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Air Flow & Signal Flow: Going with the Flow?

The Project Studio, Part VI By JD Mars
Ever been recording in a room that has no air conditioning system, with maybe just a wall unit or some fans? You can record until you reach that "threshold of sweat," and then on goes the A/C or the fans. You've got to wait till the room cools down, and then race against the clock to get the next round of recording done. Well, you shouldn't have to race against that clock, so to coin a phrase—no air flow = no signal flow.

The ideal way to deal with this situation is with a unit designed for central air conditioning. These types of A/C units will really push some air through some ducts. The ducts, if insulated and designed sensibly, will offset the noise generated by the motors and fans inherent in this or any type of air conditioning. A wall or window air conditioner is designed to treat just one room, and can do this fairly easily without pushing a lot of air. But we need the ducts. It's all about the ducts.

BTUs essentially represent the ability to turn hot air into cool air—the more you have (BTUs), the more hot air you can turn into cool air. The process of turning hot air into cool air creates heat, so this created heat must be vented away from the room-to-be-cooled in some way. Wall and window units have the heat dispersing portion of the unit placed on the outside of the building. A central air conditioning unit is generally placed outdoors, but it can also be placed inside in special circumstances. Since there's more of a current of air than with a room air conditioner, a central air unit adds one other factor must be considered—an "exhaust" must be created for this air current , or too much of a "load" will be put back on the A/C unit.

The Duct's The Thing
Shakespeare said, "The play's the thing." Shakespeare was a brilliant and insightful man, but he was wrong about this one.

In a nutshell, if you insulate the ducts and throw in a 90 degree angle or two, you'll have a ducting system that will bring cool air into your studio and isolate the noise to a reasonable degree. Obviously, whether or not one can use a central air conditioning unit Vs trying this with a room air conditioner is the deciding factor. Let's look at an attempt at this with just a room air conditioner for the time being, since for many of us in apartments, it might be the most practical approach.

If you go into a store that sells room air conditioners and suggest that you want to do anything like this, they're going to look at you like you're crazy. Room air conditioners are not designed to perform this task, so they're going to need a little help, help in the form of additional fans to move the air. This is going to take a bit of ingenuity, and perhaps someone who's handy with tools.

Electronic supply stores will have "silent" fans that run on AC power. Usually they are square and mountable, similar to computer fans that run on DC power. I ran down to my local Home Depot, and the type of ducting available there is a round aluminum type, with round to rectangular adapters that connect to the rectangular grate that interfaces with the room itself. This ducting must be connected lengthwise, so it would be possible to insert an insulating or absorptive material, plus an arrangement with a fan. The round shape might make this project overly interesting, if you will.

Rectangular ducting is also available. However, at a certain point it may become reasonable to just build the duct to the size of the fan. It may be possible, if building these ducts out of wallboard, to build right into the existing structure or the structure being built. Insulating it serves two purposes, much the same as placing absorptive material inside a studio—keeping sound from reflecting inside and keeping outside noise out.

We have three possible scenarios here, if we assume that we have one single room that we're dealing with. We can air condition a) a room that has only absorptive material on the wall (or none at all), b) a room that has a vocal booth built somewhere within it, or c) a room that has had the floor, walls, and ceiling raised, extended, and dropped, in other words, a "room within a room" has been constructed with a partition that creates a recording room/vocal booth.

Real analogies can actually be made between air flow and the flow of electricity. If ducting in two directions, consider that the air will follow the path of least resistance. Because of that, equal lengths should be considered for the two duct paths. Building an enclosure around the A/C unit will be necessary to fully isolate the noise, so some ducting must be considered if we're to feed the air intake, unless we're able to take the feed from the outside. The main thing when feeding air conditioning into two rooms, such as a control room and a vocal booth, is that each room must have its own source, receiving air from two separate ducts. This will avoid crosstalk between the rooms—definitely undesirable. It would go something like this:

Pushing the Air-velope
In the next installment, we'll get into some specs for air conditioners, and the decision-making process for buying one. We'll also explore some construction specifics. I hope that your right brain has been engaged, and the visualization process has started for actually trying to pull this off.

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Related Keywords:signal flow, studio, recording audio, digital audio, air conditioning

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  • Air Flow & Signal Flow: Going with the Flow? by DMN Editorial at Aug. 03, 2004 10:08 pm gmt (Rec'd 2)

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