To build a simple low-pass filter frequency , switch between its input and output resistor, and between the output and the common wire - capacitor.
Move the component values in SI units: the resistance in ohms, capacitance - in farads.Simple filter cutoff frequency calculated by the formula: F = 1 / (2πRC), where F - and frequency (Hz), π - number of "pi" 3.1415926535 (dimensionless), R - resistor (Ohm)C - capacitance of the capacitor (F).
To change the characteristics of the filter, choose a capacitor and resistor values.This can be done empirically, taking response after each alteration, or substituting different values into the formula and calculating the result every time.With the increase in the beginning of the resistor charac
teristics falls on the vertical axis to the origin, and with the increase in capacitance of the capacitor increases the angle between this line and the x-axis (if the schedule last characterizes frequency y).
Some filters low frequencies have variable characteristics.An example of such a device is a tone control.To collect it, are included in one filter resistor - variable.Turn it between the bottom plate of the capacitor according to the scheme and a common wire.
resistors used in the filter of low frequencies , comfortable in chains processing of weak signals.If the filter is located after the power amplifier, their use is undesirable, because it leads to a decrease in efficiency.If you are developing a device for the separation of the signal on the strip for supply to several speakers (crossover) is used in its constituent filters low frequencies resistors instead of inductors.Capacitors while such filters can be eliminated - they come in handy in the filters of high frequency .