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  • Interesting opinion on drivers and manufacturers

    While I do not necessarily agree all the time with Earl Geddes, I do usually find his posts informative and interesting, so I follow certain threads. I've learned a lot in a number of areas to say the least.

    This is another one that struck me, especially since it is counter to so many threads one finds here:

    diyAudio thread

    The comment that stands out to me is this one in post 578:

    The driver manufacturers obsess over those things that don't matter much, like TS, x-max, Klippel nonlinearity plots, and the like and don't even measure those things that do matter.
    Certainly it's not been lost on many here that x-max is not a guarantor of distortion and low-end limits, but there is a lot of emphasis placed on that as well as some other areas that he would eschew. He makes a good case if you follow his posts.

    A second point that probably would also raise some eyebrows here (though not mine) is this one:

    This first resonance is critical and IMO the only one that matters. It needs to be as smooth as possible.

    In general, a pleated surround with "doping" is the best solution and paper cones are the better damped. The only drivers that I have seen that I find acceptable at these first resonances have paper cones and pleated surrounds with heavy damping. This of course ruins any HF response, but that doesn't matter because I don't use the driver up that high anyways.
    Treated foam surrounds can be the best solution in some cases and those of SS, for example, are supposed to last 20-30 years. I've got some rather old ones that seem to be in perfect shape.

    Non-rubber surrounds are in some situations superior to rubber or other similar synthetics. But with the emphasis on huge x-max and harsh (car) environments, there's a mis-guided emphasis placed on drivers with rubber surrounds at times in gentle environments such as house systems. Interestingly, note that the recent midrange driver from SB Acoustics uses a treated foam surround:

    http://www.madisound.com/catalog/pro...oducts_id=8529



    Another good example is the venerable SS 21S/8554:



    dlr
    WinPCD - Windows .NET Passive Crossover Designer

    Dave's Speaker Pages

  • #2
    Re: Interesting opinion on drivers and manufacturers

    I agree with foam surrounds as often being a good thing, especially on whatever is doing the midrange reproduction ... then again, the Seas W22EX has the cleanest most transparent and detailed midrange reproduction of anything I've used.

    I don't pay much attention to Geddes myself. What he says is certainly worth reading and considering, but to me it seems like he's often trying to justify his approach. The posts you cite here are an example of that, and dismissive of other approaches.
    Vapor Audio

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    • #3
      Re: Interesting opinion on drivers and manufacturers

      Earl's systems are all designed to be used with a sub(s) so he isn't that interested in the low end, Xmax, etc. when he's using a 10"-15" midwoofer. The Lambda drivers follow a similar approach: accordion surround for the M (midrange) series and roll surrounds for the S, H and X series (woofers). You can see that the high end is smoother with the M series in both the SPL and impedance curves. John has experimented a lot with damping surrounds and cones and he doesn't need to damp the M series so much that it kills the HF.
      Dennis

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      • #4
        Re: Interesting opinion on drivers and manufacturers

        Originally posted by dlr View Post
        ...Treated foam surrounds can be the best solution in some cases and those of SS, for example, are supposed to last 20-30 years. I've got some rather old ones that seem to be in perfect shape.
        Roger Russell of McIntosh fame points out that many of the early foam surrounds were polyurethane, whereas the newer materials are polyether. Modern polyether foam surrounds should last a long time. I've seen a lot of references to "treated" foam, but I've never seen any real discussion on what that means, so I'm assuming that people are just guessing...

        Russell also documents how much sensitivity is lost using rubber vs foam.
        Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

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        • #5
          Re: Interesting opinion on drivers and manufacturers

          Originally posted by DoubleTap View Post
          I agree with foam surrounds as often being a good thing, especially on whatever is doing the midrange reproduction ... then again, the Seas W22EX has the cleanest most transparent and detailed midrange reproduction of anything I've used.
          That makes the point. The termination used should be optimal for the diaphragm material and geometry used. Hard cones with little self-damping require a different termination. It's a separate issue from preferences.

