Normal observers find pairs of tones with these ratios of fundamentals to be more pleasant, and intervening rations less pleasant. Musical consonance and dissonance depend on many factors in addition to frequencies of partials. For example, unlike non-musicians, classical trained musicians describe pairs of pure tones with these simple numerical ratios of frequency as consonant and intervening ratios as dissonant. The only reasonable explanations is that trained musicians are able to recognize familiar intervals and have learned to think of these intervals as consonant. In order for complex tones to attain a given degree of consonance, low tones must be separated by a larger fractions of an octave than high tones, and composers generally follow this principle.
Combination tones are due to the nonlinearities in the hearing mechanism.
They can contribute to dissonance and to beats. Reverberation is not the only effect in architectural acoustics. Our current understanding of architectural acoustics is far from satisfactory. Many voices or instruments do not sound like one voice or one instrument. It must be due to irregular changes in the overall waveform, caused by beating or head motions or by differences in attack.