LP Filter component selection

[tyguy2]

I'm attempting to remove some of the high(ish) frequency noise (15khz-20kHz) on some speaker lines, and I've decided to use a low pass filter with a capacitor and resistor. The issue arises when selecting components. The speaker is about 400 watts, and I need to make sure I don't burn out the resistor or cap. The peak voltage of the speaker should be somewhere between 40 - 50 volts, and I'm not sure if I should you low value resistor and high value capacitor or visa versa. I'm fairly sure that the higher value resistor I use, the lower the maximum volume of the speakers will be. Any ideas? I feel like this should be a pretty simple V=IR and P=I²R calculation, but I don't want to end up burning something down. Thanks in advance!

[MrAl]

I'm attempting to remove some of the high(ish) frequency noise (15khz-20kHz) on some speaker lines, and I've decided to use a low pass filter with a capacitor and resistor. The issue arises when selecting components. The speaker is about 400 watts, and I need to make sure I don't burn out the resistor or cap. The peak voltage of the speaker should be somewhere between 40 - 50 volts, and I'm not sure if I should you low value resistor and high value capacitor or visa versa. I'm fairly sure that the higher value resistor I use, the lower the maximum volume of the speakers will be. Any ideas? I feel like this should be a pretty simple V=IR and P=I²R calculation, but I don't want to end up burning something down. Thanks in advance!

Hi,

Of you tried a 0.1 ohm resistor and 100uf cap, the cut around 15kHz would be about 3db, but then the load on the amplifier would be too great at say 20kHz.  If you go up in resistance you loose top end power performance, thus i dont think it is possible to use an RC filter here with this much power.  Maybe an LC filter.

Alternately you may be able to use a shunt RC filter, but you have to watch out for the extra loading this causes on the output of the amplifier.

[ruairi]

Is the noise being picked up between the amplifier and the speaker? (this is reasonably rare IME).  If not why not filter the line level signal before the amp?

[tyguy2]

I completely forgot about using an inductor. I think I'l try out an LC filter and let you all know how it goes. I can work the math from here.