Well I know if you have them on opposite sides that would maximize air flow, I was just seeing what most people do.

I'm thinking about doing a complete new soundsystem now..

 

*persuasive voice* Do it Romer...build the complete new sound system...do it...
Here's a suggestion: If you're really worried about theft, drill a hole through the bottom of the box and anchor the box to your vehicle, that will teach the theives real fast. (also makes it ride better!)

 

Fan noise is the biggest and endless complaint of a lot of equipment...even in the stuff we build at work which has nothing to do with car audio. People want high performance (typically meaning high power dissipation) in a tiny box with no fans and the box can't run so hot that it'll burn someone who touches it. What's quiet to one is a noisy racket to another. DC fans are slightly quieter than AC fans, there are Maglev fans that are even quieter, but all are audible no matter what. Squirrel cage fans tend to be the most quiet, but they're also more $$.

Fan noise is directly proportional to the fan blade speed and air turbulence which is the result of fan blade design, all else being equal. In the most basic sense, more airflow means more heat that can be carried. Therefore, to maximize airflow and minimize noise, you'll want the biggest fan you can fit and run it at the slowest speed that'll provide enough airflow. Contrast that with a tiny CPU fan spinning at 10Krpm providing tiny airflow and radiating a piercing 10KHz whine!! Something like a 24VDC fan will run at 12VDC at roughly half-speed. Most should work fine, but some may require full voltage for initial spin-up. Or you can simply put a fat power resistor in series with a 12V fan to slow it down, but bear in mind you'll need to dump the heat that it drops somewhere as well.

Since you're gonna have stuff mounted behind a wall, I'd suggest putting the fan closest to the amp and away as far as possible from either inlet or outlet holes. That will cut down the amount of noise that comes out. Adding baffles that act as mufflers as you suggest will further attenuate fan noise. Blowing cool air directly at the amp will likely give you the best cooling (impingement cooling) rather than pulling unless all of the air passes across/through the amp. In that case there's no advantage between either. Mount the fans on something acoustically dead, so any fan vibrations don't find themselves resonating/radiating throughout the entire truck chassis

Running 2 identical fans may also create other problems. If either fan speed is slightly off from the other, the 2 will start beating on each other and you'll hear this wha-wha-wha effect if they are loud enough and high enough pitch to be heard.

there are lots of possibilities :-)

 

Through a DC motor though, couldn't noise be introduced into the lines though?

 

While I respect aquaman's very detailed post, I just must add that I am sitting maybe 2 feet from my CPU, it has no covers (better airflow) and I can't hear the two fans installed on it, well I couldn't until you mentioned them then I was like "hmm". As long as his music is going, I would find it hard to believe that he could hear the fans. I have music on right now (Big & Rich, Save a Horse, Ride a Cowboy) and it's at about an eighth of it's max volume and it's completely draining out the fans with little effort.
Just my two cents.

 

I know this is going to be way overkill, but here goes. I was looking at a new cooling fan for my pc at an online retailer. It seems now they are starting to use liquid cooling for processors and such. Obviously simply because they can. I have often thought of this as well. Putting a small radiator outside the cab and a some type of heatsink to tranfer heat to the glycol. Whole reason behind this was to eliminate fan noise. I haven't done it as now that I am a little older and deaf, I don't turn it up as loud as often, hence the amp doesn't overheat like when I used to have it cranked everywhere.

As far as noise goes. Yes, some DC fans are going to introduce a lot of noise into the system as well.

 

Yeah the DC fans can put noise in the system.

Sad the stuff you can get for your computer these days huh. Imagine telling the guy at the computer store that, "I need a new radiator."
In the end, it's always about trucks.

 

What's wrong with mounting your amps under the seats? I know, first place they look. But, mount them with a star bit screwdriver or something like that. Takes alot longer to rip them out if you have to hunt for the right tool. If you mount them under the seats, then you don't need to cool them. If you are wanting to be able to show them off to a select few, then this would be more of a problem. I run a JL Audio 12w0 on a JL Audio e150 amp with built in crossover. What do you plan to drive with these two amps? I also have 4 JL Audio 5x7s in the doors of my pickup. They run off the head unit which is a Panasonic MXE CD/MP3/WMA player 50 watt per channel. Seperate crossover and volume control for Sub outs. Plenty of power for my high end system. JL Audio speakers have built in crossovers/filters to keep from blowing my 5x7s with low frequencies. Just by good speakers and a good head unit and you don't need to worry about big amps and crossovers.

 

Yeah, you guys are right. If yer boomin, then who cares about some fan noise, or much less airport noise :-) The only time I'd be irritated is if I'm sitting at a light idling and while there's no music playing, assuming the fans were that loud.

Liquid cooling is cool stuff (pun intended). Problem is the stuff made for CPU coolers won't necessarily have the capacity to keep a high power amp cool. THey're only rated to move a few tens of watts, maybe about a hundred at best if I remember seeing right. A big'ol amp is going to dissipate a few hundred watts minimum. Well, anything would be better than none at all. Maybe here's the next business oppurtunity :-)

Induced electrical fan noise can be filtered out if it's really a problem. Since most people will get brushless fans, it's easier. But I suspect alt noise will still be the dominant noise source. In the simplest case, a few high frequency caps such as some 0.1uF and 0.001uF ceramics across the power lines at the fan should get rid or most high frequency junk. I'd also think most car amps already have decent input filtering since they know this is a problem in car electricals in general.

Unfortunately, one needs a scope or spectrum analyzer to see for sure if anything has done any good, and those aren't something everyone has lying around at home. I played around with an old Kenwood amp I bought in high school some years back. Voltage drops from bass notes aside, it was conducting more electrical noise out of its power supply wires than my car had without the amp running! Didn't cause any problems though, and it was pretty much a non-issue.

There are some shareware that use your soundcards' ADC's to let you run your PC as a 20KHz bandwidth oscope and spectrum analyzer that's good enough to see some low frequency stuff... pretty neat...

 

I have a friend who has a Civic (cough ricer cough) and soldered the amp inside of his truck after screwing it in. At least it won't go anywhere I guess. I spent a good amount of time telling him how stupid he was for running a propane torch next to his little bitty 150 watt amp. He thinks he's such a pimp with his two 12 inch subs and 150 watts. I can almost hear his car over my truck's engine. *rolls eyes*

 

I'm pretty sure I would hear my truck's engine over his car haha.

I got to thinking about it.. What about the slip type screws? You can't remove them without a special tool that's more rare than an allen wrench or torx bit, but they go in with a simple flat screwdriver. Just a thought. But I think the main thing is, he's wanting it hidden. And behind the panels would be hidden. Just make sure there's air flow and decent fans. I would also make the fans not easily visible (say from the drivers seat) that way you don't have a direct view from your eyes or ears to the fans. That usually masks sounds pretty well, especially when they're not very loud.

 

Yeah he cranked it up one day when I was sitting in front of his house and I was sitting in my truck idling waiting for him to hurry up so we could leave. A few seconds later he came over and got in the truck and was like "you feel that?" And I was like "feel what?" He just looked at me like "how did you not feel my oh so wonderful subs?"

I'm ready to get my Flowmaster in already. Then it'll drain all the outside sounds out.

 

I'm running a Flowmaster 40 without cats. It's loud.. but I've started getting to the point where I want it quieter lol. I'm tired of getting pulled over haha.

 

Check out the amp rack designs on the bcae1 site. Section 25. One includes a baffle system specifically to combat the fan noise. There are also sections covering heat sinks and cooling fans.

http://www.bcae1.com

 

Haha Romer, seems to be a trend doesn't it. I saw your post about having to go to court in January, how did that go?