LC filters are seldom used for low frequency filters due to the large inductors required and the poor tolerance of inductors.for the two pole Low Pass RL filter?
With speaker crossovers being the exception.LC filters are seldom used for low frequency filters due to the large inductors required and the poor tolerance of inductors.
RC or active filters using op amps are more common.
An equal-value RCRC filter has a Q of 0.333. I suspect an RLRL would be the same.The second RL loads down the first RL causing a VERY droopy response.
Below is the LTspice sim of two cascaded RC filters, showing the difference for them being equal, and the second having 10 times the first impedance:An equal-value RCRC filter has a Q of 0.333. I suspect an RLRL would be the same.
The best Q you can achieve is 0.5 (critically damped), where the impedance if the second part is >10 times that of the first.
RCRC filters are really useful - you can achieve 12dB/octave roll-off, there is no overshoot or ringing, no problems with pickup in inductors (or getting inductors of high enough inductance) and no problems with op-amp phase-shift at high frequency spoiling the attenuation. The low Q is the only drawback.Below is the LTspice sim of two cascaded RC filters, showing the difference for them being equal, and the second having 10 times the first impedance:
The equal filter is about 6dB down at 1kHz while the other is about 3db down, with their high frequency rolloffs being nearly the same.
View attachment 302163
Yes, for things like signal ripple reduction where a sharp rolloff is not necessarily needed.RCRC filters are really useful -
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