# High pass filter

Discussion in 'General Electronics Discussion' started by Colin-m, Apr 30, 2017.

1. ### Colin-m

1
0
Apr 30, 2017
Hey guys, I'm new here and need some help, I'm a mechanical engineer (steam and motor) and in my spare time I design and build sound systems, I use active dsp all the time but I now need to learn how to build passive crossover networks, I am starting with a passive high pass filter (50hz), I have been told this can be done with a bipolar capacitor, I have this calculator here, http://www.learningaboutelectronics.com/Articles/High-pass-filter-calculator.php#answer1. If I am doing it correctly I need a cap of 796.178343949 μF I can't find this so can I put multiple caps together? Any help with this would be greatly received.

Many thanks

2. ### duke37

5,364
772
Jan 9, 2011
An accuracy of three figures is plenty. Components of better than 1% can cost the earth.
Multiple capacitors can be used. You will need to put them in parallel, If you put them in series,you will be throwing capacitance away at some cost.

800μF bipolar will be very large and expensive.

For low frequencies such as this I would go to an active filter. Where will you get any inductors from?

Post a circuit diagram of the proposed filter.

3. ### AnalogKid

2,515
718
Jun 10, 2015
It probably is just a capacitor in series with the speaker, with the speaker acting as the shunt element. High value bipolar electrolytics for the speaker market are not as expensive as you might think, but they are specialty parts.

ak

4. ### Audioguru

3,389
732
Sep 24, 2016
A single capacitor makes a very poor filter because the slope is very gradual. A speaker crossover filter uses one or two capacitors plus one or two inductors for up to 4 times the slope.
The accuracy if the capacitor value can be 5% or 10%. An active filter circuit works better.

5. ### AnalogKid

2,515
718
Jun 10, 2015
The calculator in post #1 is for a simple R-C filter, and is not appropriate for a speaker crossover.

ak

6. ### Audioguru

3,389
732
Sep 24, 2016
I have seen a capacitor in series with a very cheap little cone speaker used as a tweeter. When the capacitor cuts frequencies below 2kHz then the speaker's resonance at 200Hz is at -20dB and is not too obtrusive.

But using a capacitor in series with a woofer at 50Hz will not do much. 50Hz will be reduced a little and 25Hz will be reduced only a little more and will add or subtract from the subwoofer. The high impedance peak of the woofer will be passed at full output by the capacitor causing a boomy sound.