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Perception and Watts: Doubling of power

There's a curious rule of thumb, which to my ears seems mostly true:

  • To double the perceived volume, you must output 10x more power.

10x power = 10 dB by the way.  We've read this as we were buying amps and trying to decide between 100w/channel and 150w/channel.  We are told, repeatedly that 50 W difference isn't really that much.

On more than one occasion I've tested this and found it's pretty much spot on.  Here's my question:

How can any of us really tell what half as loud, or twice as loud is?

I mean, think about this for a bit.  I cannot tell half as bright, or twice as bright, but it seems I actually CAN tell what half as loud is.  How does this even begin to work in the ear/brain mechanism?? 😁

erik_squires
zgas-music
82 posts
 

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. 
 

 

erik_squires OP
16,233 posts
 

To clarify a little, 3 dB is a moderate amount of change in volume.  Perceptible but not close to being perceived as double the volume.

It is however 2x the power.

hilde45's avatar
hilde45
4,991 posts
 

Great thread. I'd even call it fun. Thanks, OP!

(Glad to see the buzzkills have piped down.)

winnardt
174 posts
 

Yeah, but this one goes to 11. Sorry, I don't get that many chances to use that one, even if it is worn out.

dekay's avatar
dekay
5,628 posts
 

Erik:

Once I get past the first 2 "steps" on my dual mono volume pots each step offers an approx. 3 dB increase.

3 clicks is then approx. twice as loud.

When I hold Alexa in my hand, while she is screaming @ me, the SPL is approx. 80 dB.

When I then throw her across the room the SPL diminishes considerably.

 

DeKay

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