There are several reasons why your stethoscope may sound tinny, all related to the bass response of your headphones:
1. Are the headphones connected properly? Is the plug in all the way? If not, the plug may be too fat and you need to use the Headphone Adapter cable we provide.
2. Do the headphones seal in your ears well ? If using in-ear headphones, they MUST be well-sealed (blocking outside sound) if you want good bass.
3. Are the headphones up to the job? Some headphones don't have good bass. If you're using on-the-ear or over-the-ear headphones, you need really good quality headphones that seal out outside noise and have really good bass.
4. What Filter setting are you using? You must use a lower frequency filter setting when listening to heart sounds, for instance. Check out information about Using Filter Settings to learn more.