So all 4” drivers are created equal? Not at all.
Here’s a Klipsch bookshelf with a 5.25” that goes down to 48 Hz.
http://assets.klipsch.com/product-specsheets/RP-150M-Spec-Sheet.pdf
Here’s another (cheaper) Klipsch bookshelf with a 5.25” driver that only goes down to 62 Hz.
http://assets.klipsch.com/product-specsheets/R-15M-Spec-Sheet.pdf
I wonder if the higher price of the first one allowed them to use better materials and a higher priced woofer to achieve those results, ala PSB vs HomePod...
Where did I say all 4" drivers are equal? My original point still stands - speakers with a 4" driver can easily go well below 100Hz (which is what the poster I replied to claimed).
If you're looking for cheaper versions I suggest checking out Kanto, Plugable or Edifier for examples of self powered speakers in the $150 range (for a single speaker) that can also go well below 100Hz.