Passive vs. Active Cooling

[gckless 5,000+ posts]

What are some thoughts on fan vs. passive cooling? I know that more amps are manufactured with passive cooling, and that if the fans die on an active amp then it will be generally unusable until the fan is fixed, since it will not properly cool itself because it has been designed for the fan.

I am just wondering, because I live in a hot climate and I have heard some stories of other people's amps overheating fairly quickly, and I want to avoid this in my build.

And if anyone wants to recommend a line of fan cooled amps that would be appreciated, I am looking for both full range and sub amps. Thanks!

G

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[dipitydoo 10+ year member]

cooling techniques essentially involve the transfer of thermal energy from high temp to one of lower temp. one way is via metals such as aluminum which have high thermal conductivity. forced air systems are often used in conjunction with these masses of metal to further decrease temperature around the area where waste heat is produced. strickly based on a reliability standpoint (ie, fan), a large heat sink that is capable of properly dissipating the heat generated by the amp would be optimal. however, as amps today become increasingly smaller in size for a given output, some will add fan(s) to further help move hot air away from the amp.

if you are concerned about excessive heat in your area, you can always add external fans to help keep your amp(s) cool.

 

[gckless 5,000+ posts]

I could add fans externally, but I think it would be better, at least from a cosmetic standpoint, to go without external anything that I would need to add outside of my main components. My main goal is a very clean install, SQ at that. And that leaves me with the fan cooled option. However, I also realize there is a line between looking good and performing good in some cases. That is why I am leaning toward fan cooling.

I guess what I am looking for is either horror stories of fan cooling to dissuade me or stories of passively cooled amps holding up to high ambient temperatures.

I am also looking for recommendations of fan cooled amplifiers. I am somewhat new to car audio, as far as name brands go, the ones that aren't mainstream anyway. Has anyone had any experience with MTX amps? A buddy of mine has 2 of their amps from the RFL line and they seem to hold their own, though I don't have enough experience to really compare them to anything. They are in my price range as well, $300-350 for both full range and sub amps.

I do appreciate the help!

 

[playyamxz550 10+ year member]

I have had great luck with rockford fosgate amps never had one over heat on me even on the hottest days. Its worth the extra coin

 

[cleansoundzz 10+ year member]

Good information. I should have used the search function.

 

[mast240 10+ year member]

active cooling isnt always better then passive... and vice versa... it depends on the amp really... and even deeper then that, it depends on your set up. what impendance your running, how you have your amp installed, etc... the main reason alot of people overheat their equipment is by running the impendance on it too low, without the proper air flow, electrical, and install to sustain it.

with that being said.. if your worried about living in a hot climate enviroment, external fans are your best option, no matter which type of amp you choose. you can still get a VERY clean install, and not even be able to see that your running fans

 

[keep_hope_alive Premium Member]

^dude, best GIF i've seen in a sig yet!

i agree, depends on the amp and the load. running a 2 ohm stable amp at 4 ohms won't cause much issues. when you are operating at the minimum impedance load and commonly run at full tilt for extended periods of time - an external fan will just prolong the life of the amp.

 

[Kangaroux 5,000+ posts]

^dude, best GIF i've seen in a sig yet!

It's been there for a while now haha

 

[mast240 10+ year member]

about THE most i can get away with, without the ban hammer, lol

 

[BnGRacing 10+ year member]

Fan cooling, external at least, is probably the best of both worlds. I'll explain that later.

Fan cooled amps are cheaper to manufacture & distribute. The most expensive part of an amp is the heatsink and using a fan (convection cooling) allows the surface area and weight of the aluminum to be much smaller & lighter than non-fan cooled units. This means the case is cheaper...and since it's lighter, also cheaper to ship. Furthermore, fans can induce noise into an amplifier and they're also very prone to premature failure. Since you don't check every day to see if the fan is still working, you run into the risk of your amp frying when it does.

Passive cooling, when done right, is preferred by me. These amps tend to be more expensive as they have to have more heat sink surface area & mass to soak up all the heat. It eventually passes to the surrounding air and these amps normally get hot to the touch (AB). The downside to this setup is that some amps will freak out if they're covered or mounted upside down. Usually not a problem unless you're doing a stealthy install. But if you're doing a stealthy install or plan on competing; you'll need a small fan (preferably 2) of some sort.

Now here's where passive cooling and an outboard fan is the best of both worlds. The amp was not designed to have a fan on it but since you're constantly blowing air across the fins, it runs much cooler and lasts longer. Think of it as putting a racing radiator on your car. Engine temps stay manageable when you beat on it - same goes with amps. Also, you can mount these amps any which way you like if there's some air flowing. And if you're worried about the noise issue; use a relay and mount it on the output side. No noise. And if a fan breaks, you still have all those cooling fins taking care of the amp until you notice the problem.

