I get what you're asking, and it's a question worth answering. How come since Christ came, God never speaks to us in an audible "out loud" voice, like the sort you could tape record and playback?
Part of the Answer lies with the Holy Spirit. Before Christ came to die on the cross, the Holy Spirit didn't permanently indwell God's people. Because of this, they didn't have that 24/7 hotline to God as we do today. God spoke audibly because without the Holy Spirit within them, verbal communication and miracles were the only methods of communication with the Lord.
After Christ died for our sins, We received the Holy Spirit within our hearts. Because of this, when God wants to speak with us, he does it through the Holy Spirit, since that's one of the reasons He gave us the Holy Spirit. And because we have the Spirit within us, we no longer need to hear the audible voice of God.
Having said that, God can still speak out loud if he so chooses. For example, The voice of God that Saul heard on the road to Damascus was heard by those with him as well. However, it seems to me that God now will only speak audibly to those who don't have the Holy Spirit (e.g. the unsaved).
Interestingly, one of my roommates back in the college days claimed that he heard the audible voice of God, which was why he came to Christ. He was into about every sin you could be in, and one day sitting on an empty bus heading to the bus station, he said he heard what had to be God telling him to get off the bus. He pulled the cord, and got off at the next stop, which was interestingly enough directly in front of a local evangelical church. Now, whether you believe my friend's story or not (knowing him, I believe him, but it would be understandable for others to be skeptical), it goes to illustrate the point that God still speaks out loud, but he seems to save it only for converting the unsaved.
Hope that helps any.