Originally Posted by Champster
It requires first further reading for best interpretation ..that of how a compression driver diaphragm functions.
http://www.audioheritage.org/html/pr...logy/435be.htm
"However, it was recognized that there were compromises with the new diaphragms. Titanium does not have the internal damping of aluminum and thus has marginally higher distortion levels. The diamond surrounds, while extending frequency response, do so at the expense of transient response. Further, due to its lower stiffness, titanium goes into breakup at a lower frequency.
This issue of breakup is worth elaboration. Ideally, a dynamic loudspeaker diaphragm should act as a piston, with all points in uniform motion. However, since diaphragms are not infinitely rigid, there will be a condition at which the forces acting upon it cause oscillating deflections resulting in different points on the surface moving in different directions. Under this condition, the diaphragm is said to be in breakup, and there is an attendant increase in distortion. Both aluminum and titanium compression driver diaphragms are in breakup for much of their response. On a large format driver, the breakup modes for aluminum diaphragms occur as low as 7000hz, and for titanium diaphragms, as low as 4000hz."
The short answer is that about a certain frequency the diaphragm no longer operates in piston mode. This in fact applies to any direct radiator.
TI as a material was introduced following the aluminium for strength and at the time and the diamond surround was introduced to extend the response .
The TI diaphragm were in break up mode in fact at a lower frequency than the aluminium explains why the Be alternative are so much superior with break up mode at 15khertz or higher.
So with then Ti and diamond surround you have a relatively noisy diaphragm compared to Be that has a much higher break up frequency and no requirement for a diamond surround.
The response graphs are of very limited value to expose the true operation of the diaphragm.
Laser imaging and other approaches are far more resolving of the small movements (vibrations across) in the operation of the diaphragm.
In relation to the addition of the 2405 there are a number of variables, the specific driver, the phase plug and horn geometry that ultimately determine the accuracy and extension of the system above 10000 hertz.
JBL has adopted the diffraction of their bi radial horns to not only extend bandwidth, but also polar response at high frequencies. In vintage systems the horns that had neither extension nor a wide enough polar response at high frequencies to be useable.
JBL maintains the UHF driver in the K2 systems was provided to satisfy the marketing department as in those systems it is introduced at over 15,000 hertz.
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