The short answer to your question is "response".
Range tells you "yes, technically the speaker can play that frequency". Response simply adds "and here's how loud that frequency will be played in relation to a baseline reference".
Response is typically quoted as being within plus or minus 3dB of the baseline - this would be considered roughly "flat" or "good" response. As you get closer to the range extremes, frequencies will be played at lower and lower volumes eventually to the point where it is played so quietly it makes no difference to you.
Bass at -6dB absolutely adds to the music, even -10dB does. If you can get a look at the response curve of a speaker it will give you a very good idea of where "useable", "hearable" bass dies off.
Range tells you "yes, technically the speaker can play that frequency". Response simply adds "and here's how loud that frequency will be played in relation to a baseline reference".
Response is typically quoted as being within plus or minus 3dB of the baseline - this would be considered roughly "flat" or "good" response. As you get closer to the range extremes, frequencies will be played at lower and lower volumes eventually to the point where it is played so quietly it makes no difference to you.
Bass at -6dB absolutely adds to the music, even -10dB does. If you can get a look at the response curve of a speaker it will give you a very good idea of where "useable", "hearable" bass dies off.