Problem

the loudspeaker passes audio, but produces no high frequency (treble) content.

Solution | Workaround

Verify the following: 

• The loudspeaker is receiving full range audio signal. If another loudspeaker is available, use it to check the audio signal. 
• Reset the loudspeaker to factory default settings by navigating to Settings > Factory Reset on the Menu. 

After verifying, does the problem still exist?