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  • Powered Subwoofer Cooling

    Hi All

    I have searched for information on this extensively and can't come up with anything.  I'm assuming it's bc I'm pretty novice and this may just be "understood info" among pro's.  I have two EV SBA760's that I use with my DJ rig (I know, I know - I'm very conscious of my levels and conservative with my gear, please don't hold this against me) and I can usually get away with running them at about 9 o'clock on the gain level setting on the back of each sub.  For most electronic music it will rarely hit limit or flicker lightly.  On more low-frequency heavy hiphop (which I play little of) it may flicker more intensely and occaisionally the red VCIP-Protect thermal limit will flicker later in the night (but they have never shut off).  I've noticed that the heat sinks get very hot by the end of the night and I assume this is why I'm seeing the thermal light every once in a while.  My question is two-fold:

    1.) I purchased cheap 6" fans for the back of each sub and just used it for a wedding over the weekend.  The heatsinks remained ice cool all through the night and I saw no thermal lights.  Also, I feel lie they were hitting limit at a higher threshold.  Am I crazy or do those little fans really help out exteneded performance that much?

    2) I am deathly afraid of limit/clip lights and thermal shutdown on my gear.  If anything even flickers, I turn it right down.  However I feel like I'm driving a sports car and keeping it in 3rd gear.  Now that's my novice opinion based on limited experience.  Also, I have seen bands that run multiple powered subs at ear splitting volumes for hours with just little fans (similar to what I have) on the back, limit lights going like crazy, and they don't shut down all night.  Now I believe I understand that the highly compressed music DJ's play is vastly different than a mic'ed kick drum, so maybe that has something to do with it.  If I have the fans blowing, is it ok to let the limit light flicker away for bass heavy songs here and there?  Am I being too conservative?

    As always, I intensely value your experiences and opinions, thank you for any input!


  • #2

    The heatsinks transfer heat from the components into the air. Anything that can expedite the transfer will help...lower ambient temperatures, a better transfer medium (water-cooling is more efficient than air-cooling), larger or better-designed heatsinks, or as you are experiencing, increased airflow over the heatsinks. You're not crazy, and if the fans are keeping the bad lights off, there's no reason to stop using them.


    The only consideration I'd add would be whether you really have enough rig for the gig if you need to run the gear that hard. More or bigger stuff might be in order in the future.

    "If you don't know where you are going, you might wind up someplace else" - Yogi Berra, 1925-2015

    Comment


    • #3

      jaygabs wrote:

       

      2) I am deathly afraid of limit/clip lights and thermal shutdown on my gear.  If anything even flickers, I turn it right down.  However I feel like I'm driving a sports car and keeping it in 3rd gear.


       Hey Jay

       

      Your analogy is mostly correct.  Thermal shutdown is a potential issue but most good quality gear can continuously operate in air temperatures that you can't operate in.  No problem adding additional fans however.

       

      If your LEDs are "clip" indicators then I wouldn't want to fire them up too much (which in my opinion is firing more often than the beat).  If they are "limiter indicators you could go a little more ... at least in terms of possible damaging gear.  OTOH it will probably start sounding like crap.

       

      Don Boomer

      Comment


      • agedhorse
        agedhorse commented
        Editing a comment

        The thermal/protect LEDs may indicate more than thermal issues. Depending on the design of the DSP algorithems, they may also indicate that thermal threshold shift of the limiters is taking place, or that some other intermediate action is happening. They may also indicate that perhaps with the sensitivity control at 90 you are clipping the input differential amp (before the sensitivity control) or some other stage in your drive electronics/console due to poor gain structure. Try increasing the level to the 120 position and turn down the output from the console so that the volume ends up being the same.

         


    • #4

      Excellent on the fan use!!

      Purchasing two more Identical subs will solve  your "near limit" issue in a big way.

      With four subs you will be able to attenuate the subs down and lower distortion potential

      and have a better experience.

       

      Comment


      • #5

        I've seen a bunch of threads of people using fans to blow air on their subs heat sinks and I was wondering something. My QSC HPR subs have heat sinks and small vents top and bottom for the warm air to come out from the inside of the amp section as well the passive heat sinks. They have never run above warm and I don't see any need to ever add a fan to them. My question is wouldn't it be better to have the fan PULL warm air away from the heat sink? Have the back of the fan very close to the heat sink so it draws the heat away instead of pushing the warm air back on the heat sink and, in at least in the case of my QSC subs , push this warm air back into the sub amp section to overheat the internal components?

        Would it be better to have the fan on the ground facing up to blow the air up and across the heat sink? Does anyone feel although the heat sink fins are cooler that the inside transistors may still be very toasty? So much so as to shorten their service life?

