Mixing Amp Fan Directions

Colin

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I'm renovating an amp rack this week to integrate some new toys including one RMX4050a driving a pair of LS1208 subs. The RMX cools back to front, while the rest of the rack populated with four 17y/o Crest CKS400s cools front to back. I went into this with eyes wide open because I like the RMX and have options in this installation if it causes cooling issues, but this is the first time I've mixed amp models at all so I'm wondering how concerned I should be about the airflow, and what a reasonable, somewhat conservative approach would be.

This rack can have open front and back in a clean and secure room that stays between about 65 and 72F all year. Nothing's going to get pushed hard other than brief theater sfx and me rocking out by myself occasionally. Probably pretty "typical" academic program material. I don't expect to ever bridge the RMX and it will surely be pushed the least of all in most programming.

Should I not worry at all, close my eyes and throw the RMX in the rack wherever, or should I be concerned to any degree about cooling? If the latter, here are my followup questions:

Is the concern so great that I should put the RMX on its own outside the rack?

If not, should I leave some space between the RMX and the CKSs and how much (could do 6U easy, maybe 8)?

Better to put the RMX above or below the rest, or doesn't matter?

Should I funnel all the hot air into the CKSs until they go poof and replace them with something sexier?
 

RonHebbard

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Waterdown, ON, CA
I'm renovating an amp rack this week to integrate some new toys including one RMX4050a driving a pair of LS1208 subs. The RMX cools back to front, while the rest of the rack populated with four 17y/o Crest CKS400s cools front to back. I went into this with eyes wide open because I like the RMX and have options in this installation if it causes cooling issues, but this is the first time I've mixed amp models at all so I'm wondering how concerned I should be about the airflow, and what a reasonable, somewhat conservative approach would be.

This rack can have open front and back in a clean and secure room that stays between about 65 and 72F all year. Nothing's going to get pushed hard other than brief theater sfx and me rocking out by myself occasionally. Probably pretty "typical" academic program material. I don't expect to ever bridge the RMX and it will surely be pushed the least of all in most programming.

Should I not worry at all, close my eyes and throw the RMX in the rack wherever, or should I be concerned to any degree about cooling? If the latter, here are my followup questions:

Is the concern so great that I should put the RMX on its own outside the rack?

If not, should I leave some space between the RMX and the CKSs and how much (could do 6U easy, maybe 8)?

Better to put the RMX above or below the rest, or doesn't matter?

Should I funnel all the hot air into the CKSs until they go poof and replace them with something sexier?
@Colin The option I like best is your last suggestion; burning up the CKS's and replacing them.
More seriously; if you have a couple of feet clear behind the rack you could mount a flat panel sticking out from the rear of the rack to prevent warm air exiting from the rears of the CKS's rising and immediately being drawn into the rear of the RMX. @TimMc Thoughts??
Toodleoo!
Ron Hebbard
 
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macsound

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Does the rack itself have fans? If the fans create an upward draft and the amp that's pulling air from inside the rack is on the top, even a shelf baffle wont help, but putting the RMX on the bottom would.

Working with quality airflow reminds me of 2005era PCs where every device inside the case had a fan of its own blowing its own tornado in every possible direction, then the PowerMac G5 came out and it was a wonder of fan design and cowling.
 

Colin

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No rack fans. I think I'll try putting the RMX on top of the stack with a baffle under it on the rear of the rack to keep some of the exhaust from below out of the RMX intake, and then assume the RMX exhaust will go up and away to some degree on its own without needing a baffle on the front of the rack. I've got at least two rack shelves kicking around but all vented I think - easy to fix.
 

MNicolai

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If you have open front/back, no doors, I would probably put the RMX in the bottom and the CKs several spaces higher. The CK's run hotter, and the modern class-D's like the RMX's will be very forgiving in terms of heat output and power draw. The single RMX will have a negligible impact on the 4 CKS's.

I couldn't find a cut sheet on the 400's -- but on the 800's, rated for 670W @ 4Ω, the CK's running @ 1/8 power throw off 3584 BTU's. Whereas the RMX's, rated at 1400W/4Ω, put out only 1672 BTU's @ 1/8 power. Less than half the heat for more than twice the load. In terms of bang for the buck, the Crests are 4x hotter than the RMX's.

Where it starts to matter more is if you have closed rack doors, rack fans, or oodles and oodles of amps. Then you have to be much more cognizant about the direction of air flow and making certain you are not short-circuiting any airflow pathways. I wouldn't pull out all the stops for a single amp though.

The most important step moving those amps around is just that you clean out all the filters. If they're pretty gakked up, consider opening the chassis and really blowing the dust out. Two decades of dust on the heatsinks will make sure that the amps hold onto a lot more heat instead of dissipating it.
 
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TimMc

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Can you swap the airflow direction on one of the two systems?
Physically, yes. From a cooling standpoint, not a good idea.
 
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JD

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North Wales PA
Open front and back, in a cool room, not being driven hard? I wouldn't give it a second thought, should be fine. Amps do not like heat buildup so a closed rack or area would be a problem. That's not the case here.
 

chausman

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If the rack has rear rails and an open front/back, putting the RMX in backwards (mounted on the rear rails) would be the easiest. Then the air flow is all the same direction, even if it looks a little silly.
 
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Colin

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Eastern Massachusetts
I do have rear rails and briefly considered racking the RMX backwards but I'm re-purposing some existing ins and outs that don't have enough slack to reach around front. I wound up putting it on top of the CKSs rather than below for the same reason. If in use it seems too hot then I'll try a rack shelf baffle. I bet it'll be okay as-is. The two CKSs directly below are used sparingly (control room monitors and in-ceiling speakers in a "press box" that never gets used) and I also realized that they don't exhaust out the back but rather midway back on both sides, so there isn't a stream of hot air directly under the RMX intake anyway - just probably a bit warmer than sucking from the front. I'll report back if something goes wrong. Thanks all for the perspective.
 

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