Notch filter for RD50 help

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  • PMazz
    Senior Member
    • May 2001
    • 861

    Notch filter for RD50 help

    Calling all crossover gurus.....

    Try as I might, I can't seem to improve the notch filter on the RD50. B&G suggests a parallel notch filter with the following values: L=.05mH, C=20uF and R=8ohms.

    Problem is I still have a sizeable hump in the FR around 5K. I have tried increasing the R value, but it hasn't helped.

    Here is a measurement showing before and after tests with and without the recommended filter.



    Any ideas?

    Pete


    PS: This is when I wish I had a digital xover like the 2496.
    Birth of a Media Center
  • Davey
    Senior Member
    • Jan 2003
    • 355

    #2
    Your hump looks like it's located closer to 3500Hz. You need to raise the value of the capacitor or the inductor or both to lower the resonant frequency of the notch filter.

    Cheers,

    Davey.

    Comment

    • JonMarsh
      Mad Max Moderator
      • Aug 2000
      • 15336

      #3
      Hi Pete,

      Your plots are log based but using 200/2Khz/20kHz, so the peak does seem to be at 5 kHz.

      I don't have time this evening, but by lunch tomorrow I should be able to model this and give you a better solution. Heck, I'm going to need that myself, assuming my RD50's are similar in response to yours. Cap may have to be a skosh smaller, and inductor a skosh bigger, plus bigger resistor. Trick is getting the Q right...

      Boy, am I behind schedule on getting these projects done- I can't even remember when I got my RD50's and 7" mid woofers. So far, just making CAD drawings...

      -Jon




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      Comment

      • PMazz
        Senior Member
        • May 2001
        • 861

        #4
        I've been playing with FRD's crossover sim and have taken another shot at it. I was able to convert the raw FR of ETF to a text file and then convert it to an .frd that the sim uses. With this info, I have now altered the filter to L=.15mH, C=6.2uF and R=15ohm. I just installed it and will have a listen and take some more measurements, maybe tomorrow.

        Pete

        Edit: Jon, you snuck one in on me.
        Birth of a Media Center

        Comment

        • Davey
          Senior Member
          • Jan 2003
          • 355

          #5
          Sorry about that. You clearly have the marker below the peak and it's showing the F at 5024hz. I will shut-up now. Grin.

          Cheers,

          Davey.

          Comment

          • PMazz
            Senior Member
            • May 2001
            • 861

            #6
            Davey, no sweat. I can use all the help I can get. I was lucky to have some components laying around from other projects (mistakes from other projects, mostly)

            Pete
            Birth of a Media Center

            Comment

            • JonMarsh
              Mad Max Moderator
              • Aug 2000
              • 15336

              #7
              Sounds like you've figured out a mod which should work. My plan was to measure them when I had the boxes finished, and optimize the crossover and the notch filter at the same time, since mine would be passive all around.

              Let us know how it works out.

              -Jon




              Earth First!
              _______________________________
              We'll screw up the other planets later....
              the AudioWorx
              Natalie P
              M8ta
              Modula Neo DCC
              Modula MT XE
              Modula Xtreme
              Isiris
              Wavecor Ardent

              SMJ
              Minerva Monitor
              Calliope
              Ardent D

              In Development...
              Isiris Mk II updates- in final test stage!
              Obi-Wan
              Saint-Saëns Symphonique/AKA SMJ-40
              Modula PWB
              Calliope CC Supreme
              Natalie P Ultra
              Natalie P Supreme
              Janus BP1 Sub


              Resistance is not futile, it is Volts divided by Amperes...
              Just ask Mr. Ohm....

              Comment

              • PMazz
                Senior Member
                • May 2001
                • 861

                #8
                Well, better than it was....



                L=.15mH, C=6.2uF and R=11ohm.

                A little too much cut up ~9K, but it sounds better than it did before.

                On a sour note, while in close proximity to the speakers, I've noticed the one ribbon looks like it has hairline surface cracks at different areas. The only reason I can see them at all is to catch them when the light hits them just right. The other ribbon looks fine. It sounds fine, but I'll give B&G a call and ask them.

                Pete
                Birth of a Media Center

                Comment

                • Hank
                  Super Senior Member
                  • Jul 2002
                  • 1345

                  #9
                  Pete, keep on truckin'. What's the location of that broad trough that appears on the graph at 200 - 400 Hz? Are you going to cross the RD's over at 600 Hz as recommended by the Poohbah's?

