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Like many here I use the popular inuke amps for cheap sub and transducer power.
I am currently using a pair of nu6000DSP's, and a single nu1000DSP. I have done fan mods on each of them, as they are quite annoying with the stock fans.
I decided to do some 'empirical' testing on the effect of reversing the fans and how it impacted internal temperatures and stability.
First of all - Although I tested the nu1000DSP, the results were not significant for either direction of fan so it is not included. I am using a dead silent Arctic cooling F8 like this and it has been rock solid. This is powering 2 crowson transducers in bridged mode, and runs pretty close to clipping with the right material (ULF heavy movies).
As for the nu6000DSP's - I was using a mixture of 1 Scythe Flow2 (40CFM - discontinued) and 1 Noctua NF-R8 in each amp. The Scythe's are noticeably louder as they blow more air, and I was getting thermal shutdowns with just the Noctua's installed in a single amp. The combination of both fans has been solid for over a year now. Although not completely quiet, it was much better vs. stock.
Each channel of each amp is powering a sealed LMS-R 15".
I installed both Scythe fans in one 6000DSP, and both Noctua fans in the other for a test that would best represent common fan modifications. I fully expected to run into some power cycling with the Noctua cooled amp, as I had before (and wasn't wrong - but more on that later).
For the test I did 3 conditions with both directions of airflow - fans blowing front to back, and back to front:
1) Amps out of the rack in 'open air' idling with no signal for 30 min
2) Amps in the rack, stacked on top of each other normally, idling for 30 min. In my rack the amps are at the bottom.
3) Amps in the rack, 13 minutes of very heavy bass music played to just below clipping (the song was a compilation from a sub meetup a few years ago). I measured peaks of 128dB at the listening position.
I tested the temperature in 6 locations per amp after each test using a Raytech minitemp laser IR device:
1-4 I believe these are the backs of the transistors, where they are attached to the PCB. These were easy spots to hit accurately.
6 was the hottest spot I could find on the board.
- - - If anyone has a better idea of where to probe for temperatures I could do this again quite easily - - -
I wasn't looking to get perfect readings of the absolute temperature of certain components; I just wanted something to repeatedly compare the two fan directions.
Here are the results:
First - the difference between the Scythe and Noctua fans is evident right away, especially in the number 6 spot.
100°c is pretty hot for any piece of electronics, no wonder the Noctua cooling resulted in thermal cycling.
Spots 1-4 seem to be dependent on distance to the cool air coming in. 1 is best cooled back to front as it's nearer the fan, 4 is the reverse of that.
*No thermal/power cycling happened in this test.
In the rack idling is more of the same, just elevated temperatures in general.
*The Noctua cooled amp cycled twice during the 30 minutes - BUT only in the Back to Front fan position. This is Behringer's default direction.
This was a fun test to run twice. I made sure I beat on them pretty good, constantly lighting up the third signal light and flickering the clip signal at the heaviest times. I cut the back to front test short as the Noctua amp was cycling every 30 seconds or so.
I was actually pretty surprised how similar the temps are to the idle conditions, which tells me my probe spots weren't the best.
*As mentioned the Noctua amp cycled 5 times until I cut the test short, BUT only in the back to front position again.
Concluding remarks -
- I would like to run this again some time with better spots to record more meaningful and significant temps.
- My ambient temperature was quite low today, 17-18°c in the basement.
- 120°c seems pretty damn hot.
- I measured ~63dB with the Scythe fans, and ~55dB with the Noctua, although the Scythe has a metallic noise that is annoying.
- I am going to order another pair of Noctua's now that I found reversing them stops the cycling. I have been running both amps with some decent volume music for the last 3 hrs and no cycling (I kept both Noctua's in one amp now).
TL/DR:
Reverse your Fans in the 6000DSP! Pull the cool air in from the front, instead of pushing warm air from the rest of your equipment through them.

I am currently using a pair of nu6000DSP's, and a single nu1000DSP. I have done fan mods on each of them, as they are quite annoying with the stock fans.
I decided to do some 'empirical' testing on the effect of reversing the fans and how it impacted internal temperatures and stability.
First of all - Although I tested the nu1000DSP, the results were not significant for either direction of fan so it is not included. I am using a dead silent Arctic cooling F8 like this and it has been rock solid. This is powering 2 crowson transducers in bridged mode, and runs pretty close to clipping with the right material (ULF heavy movies).
As for the nu6000DSP's - I was using a mixture of 1 Scythe Flow2 (40CFM - discontinued) and 1 Noctua NF-R8 in each amp. The Scythe's are noticeably louder as they blow more air, and I was getting thermal shutdowns with just the Noctua's installed in a single amp. The combination of both fans has been solid for over a year now. Although not completely quiet, it was much better vs. stock.
Each channel of each amp is powering a sealed LMS-R 15".
I installed both Scythe fans in one 6000DSP, and both Noctua fans in the other for a test that would best represent common fan modifications. I fully expected to run into some power cycling with the Noctua cooled amp, as I had before (and wasn't wrong - but more on that later).
For the test I did 3 conditions with both directions of airflow - fans blowing front to back, and back to front:
1) Amps out of the rack in 'open air' idling with no signal for 30 min
2) Amps in the rack, stacked on top of each other normally, idling for 30 min. In my rack the amps are at the bottom.
3) Amps in the rack, 13 minutes of very heavy bass music played to just below clipping (the song was a compilation from a sub meetup a few years ago). I measured peaks of 128dB at the listening position.
I tested the temperature in 6 locations per amp after each test using a Raytech minitemp laser IR device:

1-4 I believe these are the backs of the transistors, where they are attached to the PCB. These were easy spots to hit accurately.
6 was the hottest spot I could find on the board.
- - - If anyone has a better idea of where to probe for temperatures I could do this again quite easily - - -
I wasn't looking to get perfect readings of the absolute temperature of certain components; I just wanted something to repeatedly compare the two fan directions.
Here are the results:

First - the difference between the Scythe and Noctua fans is evident right away, especially in the number 6 spot.
100°c is pretty hot for any piece of electronics, no wonder the Noctua cooling resulted in thermal cycling.
Spots 1-4 seem to be dependent on distance to the cool air coming in. 1 is best cooled back to front as it's nearer the fan, 4 is the reverse of that.
*No thermal/power cycling happened in this test.

In the rack idling is more of the same, just elevated temperatures in general.
*The Noctua cooled amp cycled twice during the 30 minutes - BUT only in the Back to Front fan position. This is Behringer's default direction.

This was a fun test to run twice. I made sure I beat on them pretty good, constantly lighting up the third signal light and flickering the clip signal at the heaviest times. I cut the back to front test short as the Noctua amp was cycling every 30 seconds or so.
I was actually pretty surprised how similar the temps are to the idle conditions, which tells me my probe spots weren't the best.
*As mentioned the Noctua amp cycled 5 times until I cut the test short, BUT only in the back to front position again.
Concluding remarks -
- I would like to run this again some time with better spots to record more meaningful and significant temps.
- My ambient temperature was quite low today, 17-18°c in the basement.
- 120°c seems pretty damn hot.
- I measured ~63dB with the Scythe fans, and ~55dB with the Noctua, although the Scythe has a metallic noise that is annoying.
- I am going to order another pair of Noctua's now that I found reversing them stops the cycling. I have been running both amps with some decent volume music for the last 3 hrs and no cycling (I kept both Noctua's in one amp now).
TL/DR:
Reverse your Fans in the 6000DSP! Pull the cool air in from the front, instead of pushing warm air from the rest of your equipment through them.