2.1 Channel audio systems are so popular on most home sound system with low power output(usually below 50W). It only composed of left, right and a subwoofer speaker. The signal from the subwoofer is derived from both channels and filtered to output only the low frequency usually below 200Hz. Since the low frequencies are being produced by the subwoofer, it should be cut off on the main speaker.
About the Circuit
The circuit is simple that it only uses 1 op-amp per channel which is just fine for small power audio systems. The other op-amp is used to provide the bias which serves as the mid-point reference voltage. It basically sets the output of the op-amp to 1/2 of VCC when idle. This is necessary for single supply application because the output can’t the lower than the ground level which is in this case 0V.
Changing the Crossover frequency
The crossover frequency is set to 159Hz, if you want to change the crossover frequency, here’s a simple formula:
f = 1/(2*pi*R*C)
C = 1/(2*pi*R*f)
Where:
– pi = 3.1416
– f = crossover frequency
– R = value of R1, R2, R3, R4, R5, and R15 = 10k
– C = value of C1, C2, C3, C4, C5 and C6 (unit in farrad)
for example if you need to change the frequency to 100Hz:
C = 1/(2*3.1416*10000*100) = 159nF
since there is no 159nF, you will use the closes value which is 150nF. If you use this value, you will have an actual frequency of:
F = 1/(2*3.1416*10000*150e-9) = 106Hz
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Take Note that this circuit is meant to be connected to the input of the amplifier. This circuit can’t be used to connect directly to speaker.
Simulation
Simulation is very useful to verify the function of your design, here I used Simetrix to simulate my circuit. You can also download it and play on the values and see how the values of the components affects the response of the circuit.
PCB Design
PCB design is done on a single layer only to make it easy for DIY at home. If you want to make it smaller you can download the PCB file and make it a two layer board.
Downloads:
Download the design files on our download page