Film-Tech Forum ARCHIVE: Amp rack positions: top or bottom?

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Posted by David E. Nedrow (Member # 4981) on 10-17-2010, 08:55 PM:

We just moved a new sound rack into the booth and I'm going to start mounting equipment. We'll have a new USL sound processor, DTS XD10, SDDS unit, 5 amps, and a huge honking UPS I have leftover from my computer days.

Assuming the amps will put out the most heat -- haven't checked the specs yet -- should they be mounted up top? This rack does have a fan in the top pulling air through the unit. Having them in the top makes accessing the processors a little less convenient, but assuming they've been set up properly I shouldn't have to touch them very often.

My other option is to put all of the processors in the new, enclosed rack, along with LD, DVD, and Blu-Ray players, satellite box, etc. The I would mount the new amps in the old rack.

Or, just put the amps on the bottom with the processors on top in the new one.

Any guidance?

-David

Posted by Manny Knowles (Member # 1171) on 10-17-2010, 09:03 PM:

if i had a choice to separate the amps, that's what i'd do.

if u have a mixed rack -- one that contains your amps as well as your processors -- u want the amps on bottom for two reasons -- they're heavy so u want the center of gravity to be lower -- and also u want the processor and monitor, etc around eye-level since u handle those more in the course of a day -- the amps are turned on and left alone, so u dont really have a need to have them at operator-level

Posted by Randy Stankey (Member # 64) on 10-17-2010, 09:21 PM:

So long as the amps and all the other equipment have sufficient air flow, I don't think it matters much.

Most amps I have seen, lately, have fans that draw air horizontally, across the components, usually in the front and out the back. Don't block the air ducts. Keep the filters clean. Don't let wires and junk pile up around the top and bottoms. Make sure the racks, themselves have enough air vents to let the air out. After that, I don't see much that will cause problems.

Assuming ventilation and cooling are taken care of I think you can let design considerations be the main factor in locating equipment.

Posted by Louis Bornwasser (Member # 3063) on 10-17-2010, 09:26 PM:

Avoid the bottom 7 inches of the rack for any use. That's where the dirt is and you don't want the amp-fans to inhale the sweepings. Louis

Posted by Sam D. Chavez (Member # 1841) on 10-18-2010, 01:11 AM:

I agree with Manny and Louis but you should leave room at the very bottom for the amps yet to come 9.1, 11.1, 13.1, 15.1.

Also, leave some room in the middle as well for the future.

Posted by Richard Hamilton (Member # 321) on 10-18-2010, 05:56 AM:

Here is a pic of a rack I did about 10 years ago, no problems with the amps. I was cramped for space and had to stack the amps. This is a planetarium and I had another small rack in the console at the back of the auditurium.

Here is a typical rack layout that I did. The Dolby is placed at eye level.

Rick

Posted by Manny Knowles (Member # 1171) on 10-18-2010, 06:00 AM:

yeah, i'd say that's about what i'm used to seeing -- where's that planetarium? -- i've never been to one

who's still using the fostex 24 track recorder?

Posted by Richard Hamilton (Member # 321) on 10-18-2010, 06:33 AM:

Manny, The planetarium is here . I know I've posted pics on here before. The other rack layout is at an amusement park in China. movie wonderland . I installed 3 systems there. They use the Fostex as the primary sound source. The soundtracks come on tape and are recorded onto the Fostex. The Tascam is used as a back-up if needed. They chase timecode generated by the projector. These are all MegaSystems 8/70 projectors.

Rick

Posted by Samuel Hynds (Member # 2610) on 10-18-2010, 10:43 AM:

Would put processor at eye level & amps below.

Just don't put the amplifiers on the UPS - it could starve the power supply when the sound track gets busy.

Posted by Monte L Fullmer (Member # 2797) on 10-18-2010, 08:02 PM:

..UPS the processor instead since they do contain memory that could be erased on accident - which I've seen and done with CP500's.

Posted by Tom Sauter (Member # 616) on 10-19-2010, 10:53 AM:

Amps at the bottom makes delivery and setup of prewired racks much less complicated as top-heavy racks can be dangerous to maneuver.

Heat dissipation is not just about where the devices are installed in a rack, its about proper airflow management.

Middle Atlantic has an excellent whitepaper on the topic

Posted by Scott Norwood (Member # 30) on 10-19-2010, 11:51 AM:

One thing that I would like to see in more cinema racks is a power sequencer or other method to ensure that the amps are powered on last and powered down first. Older processors (at least CP50 and CP200) make nasty pops at powerup, which can easily blow speakers if the amps are powered up first.

As an operator, I generally prefer racks that are in this order (top to bottom):

- power distro/sequencer(s) (alternatively, this can live in the bottom space)
- CD player (for non-sync)
- DA20/DTS/SDDS unit
- cinema processor (at more-or-less eye/shoulder level)
- booth monitor
- mixer for guest inputs/microphones/etc.
- guest inputs
- other stuff that doesn't normally require operator attention (e.g. crossovers, microphone preamps, etc.)
- amps
- power distro/sequencer(s) (if not at top)

Having the processor at eye/shouler level is less necessary if remote boxes for format and fader setting are installed on the front wall of the booth (which almost no one does, for some reason). Conceptually, I prefer to have video stuff go in a separate rack from cinema sound equipment, but lots of installations seem to commingle the two systems. This will result in some messy-looking racks in a few years when the video equipment gets upgraded.

The only sound rack that I have wired from scratch is for my home system, and it consists mostly of scavenged equipment. It is semi-portable (it's a 20-space Anvil rack case with wheels), and the amps pretty much had to be at the bottom for stability. The exercise gave me an appreciation for the art involved in putting together a well-designed sound rack, with consideration given to electrical, mechanical, servicing, and human-factors issues.

Here's a shot from the picture gallery (we used this for a video setup at a festival):

from top to bottom:

CD player
custom rack panel to toggle between decoded non-sync and L/R non-sync (for video)
processor
monitor
guest inputs/outputs
microphone preamp
amps

Posted by Jeffry L. Johnson (Member # 453) on 10-21-2010, 12:26 PM:

If there's room place a filtered blower in the bottom, below the amplifiers.

McLean Cooling Technology standard packaged blower web page

Posted by Gordon McLeod (Member # 33) on 10-21-2010, 01:40 PM:

In wall mount racks i put the processor at the bottom since heat rises
in floor racks i put the amp s at the bottom with a signal path flowing down the rack
i also preferr fan cooled that is like QSC back to front so it doesn't heat up the interior of the rack