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  1. #1
    Join Date
    Dec 2005
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    Bloomington, IN
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    Default Parallel vs Series Notch Filters


    Topic for Discussion: Parallel versus series notch filters

    When do you use one versus the other and why?

    Have you ever used both together for one driver and what are the pros and cons of doing so?

    Do you use multiples of either on one driver?

    Any thoughts?

    Dan

  2. #2

    Default Re: Parallel vs Series Notch Filters


    > Topic for Discussion: Parallel versus series
    > notch filters

    > When do you use one versus the other and
    > why?

    > Have you ever used both together for one
    > driver and what are the pros and cons of
    > doing so?

    > Do you use multiples of either on one
    > driver?

    > Any thoughts?

    > Dan

    Typically parallel notch filters are used in the passband and series notch filters are used in the stopband. The main reason why you don't want to use a series notch filter in the passband is that it presents a short to ground and if there isn't and impedance between it and the amp there will be a short across the amp at the resonance freqeuncy. Parallel notch filters work the opposite way and provide a high impedance at the resonance point so they are better suited for passband use although there are several occasions where I've used them in the stopband.

  3. #3
    Join Date
    Sep 2005
    Location
    latitude 40.8510 longitude -96.7592 altitude 362 meters
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    3,960

    Default Re: Parallel vs Series Notch Filters *PIC*



    Provided Link: http://www.geocities.com/cc00541/Scrappy.html


    > The main reason why
    > you don't want to use a series notch filter
    > in the passband is that it presents a short
    > to ground and if there isn't and impedance
    > between it and the amp there will be a short
    > across the amp at the resonance freqeuncy.

    Actually, this is used to our advantage to control the impedance peaks of a speaker design as the impedance compensation circuit I designed for the scrappy's. In this instance the resistor value, in parallel with the circuit impedance at these frequencies determine the resultant impedance. What you say is true if the resistor value is very small, but generally is not an issue if the circuit is designed properly.

    I might cascade parallel and series notch filters if the driver has 2 peaks. In this case the parallel filter is after the LP filter, keeping the summed impedance up. It really depends on the design and what the impedance is doing at that frequency.

    C



  4. #4

    Default Re: Parallel vs Series Notch Filters


    > Actually, this is used to our advantage to
    > control the impedance peaks of a speaker
    > design as the impedance compensation circuit
    > I designed for the scrappy's. In this
    > instance the resistor value, in parallel
    > with the circuit impedance at these
    > frequencies determine the resultant
    > impedance. What you say is true if the
    > resistor value is very small, but generally
    > is not an issue if the circuit is designed
    > properly.

    > I might cascade parallel and series notch
    > filters if the driver has 2 peaks. In this
    > case the parallel filter is after the LP
    > filter, keeping the summed impedance up. It
    > really depends on the design and what the
    > impedance is doing at that frequency.

    > C

    Good points. I guess I was considering LC filters and not RLC filters (and I really don't know what application would require a series LC notch, not RLC, in the passband now that I think about it). I've used series RLC circuits for impedance compensation before but the overall impedance is never lower than the value of the resistor used.

  5. #5

    Default Re: Parallel vs Series Notch Filters


    > Actually, this is used to our advantage to
    > control the impedance peaks of a speaker
    > design as the impedance compensation circuit
    > I designed for the scrappy's. In this
    > instance the resistor value, in parallel
    > with the circuit impedance at these
    > frequencies determine the resultant
    > impedance. What you say is true if the
    > resistor value is very small, but generally
    > is not an issue if the circuit is designed
    > properly.

    > I might cascade parallel and series notch
    > filters if the driver has 2 peaks. In this
    > case the parallel filter is after the LP
    > filter, keeping the summed impedance up. It
    > really depends on the design and what the
    > impedance is doing at that frequency.

    > C

    I guess the fundamental point that I was trying to make is that series LC filters provide a short at the resonant frequency and parallel LC filters are an open circuit at the resonant frequency.

  6. #6
    Join Date
    Oct 2005
    Location
    Ballwin, MO 38.597554, -90.547423
    Posts
    17,949
    Blog Entries
    1

    Default Succinctly put


    > I guess the fundamental point that I was
    > trying to make is that series LC filters
    > provide a short at the resonant frequency
    > and parallel LC filters are an open circuit
    > at the resonant frequency.

    But let's include the RLC, in just that way that you used it to null out a mid or tweeter impedance peak. You can use that same filter topology to shape the onset of the stop band, to control a bump in the response at the baffle-step for instance. As you stated earlier it does rely on an ample impedance between it and the amp to be effective in that application. A well padded mid comes to mind.

  7. #7
    Join Date
    Dec 2005
    Location
    Bloomington, IN
    Posts
    2,229

    Default Re: Parallel vs Series Notch Filters


    > Actually, this is used to our advantage to
    > control the impedance peaks of a speaker
    > design as the impedance compensation circuit
    > I designed for the scrappy's. In this
    > instance the resistor value, in parallel
    > with the circuit impedance at these
    > frequencies determine the resultant
    > impedance. What you say is true if the
    > resistor value is very small, but generally
    > is not an issue if the circuit is designed
    > properly.

    > I might cascade parallel and series notch
    > filters if the driver has 2 peaks. In this
    > case the parallel filter is after the LP
    > filter, keeping the summed impedance up. It
    > really depends on the design and what the
    > impedance is doing at that frequency.

    > C

    Do you guys find one to be better than the other at wide peaks in response versus narrow ones? It has been my understanding that the parallel notch was better at addressing wide peaks.

    If your impedance result looks acceptable, is there any other reason not to cascade a parallel and series notch?

    It seems that I see many more series notches in DIY designs than parallel notches.

    Thanks for the feedback.

    Dan

  8. #8
    Join Date
    Sep 2005
    Location
    Indiana
    Posts
    19,562
    Blog Entries
    29

    Default Re: Parallel vs Series Notch Filters


    > Do you guys find one to be better than the
    > other at wide peaks in response versus
    > narrow ones? It has been my understanding
    > that the parallel notch was better at
    > addressing wide peaks.

    That's my understanding too. Shunt style for sharp peaks.

    > If your impedance result looks acceptable,
    > is there any other reason not to cascade a
    > parallel and series notch?

    They were cascaded for the 3CR-Ti, so it's a non-issue with decent impedance.

    > It seems that I see many more series notches
    > in DIY designs than parallel notches.

    Whatever works, in truth.
    Later,
    Wolf

  9. #9
    Join Date
    Sep 2005
    Location
    latitude 40.8510 longitude -96.7592 altitude 362 meters
    Posts
    3,960

    Default Re: Parallel vs Series Notch Filters


    > If your impedance result looks acceptable,
    > is there any other reason not to cascade a
    > parallel and series notch?

    Nope

    > It seems that I see many more series notches
    > in DIY designs than parallel notches.

    This is likely due to the impedance constraints.

    The series/parallel notch filters are actually two different iterations of the same phenomenon, differing mostly in the resistance function is inverted between the two. They can both be described by their resonant frequency and their Q, and will have identical transfer functions. Which one works best in a given situation depends on the impedance networks into which they are placed.

    C



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