Intensity without loudness
“Never Will I Marry” from the album “Nancy Wilson and Cannonball Adderley” is a clear example of a rhythm section generating incredible intensity without relying on loudness.  Instead of loudness, Lois Hayes and Sam Jones (the drummer and bassist respectively) push the groove forward to generate a sense of urgency in the music.  If you listen to the way they are locking up on the quarter note pulse, they are playing as far on top of the beat as possible without rushing.  It is because of this ability to generate intensity by playing on top of the beat at any dynamic or tempo that they are one of the greatest rhythm sections in the history of jazz. 
As a jazz drummer and teacher, the idea of intensity without loudness is central to everything I do.   Because the drums are a naturally loud instrument, the tendency amongst beginning drummers is to use loudness as the default way to generate intensity.  Learning to control the drums dynamically and to generate intensity through controlled forward momentum instead of just loudness is something I am constantly working on with both my students and myself.  In my opinion, the ability to play this way is the mark of the truly mature drummer. 
Why does this matter?
Some music calls for drummers to rely on loudness to generate intensity, sometimes in combination with increased density of notes.  This type of playing has its own set of challenges that need to be overcome, and I am certainly not denigrating it in any way. 
However in my experience the drummers who play the most often with the greatest number of people are the ones who can play with intensity at any dynamic level.  Without this ability, there is a huge range of music that is simply unapproachable. 

How to develop this ability
The most important and obvious thing to do to develop the ability to play quietly and with intensity is to play along to and listen to music that features this kind of drumming.  A surprising number of my students don’t do this, and make no significant progress as a result.  If you think of learning music like learning a language, then learning how to play this way is something like learning how to speak with a particular accent.  The only way to do this and sound natural is to spend a lot of time speaking with this accent around people who speak with this way.
The recording above is a great place to start.  I would also recommend recording yourself playing along to see how you actually sound.  Here is an example of me playing along to this music:

Notice that the idea is not to play with no dynamic variation, but rather to keep the dynamics under a certain level.  Todd Bishop at Cruise Ship Drummer also wrote an excellent article with a list of things to do to further develop this ability.