforce each other.) Any closer, and the decibel reading cannot be trusted to be accurate. Taking noise measurements at 3mm would tend to compress the data range -- ie, the louder ones and quieter ones will both tend to be measured as louder, and the differences between them will tend to be smaller because all of them would have artificial boosts in the lower freq. Any serious acoustics handbook will at least mention this issue of measurement distance. Here is one references on the web I found in a quick search: MikeC, editor,
  2. Thanks for the welcome, gents. We keep trying. Based on your comments, jtr1962, I think I might try using a bank of lower power but higher precision resistors in a parallel circuit. The higher precision + averaging aspect of parallel circuitry should mean better accuracy. I don't have a 5.5 digit bench multimeter is accurate to 0.005%...
  3. Eugene and jtr1962, Very nice test tool. We started doing power measurements on HDDs at in May this year precisely because temperature testing is difficult to do reliably. There's no question that power draw and heat generation are equal. The differences caused by varying internal approaches to cooling and any external "thermal dissipation design" are too small to be significant. Here's the page from our HDD Test Methodology article that discusses this & related issues: Our crude-looking HDD power test rig is shown at the bottom of this page -- It's a simple circuit interrupt that inserts 0.25 ohms of resistance in the +12V line and 0.2 ohms of resistance in the +5V line. The voltage drop is measured, and we use Ohm's law to calculate power for each voltage line from that. Add the 2 power numbers and we get total power draw for the drive. We measure during idle and seek (with and without AAM). Despite the simplicity of our test method, comparing some of the same HDDs SR tested, it looks like our resuilts are generally close, within a watt for both idle and seek. Most of our measurements are lower except for the seek power of the Hitachi 7K400, which we reported as 15.5W compared to SR's 13.8W. It would be nice to find out whether the differences are due to the different test setups or to sample variances. We'll never know -- unless SR & SPCR decide to start swapping drives... unlikley given the hassles and minor dis crepancies... Anyway, just thought the SR community would be interested. We always refer our readers to SR for HDD performance testing results -- we focus entirely on acoustics, vibration and heat. Mike Chin, SPCR