Hi, this is my first post here in this very cool and interesting forum.
When it comes to budget speakers, I would suggest analyzing the ones available on the mass market and being bought by many customers, like those bluetooth speakers or "smart" speakers. I think this would give an interesting insight how good or bad those speakers are.
For example, I use the Bose Soundlink Revolve in my office and outdoors - and it doesn't sound good at all (without heavy equalizing).
Here are my quick-and-dirty measurements of this speaker:
Of course, the boomy sound gets worse in the office when the speaker is placed on a desk close to wall and monitor.
Also, the highs sound very harsh due to the resonances at high frequencies and the 2.5 kHz peak is something like the counterpart of the BBC dip.
I have measured this speaker being placed directly on the floor as its natural habitat is somewhere on furniture or floor. The free-air performance differs above 3 kHz but does not become much better. (The lowest half-inch of the grill is where the sound of the small down-firing full-range speaker comes out.) If interested, I can do more measurements on that speaker, but this will take time.