CP 950 Power Off

[Marco Giustini]

We've used QSC amplifiers, pretty much exclusively in cinemas. They've always vented properly...rear-to-front. This pulls heat from the back of the rack and blows it into the room rather than convection up to the upper equipment.

Do I remember correctly that the latest QSC amps have a hideous side opening blowing very hot air inside the rack? Those amps run much warmer than the older class H DCA ones and I found that opening to be a bad idea as then the top of the rack gets pretty warm.

[Steve Guttag]

For cinema, QSC has the DCA and the ISA for linear amps...both are rear-to-front vent. For Q-SYS, the CX-Q...vents rear-to-front.

The only side-to-side venting I've seen from QSYS has been some cores (e.g. 110c/110f). Some of the newer Cores, like the Nano, has vent holes on the front (the 110 and 510 had full faceplates without vents).

[Marco Giustini]

QSC have changed naming so often I've lost count but this is a random picture of a DPA-Q I found online.
I'll draw your attention to that side vent which will blow hot air in your rack as the fan is at the back pushing towards the front as you say.
I see the CX have retained the same chassis.

qsc-qsys-dpa88qn-soundsale-2.jpg

[Steve Guttag]

The DPA-Q and CX-Q are identical. Before QSC dissolved the Cinema division, they kept the product lines/accessibility separate between cinema and A/V. Have you confirmed that the holes on the side do exit the blown air? I know that the holes on the front vent the hot air. Those amps do get pretty toasty (they are 4 or 8 channels with up to 8KW of power...as such, even being efficient they are going to get warm).

[Marcel Birgelen]

In datacenters, the standard has been to draw cool air from the front and exhaust it to the back. Some modern switches allow you to switch the PSU and/or fan modules to adjust airflow. It would be great if audio equipment would start to conform to a standard. I think that the front-to-back venting makes the most sense. Most "human interaction" with this equipment happens at the front, so it makes sense to keep that side cool and dump the warm air into the back. If all the equipment in the rack conforms to this airflow, managing an efficient airflow and keeping equipment within safe operational limits will become much easier.

[Steve Guttag]

Honestly, I think front to back venting is down right dumb. To do it that way, you have to have filters on EVERY piece of equipment. If you vent rear to front, you can put in a single filtering system so the equipment remains clean as well as cool. It also has each piece of equipment exit its own hot air rather than leaving it for the next equipment above it.

[Marcel Birgelen]

Front to back has been established as a standard in the server industry. Just like the modern booth, the datacenter has become largely a "lights-out" operation, with very little human interaction involved in day to day operations.

In the past, a lot of the server equipment used to have air filters in the front, that's almost always gone now. The idea is that you keep the air in the room clean. I'd say that's not a bad concept for modern digital-only booths either. Besides fans, there aren't many moving parts anymore and all your equipment will thank you for keeping the air clean. The booth in our screening room has a raised floor with vents inside the floor and two downflow units with air filters nowadays, as we use it to house most of our servers too nowadays...

[Marco Giustini]

Have you confirmed that the holes on the side do exit the blown air?

Yes, I've installed quite a few of them first hand and immediately noticed the racks were getting very warm at the top because more or less half of the hot air comes out from that side vent unfortunately. The top amps on a large system would always run much warmer because of that. The hot air would float, exit the rack at the top where it would be sucked back in by the top amplifiers.

[Ryan Gallagher]

I think the front-to-back convention developed in datacenters because of their HVAC integrations. At one stage of their design they had "hot rows" and "cool rows"... the entire aisle was treated as either an exhaust or an conditioned air inlet from the building sized HVAC plan.

[Harold Hallikainen]

Back on the original subject (CP950 shutdown), it was mentioned that it would be possible to have a network command to shut it down, but then you would not have a way to start it up again. However Wake On Lan ( https://en.wikipedia.org/wiki/Wake-on-LAN ) would allow a networked device (like the CP950) to be started up over the network. It would be interesting to have this implemented in various network devices around the theater.

[Marcel Birgelen]

Wake-on-LAN has been around for ages, but I've seldomly seen it being used in production. It's often frowned upon, because of lack of security. Everybody that knows your MAC on the same LAN can send a magic packet for example. A low-power mode where the Ethernet interface is still reachable and accepting a "Wake-Up" command would, IMHO, be the best solution, as this would easily integrate with most current automation practices in cinema.

I think the front-to-back convention developed in datacenters because of their HVAC integrations. At one stage of their design they had "hot rows" and "cool rows"... the entire aisle was treated as either an exhaust or an conditioned air inlet from the building sized HVAC plan.

If you ever have been in any sizable modern datacenter, you may have noticed that the hot corridors really are pretty toasty. The idea of the "cold rows" on the front of the equipment is mostly inspired by that most human intervention takes place via that side. If that's true in practice is doubtful, especially in modern datacenters, where most management is done remotely. You could argue that the choice might be bad, because you're now exposing the back side, where most of the cabling is, to considerable heat. Some cabling becomes brittle under constant heat loads. The more important thing though: there is a standard, on which you can base your airflow design.

Front-to-back or back-to-front, one choice might be more practical for any given application, but my main point it's good to have some kind of standard across the board. Too many equipment is still designed in a way that it sucks in air at any given random opening and pushes it out at any other given random opening. This may be fine in a low-density environment, but as soon as you start stacking up this equipment in a tight space, keeping this stuff cooled can become a challenge. If you put one unit in a rack that has a back-to-front flow, whereas all the other units are front-to-back, that unit is going to have a hard time in there.

