MOMS PLEASE HELP!

Sarina💋 • I'm 25 • FTM • I gave birth 3 weeks early to an amazing little boy named Cameron • 10/6/15 • 7lbs 8oz • 20in
I'm worried my 6 week old might be deaf. I'm probably overreacting but I feel like he doesn't respond to loud noises or even my voice when I try and wake him. He passed both ears at the hospital but I'm still concerned. How old do babies have to be before they start responding to noises or voices?