Eminence Sigma Pro-18 Xmax? - diyAudio
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Old 27th September 2001, 05:28 PM   #1
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According the the official literature from Eminence, the Sigma Pro-18 woofer has an Xmax of 6mm. Other 18" pro woofers I have seen advertise an Xmax of 12mm or more. Is this possibly a mis-calculation by Eminence, or is that why their drivers are so inexpensive?

Evan
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Old 27th September 2001, 05:50 PM   #2
Super is offline Super  United States
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That could very well be a misprint, though it could also depend on the driver's surround material. That seems suspiciously low for an 18 inch driver though...
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Bryan
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Old 27th September 2001, 09:50 PM   #3
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Any chance it's the transit one-way, instead of peak-to-peak?

Grey
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Old 28th September 2001, 12:00 AM   #4
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Yeah, it's gotta be one way, but I was kind of under the impression that the standard for Xmax was one way. Maybe the JBL of the same size is p-p (I think it was about 13mm), seems like 26mm p-p would be a lot. Anybody know where that sort of info might be posted?
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Old 28th September 2001, 01:20 AM   #5
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I've seen them both ways.

Grey
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Old 28th September 2001, 07:32 PM   #6
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Oh well, it's already ordered. But it's kind of critical for box volume calculations and port sizing.
Thanks all.

Evan
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Old 28th September 2001, 07:43 PM   #7
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Here's what diysubwoofers.org says:


Xmax = Linear (one-way) travel of the cone. Xmax is used to determine the
maximum linear SPL capability of the driver, and can be defined in a number
of ways. The DUMAX definition is objectively the best one, and it is
defined as the shorter of the Xmag and Xsus values, in each direction of cone
travel. This definition is more useful than the older definition of Xmax,
which was solely dependent on the length of the voice-coil vs. the length of
the gap.
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Old 29th September 2001, 01:59 AM   #8
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Default Eminence Xmax Ratings

We always specify Xmax as one way. We calculate it by taking (VC leng- air gap HT)/2. This is very conservative; real world testing (DUMAX) often shows a bit more Xmax.

6mm on a Pro Sound 18" is pretty normal. If you need more Xmax, the Kilomax Pro18A has more and works well in a sealed box for HT. If you use the Kilomax for pro sound, go with a big ported box (9+ cft).

Thanks!
McJerry
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Old 1st October 2001, 09:35 PM   #9
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Hey, straight from the horse's mouth. At any rate, the box is already built for a Sigma Pro-18, about 7 cubic feet, calculated as per:

http://xsspl.tripod.com/Audio/KeeleBox.htm

I came up with two 4" dia. X 4.5" long ports. We'll see how the math works when the driver gets here, hopefully very soon!

Evan
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Old 19th August 2005, 05:44 AM   #10
rcw is offline rcw  Australia
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Default re Sigma 18

This type of driver is really intended for maximum output down to 60Hz.
In a filter assisted QB5 class II box you can use its full 650Watt voice coil rating down to 60Hz. with out exceeding its rated linear excursion limit, resulting in an average output of around 128db.
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