Scanspeak Illuminator 18WU/4741T00 xmax?

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kkant

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Joined 2009
#1
The company websites list the linear one-way xmax for the Illuminator woofer as 9mm:
http://www.tymphany.com/18wu_4741t00
http://www.vifa-speak.com/datasheet/18WU_4741T00.htm

But most retailers list it as only 6mm. For example:
http://www.madisound.com/catalog/product_info.php?products_id=8495
https://www.solen.ca/pdf/scan/18wu8741t00.pdf

Is the correct value 6 or 9? Has anyone done a dumax or klippel test to verify this? At what THD is the 6mm or 9mm figure reported at?

Thanks for any help you can give!
 
#2
If the criterium for linear excursion is staying inside the top plate, then the p-p excursion is (20-8)=12mm. I'd say this is the upper limit of excursion since there's no way an underhung coil can remain fully immersed once it's outside of the top plate, and probably won't be fully immersed even before that point.
 
#3
Xmax calculations may not be that simple, measurements might show different
Besides, the field strenth may bend a bit outside the magnetgap
Anyhow, "linear" may not mean exactly linear at all, but may have a small allowed +/- variable

I believe that improved linear Xmax beyond the "mechanical" calculated is one of the properties of the "XBL" poleplate design...I do know this isnt XBL, but underhung, but anyhow
 
#6
Thanks for the replies, folks. Seems like 6mm is the right number then, or maybe even less. But perhaps this depends on whether Scanspeak has done some kind of special engineering to extend the field past the "normal" underhung limits.

That's kind of a bummer. I have seen the review of this speaker at zaphaudio, where it has worse distortion performance than the older Revelator at 92 db. I was thinking that those conditions might reverse at higher output levels, if the xmax was larger. But it looks like that is not the case.
 
#7
Unfortunately Zaph never tests with large signal excursions> so we never get a sense when/where compression is on a particular driver/motor.
As you approach compression is were the real non-linearities are. That's were this Illuminator woofer may shine above the rest.
 
#8
kkant said:

That's kind of a bummer. I have seen the review of this speaker at zaphaudio, where it has worse distortion performance than the older Revelator at 92 db.
Click to expand...


Several people do claim the "old" 18W to be better
But regarding Zaphs measurements...I doubt you will actually be hearing what the measurements show
One better than the other, fore sure, but both still good, I suppose
Just because a driver measures slightly better doesnt mean that it actually sounds better too

If you want really low distortion you may need to use very stiff cones, which have their own problems to deal with

Vifa has announced new "look alike" drivers

Maybe look at what linear Xmax really is
It doesnt seem to be linear at all...and the reason fore push-pull designs 😡

So which one is closest to 100% linear, in reality 🙄
 
#9
It may, though given its smaller coil-length-derived xmax and worse performance at lower levels, it seems less likely. I'd like to see large signal tests of both these speakers. Hopefully someone will do them. At a 50% higher price, I wonder what benefits the new woofers have.
 
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