Honestly, I think computer noise may have been quite audible for a very long time now, but it's only been in the last several years that people have noticed it (I recall our original Pentium processor coming with a fan on the heat sink, and hard drives have had ball bearings long before fluid bearings) .
My counterpoint: The first PC I ever had was a 286 in a pretty desktop box. It was so noisy that I couldn't stand having it on for more than an hour at a time. I ended up stuffing it in a big cabinet inside my desk, atop a big piece of foam, and surrounded by more foam. I didn't block the fan though. That damped the HDD whine/scream/jet engine emulation and the horrific roar of the PSU fan enough that I could leave it on for 2 hours. Whether it overheated or not was something I never thought about at the time.
I think PCs were mostly noisy most of the time; most of us just accepted it because we didn't think there was any choice.
Ideally, there should be a metric more accurate than dBA to help us with what is generally audible to most people in an office or a home, or wherever. Something along the lines of frequency overy frequency (yes you read that right) or even frequencies over time.
Yes, but it's not going to be any single number. The acoustics are just too complex to be summarized into any single number. Maybe a composite of several different parameters, but each with its own score -- one for loudness, one for tonality/smoothness, and one for temporal constancy (ie, lack of change over time).
good example of a tone pulse that's far more annoying than it's constant version.
That would be illustrative... but it's really easy to demonstrate how useless sound power or SPL tests just by themselves are. It doesn't require any programming. Just try this: Take white/pink noise of a certain amplitude. Listen to it for a minute. Now listen again, but have someone randomly introduce a split second pause in the white/pink noise over the same period. The signals' total energy output difference over that minute will be immeasurable, and it's average spectrum will be the same -- but the second session will drive you batty.
- - - - - - - - time passes - - - -
In fact, in the 10 minutes since I wrote the above, I used one of my recording programs to generate two 30 second streches of pink noise in one file. The second 30 seconds are punctuated by little random gaps of slightly varying lengths. Trying listening to it. It's at a fairly high level, so you might want to turn your speakers/headphone down a bit. I think if you turned it down enough, you could easily sleep with the steady pink noise on. Most of you will probably agree that the intermittent pink noise would be pretty distracting at almost any level.
The annoying pink noise
(Warning: The file is almost a megabyte.)