Would it perhaps be because the bluetooth speakers typically cannot reproduce bass below a certain range and so play the harmonics of the bass note or use the r

Would it perhaps be because the bluetooth speakers typically cannot reproduce bass below a certain range and so play the harmonics of the bass note or use the resonance of the item they are placed on to "produce" the bass note? In truth you are not hearing the bass note - you are hearing the harmonics and your brain is making up the missing low note.