Located heartbeat but haven't heard it?

Jennifer
I've had two ultrasounds. One at the ER and then a scheduled one with a tech. At the ER they told me the heartbeat looked good but never let me hear or see it. The second time they showed us the baby on the screen and showed us the heart beating but didn't let us hear it. Is that normal early on? I'm 8 weeks and my sister said she got to hear it at 6. Doctor went over ultrasound with me on the phone said everything looks fine.