Perception and Watts: Doubling of power
There's a curious rule of thumb, which to my ears seems mostly true:
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?? 😁
Here's a blurb on meters. I recall a few vintage pieces with fast/slow meter settings, but the Carver switch is marked low/high. The Carver has not been used for @ least 10 years (afraid to power it on). http://www.cordellaudio.com/instrumentation/power_level_meter.shtml DeKay |
How can any of us really tell what half as loud, or twice as loud is? Using music as a test signal for determining half or twice loudness is indeed difficult. Music varies in pitch and loudness and so is a moving target. The bel scale was developed by Bell Labs using steady tones on multiple test subjects and determining an average estimation of half or twice as loud. The difference in acoustic pressure called a bel. Decibel, of course being 1/10 of a bel. So a bel is what the average human perceives as twice of half as loud. The actual acoustic pressure between the threshold of hearing and the threshold of pain is more than a million to one. The human ear/brain compresses this range in a logarithmic manor so as to be manageable. This is why the objective acoustic power must be increased by 10x to be perceived as twice as loud. To answer the original question: there is generally no reason for us to worry about what is half of twice as loud. But, it is good to understand that a 200 W amp will only play 3db (21.9%) louder before clipping than a 100 W amp. |
audioguy, with respect, I believe you are mis-reading things. "A 3 dB change yields a 100% increase in sound energy and just over a 23% increase in loudness." (from the article you included). 3dB is indeed a doubling of actual acoustic energy as measured in millibars of atmospheric pressure change. "Loudness" refers to what humans perceive as volume change. A doubling of amp power or acoustic energy is perceived by humans as around 23% louder. "Louder is better, David. In this universe louder is better" Jerry Garcia to David Grisman |
@audioguy85 I believe @hertzhead has correctly explained the issue.
3 dB corresponds to 2x the voltage at the speaker terminals, but we do not actually hear it as twice as loud. We hear it as a noticeable increase, but not twice. You can try this yourself with an SPL meter. Use a test tone and try increasing/decreasing by 3 dB. |
