I'm traveling to DC for a conference in November.
For ambiance, sound quality,historical significance and artist lineup I'd have to say Bohemian Caverns in the U street corridor.
Chez Billy is great if you'd also like to pair jazz with dinner. There's also Blues Alley and the The John F. Kennedy Center for the Performing Arts. Check out their lineups on their websites.
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Check out. Columbia Station Inc in Adams Morgan, bohemian caverns on U St. Or HR 57 on H St. NE