          I don't pay much attention to Geddes myself. What he says is certainly worth reading and considering, but to me it seems like he's often trying to justify his approach. The posts you cite here are an example of that, and dismissive of other approaches.
          I don't think he's justifying, that's not really necessary as no one is claiming his approach to his goal is wrong. I talk it as explaining his goals and choices made towards his goal and commenting on what he sees as not useful or important in a driver from his usage and perspective.

          I happen to agree with a number of his positions, though not all. Manufacturers are trying to satisfy market demand, ours included. If we as a group obsess on some aspect of a driver regardless of it's actual importance in perception, then the manufacturer is going to target that rather than focus on the absolute performance.

          I've seen more than one instance of negative comments about a foam surround on a driver that was just ignorance of the function and effectiveness of different surround materials. In essence, foam=bad.

          dlr
          WinPCD - Windows .NET Passive Crossover Designer

          Dave's Speaker Pages

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          • #6
            Re: Interesting opinion on drivers and manufacturers

            Originally posted by neildavis View Post
            Roger Russell of McIntosh fame points out that many of the early foam surrounds were polyurethane, whereas the newer materials are polyether. Modern polyether foam surrounds should last a long time. I've seen a lot of references to "treated" foam, but I've never seen any real discussion on what that means, so I'm assuming that people are just guessing...

            Russell also documents how much sensitivity is lost using rubber vs foam.
            The current treated foams do last a long time, I've got an older pair of SS 21W/8554. They look essentially new and measure just fine.

            I forgot about the loss of sensitivity with rubber. Another reason to use treated foam if the application indicates it's optimal. Unfortunately, that might mean significant loss of sales due to perceptions of it's quality.

            dlr
            WinPCD - Windows .NET Passive Crossover Designer

            Dave's Speaker Pages

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            • #7
              Re: Interesting opinion on drivers and manufacturers

              Originally posted by dlr View Post
              That makes the point. The termination used should be optimal for the diaphragm material and geometry used. Hard cones with little self-damping require a different termination. It's a separate issue from preferences.
              True ... you'll never find a hard cone with foam surround. Unfortunately if preferences are toward detail and neutrality over non-fatiguing and musical then your conclusions would be totally inverse of Geddes'. Neither is right or wrong, but Geddes in those posts clearly states his preference.

              I don't think he's justifying, that's not really necessary as no one is claiming his approach to his goal is wrong. I talk it as explaining his goals and choices made towards his goal and commenting on what he sees as not useful or important in a driver from his usage and perspective.
              Sure he does say "IMO", but I read the last couple pages of that thread and took his comments as somewhat dismissive of individuals and manufacturers who don't necessarily subscribe to his line of thinking. Although it is the internet, and it's easy to misinterpret forum posts ;)

              I happen to agree with a number of his positions, though not all. Manufacturers are trying to satisfy market demand, ours included. If we as a group obsess on some aspect of a driver regardless of it's actual importance in perception, then the manufacturer is going to target that rather than focus on the absolute performance.
              There's an incredible array of design approaches out there today. Sure companies like RCF and 18Sound aren't as much the household name as Seas and ScanSpeak, but they do exist and are producing plenty of drivers available to us all. I think it's great that some manufacturers obsess over things like X-max, Klippel, and TS params. If none did then the engineering to satisfy those goals wouldn't exist and we'd be stuck with 1960's Goodmans paired with Altec horns
              Vapor Audio

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              • #8
                Re: Interesting opinion on drivers and manufacturers

                "This first resonance is critical and IMO the only one that matters"

                Perhaps "the only one that matters" is a bit of hyperbole, but not by much. The solution proposed (accordian surround and paper cone) is not, however, the only effective solution . . . a steep crossover far enough below the first breakup (preferably with a notch on the breakup) accomplishes the same thing, while preserving other benefits a more rigid cone might have (like raising the frequency of that first breakup, the W22 and RS180 being two examples). Depending on the cone for self-damping reduces its resistance to breakup . . . it's a tradeoff that can work in some circumstances, not work in others. Keeping the cone out of breakup altogether seems the better solution . . .
                "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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                • #9
                  Re: Interesting opinion on drivers and manufacturers

                  Originally posted by Dennis H View Post
                  Earl's systems are all designed to be used with a sub(s) so he isn't that interested in the low end, Xmax, etc. when he's using a 10"-15" midwoofer.
                  Right. Not everyone has the practical space (or patient spouse) for speakers that large. Some people can only fit a small 2-way; and some people cannot tune a sub if their life depended on it. And for them, drivers with carefully engineered T/S parameters do matter.
                  Isn't it about time we started answering rhetorical questions?

