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Shareware Overload Trio 2
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Shareware Overload Trio Volume 2 (Chestnut CD-ROM).ISO
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PERFECT1.DOC
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1989-04-11
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*** Perfect1.doc ***
I want to comment on the BOXDATA records that I have been
receiving on your disks. First, I think that many users are
confusing the definition of the X-max parameter. The typical
ranges for X-max range from 0.1 inches to 0.25 inches with 0.5 on
the JBL 18" 2245H being the largest I've seen (Have you ever seen
one, they are huge.) If you don't know the X-max value,
approximate it with 0.1 to 0.15, 0.2 for large suspensions.
Note that X-max is NOT the total possible cone
movement allowed by the suspension, which on large drivers
could be at least an inch. I have seen specification
sheets from a few manufacturers (Credence is one) that give an
"X-max" and a "X-lin" (for X-linear?) value. As far as I can tell
from these, the X-lin is really the value of X-max as normally
defined. And the "X-max" value is the maximum cone travel
possible. Contact the manufacturer if you are confused about
their specifications. I hope that a standard for "X"
measurements will surface soon.
The X-max measurement defines the peak (not to be confused
with peak-to-peak) distance that the voice coil can travel
without extending beyond the magnetic field as determined by
the pole piece length. The voice coil may be longer in length
than the pole piece. This is defined as "voice coil
overhang." The PB program uses the X-max measurement in
calculating the Maximum Sound Pressure Level (SPLmax), and thus
is a key factor in the Excursion Limit Plot. Theoretically, the
driver is "linear" only if the cone travel is within the X-max
limits! Think about this the next time you watch your low-end
drivers move 3/4 " peak, from the rest position!
In general, (not always,) low Q drivers are intended for
4th order systems, and typically have what is coined as
"long-throw suspension." Also, remember that PERFECT BOX model
is valid up to Qts of 0.7, and the Marquis 12G38BPP1H is slightly
over that value at 0.72. Of course, each individual driver will
vary from the manufacturers published specs, so you might want to
measure them yourself to be sure.
Good luck in your new designs, thanks again for all of your
generous support. If you have any specific questions or would
like chat about loudspeaker topics, drop me a letter, or call my
BBS, "UCF Health Topics" at (407)-281-5522, 2400 N-8-1.
You will find the latest release of Perfect Box posted here.
My BBS is an node in FidoNet, (1:363/507), and thus
will accept "Electronic Mail" 24 Hours a day. If you are a
FidoNet SysOp or know a friendly one with a "FIDO
compatible Mailer", you can file request PB with the magic
filename "PERFECT", for the current MS-DOS version, or
MACPERF for Macintosh (when available.) Of course, you
could always File Request by the current archive name
"PERF410.ARC." Also, I host a local echo-mail (E-mail)
roundtable called, "Audio Topics". You can find many questions
regarding Loudspeakers, etc. answered there.
You now can save the "RAW data" to an ASCII comma-delimited file
for use with other graphics programs. Press F7 at the Output
Menu, to Create a new file, and F8 to re-load a previously
saved file. You can "jump" to the Output Menu from the Opening
Menu by pressing F6. Thanks to Registered User, Bob Schiers, of
Ames, IA, for this very helpful suggestion.
Warren A. Merkel
*** End of Document ***