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6Db. crossovers????

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  • #46
    Re: 6Db. crossovers????

    Originally posted by johnk... View Post
    Unfortunately the paper you are referring to is 1) dealing with a Bessel crossover, not just a HP filter alone, and 2) Out of date and not really correct. Bessel crossovers do not sum flat under any conditions. The HP and LP filters can be over or underlaped to approximate flat response. The group delay of a Bessel LP filter is maximally flat, meaning the region of linear phase extends as far as possible toward the cut off point while remaining constant. This make the Bessel LP filter approximately linear phase. However, the same can not be said for the Bessel HP filter. The phase and GD of the HP Bessel filter is not all that much different that that of a HP Butterworth of Linkwitz filter of similar order. There have been a number of approximate linear phase speaker designed using a Bessel LP response coupled to various order HP response where, to match the GD of the LP section the tweeter is offset significantly. Spica speaker followed such a design process. However, now of these approaches addressed the nonlinear GD associated with the HP cut off of the woofer.

    So we may differ on our interpretation of the impulse response and also based on how the cut off frequency of the Be3 is defined. But that alone is n ot the issue.
    My interpretation of the impulse response of the Be3 and B2 HP is as follows. After the initial positive pulse there is a negative swing and then a positive over shoot and then continued oscillation as the impulse decays. In the case of the BE3 the overshoot, while happening faster that for the B2, is greater in magnitude that for the B2. I consider that worse. However, I also stand by my initial point that the ringing of the impulse has little to do with the quality of bass reproduction as any bass instrument will typically have a much higher Q response than any of these HP filters. So it really makes little difference whether we agree or disagree on whether the impulse of a Be3 is better or worse than that of a B2.

    Another way to look at this is to examine the group delay of the B2 and Be3 HP. If the B2 and Be3 are set up to have the same -3dB point then they have very similar, nonlinear GD though around cut off and into the pass band, but the Be3 shows a slightly more rapid increase which would correspond to poorer transient response. On the other hand, if the Be3 is aligned based on phase so that the phase of the Be3 is 135 degrees at the same point he B2 is 90 degrees, (the BE3 will be down about 6.3dB at the frequency the B2 is down 3dB) then the Be3 will have considerably higher GD in the low frequency part of the pass band.
    John, I don't understand why you go on about Be3. It was cheap and easy and forgiving for a time when testing was slow and costly while tolerances were wide and loose. But now I can turn any laptop into a test machine and a frequency generator. I don't really have to worry about manufacturing tolerances any more. Put a threaded slug into the cabinet and adjust on the fly for desired Qtc. As a fourth order you will end up with two alignments to choose from. I think for a fourth order bessel its around Qtc=0.5 and a Qtc=0.7 just pick one pair as speaker and other as xover.

    I think you should start discussing Be4. it seems like the more modern implementation and avoids odd order problems.

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    • #47
      Re: 6Db. crossovers????

      Originally posted by Pete Basel View Post
      Gain is usually needed.
      maybe I don't understand what Linkwitz was doing. I would have thought the need for gain was only tied to one special case - the desire to boost output at specific frequencies. way back in basic filter theory 101 they teach you that any huge bubbanomial can be broken down into a series of small polynomials multiplied together. The link you gave earlier seemed to indicate that Linkwitz was just saying the same thing in a reformatted package with no clear demand of active v passive or boost v flat.
      Last edited by moron#99; 03-12-2012, 01:11 AM.

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      • #48
        Re: 6Db. crossovers????

        I did say usually not always. An LT is most often used for bass extension where gain _is_ needed. He might not have needed it for the tweeter LT in his 1980s design but it was an active crossover anyway so he used OP amps.

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        • #49
          Re: 6Db. crossovers????

          Originally posted by Pete Basel View Post
          Jeff, Linkwitz explains the theory with poles and zeros and then comes up with a solution and a real world example, nothing wrong with that. His 1980 paper is an excellent example of designing with active crossovers and he really covers all the bases.
          I understand Linkwitz' tutorial, I was referring to #99's Bessel breakdown.
          Click here for Jeff Bagby's Loudspeaker Design Software

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          • #50
            Re: 6Db. crossovers????

            Originally posted by moron#99 View Post
            John, I don't understand why you go on about Be3. It was cheap and easy and forgiving for a time when testing was slow and costly while tolerances were wide and loose. But now I can turn any laptop into a test machine and a frequency generator. I don't really have to worry about manufacturing tolerances any more. Put a threaded slug into the cabinet and adjust on the fly for desired Qtc. As a fourth order you will end up with two alignments to choose from. I think for a fourth order bessel its around Qtc=0.5 and a Qtc=0.7 just pick one pair as speaker and other as xover.

            I think you should start discussing Be4. it seems like the more modern implementation and avoids odd order problems.

            I'm not "going on" about Be3. I am just responding your comments.

            As far as 4th order Bessels go, they are not cascaded 2nd orders with Q = 0.5 x Q= 0.7. You have the wrong Qs. Additionally; each 2nd order HP section has a different Fc. And if the idea is to improve impulse response you are going in the wrong direction. I'm done here. This is just trolling at this point.
            John k.... Music and Design NaO dsp Dipole Loudspeakers.

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            • #51
              Re: 6Db. crossovers????

