I was wondering - What's the relationship between CFM, RPM, and dB levels? Let's take a hypothetical dual-bearing fan. It puts out 100 CFM, 45 dB, and runs at 3000 RPM. Now, let's cut the RPM in half. Is the relationship linear, and the CFM and dB would be cut in half, resulting in 50 CFM and somewhere around mid-30's dB, or is it exponential, and it would move less than 50 CFM? Any ideas?