                  Paul Carmody's DIY Audio Projects
                  Twitter: @undefinition1

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                  • #10
                    Re: Interesting opinion on drivers and manufacturers

                    I've been following Earl since '05 not exactly sure of what month and he does seem to get into intellectual quarrels quite readily.
                    Best example that I particularly like is the gedllee vs. Zilch;
                    http://www.diyaudio.com/forums/multi...eguide-21.html
                    Anyways, people who had met him personally say he's quite different and intellectually coherent, so maybe forums and text is not his forte.
                    I like him. sometimes genius - sometimes the devil's advocate. Good reading...

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                    • #11
                      Re: Interesting opinion on drivers and manufacturers

                      I know the late 80s and early 90s vifa foams in my colletion all rotted out. When they talk about foam treatments, are these anti-mould chemicals? What eats the foam is mould, from my understanding. I lost all foam surrounds in 2 years when I lived in a house with mould problems, so I would like to see some reliability data before I paid for foam again.

                      Catch Sean Olives latest blog, where he compares something a smundane as ipod music stations and finds despite similar measured performance, they have very different acceptance scores. One theory he floated was that it could be low frequency distortion with excurison.

                      Dr Geddes is briliant in niches, but like almost all audio scientists, the spent their entire careers putting very low emphasis on cognition, psycho-acoustics etc. They all seem to be trying to reinvent themselvs lately as subjective experts, but I'm not buying it. You don't just become an authority at this stuff overnight. A person of considerable technical accomplishments would look with skeptisism at an auditory psychologist that claims signal processing/acoustics/electroacoustics expertise in very short order.

                      I find Earl sometimes ignores the facts that don't fit his paradigm, often receives and considers ideas as much for who said them as to what is said and is a late comer to audition, so its easy to take his subjective claims with a grain of salt.

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                      • #12
                        Re: Interesting opinion on drivers and manufacturers

                        Originally posted by DDF View Post
                        its easy to take his subjective claims with a grain of salt.
                        Even if his claim that his horns don't sound like horns doesn't raise your eyebrows his claim that speakers that go from omnidirectional to a 80-90 degree beam are "constant directivity" should.
                        "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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                        • #13
                          Re: Interesting opinion on drivers and manufacturers

                          Originally posted by rudyjakubin View Post
                          Best example that I particularly like is the gedllee vs. Zilch;
                          http://www.diyaudio.com/forums/multi...eguide-21.html
                          Heh, heh.

                          Earl has given up ignoring me of late.

                          [We're not exactly forum pals, but we could be.... :D ]

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                          • #14
                            Re: Interesting opinion on drivers and manufacturers

                            Originally posted by Paul Carmody View Post
                            Right. Not everyone has the practical space (or patient spouse) for speakers that large. Some people can only fit a small 2-way; and some people cannot tune a sub if their life depended on it. And for them, drivers with carefully engineered T/S parameters do matter.
                            He does tend to put everything into the perspective of his usage and preferences. He's a bit dogmatic in that regard.

                            dlr
                            WinPCD - Windows .NET Passive Crossover Designer

                            Dave's Speaker Pages

                            Comment


                            • #15
                              Re: Interesting opinion on drivers and manufacturers

                              Originally posted by DDF View Post
                              I know the late 80s and early 90s vifa foams in my colletion all rotted out. When they talk about foam treatments, are these anti-mould chemicals? What eats the foam is mould, from my understanding. I lost all foam surrounds in 2 years when I lived in a house with mould problems, so I would like to see some reliability data before I paid for foam again.
                              That would make one rather reluctant. My understanding is limited in that I believe that the treatment is meant to provide a flexible, air-tight seal to extend the life. In those I have on-hand it's been effective. It probably is not expected to add much help in harsher environments. Still, I would not have expected to see what happened to yours.

                              dlr
                              WinPCD - Windows .NET Passive Crossover Designer

                              Dave's Speaker Pages

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