Also, crucially: dB is a measure of sound pressure level at a point in space. It is not at all a measure of total sound output. And it tends to fall off at a rate of 6dB per doubling of distance.
So by halving the measurement distance and changing nothing else, a thing reads as being about 6dB louder. And by doubling the measurement distance and changing nothing else, a thing reads as being about 6dB quieter.
So stating that a jackhammer is 100dB and a television is 60dB is rather meaningless by itself.
If the jackhammer is measured at 0.5 meters (the distance of the operator's ears, say) and the television is measured at 2 meters (the distance of the viewer's ears, say), then there is a measurement delta of 12dB, which is a difference more than an order of magnitude in energy intensity.
And all we did to produce that massive delta was vary the distance where we've placed the meter.
(And, no, there is no standard measurement distance. Loudspeakers are often [but not always!] measured at a distance of 1 meter, and generators are often [but not always!] measured at a distance of 20 feet. It needs to be explicitly stated.
In all cases, if the only parameter relayed is "dB" then it doesn't really mean very much.
And this isn't even getting into other important factors, like if the measurement is performed in a half-space or anechoic or whatever environment.)
So by halving the measurement distance and changing nothing else, a thing reads as being about 6dB louder. And by doubling the measurement distance and changing nothing else, a thing reads as being about 6dB quieter.
So stating that a jackhammer is 100dB and a television is 60dB is rather meaningless by itself.
If the jackhammer is measured at 0.5 meters (the distance of the operator's ears, say) and the television is measured at 2 meters (the distance of the viewer's ears, say), then there is a measurement delta of 12dB, which is a difference more than an order of magnitude in energy intensity.
And all we did to produce that massive delta was vary the distance where we've placed the meter.
(And, no, there is no standard measurement distance. Loudspeakers are often [but not always!] measured at a distance of 1 meter, and generators are often [but not always!] measured at a distance of 20 feet. It needs to be explicitly stated.
In all cases, if the only parameter relayed is "dB" then it doesn't really mean very much.
And this isn't even getting into other important factors, like if the measurement is performed in a half-space or anechoic or whatever environment.)