The smaller is better? I have the same experience. Some time ago I made two very small boxes like below from 6mm MDF (the slot vent too long, had to shorten it). Both contain 6.5" B&C 6NDL38 speaker. I would describe the sound difference between them using exactly the same words as quoted.
I'm happy somebody starts to create these ultra small boxes professionaly. I'm using mine for years now. For a small jazz gig with silent drums one is enough. For bigband practises, I use both boxes stacked for better coverage. Never needed to be more loud. I don't need to put up the lows, but my bass has a lot of lows on itself. Using these small boxes allows me to play around central Prague (where it's impossible to park) without need of a car.
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