Is the noisy nature of appliances (like computers, toaster ovens, microwave ovens) due to the fact that engineers don't go to any trouble to design how these machines sound? Or is there no practical (including inexpensive) way to make them quieter?
Sound is hard to "block". The fact that it is detectable through massive objects always amazes me. I don't think it is reasonable to expect the case of a machine to block the sound of the machinery inside. However, could there be designs that don't hum and buzz?
The fans and motors in equipment like a desktop computer aren't very powerful, but the equipment is operating at roughly constant frequency so resonances develop. If you have good hearing, you detect that most desktop computer cases hum. The really irritating ones develop a rattle or buzzing sound. Some toaster ovens buzz because their heating elements vibrate.
In designing antennas it is important how the physical length of the antenna compares to the wavelength of the signal. In examining and modifying the cases of computers, altering the physical dimensions of the surfaces of the case don't seem to have much effect on keeping them from resonating. Why this disparity between the two situations?
Perhaps it's an illusion of judgement. Perhaps to make a case that resonated really well, we would have to design them very precisely and they would hum a hundred times louder than the average case.
Perhaps it's something to do with the wavelengths involved or with the fact that the problem is in 2 or 3 dimensions instead of 1-dimension.
I have a table saw blade that is a "vari-tooth" design. The teeth aren't spaced evenly apart around the blade. This is supposed to make the blade operate more smoothly. I suppose the idea is to alter the way that the blade "rings". Would running a fan or motor at an irregular rate would make equipment cases resonate less?