Generally, it is normal for the Audio Box to sound quieter than expected for most audio systems; however, the audio should resonate fully and completely with the volume knobs at 80-90%.
If the audio still seems too quiet, you can import the audio file into Audacity and check the gain levels for the left and right channels.
And finally, changing the USB drive can sometimes make a difference. We recommend using the certified COBRA USB Drive for the best performance and reliability.
For more information on audio formatting, see the video below.