                  Comment

                  • ThomasW
                    Moderator Emeritus
                    • Aug 2000
                    • 10940

                    #10
                    Pete

                    They aren't 'cracks', if they were the ribbon wouldn't play. They are instead small flattened wrinkles in the foil when it's glued to the plastic membrane. Although it looks funny it has no impact on performance.




                    theAudioWorx
                    Klone-Audio

                    IB subwoofer FAQ page


                    "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                    Comment

                    • PMazz
                      Senior Member
                      • May 2001
                      • 861

                      #11
                      Hank, the trough that you see really isn't too bad. Don't forget, the graph is in 3 dB increments and the measurement was taken at ~2 meters, so at the listening position things change a bit.



                      I still have them Xed over at 450 Hz. I'm going to make new enclosures for the CSX10s to raise the RD50s up higher and will make it with an upward angled baffle to point the CSXs to the listening position. They don't seem quite "together" as they are,so hopefully, this'll get them to integrate with each other better. They don't sound bad when you're seated, but need help if you're standing. If that doesn't work, I'll have to go Jon's route and create a line of drivers next to the ribbons.

                      Tom, thanks, that's a relief. It's just that I never noticed it before and the other one looks perfect. It does sound fine. I was worried it was a problem that would get worse until it finally failed.

                      Pete
                      Birth of a Media Center

                      Comment

                      • PMazz
                        Senior Member
                        • May 2001
                        • 861

                        #12
                        Well, after extended listening, I decided I was a little too heavy handed with the new notch filter. It was taking too much of the top end "sparkle" out of the ribbon. More work with FRD's crossover sim and yet more components from PE and I'll try again.

                        New filter is 9.1 uF, .1 mH and 12.5 ohm. So far it sounds like it put the life back into the ribbons. I'll take some measurements and have a look.

                        Pete
                        Birth of a Media Center

                        Comment

                        • PMazz
                          Senior Member
                          • May 2001
                          • 861

                          #13
                          Here's a quick measurement with the new notch installed (Green). The top end is definitely better vs the old notch (blue).



                          Pete
                          Birth of a Media Center

                          Comment

                          • JonMarsh
                            Mad Max Moderator
                            • Aug 2000
                            • 15336

                            #14
                            Yup, that looks a lot better, Pete.

                            When I finally get around to measuring mine in a baffle, I'll investigate with LSPCAD and see if there's any further room for improvement. Judging from what you've plotted here, there may not be, but who knows? At this rate, it will be December befor that happens, though.

                            Regards,

                            Jon




                            Earth First!
                            _______________________________
                            We'll screw up the other planets later....
                            the AudioWorx
                            Natalie P
                            M8ta
                            Modula Neo DCC
                            Modula MT XE
                            Modula Xtreme
                            Isiris
                            Wavecor Ardent

                            SMJ
                            Minerva Monitor
                            Calliope
                            Ardent D

                            In Development...
                            Isiris Mk II updates- in final test stage!
                            Obi-Wan
                            Saint-Saëns Symphonique/AKA SMJ-40
                            Modula PWB
                            Calliope CC Supreme
                            Natalie P Ultra
                            Natalie P Supreme
                            Janus BP1 Sub


                            Resistance is not futile, it is Volts divided by Amperes...
                            Just ask Mr. Ohm....

                            Comment

                            • PMazz
                              Senior Member
                              • May 2001
                              • 861

                              #15
                              Jon, I'd bet the ranch and dog that you'll get it right. I'm just applying a band aid till you're ready.

                              Of course, now that I just changed the baffle on mine, it might be a moot point. I can always just blame Hank for turning me on to the new Daytons.

                              Pete
                              Birth of a Media Center

                              Comment

                              • Hank
                                Super Senior Member
                                • Jul 2002
                                • 1345

                                #16
                                Yeah, that's it, blame Hank, just like at work. Pete, you're really pumping out the work these days! The price and Xmax of the new Dayton's attracted me. As for sound quality - that's the big IF. Hey, if they don't work out, order the MCM's and use the Dayton's to build some low-cost 2-ways for sale.
                                I hate to sit on the sidelines and not put my $ where my mouth is, but financial planning didn't work out this year - having to subsidize my 2 college students more than planned, and then there's my high school guy.
                                Oh well, I'm building a 7.1 speaker system for a customer that will help a bit.

                                Comment

                                • PMazz
                                  Senior Member
                                  • May 2001
                                  • 861

                                  #17
                                  Hank, to say I'm impressed with the sound coming from these is an understatement. The Daytons were definitely worth the risk. Hey, how bad could they be? They're only covering a couple octaves. But, when in doubt, it never hurts to have someone else to blame.

                                  Works been a little slow, so gives me more time to get in trouble....

                                  Pete
                                  Birth of a Media Center

                                  Comment

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