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Definition of loudness

From Leo L. Beranek, "Acoustics" (American Institute of Physics, 1985), we read:

"Loudness is defined as the intensive attribute of auditory sensation, in terms of which sounds may be ordered on a scale extending from 'soft' to 'loud.' Loudness is chiefly a function of the sound pressure, but it is also dependent upon frequency and waveform. The unit is the sone."

Loudness and audio level

When audio signal level is increased 3 dB, the signal power has doubled. The human hearing does not work linearly and that 3 dB does not sound to be twice as loud. The PERCEPTION of twice as loud corresponds to considerably more than twice the total acoustic power. Typically literature states that 10 dB increase of sound level is heard as "twice as loud". While it may not be exactly 10 dB, that's a reasonable figure.

Once upon a time there was determined a "bel". It was shown to be the amount a sound would need to change in order to be perceived by the "average" person as twice as loud. When divided into ten parts these parts are called "decibels". Soon measurements and standards people determined objective measures for a "bel" and a "decibel" and the measurement system was born.

Of course it's subjective. But it's a standard based on objective analysis of a number of subjective opinions. An average, so to speak. But the numbers used now are not subjective. And the average person will perceive an increase of 10dB (appr) as twice as loud. And it does require doubling the acoustic power to get an increase of 3dB.

Loudness table

subjective change            objective change
much quieter                 less than -10 dB
half as loud                           -10 dB
quieter                                 -5 dB
just perceptibly quieter                -3 dB
just perceptibly louder                 +3 dB
louder                                  +5 dB
twice as loud                          +10 dB
much louder                  more than +10 dB        

Examples of sound levels


Example of sound sources


Quiet garden, electric-clock ticking, drizzling rain


Blast of wind, whisper at 1 m.


Countryside areas, quiet apartment, wrinkling paper at 1 m.


Residential areas, quiet streets, fridges, conversation at 1 m.


Offices, air-conditioners


Alarm-clocks, radio & TV sets at normal volume


Washing machines, quiet typewriters


Hair-dryers, crowded restaurants


Dish-washers, floor-polishers


Loud conversation, noisy street, radio & TV sets at high volume


Vacuum cleaners


Telephone ring, mechanical workshop


Passing trucks, noisy hall or plant, shuffling at 1 m.


Passing train, pneumatic hammer, car hooter at 1 m.


Mega "disco", circular saw


Motorcycle without silencer