In this photo (below) you can see the ductwork that pulls air out of the back
of the hushbox.
This 6" ceiling duct leads to a 110CFM Nutone silent bathroom ceiling fan in
an adjacent room that is used to suck the air out of the hushbox:
Even though the fan is in an adjacent room, rubber bungee cords are used to
hang the fan from joists to ensure that it is completely silent.
I tapped into the voltage off the projector fans in order to drive a small
120VAC solid-state relay (with 3-15VDC 'coil') which automatically turns on the
bathroom fan whenever the projector's powered up. The relay coil is of very high
impedance so there's no extra current being drawn from the projector to switch
this relay.
Another (possibly easier) option is to use a duct fan thermostat to
automatically turn on the fan when the temperature reaches a predetermined
level. Smarhome.com sells one here: http://www.smarthome.com/3018.html.
By remotely locating the evacuation fan, we are ensuring that the home theater
remains as quiet as possible.
Note: Check the direction of venting of your projector to make sure you push or
pull air correctly. Most projectors (such as the one detailed here) pull air
into the unit from the front around the lenses and vent out the back, but some
models do the opposite.
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