“ויצא משה ואהרן מעם פרעה ויצעק משה אל ה’ על דבר הצפרדעים אשר שם לפרעה” (ח’,ח’).
The Meforshim ask why it says ויצעק by מכת הצפרדעים while by the other makkos it says ויעתר. The שפתי חכמים answers that it is because of the halacha המתפלל צריך להשמיע לאזניו. When one is davening he must hear the words he is saying. Since the frogs were making a lot of noise, Moshe could not hear himself. He therefore needed to raise his voice in order to hear the words he was saying.
The מחבר (סימן ק”א סעיף א’) writes לא יתפלל בלבו בלבד אלא מחתך הדברים בשפתיו ומשמיע באזניו בלחש – when one is davening it is not enough to think of the words rather he has to speak them out and also hear the words he is saying in a quiet manner. ואם אינו יכול לכון בלחש מותר להגביה קולו,והני מילי בינו לבין עצמו אבל בצבור אסור דאתי למטרד ציבורא – if it is difficult for one to have kavannah davening quietly and he is davening alone, then he can daven out loud. However if he is davening with the tzibbur he is not permitted to raise his voice because it will disturb everyone else. The חיי אדם says that לכתחילה the person standing next to him should not be able to hear the words. If this is not possible he may daven a little louder as long as it is not disturbing. The Poskim all say that בדיעבד if one did not hear the words he is still יוצא since he spoke them out.
The ביאור הלכה brings from the פרישה that if one is unable to have kavannah if he davens quietly with the tzibbur, then he may go home and daven by himself. The פרי מגדים however says that today one should not do so for others will come to learn from him and daven by themselves even though they have no need to do so. Unless he is a גדול הדור and everyone knows that everything he does is לשם שמים.
Can one scream out in middle of their תפילת לחש the words משיב הרוח or יעלה ויבוא to remind the tzibbur to say it? The ביאור הלכה (סימן קי”ד ס”ב ד”ה אסור) writes that even though the מגן אברהם says that the ש”ץ may scream it out in middle of his own שמונה עשרה it is not proper to do so. The חזון איש זצ”ל as well says that it is not derech eretz for Teffilah for anyone to do so. Reb Shlomo Zalman zt”l says that it is a דבר מבוזה to do this while standing in front of the מלך. Reb Chaim Kanievsky shlit”a says that nevertheless the minhag is to be lenient and one can say it out loud in middle of their תפילת לחש.
There are two ways how to understand this halacha of צריך להשמיע לאזניו. Is the reason because if it is not said in such a manner it is not considered a דיבור and it is as if he never said the words? Or it is a separate halacha, that even though he said the words, still there is an additional halacha by שמונה עשרה that he must actually hear the words? The difference would be if he is in a place we there is a lot of noise and he cannot hear what he is saying, even though he is speaking loudly. If the reason is because it is not considered a דיבור in this case he is saying it loud enough to be considered a דיבור even though he does not hear it. However, if it is an additional halacha that even though it is a דיבור if he does not hear it, but he must hear what he is saying, then when there is a lot of noise and he is unable to hear himself, he would not be יוצא. This is the opinion of the שפתי חכמים mentioned above.
There is a dispute amongst the Poskim as to the opinion of the Zohar in regards to davening quietly. Many who follow the derech of תורת הקבלה understand the Zohar that one should be careful not to hear the words he is saying. However the גר”א and other אחרונים hold that there is no machlokes between the psak of the שלחן ערוך and the זוהר.
Prepared by R’ Avrohom Yehoshua Ziskind
 Sources;משנה ברורה,חבצלת השרון,דרשו,פסקי תשובות