I should also say that many fan-cooled amps are designed poorly as they do not flow air around the hot bits and just kinda put it in the middle. The Zapcos and Adcoms and Xtants all do it right as air is directed to the hottest points on the amp. Cheaper amps? It's like they cut a hole in the amp case and glued a fan there.

Putting a fan on a massively heat sinked amp is always a good thing.

 

[hispls 5,000+ posts]

The Zapcos and Adcoms and Xtants all do it right as air is directed to the hottest points on the amp. Cheaper amps? It's like they cut a hole in the amp case and glued a fan there.

Too true.

If you explain your power needs, space, and what the location looks like it'll help decide. Plenty of amps won't run too hot unless you really beat on them or have them mounted with absolutely no space around them.

 

[cleansoundzz 10+ year member]

Too true.
If you explain your power needs, space, and what the location looks like it'll help decide. Plenty of amps won't run too hot unless you really beat on them or have them mounted with absolutely no space around them.

I was just deciding between an Digital Designs SS4 (fan cooled) and a Digital Designs C4B (non fan cooled). The wattages are the same but the SS4 is a little cleaner.

 

[gckless 5,000+ posts]

^dude, best GIF i've seen in a sig yet!

I have to agree with this!

I should also say that many fan-cooled amps are designed poorly as they do not flow air around the hot bits and just kinda put it in the middle. The Zapcos and Adcoms and Xtants all do it right as air is directed to the hottest points on the amp. Cheaper amps? It's like they cut a hole in the amp case and glued a fan there.

^This. Before I get to that I want to say good write-up. Not trying to be rude, but I did understand everything that you said. It is all valid. Ideally, you are right, external fans on a passive amp are the best way to go, and honestly I prefer that as well. Less things to go wrong. You don't have to worry about a fan dying, and then pray that the amp's thermal protection works correctly. But I am trying to go for the cleanest install with the least amount of extra wiring to do, and an external fan doesn't lend itself to that. It can be done for sure, probably easily at that, but it's more work than I want to do and/or above my skill level //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif So that brings me back to either a passive amp, no external fan, or active. I am excessively paranoid about heat demolishing components, I guess I can probably blame that on my job, so I am really leaning active.

So what I quoted is what I'm afraid of with what I did purchase. I got an offer on an MTX RFL1200D that I couldn't pass up. Anyone have any experience with these amps? Its rated for 1366 RMS@1 Ohm. The components look fairly solid, it looks like it will keep up, but there's fans blowing from the top into the center heatsink channel with no apparent direction given to the exhaust. They are offset, so it kinda looks like some thought was given as to where the hottest part of the heatsink would be. I dremeled out some of the cross-braces on the exhaust side, so it should allow a bit more air flow.

I guess what I am saying is I am going to try to rock this amp when I eventually do get around to installing everything, but I am really trying to do a one-time, full trunk fiberglass install, so I am really trying to get the right amps right from the get-go. I will sell this and buy another if this is a POS, depending on what people say.

Appreciate the help!

 

[BnGRacing 10+ year member]

1366@1ohm. Let's pretend this rating is at 13.8v and see, mathematically, how much heat that thing gives off;

1366w = 13.8v * CURRENT * 65% amp efficiency

1366w/65% = 13.8v *current

2101/13.8 = current

152 = current

So the amp ***** up around 150A. Input wattage would be 2100 and output wattage is 1366. You have lost 730+ watts of power to heat (and even more if voltage dips). To give you an example of how much energy that is, I did a google search for 800w heater and came up with this;

At full tilt, your amp will give off enough heat to warm up a small basement. Not exactly what I'd use in a stealthy install if it's going to be covered.

 

[gckless 5,000+ posts]

1366@1ohm. Let's pretend this rating is at 13.8v and see, mathematically, how much heat that thing gives off;
1366w = 13.8v * CURRENT * 65% amp efficiency

1366w/65% = 13.8v *current

2101/13.8 = current

152 = current

So the amp ***** up around 150A. Input wattage would be 2100 and output wattage is 1366. You have lost 730+ watts of power to heat (and even more if voltage dips). To give you an example of how much energy that is, I did a google search for 800w heater and came up with this;

At full tilt, your amp will give off enough heat to warm up a small basement. Not exactly what I'd use in a stealthy install if it's going to be covered.

//content.invisioncic.com/y282845/emoticons/wow.gif.23d729408e9177caa2a0ed6a2ba6588e.gif Never did the math on the heat output, it's fairly surprising to see what the actual numbers are.

Are you using 65% specifically for that amp, or are you using that as a general class D number? Either way, I'm sure it's not far off. I am wondering because if that number is specifically for my amp, I'm curious to see how that would compare to other amplifiers.

When I do get around to installing it, it will not be covered, it will be displayed and open in a trunk. Trunks around here get VERY warm though. It would be interesting to see what the equilibrium temp on a couple different amp's heatsinks, passive vs. active, in say a 130* trunk would be. Though I'm sure that's an experiment no one has tried nor wants to try.