The words of the wise are heard with pleasantness (Ecclesiastes 9:17).
The Talmud states that on Friday afternoon, a person must alert his household to prepare the necessities for Shabbos. However, he must do so in a soft voice, so that his words will be obeyed.
Many late Friday afternoons, people feel themselves under pressure while rushing to prepare for Shabbos. If one sees that some things have not yet been done, it is easy to lose composure and scream at other members of the household. The Talmud cautions against doing so and implies that shouted instructions are less likely to be carried out.
A politician who had concluded an address inadvertently left a copy of his speech on the lectern. In the margins were comments indicating manners of delivery, e.g. "gesture," "clap hands," "slow and emphatically," etc. At one point he had written, "Argument awfully weak here. Scream loudly."
If we have something of substance to say, the message will be adequately conveyed in a soft tone, because the content alone will carry it. Only when our words have little substance do we seek to make an impression by delivering them with many decibels.
Even in situations of great urgency, we have no need to lose our composure. I can attest that when life-threatening emergencies presented themselves in the hospital, greater efficiency and more rapid response ensued when everyone kept a cool head.
The words of Solomon are correct. The wise speak pleasantly, and those who shout may not be wise.