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Old 31st March 2013, 12:43 PM   #1
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Default Crossover help

I have a set of speakers that I have recapped and now would like to play with the low pass section. If I place a inductor and capacitor in standard 12db format to the low pass section, it currently has nothing, do I understand correctly I now have to reverse the polarity to this woofer. The band pass section has a 12db format and the high pass section has what I read as a 18db format with these both having the polarities swithched at the speakers. First post as a new member to this forum.
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Old 1st April 2013, 06:10 AM   #2
AllenB is offline AllenB  Australia
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Not necessarily, and from here on in things become a little uncertain

I would first be questioning why there is no crossover on the woofer. Is it an acceptable choice or was it a cost compromise? Chances are you could make an improvement if you knew what to do to cross the woofer better but was the mid crossed with the woofer's failings taken into consideration, meaning you'd want to tweak that one too?

With regards to polarity, if you imagine speaker phase as being somewhere on a 360 degree continuum (a circle), and the two polarities offering to add/subtract 180 degrees. If this were a compromised speaker then who's to say where on that circle it is now, and whether you wouldn't need something between those (meaning proper design with measurements). Your best bet would probably be using the pink noise test described on this site by Speaker Dave. It's not the end of the world if it isn't perfect.
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Old 1st April 2013, 09:03 AM   #3
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by amb426amb1 View Post
If I place a inductor and capacitor in standard 12db format to the low pass section, it currently has nothing, do I understand correctly I now have to reverse the polarity to this woofer. The band pass section has a 12db format and the high pass section has what I read as a 18db format with these both having the polarities swithched at the speakers. First post as a new member to this forum.
Here what I understand:

Woofer: full range (no filter)
Midrange: second order (12dB)
Tweeter: third order (18dB)

So the woofer is crossed very high, by its natural roll-off.
The midrange is most probably one of those cheap paper cones.
The tweeter is also cheap, most probably paper, but plastic is possible.

So if you add 12dB filter to the woofer (which means a lower frequency cut-off than its natural roll-off), you have to cross the midrange lower also, which means you have to replace the midrange with the one capable of lower frequency cut-off.

About phase, only certain theoretical slopes have phase difference of whole good number (such as 180deg). In practice (such as your filter), the slope is not theoretical, and the phase is not a good number.

But assuming the difference is 180deg, you can test it by ears (well, may be not easy for beginners) by switching the cable to the woofer (or midrange).

BTW, in general (as a prediction) when you add an inductor to the woofer, the phase is inverted, when you add a capacitor the phase is inverted again. So most probably you don't need to invert anything after adding the 12dB filter to the woofer.
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Old 1st April 2013, 11:44 AM   #4
AllenB is offline AllenB  Australia
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In theory a reactive component will roll 90 degrees, and reaches 45 of those degrees at its cutoff.
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Old 1st April 2013, 03:37 PM   #5
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Default crossover

here is what i'm dealing with. Tweeters are horns and super tweeters are paper. Midrannge is paper.
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Old 2nd April 2013, 11:59 AM   #6
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Also the listed cross points are 1000, 7000, 10000, and 15000.
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Old 2nd April 2013, 08:27 PM   #7
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Disconnect the super tweeters. Put 10 or 20 ohm in parallel with each of the tweeters to attenuate them right. Try 1 mH and 7 uF on the woofer.
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Old 3rd April 2013, 01:22 PM   #8
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Ok let me study that idea. I was thinking around those values on the woofer. Pulled the drivers and the woofer is marked with a frequency range of 45-1000htz and the mid at 1000-4500. do i have it right that this design was to have the woofer use only natural roll off? And do i end up with too much gap if i add the 1 mH, 7uF combo to the woofer.
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Old 3rd April 2013, 04:00 PM   #9
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If they were measured in the factory (recognized manufacturer) yes.
Probably Le is also very high in that woofer driver.

Last edited by Inductor; 3rd April 2013 at 04:05 PM. Reason: Le vs. crossover layout
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Old 3rd April 2013, 04:36 PM   #10
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For the tweeters, if they are loud, it's enough with one 20 ohm resistor in parallel with the 0.27 inductor.
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