              Originally posted by johnk... View Post
              I'm not "going on" about Be3. I am just responding your comments.

              As far as 4th order Bessels go, they are not cascaded 2nd orders with Q = 0.5 x Q= 0.7. You have the wrong Qs. Additionally; each 2nd order HP section has a different Fc. And if the idea is to improve impulse response you are going in the wrong direction. I'm done here. This is just trolling at this point.
              It is really rather moot whether or not I can remember the right Q value after 35 years. Pete has probably done similar designs but never forced the Qtc with a premeditated intent of going passive. Perhaps he would know the right label but until then "passive Linkwitz alignment" seems appropriate.

              It is obvious no-one has done these types of speakers. If they had then you would understand it better. Which is good. Now I can go out and buy some testing software and I have a brand new road to explore.

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              • #52
                Re: 6Db. crossovers????

                Originally posted by moron#99 View Post
                It is obvious no-one has done these types of speakers. If they had then you would understand it better. Which is good. Now I can go out and buy some testing software and I have a brand new road to explore.
                Really? Check my web site: "As with the NaO II, the NaO Note panel is integrated with a dual driver, damped, U-frame woofer system. While
                similar in size and principle to the NaO II U-frame, the woofer system has been completely redesigned. The low frequency response follows a 3rd order Bessel alignment with -3dB point at 30 Hz and -6dB point at 22 Hz."

                However, the reson for using a BE3 HP woofer response has nothing to do with impulse response. I think you will find that many people have done many more things that you can imagine.
                John k.... Music and Design NaO dsp Dipole Loudspeakers.

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                • #53
                  Re: 6Db. crossovers????

                  Originally posted by Jeff B. View Post
                  I understand Linkwitz' tutorial, I was referring to #99's Bessel breakdown.
                  In my case, I like bessel and define the output as Ao=bessel. You are free to make to make it butterworth. You just build a different cabinet with a different Q so that your speaker poles line up with the selected butterworth. That will also define the HP crossover design of your sub. I can't imagine why it does any good to treat tweeters this way. Their Fc is well into the self-destruct range.

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                  • #54
                    Re: 6Db. crossovers????

                    I just throw sh!t in a box and tweak values until I like how it sounds. Double check with measurements, give it a spit shine and close the notebook.
                    Don't listen to me - I have not sold any $150,000 speakers.

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                    • #55
                      Re: 6Db. crossovers????

                      I just use my Virtual Crossover Box when I can until the measurements and listening look and sound right. Check the box's component values and order good ones and done - well most of the time. :D
                      Live in Southern N.E.? check out the CT Audio Society web site.

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                      • #56
                        Re: 6Db. crossovers????

                        Originally posted by moron#99 View Post
                        I can't imagine . . .
                        It's really not a matter of "imagining". But the whole discussion, while a bit amusing, is pointless until you take the time to catch up on what (many) others have figured out in the 35 years since you last "imagined" about the subject . . . that crossover topology, while interesting and of some minor importance, is far from
                        "It suggests that there is something that is happening in the real system that is not quite captured in the models."

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                        • #57
                          Re: 6Db. crossovers????

                          Originally posted by Deward Hastings View Post
                          It's really not a matter of "imagining". But the whole discussion, while a bit amusing, is pointless until you take the time to catch up on what (many) others have figured out in the 35 years since you last "imagined" about the subject . . . that crossover topology, while interesting and of some minor importance, is far from
                          so I can take an old pair of bose from the attic and make them sound like atom's just by moving them around in the room. I bet if i move them again then they will sound like Canton's. maybe another few inches and it will sound exactly like a strativarious.

                          wow, thanks! you just saved me a ton of effort.

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                          • #58
                            Good thread....

                            Very good nitty-gritty tech in this one!

                            Thanks, Mr. Kreskovsky!
                            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*

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                            • #59
                              Re: 6Db. crossovers????

                              Originally posted by moron#99 View Post
                              so I can take an old pair of bose from the attic and make them sound like atom's just by moving them around in the room. I bet if i move them again then they will sound like Canton's. maybe another few inches and it will sound exactly like a strativarious.
                              Of course not... you didn't change the crossover to a bessel :rolleyes:
                              :blues: Flat frequency response, a smooth sound power response free of resonance, careful driver-integration, and high dynamic range both upward and downward :blues:

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                              • #60
                                Re: 6Db. crossovers????

                                so, I am going to build myself a little test lab. i am so looking forward to updating this design family. If i could have traveled back in time 30 or 40 years and handed myself a laptop with software i would have peed my pants with excitement. Laptops beat the heck out of slide rules.

                                What software would you recc.?
                                For a guy who has never used PC testing software, likes detailed mathematics, and doesn't want a steep learning curve which would be the best software for testing Thiele Small parameters including Qtc and Fc? I downloaded Jeff's stuff, but it balked at my old Offfice97 excel.

                                What woofer would you reccomend?
                                I need to find a good small woofer. It needs to have Qas under 0.4 and a small Vas. I'd like to keep it cheap enough to be disposable but with fairly consistent T/S from one to the next. If one driver has Vas=20L and I blow it up then the next driver needs to be fairly close.

                                Is there already a cabinet with adjustable internal volume?
                                or do I need to build it?

                                thanks

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