The problem is the second console.log is executed right after resources.load is called, but the first log is asynchronous when loaded. It may take 0.1s, 1s, or more.
The correct program order is:
1. this.voicePool = []
2. cc.resources.load
3. console.log(this.test.duration);(the second one in your screenshot)
4.(a few moment later) function(err,assets){
self.test = assets
}