Thanks everybody.
I did some research and this what I found in my issue of "Bulletproof Saxophone Playing" (available on bestsaxophonewebsiteever.com):
"Getting the Overtones in Tune
To get a clear picture of whether or not your overtones are in tune with each other, Dr. David Demsey recommends that you find a large and highly resonant room such as a classroom with no carpeting, or ideally, a room that an 80-voice choir or concert band would rehearse in. For many of us, a recital hall or even a classroom is not going to be an option for us, but if you have a particularly resonant living room, or really, any relatively large room without much carpet or sound insulation, that will be fine.
If you have a saxophone teacher or friend who is attuned to this concept, have them stand in the room with you as you play long tones and have them point out when your overtones are in tune and when they're not. If you are going to be doing this alone, listen as closely as possible to the upper partials of your sound. When they're in tune with each other, you'll feel a distinct ringing sensation in your head. It's much like the concept of hitting a baseball in the perfect spot on the bat, causing the ball to fly an astonishing distance into the air. When your overtones are in tune, your sound will become effortlessly powerful. Being heard will no longer be about playing as loud as possible. In fact, you will probably be heard quite clearly playing expressively at a medium level of volume.
This is due to the fact that your overtones are resonating powerfully off of one another, turning your tone into a virtual "giant truck of sound" plowing beautifully through anything standing in its way."
Yeah, well I don't know how much physics he knows or what he's actually talking about.
Every note on the Sax has a fundamental (bottom tone) and higher overtones and these higher overtones don't follow equal temperament (as do the regular notes on the Sax) but they follow a just intonation overtone scheme (where the interval pitches are a bit off from equal temperament pitches) where the first overtone is an octave higher and the next overtone is a fifth higher etc etc.
So a note on the Sax goes, fundamental (bottom tone), first overtone (octave higher tone), second overtone (fifth higher tone) etc etc.
If the player wants to play the first overtone then they have to lose the fundamental (bottom tone) somehow and they do it by increasing the pressure behind their airstream (raising their own oral impedance).
Just say the player has done that and they have lost the fundamental (bottom tone) then the pitch will go up to the first overtone which is an octave higher pitch.
This new octave higher pitch will arrange a new fundamental (bottom tone), first overtone (octave higher tone), second overtone (fifth higher tone) etc etc from itself, because the new octave higher pitch has basically become a new fundamental (bottom tone).
So just say we start with a low Bb note, then as we go up the low Bb's notes overtone ladder we will hit a Bb note an octave higher (first overtone) and this note will have it's own overtones (ie octave higher than fifth higher).
Then we go up to the low Bb notes next overtone (second overtone ) which is F and this note will have it's own overtones (ie octave higher than fifth higher).
The (bottom tone), first overtone (octave higher tone), second overtone (fifth higher tone) etc etc ladder scheme is part of any Sax note and is responsible for the tone/timbre.
No one has to align up anything because it just happens automatically.
It might seem confusing but it's really pretty simple how overtones work on the Sax once the basic overtone ladder stuff is understood and how every bottom tone produces it's own overtone alignment (ie octave, fifth etc etc) and the bottom tone can be a higher overtone of a regular note and the tones below it have been muted by the player so that a higher pitch results.
I think hat you might mean i some sort of practice routine that produces clear stable overtones and that's just all about practice and using your ears.