        Just pondering if adding a fan is really fixing the problem or if its just hiding it and letting the output transisters running hotter than they should internally. More to the point what does the Thermal Shutdown switch monitor? Does it look at each or 1 output transister temp. or does it look at the overall heat sink temp? If it is looking at the heat sink (fins) temp. then does the fan keep the fins cold even though the transisters are running above their temp range making things worse?

        Regardless when a power amp section is designed I would think the heat sink area, thermal shutdown switch temp selection, and output temp of the transisters would be carefully designed to work together. Lets say you triple the radiator size on a car. Does that mean because the temp gauge doesn't read above normal that you can run the car to the mat? Running the car to the mat will cause it to run too hot amoung other things that will cause it to fail. Putting a large radiator on it will keep the car cooler but that doesn't mean its not trying to do more than it should. The car is still trying to do more than it should even though it doesn't seem to be hot?

        Dookietwo 

        Comment


        • agedhorse
          agedhorse commented
          Editing a comment

          Dookietwo wrote:

          I've seen a bunch of threads of people using fans to blow air on their subs heat sinks and I was wondering something. My QSC HPR subs have heat sinks and small vents top and bottom for the warm air to come out from the inside of the amp section as well the passive heat sinks. They have never run above warm and I don't see any need to ever add a fan to them. My question is wouldn't it be better to have the fan PULL warm air away from the heat sink? Have the back of the fan very close to the heat sink so it draws the heat away instead of pushing the warm air back on the heat sink and, in at least in the case of my QSC subs , push this warm air back into the sub amp section to overheat the internal components?

          Would it be better to have the fan on the ground facing up to blow the air up and across the heat sink? Does anyone feel although the heat sink fins are cooler that the inside transistors may still be very toasty? So much so as to shorten their service life?

          Just pondering if adding a fan is really fixing the problem or if its just hiding it and letting the output transisters running hotter than they should internally. More to the point what does the Thermal Shutdown switch monitor? Does it look at each or 1 output transister temp. or does it look at the overall heat sink temp? If it is looking at the heat sink (fins) temp. then does the fan keep the fins cold even though the transisters are running above their temp range making things worse?

          Regardless when a power amp section is designed I would think the heat sink area, thermal shutdown switch temp selection, and output temp of the transisters would be carefully designed to work together. Lets say you triple the radiator size on a car. Does that mean because the temp gauge doesn't read above normal that you can run the car to the mat? Running the car to the mat will cause it to run too hot amoung other things that will cause it to fail. Putting a large radiator on it will keep the car cooler but that doesn't mean its not trying to do more than it should. The car is still trying to do more than it should even though it doesn't seem to be hot?

          Dookietwo 


          Generally, on properly designed products used according to the application that they are inteded for, it's unnecessary to add cooling or power supply filtering or whatever the market might think is "bitchin" at the time. Transistors are designed to run at temperatures that we would find very hot... this is fine as we are not transistors and transistors are not humans.

          The thermal monitoring circuits vary, they typically monitor the overall heatsink temperature in a representative location that the designer has thermally modeled. In fact, you could throw the tracking off between the sensor and the parts that are being sensed depending on the design. This is especially true on SMPS-class D amps where there may be 4 or 5 different sensing points for different aspects of the circuit(s) and disrupting the modeled airflow may indeed cause problems due to mistracking.

          Using your car model, adding a turbocharger or some other mechanical means to increase the amount of fuel/air into the cylinder and thus increase the horsepower above what the engine is designed to do may cause damage to the engine even with increased cooling. Increasing the cooling beyond what the engine needs would just result in the thermostat closing down more to maintain outlet temperature set point. Generally this won't cause problems unless there are specific minimum design flows that are needed to prevent hot pockets or destructive thermal gradients across the block or head. It might also affect automatic transmission operation if the transmissionis designed around a specific cold tank range (which will be much cooler with lower flow. Now in very hot or very cold climates, it might be helpful to scale the cooling accodingly but these are specific "out of bounds" design cases.


        • RoadRanger
          RoadRanger commented
          Editing a comment

          Dookietwo wrote:

          I've seen a bunch of threads of people using fans to blow air on their subs heat sinks and I was wondering something. My QSC HPR subs have heat sinks and small vents top and bottom for the warm air to come out from the inside of the amp section as well the passive heat sinks. They have never run above warm and I don't see any need to ever add a fan to them. My question is wouldn't it be better to have the fan PULL warm air away from the heat sink?


          The turbulence on the "blow" side of the fan maximizes the heat transfer between the heatsink and the air. The air going into the fan on the "suck" side is relatively unturbulent.













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