Ibn 'Abbaas Radiyallahu 'Anhu says:
"Rasulullah Sallallahu 'Alayhi Wasallam raised his voice only to the extent, that it might have been possible that if he recited in the house, those in the courtyard might be able to listen".
English reference: Book 43, Hadith 304
Arabic reference: Book 44, Hadith 321