because decibels is a logarithmic measure, every 3dB increase is a doubling of the sound. So a 6x louder sound than 100dB would measure 118dB.

Something else, which compounds the effect of 3kHz, is that our hearing is most sensitive between 2-4kHz (and a bump at 1kHz). This is documented as the Equal Loudness Contour aka 'The Fletcher-Munson Curve'. It's logical to think that our voices and hearing are evolutionarily married to one another.

3:33 is it possible to learn this power

How vocal folds produce harmonics I,e multiple frequencies at the same time

Decibels are on a logarithmic scale. So 6×100db is around 115db

The cathedral organ is the loudest instrument at full volume

The plexiglass is only there around the drum set because those mortals can't handle our power. 😜

Formant is not the same as harmonic - formants are NOT correlated to the fundamental pitch