Total dB level adding of two incoherent uncorrelated sound source - combining decibels or SPL sound pressure level add signal noise levels

● Total Level Calculation ●

Adding the level of two uncorrelated (incoherent) sound sources,
Combining the levels of e.g. a violin and a violoncello

Total adding of two incoherent sources

For beginners: incoherent means the signals of the two channels are irrelative like a violin and a cello,
that means having no correlative relationship. Often we say uncorrelated when we mean incoherent.

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Decibels are logarithmic "units", they may not be added linearly like other figures.
If a sound source creates a sound level (SPL) of L₁ = 60 dB and another source
with L₂ = 60 dB is added, then it is not the level of 120 dB, but gives a summing
level of 63 dB. If both values are equal, it is easy. More than 3 dB greater than the
higher of the two levels is not possible for the total sum in dB.

Combined Sound Pressure Levels - sengpielaudio

Level difference between the two sound sources

Adding of two levels in dB

For the sound level of n incoherent radiating sound sources we get:
SPL Addition 01

p₀ is the reference value of the sound pressure. Auditory threshold at 1 kHz = 0.0002 Pa.

Adding of two incoherent sound pressure levels or voltage levels:

Adding of two values of the same level give an increase of the total level of (+)3 dB.
This equation is used for electrical adding of incoherent signals,
and for the calculation of the energy level of two loudspeakers.

Adding of two coherent sound pressure levels or voltage levels:

Adding of two values of the same level give an increase of the total level of (+)6 dB.
This is obtained by feeding two side-by-side loudspeakers with the same signal.

Level adding of up to four sound sources

Adding decibels - combining up to ten acoustic levels
Combining decibels of one-third octave bands to level of octave band and vice versa
How many decibels (dB) sound level change is twice (double, half) or three times as loud?
Damping of sound level with distance

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1st sound source Level L₁: dB	2nd sound source Level L₂: dB	Total level from both sounds: dB