No Sound (or Barely any) from Double Bass

The project itself (cut down to the first four bars, say) would be much more useful than a PDF and an MP3.

There’s all manner of stuff you may have done to give this result. It’s equally possible that you’ve done nothing at all to create this result, and it’s bad programming or bad design from whatever playback library you’re using. We can’t possibly know without either inputting some of this music again, or seeing the actual file.

(See Four simple guidelines to help us help you)