Loudness / intensity is the crudest salience lever: a physically stronger signal — high volume, ALL CAPS, saturated or flashing visuals, stacked exclamation marks — reliably wins the automatic orienting response, whether or not it carries more or better information. The source turns up the sensory “gain” so its message is processed first and hardest.
Because the orienting response to intense stimuli is largely involuntary, your attention is captured before evaluation begins. The manipulation is the substitution of intensity for substance: loudness does the persuading that argument and evidence cannot. Unlike contrast, which wins by standing out from a quiet background, intensity wins by sheer magnitude — and often escalates into an arms race where everyone shouts, so each shouts louder.
It is among the easiest techniques to spot — you notice you are being shouted at — but the reflexive capture is momentarily hard to switch off. Crucially, intensity buys attention, not conviction; loud, high-arousal appeals can even reduce message processing.