A great and wonderful method of avoiding anger is to accustom yourself to speak always in the lowest voice possible. This is more effective than any other method for attaining to the quality of patience. With other methods you are not able to work regularly on changing your nature, but just at those times when someone is insulting you or doing something against your will, and there can be a long period when something like that does not happen. As a result, it is hard to change yourself using those methods, because changing one's nature requires regular and consistent work to alter ingrained habits. … But this matter of speaking with a low voice is something that can be done consistently, and therefore, with enough effort it is easily possible to change yourself so that you get in the habit of always speaking in a low voice. As a result of this you will automatically be protected from anger.

Therefore, anyone who is an angry type by nature, and wants to overcome his fault, should put all his energy into this. He should always speak in the lowest voice possible. With God's help it will enable him to become patient and to move towards great lowliness and humility also. Furthermore, it is a wonderful aid in achieving purity of speech, because when you are always alert to be careful to speak in a low voice, you will also be reminded to be careful about forbidden speech [slander, for example] and idle conversation. … In Or Tzaddikim it is written that: "Someone who speaks with a low voice and favors silence, becomes a chariot for the Divine Presence." (Erech Apayim, 4:13, pp. 83-84)

Yitzhak Buxbaum in Jewish Spiritual Practices