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RC vs RL filters?

  1. Dec 5, 2014 #1
    this guy on youtube said "if you try pushing more than a few miliamps through an RC filter then you get significant power loss" and that therefore the RL filter was more preferable.

    @ 2:40:


    i thought L & C components don't dissipate any power, so whats the difference between running the same amount of current through either filters?
     
    Last edited: Dec 5, 2014
  2. jcsd
  3. Dec 5, 2014 #2

    meBigGuy

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    WOW --- conclusion with no explanation. There is no power loss in in an ideal inductor or the capacitor. But, that is not the issue. He quickly showed a low pass filter with a capacitor, which is a shunt low pass filter. Pause at the last schematic, at the very end (2:49). The power loss is in the series R (he shows heat radiating from the R).
    A lot of what he says makes me cringe, but it's not outright wrong. And, demo-ing a woofer with no enclosure --- wow.
     
  4. Dec 5, 2014 #3

    sophiecentaur

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    I think the point he is trying to make is that the R in the RL filter is the drive unit itself and (particularly when the unit is in a proper enclosure ) the Resistance component in the RL, actually consists of the acoustic load, pushing sound out into the room. That is more efficient than with an RC filter with a series, dissipative resistor which, even near DC, will be dissipating a significant amount of the amplifier power.
     
  5. Dec 5, 2014 #4

    meBigGuy

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    I think you are a bit confused. He is describing an RL and RC crossover network driven by a low impedance amplifier.
    Audio amplifiers do not have 8 ohms out. The point he is making is that the R in the RC filter drops power when the C shunts audio.
     
  6. Dec 5, 2014 #5

    sophiecentaur

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    Not confused. For the C to work, there needs to be a series R first. A Low Impedance (Voltage Source) will not be affected by a shunt C; it needs a series R. That will waste power. The dissipated power in the RL arrangement is partly (if not totally) in the form of radiated sound energy (radiation resistance - to use an antenna term). In the right enclosure, the resistance of the voice coil will not be the only 'R' element involved.
     
  7. Dec 5, 2014 #6

    sophiecentaur

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    Ahh. I see what you are saying now and it makes sense. In my vocabulary, the 'drive unit' is the moving part of the loudspeaker - and a loudspeaker consists of the box, ports, damping and the drive unit etc. etc.) I did not mean the Amplifier had a poor output impedance. Not an 'understanding' problem - just the use of terms. :)
     
  8. Dec 5, 2014 #7

    meBigGuy

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    I think we are in sync. I misunderstood "drive unit". We just call it the driver. You are correct that the driver is the R in the RL filter, which is an important point.
    He certainly leaves room for misunderstanding in his last paragraph, though.
     
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