[Arny Krueger]

"Dick Pierce" wrote in message
...

Third, the effective moving mass of the 4" driver is at a
minimum or order of magnitude (that's a factor of 10) higher
than that of a 1" dome tweeter. Why? Because the 1" dome
tweeter's moving mass is not encumbered with the moving mass
of the spider, the entire rest of that 4" diaphragm, the
surround, the lead-in wires, and so on.

As I understand the operation of speakers, they are mass loaded over most of
their upper frequency range. The primary effect of larger mass given all
other things are equal is that efficiency is reduced. This would be
broadband efficiency, not just efficiency at high frequencies.

I think it is fair to say that if the diaphragm does not break up,and if
the voice coil does not decouple from the diaphragm, then the speaker
cone+dust cap acts like a piston driven with a magnetic motor at all
reasonable frequencies.

Secondary effects are provided by the inductance of the voice coil and the
large piston causing stronger directivity effects at higher frequencies.

Fourth, the radiating area of a 1" dome tweeter at 10-15 kHz
is pretty much a 1" diameter dome. That of a 4" driver at
those frequencies is substantially greater.

The point being, the claim that "the dust cap behaves like a
tweeter at the highest freqs" is unsubstantiated, technically
unsupportable specualtion.

Seems to me that without knowlege of break up modes and possible decoupling
from the voice coil, all relevant facts are not known.

The idea that just the dust cap (as opposed to the entire diaphragm+dust
cap ) is in play seems to presume signficiant break up of the cone/dust cap
asssembly.

I am informed that this break up mode can be controlled to a useful degree,
but I would surely defer to more experienced practitioners.