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I am looking at a woofer that is fairly flat and has a natural 12 db roll off at
5000 Hz (Silver Flute W20RC38-04)
I am looking at a ribbon tweeter that needs to be crossed over at at least4500 hz (according to manufacturer RT1CA HiVi)

If I run the woofer without a lowpass how then does one determine the highpass frequency and slope for the tweeter?
 

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do you have any measurement tools ?

Ribbons (mostly) are able to work 2-3 KHz and higher (2-nd order HPF) So, if you'll use the 1 order HPF - you may try to cut them at 4500-5000
 

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Elite Shackster , HTS Moderator Emeritus
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I second the recommendation for measurement tools. A nice mic (several recommendations in the REW forums), a sound card, and REW can take some basic measurments to determine the roll-off.

You can make more advanced measurements, like gating and such with REW, or move to a speaker design package like SoundEasy, Speaker Workshop, TrueRTA's speaker program, MLSSA, etc.

But I would not just blindly trust the manuf. curves as the baffle and environment they test in is likely different from your speaker design and application.
 

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You can run the woofer full range, with a small cap in series with the tweeter to prevent over-voltage, but only if you like it's response in the intended application.

The XO not only divides the load, it lets you do "cosmetic surgery" to the frequency response. Things like baffle step compensation and notch filters have nothing to do with splitting power at a certain frequency, but they have a lot of beneficial effects on the result.

I can't speak for others, but I determine the highpass frequency and slope for the tweeter by loading the frequency response and impedence characteristics of the two drivers into Jeff Bagby's PCD spreadsheet and then playing with XO topologies and values until I like the result. Learn more here:
http://www.pvconsultants.com/audio/frdgroup.htm

Have fun,
Frank
 
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