Fans in canopy generating harmonics...help!!!

[plankton123]

OK About a month ago I setup a 12" tall canopy for my 100 that measures 60"x18"x12" with two 4" Toyo 75 CFS fans on each end. They work great and only produce 30 db for the 75 cubic square feet of air per second.

THE PROBLEM: When the two fans are on they setup a low resonance harmonic in the canopy that can be heard (felt?) from anywhere in the house! If I turn one off then it stops. But, if they are both on which of course is necesary to keep the canopy cool with 3-175 halides in it then there's the harmonics. The back of the canopy is open and the front has two doors. Openning the doors slightly changes the harmonics but not by much.

What are my options!!!

Thankyou for your time.

Scott

 

[squeezix]

Try either fiber or rubber washers where they screw into the canopy.

 

[plankton123]

Albert,

Thanks for the reply and I'm going to replace my 1/2" nylon spacers with rubber ones.

Scott

 

[Enkidu]

The harmonic effect is mostly a function of the mass of the blade assembly. If you increased the mass, the frequency of the oscillations would shift, and the harmonic would likely stop. Try taping a small weight to the center of one of fans (the rotating side) to see if that works. If it does, glue it on permanently. Good luck!