I know that the Halichos Shlomo says (page 93, or chapter 7 halacha 18) in the name of Rav Shlomo Zalman Aurbach that one should say the bracha out loud, because all of the Acharonim who say mehalchim in how to say it correctly, do not mention this technique. However, he says that if the tzibbur is makpid to say it quietly, then the chazan should act according to their minhag. Ask your Rav.