[Gary Eickmeier]

"Dick Pierce" wrote in message
...
Gary Eickmeier wrote:
How can my 901s do
such a show of dynamics? Well, most speakers have but one little 1 inch
dome
tweeter, maybe one or two midranges. I have NINE - on each box (the dust
cap behaves like a tweeter at the highest freqs)

This is not about Bose, but rather about Mr. Eickmeiers specific,
testable technical assertion:

"the dust cap behaves like a tweeter at the highest freqs"

Simply stated, it most assuredly does NOT.

WE may safely assume that what Mr. Eickmeier is claiming is
that the 1" dust cap of a 4" driver has the same behaviour
as a 1" purpose-designed dome tweeter. The two differ
in profound and fundamental ways. Let's just look at a few.

First, let's compare the voice coils. The voice coil and
former of a 4" driver is longer, thicker, has more wire on
it and thus is SUBSTANTIALLY heavier than the voice coil of
a purpose-built 1" dome tweeter. By "substantial" I assert,
having measure literally thousands of such beasts, it's
a minimum of 4 to 5 times heavier.

Second. the mechanical tolerances required of a 4" driver
are very different and result in the magnetic gap being
substantiall (by a factor of 2) wider than that of a typical
1" dome tweeter. The result is a substantially lower
magnetic reluctance and thus a higher flux density in the gap.

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.

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.

Well then it is Amar Bose doing the "speculation" because that is what he
told me. I just assumed that it sounds reasonable because at the highest
frequencies the center of the driver is probably all that can move that
fast.

Bose may have all kinds of test equipment to look at the vibrational
behavior of a moving driver. Isn't there equipment that does vibrational
analysis?

What do you say is happening at the highest frequencies? The whole driver
moving as a solid unit? This isn't the only full range 4 inch driver out
there - what generally do they do at the highest freqs?

Gary Eickmeier