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  • "tweeter protection" and filter orders

    This goes back a year or two, but I vaguely remember Professor Bagby saying something to the effect that "even order filters offer more tweeter protection." How is this true? Also, do L-pads offer more "tweeter protection" than series resistors? And what do we mean by "tweeter protection"?
    Isn't it about time we started answering rhetorical questions?

    Paul Carmody's DIY Audio Projects
    Twitter: @undefinition1

  • #2
    Re: "tweeter protection" and filter orders

    Originally posted by Paul Carmody View Post
    This goes back a year or two, but I vaguely remember Professor Bagby saying something to the effect that "even order filters offer more tweeter protection." How is this true? Also, do L-pads offer more "tweeter protection" than series resistors? And what do we mean by "tweeter protection"?
    I suppose a traditional L-pad is more 'protection' from things due to minimizing the Fs region with the parallel resistor.

    As to the other, I recall and remember not. So- I'm due for a refresher as well! :rolleyes:
    Later,
    Wolf
    "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
    "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
    "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
    "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

    *InDIYana event website*

    Photobucket pages:
    https://app.photobucket.com/u/wolf_teeth_speaker

    My blog/writeups/thoughts here at PE:
    http://techtalk.parts-express.com/blog.php?u=4102

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    • #3
      Re: "tweeter protection" and filter orders

      Paul, I remember something along those lines too. Is there also something about LR2 being less prone to tax the tweeter than LR4 in some cases? I would also like to know more. I am hearing something not quite right after moving from 2nd to 3rd order electrical. Response is better, Fc is a tad higher, but something is just not right.
      Co-conspirator in the development of the "CR Gnarly Fidelity Reduction Unit" - Registered Trademark, Patent Pending.

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      • #4
        Re: "tweeter protection" and filter orders

        Originally posted by Paul Carmody View Post
        This goes back a year or two, but I vaguely remember Professor Bagby saying something to the effect that "even order filters offer more tweeter protection." How is this true? Also, do L-pads offer more "tweeter protection" than series resistors? And what do we mean by "tweeter protection"?
        Good memory. Yes, in this case though we are talking about even order electrical filters and tweeters that tend to have a high impedance peak at Fs, like the non ferrofluid types or the ones with a higher resonance with no back cavity. Tweeter's with a low Fs that is fairly well damped will not benefit much from the this feature. However, the reason the second order electrical filter is beneficial is due to the inductor being placed in parallel with the tweeter. This can provide reasonably effective damping of the tweeters impedance peak at resonance. A third order filter, while providing a greater roll-off ultimately will endure some peaking due to the cap being in series with the tweeter interacting with the peak in the impedance - of course, optimizing can help. L-Pad resistor arrangements work the same way. By placing the resistor in parallel with the tweeter you can very effectively control the impedance peak at resonance and make crossover design much easier.

        It works on mids too. Here is an actual plot of the open baffle PHL mid used in the speaker in my avatar with only an L-Pad placed on it.

        Click here for Jeff Bagby's Loudspeaker Design Software

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        • #5
          Re: "tweeter protection" and filter orders

          Jeff, Is there an optimum ratio of parallel resistance presented by the L-pad (or inductor) to the Fs impedance peak?
          Co-conspirator in the development of the "CR Gnarly Fidelity Reduction Unit" - Registered Trademark, Patent Pending.

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          • #6
            Re: "tweeter protection" and filter orders

            A quick comment in case anyone is confused. What Jeff means is that even order filters are generally not affected by the impedance peak of a tweeter with respect to achieving the intended transfer function. This does NOT mean that 2nd order filters provide higher attenuation for a tweeter's low end than 3rd order filters. A 3rd order filter will give a steeper filter slope, of course, but the attenuation will not be as effective as predicted (or intended) by the filter order around the frequency of impedance peak. This can be resolved by a parallel resistor (if the design allows overall attenuation) or a conjugate notch filter. But in some cases, you can still use odd order filters without worrying about the peak if the bumped response occurs far below the xover point, thus being attenuated sufficiently.

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            • #7
              Re: "tweeter protection" and filter orders

              Originally posted by jkim View Post
              A quick comment in case anyone is confused. What Jeff means is that even order filters are generally not affected by the impedance peak of a tweeter with respect to achieving the intended transfer function. This does NOT mean that 2nd order filters provide higher attenuation for a tweeter's low end than 3rd order filters. A 3rd order filter will give a steeper filter slope, of course, but the attenuation will not be as effective as predicted (or intended) by the filter order around the frequency of impedance peak. This can be resolved by a parallel resistor (if the design allows overall attenuation) or a conjugate notch filter. But in some cases, you can still use odd order filters without worrying about the peak if the bumped response occurs far below the xover point, thus being attenuated sufficiently.
              Yes - I thought this was what I was saying, but if that wasn't clear, then thanks for posting the clarification. You are correct.

              Jeff
              Click here for Jeff Bagby's Loudspeaker Design Software

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              • #8
                Re: "tweeter protection" and filter orders

                Originally posted by Jeff B. View Post
                Yes - I thought this was what I was saying, but if that wasn't clear, then thanks for posting the clarification. You are correct.

                Jeff
                Yes, looking at your post again, I said essentially the same thing. I just wanted to clarify that a 3rd order filter is not necessarily a bad thing in itself even with an impedance peak not flattened. It can still be useful for achieving the intended phase tracking while providing as much attenuation as a 2nd order filter at the peaking frequency.

                Jay

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                • #9
                  Re: "tweeter protection" and filter orders

                  Originally posted by jkim View Post
                  Yes, looking at your post again, I said essentially the same thing. I just wanted to clarify that a 3rd order filter is not necessarily a bad thing in itself...
                  Heh, can't be that bad. I've sure used them lots of times and no ears have died. :p

                  But seriously guys, thanks very much for the clarification. Makes perfect sense now.
                  Isn't it about time we started answering rhetorical questions?

                  Paul Carmody's DIY Audio Projects
                  Twitter: @undefinition1

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                  • #10
                    Re: "tweeter protection" and filter orders

                    *snicker*; NEHD!!!
                    Teehee,
                    Wolf
                    "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                    "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                    "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                    "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                    *InDIYana event website*

                    Photobucket pages:
                    https://app.photobucket.com/u/wolf_teeth_speaker

                    My blog/writeups/thoughts here at PE:
                    http://techtalk.parts-express.com/blog.php?u=4102

                    Comment

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