I am using a 400w philips MH lamp envelope lamp and a standard OHP spherical reflector. I am able to keep everything at the right temperatures with 2 x 12cm 12volt fans. One is exhausting the light chamber heat the other is pulling cool air between the small gap separating fresnel from lcd.

The problem is the the fan noise seems to be magnified dramatically when placed against the 1.2mm aluminum sheet that encloses the side of the box. I have mounted the same fan in a hole of a standing mdf projector box and the noise is much less.
I tried placing 7mm thick tire rubber separating the plastic 12cm fan from the aluminium sheet but this does not help much.
This seems like a big con towards using aluminium sheeting for your box or any thin metal sheeting for that matter.

The only solution I found was to position the fan about 1.5 inches away from the aluminium. This would mean there would have to be 1.5 inches of rubber between the aluminium and the fan on all 4 corners. Now just positioning the fan unmounted at 1.5 inches seems to be reasonably quite but I wonder once the rubber is making contact between fan and aluminium if it will be worse.

I was also considering placing the fan inside the box at about 1.5 inches away from the aluminium side once again but mounting it using 2 x L brackets to the fan and the bolted to the base of the box. The base for the mount would have a 1cm mdf and 1cm thick hard tire rubber. Perhaps this would work even better since I can reinforce the thickness of the base with mdf and even thicker larger surface area rubber.


Comments? Suggestions?

Maybe try the rubber fan mounts in the LL store? I noticed this too when I tried mounting them in metal. How about mounting them in mdf and the mounting the mdf to the aluminum with rubber?

One solution might be to place the fan inside a wood frame and connect the frame to the metal. The wood may absord the vibrations.

Thanks for your inputs. What Ive done is this. I took 4 x 3 inch bolts and placed the bolts sticking out of the aluminium side of the box. I then placed the 12cm fan on the bolts but with 2 inch space between box and fan. So looking from the side I got the aluminium sheet, air conditioner filter, 2 inch space, 12cm fan blowing air in.

It was surprised how quiet it is. I always compare the noise to when I hold the fan in my hand and I could not really hear a difference between mounted and in my hand.

The gap on the exhaust side of the lcd is about 1 inch wide by 4 inches high(height of lcd). So the air is only being pulled on the back side of the lcd. I am using unsplit design. I think if I widen the gap from 1 inch to say 2 inches and center the 12cm fan on this 2 inch wide gap I should cool the lcd even better. My plan was to only pull cool air over the back of the lcd or the space between double fresnel and lcd. However I think now pulling cool air over the front of the lcd as well will help.
Sorry dont have dig camera at the moment. Comments?

Just gotta be creative with soft rubber and/or some kind of closed cell high density foam mounting scheme. Any "hard" mount will transmit the vibrations and cause noise. Good luck!