# Determining correct crossover point



## TomFord (Jul 15, 2014)

How's it going gentlemen? 

Have 2 KEF 6.5 uni-Q speakers that I'm going to build as book shelves or more Dolby Atmos speakers that set atop the towers. 

Would do the dimensions of the Q300 or similar to the newly announced KEF R50 making the adjustment of the enclosure slightly bigger for the 6.5 opposed to the 5.25 that it's fitted with. Tried copying pic, but only link would display

http://homemedialimited.co.uk/wp-content/uploads/2014/08/KEF-R50.jpg

Per the KEF site frequency range is 42Hz-40kHz at 8 ohms (when I test it with my multimeter it's always below 6 ohms). Would you stay with the 2.5kHz that they use or build a different one? 

Just got a free app of a crossover calculator that seems very helpful. The options on its calculations are passive crossover, narrow bandpass, & zobal. Assume passive is the one to choose yet want to look into other two. Though in determining the calculation it has ohm, frequency, & lowpass frequency. Thought the lowpass would be the 42Hz but when I put that it states lowpass must be higher than frequency. 
What would the #'S of the lowpass & frequency sections of the calculator be?

Also, would like to donate to the site with all the helpful assistance & planning on getting the room correction software soon. Where do I do that? 

Thanks for any assistance Gentlemen


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## mechman (Feb 8, 2007)

You can become a donating member here. :T


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## ajinfla (May 10, 2009)

Hi Tom,

Without measurements, you will be flying blind. Those "calculators" are not terribly useful, there are modelling programs where you import either your measured, or the manufacturers measured responses of the individual drivers. Unfortunately, you won't find those for your KEF, unless someone did some independently. What Uni-Q driver? the Q300?
The new Q series uses a simple first order with impedance compensation, so 3 parts. No clue what the values are for your driver.
Your multi-meter will measure the DC resistance of the drivers. This is not the same as impedance. Unfortunately, you need hardware to measure that as well. Something like the Dayton WT3.

cheers,


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## Mike Edwards (Mar 10, 2011)

i'm with ajinfla... without measurements it's pure blind stumbling in the dark.


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## robbo266317 (Sep 22, 2008)

Taking into consideration the fact, as stated above, that you do not have the specs for these drivers, I would use the manufacturers crossover point of 2.5 Khz and assume their nominal impedance is 8 ohms (not resistance as measured by a multimeter).


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## ajinfla (May 10, 2009)

robbo266317 said:


> I would use the manufacturers crossover point of 2.5 Khz and assume their nominal impedance is 8 ohms (not resistance as measured by a multimeter).


You'd be in trouble if it's a Q300  ....which I believe uses the same tweeter as the Q100, shown below:
 
More like 3 ohms.

cheers,


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## ajinfla (May 10, 2009)

Tom,

Maybe you could ask around here and other DIY forums (PE, AVS, DIYA, etc) if any DIYer in the Houston area (which I'm sure there are) could help out with some measurements of the driver?
Just a thought.

cheers


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## GranteedEV (Aug 8, 2010)

I really can't stress enough the importance of having measurement gear, or someone nearby who has some. Anything else is just a guessing-game.


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