Perception and Watts: Doubling of power

I really did just want to ask, how can we tell what twice as loud is? I mean, I think I can, and it happens to match 10 dB.

Hi Erik, twice the volume, i.e. twice as much sound pressure level, is 6dB(spl). And this requires 4x the power in watts.

It seems that 10dB is what most of us perceive as double sound intensity, i.e. from a psychoacoustic point of view.

And even then, our perception is affected by the frequency. The lower the frequency, the lower our sensitivity, so +10dB may not be enough in the bass, for example... Interesting stuff!

@iseland I think you mean an increase by 3db requires double the power (or watts)

Certainly this is not a tripling of average SPL

Back in the day we found that more speakers (specicially: tweeters) got killed by too SMALL amp that were clipping like crazy when playing louder, and the clipping sent huge amounts of watts to the tweeter. Most tweeters blow at 10W (just throwing a number at it), so a 20watt amp is capable of killing a tweeter (if sending a lot of high frequency clipping noise to the tweeter). 

Couple of things come to mind. 
 

When you buy an amp w twice the rated power, the power supply in that amp is generally much bigger than in the smaller one. 
 

As was mentioned in a post above, a bigger amp playing at the same volume as a smaller amp will sound more dynamic - provided they are built to the same quality level. I tend to believe this difference is connected to the size of the power supply, more so than the power (watt)  capability of the amp. The Hiraga Super 30 watt class A amp I built, has 192K uF in the PS, with a 500VA transformer. People build these amps with insane amounts of capacitance, but for this built, I went with this. Next time I build this amp, I’ll be building it as a dual mono design with greater capacitance in the storage so I can hear first hand how that translates into real world listening experience. 
 

I recently built a single ended EL84 based amp. It’s about 3 watts. Love the sound, but want a bit more usable volume. So I’m about to built a single ended EL34 based amp that will get me approximately 6 watts. Double the power. Different tubes and circuit design, I know, but I’m just curious how that 6 watts will present compared to 3 watts. 3 watts don’t mean a hill of beans if your amp is pushing 200watts into the speakers, but going from 3 to 6 is doubling the power. Thankfully, going from 3 to 6 watts is a heck of a lot less expensive than going from 150 to 300 watts :)

Stated a different way, a 3dB increase in loudness requires twice the power.  This is the reason speaker sensitivity is so important when matching to the power amp. If your speakers are inefficient and maxxing a 300 watt amp, 600 watts gets you just 3db. 
 

Re. the original post, humans are remarkably good at judging relative sound pressure differences. I read about this long ago so I can’t cite the research. But for grins I tried this with my sound pressure meter. I was pretty darned close doubling or halving loudness by ear.