Verify and if needed, install proper audio driver.  Anytime you plug in a device, Dell Audio popup will ask to confirm plugged-in device.  Selecting incorrect output speaker will lead to lack of bass ( such as internal speaker).

You can do the setup manually, first, launch the Dell Audio app (from tray icons area), then select speaker/headphone tab (from top), select speaker setup (from left) and making adjustment to speaker size, the larger the more bass sound you will get.