[Steve Guttag]

Harold...I know I mentioned the whole shutdown and a means to boot it back up and here is my quote:

While you could, via software, turn something off...you'd need to have a means to turn it back on and that would be a hardware connection or have a WOL type thing...meaning it isn't self-sufficient. It can do its own reboots. But, when it has power, it boots up and runs. 99% of its use-case is going to want that.

I mentioned WOL then. But again, that is bad design as it isn't a self-sufficient device in that it needs something other than itself to turn itself on. You'd need a button of some sort to initiate a boot up.

Yes, I've installed quite a few of them first hand and immediately noticed the racks were getting very warm at the top because more or less half of the hot air comes out from that side vent unfortunately. The top amps on a large system would always run much warmer because of that. The hot air would float, exit the rack at the top where it would be sucked back in by the top amplifiers

Interesting...I too have noted the convection nature of the DPA/CX-Q amps. I never even thought of the holes on the side of the amps because QSC always went from a rear-to-front design. Their "Q" amps just seem to run pretty warm as compared to their linear amps (counter intuitive for Class-D seem less efficient than AB, or H). Furthermore, when standing in front of them, they definitely breathe hot air...even in standby. Since one can monitor fan speed on them, I've noted that one can tell where the amp is in the stack by comparing the fan speeds. The higher in the stack, the faster the fan. I wonder if they didn't have sufficient openings in the faceplate to vent it all or it was found too objectionable to have that much air/noise coming out the front (they are not the quietest of amplifiers either). It might be worth experimenting with covering the side vents to see if it addresses the convection heat.

The front-to-rear venting remains still dumb and I don't care how many data centers do it. If you have a raised floor with conditioned/filtered air, you can send that up the bottom of the rack and rear-to-front works still. Front-to-rear still puts more and more heat into the rack and needlessly heats components. Venting into the room, which will have more volume of air than the racks will have less of an impact...especially considering you are still pumping it into the room at the top of the rack. However, every piece of equipment had to be washed by the heat of what was below it. The realities are, projection rooms are not built as clean rooms. Some "pods" are built a bit more like it but I haven't seen any evidence that cinemas are keeping their booths museum like clean. We have one site where when I do annual maintenance I also clean the projector filters (Barco B series). Even after a year...a very light dusting with a vacuum is all they need. Conversely, I can tell you which projector (or sound rack) is closest to the stairway that leads downstairs (and how close a human work area is) by how dirty and what sorts of dirt are on the filters.

[Marcel Birgelen]

The front-to-rear venting remains still dumb and I don't care how many data centers do it. If you have a raised floor with conditioned/filtered air, you can send that up the bottom of the rack and rear-to-front works still. Front-to-rear still puts more and more heat into the rack and needlessly heats components.

In a modern "datacenter setup" you don't vent into the bottom of the rack, but in front of the rack. Those racks have perforated doors, both on the front and the back. The ultimate idea is that you have two isolated zones: A hot and a cold zone, usually arranged in corridors, both with a reasonable buffer volume. It's not uncommon to install "blinds" in such datacenters on rack units that aren't used, to cover the holes between the back and the front side. The hot and cold-zones are also physically separated, as much as possible.

We currently don't go to that extreme as we're not running a high-density datacenter and our current setup is fine for what we need. Hot air will automatically rise to the top of the room at the backside of the racks. The downflow units will catch it from there, do the HVAC things you expect from those units and push it back under the floor. The cold air will be pushed out of the floor through the grates in front of the racks. From there, the equipment inside the rack will pull it through and dump it at the back of the rack, where it will vent out through the perforated door and rise to the top of the room. At least, that's the theory and it works well with servers and most other IT equipment, but not so much with anything else.

Yeah, booths weren't constructed as "clean rooms", but times are changing. The world of digital cinema and IT is already becoming more and more intermingled in every iteration. With ever more centralization of essential equipment, having a decent "Main Equipment Room" furnished like a mini-datacenter might not be a bad idea though. Designing your booth to be that room might be worthwhile exercise going forward. Given the fact that humans have become rare species in daily operations in those rooms, we don't really need to optimize those rooms for their well-being.

[Marco Giustini]

H It might be worth experimenting with covering the side vents to see if it addresses the convection heat.

I feel it would work totally fine, the front vent opening is large enough for that small fan at the back IMHO. But I'm sure it would void the warranty!

If you ever end up experimenting, let us know your findings!

Their "Q" amps just seem to run pretty warm as compared to their linear amps (counter intuitive for Class-D seem less efficient than AB, or H).

Indeed. The amount of heat generated by a large rack is impressive. Which saddens me when you consider that very often those racks are left on 24/7 because there is no staff able to diagnose a "no sound" situation caused by the racks being off.

Yes, I am fully aware that those amps can be turned off super-easily via QSYS/Playlist but hey...

[Glenn Woodruff]

I can confidently say that you're welcome to pull the power on a CP950 or CP950A at any time without any worry*. It's not a desktop computer, it's an embedded device. And there is no other way to turn it off.

*Except during an upgrade.

Edit: - signed Glenn at Dolby