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"13 ohms is indeed the best impedance value to start your calculations.
We use as crossover frequency mostly about 1300-1400Hz 1st order, and
don't worry to much about damaging the unit in home stereo. As long as
you keep the average voltage below 27Vrms there will be no problems.
This means a peak voltage capabilty of your amp of 86Vrms (925W@8ohms)."

DeHaan@StageAccompany.com
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The Griffin Loudspeaker uses the SA8535 driver.
http://www.griffinspeaker.com/

Their crossover is;
1700 Hz, Linkwitz-Riley 4th order acoustic, No passive equalization

During my listening tests, even though the driver is able to go
lower, I still prefer any tweeter to be crossed over at around 2khz
plus or minus. For crazy SPL, I will use 2.5khz 3rd order because
that is what I have right now, later I will use a better and more
flexible active crossover.

The midrange that I like to mate with this beast is the 8" PHL2520,
100db sensivitity. I heard good things about the 10" midrange - PHL3450 (3451) from Andre at e-speakers.com it's 101db sensitivity.
I think these two midranges would be optimal for great sonic
impact of the music, but as you see, the Griffin uses dual Seas
Excel probably with more power to drive the lower sensivitity drivers.

Using the PHL has tradeoffs, it's only useable down to 200-300hz,
so you need to find a low pass 300hz solution (some type of bass
subsystem).. I struggled with this solution last year. Since I
want to line source four SA and four PHL 8" per channel, I need
ideally maybe four 15" woofers, but only three woofers will fit
the house (hehe)...

Tech doc.
http://www.stageaccompany.com/download/files/product/techdoc sa8535.pdf

Using this driver down to 1300 - 1400hz as mentioned by SA, is probably
the lowest you want to go, but I would imaging you can drop this
down to 1khz if you keep the power minimal. I was driving this
driver with about 19 milliwatts directly off my portable el'cheap
Sony CD player (headphone jacks), and it worked. Not much spl,
but I can hear the sounds from 5 feet away and using no crossover.
Two of these drivers strapped to someone's head would make cool
headphones (hahah), even a few watts would drive this nicely,
probably with no crossover. /heh