[Amps] LK 500 ZA heat

Tom Rauch w8ji at contesting.com
Mon Aug 13 17:05:27 EDT 2007


> My question is: Would it be advantageous to add additional 
> cooling via
> something like added muffin fans on the sides pushing air 
> into the amp?

Hi Gary,

The answer really depends on the restrictions and the fan, 
but for any given fan the air movement is always much higher 
when the inlet is not restricted. Fans and blowers are all 
air inlet critical.

They actually behave like pressure amplifiers, where a small 
change on the inlet results in  a large change on the 
outlet.

If you had a given size fan that was adequate to handle the 
flow and added it to the inlet of the PA, the flow volume 
would increase significantly more than the very same fan 
added to the outlet. The problem is when we disturb an open 
flow system like the 922, we might move airflow away from an 
area where we need the airflow. It isn't as straightforward 
as having a small defined inlet and adding pressure there.

It's interesting to get something to measure flow and noise 
and watch the difference in noise and flow when a 
restriction is moved from an outlet to an inlet, or when a 
booster fan is added.

I hate to dredge up cars again, but think of the difference 
between boosting the air inlet on the engine vs. just 
sucking on the tailpipe. The largest change is always on the 
inlet, whether it is boost or restriction.

This doesn't mean the other way doesn't do anything, it just 
means it is significantly more efficient to keep inlet 
pressure up than outlet pressure down.

73 Tom 




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