Speech That Enters the Heart
Rav Yechezkel charged a rav with the difficult task of cultivating good rhetoric and proper speech. “Just as in music,” he once wrote, “every note in speaking must be weighed and measured, and every tone which is out of place is jarring. In speech, words do not enter the hearts, and surely do not cause them to tremble, if the diction is not measured and weighed.” On the words of Chazal, divrei chachomim benachas nishmo'im (the words of the wise are heard when spoken calmly), he said, “Nachas doesn't necessarily denote just a lack of anger. Every raising of the voice that is inappropriate causes harm. Even if the words are filled with rich content, they won't make the proper impression if they are not spoken with appropriate calm.”
Source: Rav Yechezkel's writings; on divrei chachomim benachas nishmo'im