Capacitor tolerance importance for high end crossover filters? - diyAudio
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Old 11th February 2012, 11:41 AM   #1
diyAudio Member
Join Date: Feb 2012
Location: Sydney, Australia
Default Capacitor tolerance importance for high end crossover filters?

I am struggling to find any sort of information at all as to how capacitor tolerance applies to accuracy of crossover filters and summed frequency response?

I am building some high end scan revelator/scan ring radiator air circ 2 way towers and am comparing between 5% tolerance vs 3% tolerance caps for this design.

The 3% ones (I deal with one supplier only and am happy with them wont buy elsewhere) are hellishly expensive compared to the 5% ones however if there may be a noticable difference in crossover point shift (example say 1-2db) of summed frequency response output, for this type of high end design, I will just get the 3% ones however I have no experience with summed response measurement output and capacitor tolerance accuracy and if its less than 1db, its just not worth more than double the price.

Cheers in advance
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Old 11th February 2012, 01:00 PM   #2
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
There are standard formulae for calculating the value cap you need - as well as the other components - for a crossover. A change in capacitance will result in a change of frequency. The tighter the tolerance, the less variance from that design frequency.

For example, if you calculate a crossover needs a 10uf cap for some target frequency. Redo the calculation for 10.5uf and 9.5uf. That will tell you in your case how far the crossover frequency will range within a 5% variance of that cap. Now try 10.3uf and 9.7uf. That is the spread for 3%. Then you can see the diference and decide if it matters.
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Old 11th February 2012, 01:52 PM   #3
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Join Date: Feb 2012
Location: Sydney, Australia
I have tried designing crossovers from mathematical calculations which takes well...lets just say a VERY long time and sound...terrible so now I get someone to design them for me and they sound great!

That is a very good point though once I get the filter/driver responses I could factor in a percentage of tolerance and rework the graphs summed response to +/- reasonable accuracy.

question is how does the capacitors tolerance effect the low pass vs high pass (paralell/series) how much weighting on frequency rolloff does the coil vs cap have on the filters response? eg. if the lowpass series coil has more of a bearing on lowpass the paralell caps tolerance could be negligable...And then what about 18db low pass with 2 coils...this is where it gets really difficult for me to accurately estimate
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