Quite smart idea, not for throttling when the fans are heard, but SPEEDING THEM UP while they are NOT heard, based on the noise floor of the current environment.<p>This, combined with an assessment how much of the environment the user currently hears (i.e. maybe he is watching a movie), could provide a lot of headroom for additional cooling without bothering the user.
Another trick is not to use constant RPM because you can hit some mechanical resonance point, but constantly varying RPM around target RPM so that the system even if it hits resonance stays there only for a brief moment and won't start vibrating.
For those who are confused: the title is a bit misleading, it's actually the other way people might expect (if you read the thread)<p>Noisy environment: turn the fans all the way as the user -> more cooling -> processor doesn't throttle<p>Quiet environment: turn the fans down -> processor throttles