Filter Equations.

tade · 16th May 2005, 03:39 AM

I would like to see a general discussion of the math behind crossovers.
I have scoured the internet and cannot find anything on them! I need a low pass filter with 12db roll off at 40hz. 12db because i heard that that puts the phase 180 out, which is easy to correct by swapping wires. what sort of components will it need?
I cannot hink of anything else to ask, so i will check back often!
thanks guys.

bigmike216 · 16th May 2005, 09:02 AM

http://focus.ti.com/docs/toolsw/fold...filterpro.html

jcx · 16th May 2005, 03:09 PM

you could go to "the source" - http://www.linkwitzlab.com
and see what the designer of the most popular crossover response has to say

Cal Weldon · 16th May 2005, 04:04 PM

Are you looking for a XO calculator?

http://www.mhsoft.nl/spk_calc.asp

Cal

AndrewT · 16th May 2005, 10:33 PM

Hi,
two pole filter is 180 degree phase shift only at the -3db point.
It will reduce gradually as you move in towards the pass band and at about F/10 phase shift is almost 0degrees.
Look up National Semiconductors application notes AN779, oa21, oa26, oa27, oa28, oa29, Burr Brown ab034b, ab017c,
Plenty reading & maths in that lot.

theChris · 17th May 2005, 07:03 PM

yes, how general are you looking to make the math.
http://www.maxim-ic.com/appnotes.cfm...te_number/1795
is about the best math-based site i can find.

tade · 18th May 2005, 12:39 AM

I see lots of good stuff on RC low pass filters, but i think you can build on using only an inductor, am i right? Aren't RC circuits **** por too because they load resistore which dont have anything to di with producing sound?
what value of inductor should i wire in series to get a crossover of 30hz?

AndrewT · 18th May 2005, 07:21 AM

Hi Tade,
do you want a passive low pass filter? or active?
Passive @ 40Hz into low impedance will require a large inductor!

tade · 19th May 2005, 02:02 AM

good point. so an active filter which would go before the amp will be cheaper perhaps? but require an extra amp.
(i have the extra amp but am not nuts about taking it back to school. the nine cubic foot sub box is bad enough!)
In my room it sits behind and to the left. I have it crossed over at about 200 and it is clearly directional, plus boomy because of the poor quality materials and general construction. Maybe i do not need 30hz?
PE sells an active crossover simulator which i believe you wire in between your source and the amp. I could buy a pair of those as a low pass. A solution?
thanks

Bill Fitzpatrick · 19th May 2005, 02:21 AM

May I ask why you have a 9 cuft sub enclosure?

16th May 2005, 03:39 AM	#1
tade diyAudio Member Join Date: Feb 2005 Location: Ralieigh nc	Filter Equations. I would like to see a general discussion of the math behind crossovers. I have scoured the internet and cannot find anything on them! I need a low pass filter with 12db roll off at 40hz. 12db because i heard that that puts the phase 180 out, which is easy to correct by swapping wires. what sort of components will it need? I cannot hink of anything else to ask, so i will check back often! thanks guys.

16th May 2005, 04:04 PM	#4
Cal Weldon Speakerholic diyAudio Moderator Join Date: Jan 2004 Location: British Columbia	Are you looking for a XO calculator? http://www.mhsoft.nl/spk_calc.asp Cal __________________ Next stop: Margaritaville Some of Cal's stuff \| Cal Weldon Consulting

16th May 2005, 10:33 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, two pole filter is 180 degree phase shift only at the -3db point. It will reduce gradually as you move in towards the pass band and at about F/10 phase shift is almost 0degrees. Look up National Semiconductors application notes AN779, oa21, oa26, oa27, oa28, oa29, Burr Brown ab034b, ab017c, Plenty reading & maths in that lot. __________________ regards Andrew T.

17th May 2005, 07:03 PM	#6
theChris diyAudio Member Join Date: Dec 2001 Location: SIUE, Illinois, USA	yes, how general are you looking to make the math. http://www.maxim-ic.com/appnotes.cfm...te_number/1795 is about the best math-based site i can find. __________________ if only it could be used for good, not evil...

18th May 2005, 07:21 AM	#8
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi Tade, do you want a passive low pass filter? or active? Passive @ 40Hz into low impedance will require a large inductor! __________________ regards Andrew T.


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16th May 2005, 09:02 AM	#2
bigmike216 diyAudio Member Join Date: Jul 2004 Location: BC, Canada	http://focus.ti.com/docs/toolsw/fold...filterpro.html

16th May 2005, 03:09 PM	#3
jcx diyAudio Member Join Date: Feb 2003 Location: ..	you could go to "the source" - http://www.linkwitzlab.com and see what the designer of the most popular crossover response has to say

18th May 2005, 12:39 AM	#7
tade diyAudio Member Join Date: Feb 2005 Location: Ralieigh nc	I see lots of good stuff on RC low pass filters, but i think you can build on using only an inductor, am i right? Aren't RC circuits **** por too because they load resistore which dont have anything to di with producing sound? what value of inductor should i wire in series to get a crossover of 30hz?

19th May 2005, 02:02 AM	#9
tade diyAudio Member Join Date: Feb 2005 Location: Ralieigh nc	good point. so an active filter which would go before the amp will be cheaper perhaps? but require an extra amp. (i have the extra amp but am not nuts about taking it back to school. the nine cubic foot sub box is bad enough!) In my room it sits behind and to the left. I have it crossed over at about 200 and it is clearly directional, plus boomy because of the poor quality materials and general construction. Maybe i do not need 30hz? PE sells an active crossover simulator which i believe you wire in between your source and the amp. I could buy a pair of those as a low pass. A solution? thanks

19th May 2005, 02:21 AM	#10
Bill Fitzpatrick diyAudio Member Join Date: Jun 2001 Location: Eugene, OR	May I ask why you have a 9 cuft sub enclosure?

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