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Well, the brightness of celestial objects is also sometimes negative:

> The apparent magnitude of known objects can range from −26.832 for our Sun to about +31.5 for objects in deep space imaged by the Hubble Space Telescope.[3]

See https://en.wikipedia.org/wiki/Apparent_magnitude

by Sharlin9 hours ago|

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And this is because Ptolemy’s catalog in which he ranked stars by their apparent brightness on a scale of one to six, one being the brightest. Ptolemy’s scale was (much later) retrofitted to a log scale (base 100^(1/5) or about 2.512), allowing extrapolation to both brighter and dimmer objects. The brightest of Ptolemy’s first-magnitude stars actually have negative magnitudes by the modern definition.

by deepspace17 hours ago|

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0db is usually defined as the loudest sound that the audio system can produce. Hence, everything else must be negative.

by rdbl2715 hours ago|

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More specifically, 0 dB is the loudest sound the audio system is rated to produce without distortion. It's common to be able to actually drive systems harder than their specified engineering limits, which is why meters have a short positive dB section marked in red.

by mitthrowaway216 hours ago|

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Of course, typical of the wonderful ambiguity of decibels, 0 dB is also usually defined as the quietest sound that the human ear can perceive.

https://en.wikipedia.org/wiki/Absolute_threshold_of_hearing

by ianburrell15 hours ago|

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That's why important to give the scale. dBfs is full scale level, and db SPL is sound pressure level.

by rramadass3 hours ago|

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Yep.

"Sound Power Level SWL", "Sound Pressure level SPL", and "Sound Intensity Level SIL" are different quantities which should not be confused. - https://sengpielaudio.com/calculator-soundpower.htm

A sound source produces sound power and this generates a sound pressure fluctuation in the air. Sound power is the distance independent cause of this, whereas sound pressure is the distance-dependent effect.

Sound pressure p is a "sound field quantity" and sound intensity I is a "sound energy quantity". In teachings these terms are not often separated sharply enough and sometimes are even set equal. But I ~ p2.

by rramadass2 hours ago|

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Articles:

Understanding dB - http://www.jimprice.com/prosound/db.htm

dBFS - https://en.wikipedia.org/wiki/DBFS

Videos:

Understanding dB level by Paul McGowan - https://www.youtube.com/watch?v=t3Via4c8SlI

Paul explains 0dB and why there's a minus sign on volume - https://www.youtube.com/watch?v=NgEr6NEDPd4

by kevin_thibedeau17 hours ago|

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That is dB full scale where 0 is an absolute ceiling and you can deduct from there.