Fans...A good thing?

Discussion in 'Archived Threads 2001-2004' started by Ian C, Jan 17, 2003.

  1. Ian C

    Ian C Stunt Coordinator

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    I've been seeing people dissing H/K and NAD for having fans in their receivers, but other than the NAD quality-control issues I wonder if this might actually be a good thing...and something all companies should be doing. I guess you can't really compare a computer processor to an A/V receiver, but I tend to think of it the same way. The faster the processor, the more cooling you need (generally). Shouldn't it be the same? With these companies sticking seven channels of amplification in these boxes and the receivers getting more and more complicated, shouldn't they have a fan in there to cool off...just in case?

    People seem to be looking at fans as a sign of an improperly built product. I look at it as a sign that they are covering all bases...but please feel free to let me know if my thinking is incorrect.

    Ian
     
  2. Yogi

    Yogi Screenwriter

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    In audio where you are trying to push the S/N ratio to over 100db it would mean that the background noise will have to be pushed to a minimum. If you have a noisy 30db fan behind your receiver you wont be able to tell the difference between a 98db S/N ratio and a 115db S/N ratio, just because the low level details will be masked by the fan noise.

    A well build product will try to dissipate the heat by using well build heat sinks will a large surface area. Heat sinks are heavy and hard to make adding cost to your product. The most expensive Class A amps utilize 4-6" heat sink fins to dissipate the huge amounts of heat generated. A fan is way cheaper to use and will dissipate way more heat than any heat sink due to forced convection but it also indicates a cost cutting measure on the manufacturers part. This is not to say that the product wont be fine sounding, like HK and NAD amps that are very musical. Just look inside a HK520 and you'll see the piss poor aluminum foil bent in the shape of a heat sink to dissipate heat. Now that just to me is poor design and cheap build quality.
     
  3. Terry St

    Terry St Second Unit

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    Electrical devices produce heat. This heat must be dissipated at a rate sufficient to keep the device's temperature within its operating range. While there are many ways to dissipate heat, most audio amps and receivers disspate heat with passive heatsinks or with fans blowing across heatsinks.

    Both methods operate on the same principle. The heatsink is made of a material that conducts heat well and is typically in physical contact with the parts of the device that generate significant ammounts of heat. The ammount of heat that a heatsink dissipates is a product of it's thermal conductivity, surface area, and the average temperature of the air in contact with that surface. A passive heatsink relies on convection (warm air rises to be replaced by denser cooler air) to move hot air away from its surface. The air right by the heatsink does have to heat up a bit before it will move away on it's own. Fans move the air much faster, so the average temperature of the air surrounding a fan-cooled heatsink is much lower. (Although it can never go below ambient)

    So a fan-cooled heatsink doesn't have to be as big or can be made of less conductive material than a passive heatsink. With a fan you also don't have to worry about leaving the chassis open enough to allow heat to escape by convection. However, by making the heatsinks bigger or out of better materials you can achieve the same ammount of heat dissipation and get rid of the fan. The only difference is that fans are cheaper and more compact, while larger heatsinks cost more, weigh more, and take up more space.

    So why doesn't everyone use fans? Fans have two major drawbacks. Noise and durability. Fan cooled equipment can be very quiet, but it will never be totally silent. In some rooms it may be well below background noise levels and hense not perceptible. Thus, it can be practically silent. However, the fans themselves are moving parts that do wear out over time. What happens when they stop working? The formerly fan-cooled heatsink would be reduced to a passive heatink, only it might not have been designed to dissipate enough heat. The receiver/amp may have protection logic to shut itself down, or it may just fry something. (Ever had a CPU fan go on one of the older Athlons that had inadequate thermal protection circuitry?) Either way, you're going to have to fix something.

    Bottom line, you can achieve the same heat dissipation, and hence thermal stability, with both passive and fan-cooled approaches. The latter is cheaper, lighter, and more compact. The former is potentially quieter and more reliable. So fans aren't a sign of a "improperly built product", but they are a sign of cost-cutting. If you can get a lot more for your money by going with a fan-cooled unit then go for it, but if all else is equal, take the passively cooled one.
     
  4. TimothyE

    TimothyE Stunt Coordinator

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    I've only had my H/K AVR-325 for about two weeks, but so far I have yet to see or hear the fan run, even after prolonged high volume use.

    The talk I see here of a heatsink being sufficient without a fan is amusing. A heatsink will not let go of its heat if there is NO airflow, so utilizing a heatsink, no matter how elaborate, requires the assumption that the only place anyone will ever put a receiver is where there is adequate airflow. Air that is not moving is an unbelievably good insulator, and heat will not just jump off a heatsink into it. Even the largest heatsink will eventually fill itself with heat, it just takes longer.
    Maybe using a fan IS a little less costly than an elaborate heatsink, but it allows for a lot more variables in installation of the receiver, such as putting it in a cabinet where the airflow can be uncertain.

    Now, the best of both worlds would be to have both an effective heatsink AND a fan to dissipate heat when the temperature rises beyond a safe limit. As an engineer myself, I would not want to buy a unit that doesn't protect itself against excessive temperatures via an automatic shutoff or a fan to kick in.

    Tim
     
  5. Terry St

    Terry St Second Unit

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  6. Ian C

    Ian C Stunt Coordinator

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  7. Yogi

    Yogi Screenwriter

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  8. LanceJ

    LanceJ Producer

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    Some people are assuming that these fans operate constantly like on a computer. I'm pretty sure they don't. On my Technics SA-DA8 receiver it only comes on during loud explosions or, when the volume is turned past the "10:00" position and when busy rock music is playing or during a movie's chase/shoot-out/tornado scene occurs. Otherwise, it just sits there. As a consequence, I have NEVER heard it when it is operating.
    I really don't think there is any way to price a 5/6/or 7 channel receiver at a reasonable price without a forced-air cooling system.
    LJ
     
  9. Kevin C Brown

    Kevin C Brown Producer

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    No fans for me. I don't want to take a chance on:

    1) hearing them
    2) any kind of electrical interference between the fan and any sensitive audio/video/analog/digital circuitry
    3) if the fan breaks, dies, or starts to make more noise than it was designed to do, what do you do then? Just another (moving) part that can fail.

    IMO, a well designed component shouldn't need a fan. There are *many* quality receivers out there without them. Why take the chance?
     
  10. Guy Usher

    Guy Usher Supporting Actor

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    X amount of power requires X amount of cooling = X amount of heatsink area.
    Put 7 channels of high power plus processors etc in a shoebox. . . where are you going to put all the heatsink area required to keep it below meltdown. . .
    If you dont want a fan. . .increase the heatsink area (BTW it doesnt have to look good to work), reduce the power levels, increase the size of the box etc.
    I think I vote for the fan, I have seen inexpensive fans that for all intent are silent and many only come on when needed. I certainly would not reject a piece of audio gear because of a fan, even cheap fans are much more expensive than heatsinks.
    Certainly I would like to have it all and not have to worry about a fan, many equipment racks have fans built in. . .
     
  11. TimothyE

    TimothyE Stunt Coordinator

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    Terry St wrote:
     
  12. Kevin C Brown

    Kevin C Brown Producer

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    "Mean free path" ... All molecules, atoms, electrons have a certain amount of kinetic energy at the respective temperature they are at. You do get a certain amount of air circulation *automatically*, for free. But obviously like it's been alluded to, an "open" designed rack is better than a closed rack, more open space around equipment is better, not stacking eqp, etc. [​IMG]
     

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