You got the Smith job. Rack-  or shelf-mounted components in a cabinet; a satellite receiver, Blue-Ray player, a surround-sound processor/receiver, and an amp driving speakers in other parts of the house. The whole thing gets tucked into an alcove beneath a 54” TV panel, and makes a nice, if modest, home theater system driving 5 decent speakers and a powered subwoofer.  The only problem is one you’ve faced before — the wife wants it all hidden behind closed doors.  She’s not being unreasonable; there’s a 4 year old running loose in the house, and he’d love to get his hands on all those knobs and buttons.  He might not break anything, but Mrs. Smith knows best.  Mr. Smith doesn’t care – he’s getting his home theater and permanent possession of the fancy does-everything-you-could-imagine remote……!

The problem is that this system is going to generate enough heat to cause problems if you don’t do something about it. You’d just as soon not go through the DVD player locking up, satellite receiver melting its access card, and amplifiers popping fuses every time someone blows up a building.  Every heat-generated problem is a potential nuisance service call, too many of which you wind up eating in the name of good customer relations.  But the closed-in setting guarantees heat build up.  Small openings don’t help much, and unless some thought is given to the problem before the system is installed, expensive retrofits may be needed later.  This is a problem that’s FAR cheaper and easier to fix before, rather than after, the fact.

If a wooden enclosure has no openings other than incidental holes for power cords, etc., little hot air will escape, and very little heat will pass through the enclosure walls. (We’ve written a white paper on the fundamentals of thermal problems; download it at the Technical Info page at or call us for a copy.)  Some openings have to be provided; one for heated air to escape through, and another for cool room air to enter.  For every bit of hot air that escapes, an equal volume of cooler air MUST enter, otherwise airflow will stop – we’re not using vacuum pumps here! Although occasionally you have a client who insists that there be no visible openings in their cabinetry, a quick explanation of the importance of good ventilation to ensure a long, trouble-free life for the A/V equipment  will often change his (or her) mind, and allow reasonable vent openings. More often than not, however, there’s little resistance to modest vent openings, and these can be designed into the cabinet at the planning stage.

Now the trick is to use these to best advantage – move enough air to keep the equipment cool WITHOUT making more than minimal noise.

Noise is the other side of the equation, because ventilation that creates an annoying level of noise just creates other problems……….

Active Thermal Management has developed an entire line of extraordinarily quiet air movers in two categories; equipment coolers that ventilate one piece of equipment that may have restricted ventilation, and enclosure coolers that can cool small, mid-size, or large enclosures easily and quietly. We will discus just one of those here.

Our most popular product is one that fits a wide range of installations – the System 2 Kit. Using a proportional control, the System 2 Kit is ideal for situations similar to the one outlined above, whether retrofitting a problem installation or designing it in at the planning stage.

A thermal “first-aid kit” in a box, it consists of two 4.7″/120 mm DC fans, power cube (“wall-wart”), two thermistors, and a proportional-control electronics package – more about that one later.  We’ve made installation, whether by the installer or the cabinetmaker,  quick and easy.  Just cut a 4 1/2″ round hole for each of the two fans, wire them to the control box, put the thermal sensors where they can “feel the heat”, and you’re done. Deciding where to locate the fans is usually the most difficult part of the job…

Mounting arrangements are very flexible. If the cabinet was built with the System 2 Kit in mind, intake slots could be cut in the toe-kick panel and floor, letting air flow into the space under the bottom shelf & up into the enclosure, with the fans at the top rear or sides, blowing hot air out, as in Figure 1.  If the cabinet will have at least 2” of space behind it, both fans can be mounted on the rear panel, as in Figure 2, with the lower fan pulling fresh air into the cabinet, while the upper fan pushes hot air out. The picture shows a vertical divider; if present, generous openings must be provided for sideward airflow.

In a retrofit situation, where the space behind the toe-kick and under the bottom shelf can’t be reached, mount one of the fans low on the side or rear panels of the enclosure, using one of  the supplied grilles to keep little fingers out of the blades, and the other fan high and on the rear or side panel.  The only limitation is your imagination…..  Each fan has a 4′ cord that connects to a terminal strip on the controller, allowing easy wire routing within the cabinet.

Next, place the thermistors (prewired to the control box) at the heat sources, usually the largest amp and satellite receiver or cable box. Use the double sided tape on the rear of proportional control electronics box to mount it in a convenient location, plug in the wall-type power supply, and the job is done.

The fans spin up to full speed for 2 seconds at initial power-up, then drop back to a speed appropriate for the temperature being sensed by the thermistor. From then on, the fans will run at a speed proportional to the temperature rise in the enclosure. At moderate temperatures, the fans spin slowly; when hot, they turn faster. After the system is turned off, the fans will remove the heated air from the enclosure, then turn off.

Please note that the heat from satellite receivers or cable boxes may be sufficient to keep the fans running at the lower end of their speed range at all times, as these devices dissipate heat even when not in use.

There’s no need for triggers or any other control; the temperature in the enclosure controls the fans at all times. Noise (both fan motor noise and air sounds) is extremely low, as the fans never run at full speed, except for the first few seconds after power-up (which helps assure that dust and dirt build-up won’t “freeze” them – the momentary full power will break them free even after years of operation.

Active Thermal Management can be reached at (661) 294-7999 or  Visit our website at