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James Lehman
 
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No one has made the observation that all things the same, a woofer cone
driven by a sine wave of a given frequency will have a greater velocity at a
higher excursion. I think that is what "fast woofer cone" really is all
about. Also consider the fact that at low frequencies, a woofer tends to
move much like a piston, while at higher frequencies, the force from the
coil tends to propagate from the center of the cone to the edge as a
transverse wave in the cone material, otherwise known as ripple.



"Arny Krueger" wrote in message
...
wrote in message
oups.com
I have a question. Someone on a message board I usually

post
on talked about woofer speed. I assume what this

translates to
is frequency response (ie 1/time=frequency). He also

posted a
link, which I read:
http://www.adireaudio.com/Files/Tech...ooferSpeed.pdf
At the end of the page it shows a graph, with the

frequency
response of the speaker they used. To me, inductance would
have little or no effect on a speaker unless, it were a
midrange or a tweeter. And from this graph, mass still

seems
to dampen the signal more throught the frequency range

than
does the inductor, which is should I would think. (ie
xl=2(pi)(f)(l)) When it does eventually does get to the

higher
end the inductor does not seem to cut the signal all that
much.


So what I would like to know is, if the inductance is the

most
important part, why not make it small, and increase your
frequency response of the speaker?


Because frequency response isn't everything. Dispersion is
also important. Dispersion is largely based on the diameter
of the radiating surface. The larger the diameter of the
speaker, the less dispersion at high frequencies. As a rule,
people don't want beamy-sounding speakers, speakers that
beam sound like tight laser beams, speakers that have a
sweet spot the size of a dime.

This probably would not
effect a woofer all that much if the woofer was used for

bass
only or would it?


Exactly. A very high proportion of all woofers in 2-way
speakers have additional inductance placed in series with
them. The inductance is part of the speaker's crossover, and
the goal of the woofer crossover is to further limit the
high frequency response of the speaker.

The idea of fast woofers is a fallacy because almost all
woofers are driven through low-pass filters that reduce the
high frequency response and slow down the transient response
of a woofer even more than the mechanical limits thusfar
described.

Another reason why electrical circuits are used to slow down
woofers and reduce frequency response well below mechanical
the mechanical limits of the driver relates to the
smoothness of frequency response. Just because a speaker
responds to some higher frequency doesn't mean that the
response is smooth in that area. The extreme case relates to
bandpass woofers that often have peaks in their response at
relatively low frequencies like 250 Hz or less. These
speakers are going to sound pretty honky in the lower
midrange unless an electrical network is used to roll-off
the woofer's response below this peak.

I find it hard to believe that the mass of
the cone has nothing to do with this at higher

frequencies,
which is why you cannot use a tweeter for a woofer.


You've got that reversed. The mass of the cone has a lot to
do with low frequency response, which is why you can't use a
tweeter for a woofer. When you add mass to a speakers cone
and retune the enclosure for the new massier woofer, you get
greater bass extension at the cost of lower efficiency.

And by cutting down the inductance would also mean a

smaller
coil and maybe larger wire? Wouldn't that be a problem?


Voice nductance is usually relatively unimportant in woofers
because it is common to put even larger external inductors
in series with their voice coils.