Jim Griffin's new white paper

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  • Dennis H
    Ultra Senior Member
    • Aug 2002
    • 3791

    Jim Griffin's new white paper

    Jim Griffin has a new line array white paper. He addresses many of the issues he didn't cover in the first one. While not a complete design guide (and I think the poobahs may disagree with some of his conclusions ), it's a good read.

  • Hank
    Super Senior Member
    • Jul 2002
    • 1345

    #2
    Before I even read it, I say:
    Let the Games Begin!

    Comment

    • JonMarsh
      Mad Max Moderator
      • Aug 2000
      • 15259

      #3
      An interesting addition to his prior work.

      I take some issue to his definition of near field and far field, as he excludes any point source driver from having a "near field" zone; this is contrary to my years of studio experience in the use of "near field" monitors.

      Some rooms are well suited to his concept for a line array which uses the reflected image from the floor and ceiling to gain an apparently greater line source height; in CA, an awful lot of modern houses (built since 1970) have ceiling heights which make banking on this impractical. Hence the experience some listeners have with commercial line source speakers of having to sit with the ears very close to the floor to get the intended balance. There are also integration issues with minimum distance from the array, as well as maximum, which B&G addresses with recommendations regarding the implementation of their drivers in systems.

      I also think it's telling that even for multiple 5" drivers, the most optimistic upper crossover is 2500, and only if you do it damn steep (the comb filtering is already affecting the crossover region overlap, which ideally you'd want to avoid). A more reasonable guideline would be 1.25 kHz for 5" drivers, and about 1 kHz with 6-1/2" to 7" drivers. 600 Hz should be fine, of course. :W

      Last, it would please me to no end to see combinations of MLS and 1/12 octave gated RTA measurements in room to back up the claimed benefits of specific examples of this configuration in specific rooms. That, so far, is not forthcoming.

      And yes, I have heard well constructed examples of improved LINUS Arrays. Though I brought measurement gear, the owner/constructor declined finding out what they really do. I only recommend that anyone considering constructing one of these give them a serious listen to be sure they like what they're geting, preferably in concert with some alternative desgins. A good venue is one of the many DIY speaker meets which have been organized in various parts of the country, like the one we had in Sacramento the end of May.

      Best regards to all, unfortunately I'm off to work again this AM!

      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
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      In Development...
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      Obi-Wan
      Saint-Saëns Symphonique/AKA SMJ-40
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      Resistance is not futile, it is Volts divided by Amperes...
      Just ask Mr. Ohm....

      Comment

      • Dennis H
        Ultra Senior Member
        • Aug 2002
        • 3791

        #4
        Though I brought measurement gear, the owner/constructor declined finding out what they really do.
        Well, that sounds a bit odd, to say the least! What's up with that? Ignorance is bliss? :roll:

        Comment

        • Davey
          Senior Member
          • Jan 2003
          • 355

          #5
          Jon,

          There's a couple of measurements for the Linus2 array shown on Rick Craig's web site. These don't really correspond to the measurements you'd like to see, but they're the only ones I've seen.








          I think some of the line array owners probably have an outlook similar to the the SET or high-eff speaker folks....objective performance is really not that high on their priority list. More than likely you would have measured something that didn't look very pretty in comparison to some of the highly optimized conventional box designs. Maybe that's why the owner you mentioned wasn't interested in measuring his speakers?

          Cheers,

          Davey.

          Comment

          • Dennis H
            Ultra Senior Member
            • Aug 2002
            • 3791

            #6
            Danny has some measurements of the Alpha LS as well. I can't find it now but I've seen a single on-axis measurement of the Excelarray and it looked pretty good.



            But none of them have really done a study of the changing FR with distance and that seems to be the weakness in Jim Griffin's thesis.

            Comment

            • JonMarsh
              Mad Max Moderator
              • Aug 2000
              • 15259

              #7
              The Excel-Array is a somewhat different critter, being a combination of a shorter midwoofer array and a ribbon mid/teeter, capable of a lower crossover. It will have some of the same issues, as I will be "fighting" with my RD50 based system.



              In the right room and configuration, a floor to ceiling line source can be very good, such as ThomasW's setup in his living room.




              In this situation, things are almost idea, because it is pretty much true floor to ceiling, and there's no issue with regards to comb filtering of individual midwoofer drivers near the crossover.

              Besides the thing with the change in balance with distance on the Linus2 Array which (in the large room I heard them in) was something of a problem, I also felt that the overall integration between the 5" drivers and tweeters was a little problematic off axis. Well, maybe more than a little. :W

              Now, don't get me wrong, if you set them up with some care, and pick the listening distance correctly, they can sound pretty cool, as long as you're not expecting much bass below 75 Hz. They are efficient, and quite dynamic. An RD50 setup, for example, won't match the efficiency, not by a long shot. But, I think it will produce a better integrated and more coherent midrange with more consistent on and off axis response up to 7-8 kHz than the Linus, at least based on my experience with the RD75. That's why I think it would be useful if there were some published plots on the Linus array similar to the one's I've done for axial response of the M8.




              Davey, I think you have a very good point, in that for a lot of listeners, there's some quality they really like about the gear they have, and for them it overides possible shortcomings in other areas- they're happy to live with it, and bring up the objective flaws doesn't serve their emotional enjoyment of the system. And since music is about emotions, who's to say they're "wrong"? 8)


              Hopefully, when I finish building these big guys, I won't mind publishing "the truth, the whole truth, and nothing but the truth", re how they work.



              But at the rate I'm working weekends (third one this month), getting those done seems a long ways off- which is particularly annoying since I have all the drivers.




              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
                The only observation I can add is a measured FR of the RD50/CSX10 at 2 meters (blue) vs. 3.5 meters (green). Disregard anything below 500 Hz.



                According to Jim's chart, the NF/FF transition for the 2m measurement is ~900 Hz, while the transition at 3.5m should be ~1.7kHz. I just don't see any appreciable difference in the in-room measurements I've done. About the only thing I wind up seeing is I need to add a 1-2 dB boost to the CSX10 xed at 450 Hz when changing the measurement distance fron 2m to 3.5m (listening distance).

                Jim's first paper initially got me interested in trying a LA, and my hat's off to him for this updated version. So, thanks Jim!

                Pete
                Birth of a Media Center

                Comment

                • Hank
                  Super Senior Member
                  • Jul 2002
                  • 1345

                  #9
                  Here's a new P.E. Dayton 7" driver with 36 Hz Fs and 4.25mm Xmax:

                  Might be a consideration for a L.A.

                  Comment

                  • PMazz
                    Senior Member
                    • May 2001
                    • 861

                    #10
                    Nice find, Hank. It certainly looks good on paper. Right price too!

                    Pete
                    Birth of a Media Center

                    Comment

                    • Hank
                      Super Senior Member
                      • Jul 2002
                      • 1345

                      #11
                      Thanks Pete, it's in my new P.E. flyer. If the Grand Poobah's will model it, we'll see how it stacks up against Jon's recommended MCM driver.

                      Comment

                      • JonMarsh
                        Mad Max Moderator
                        • Aug 2000
                        • 15259

                        #12
                        I saw this one last week, it looked a bit interesting, other than sensitivity being on the low side; they rate it at 85 dB/watt, but the sweep curve looks more like 83-84 in most of the range, versus 87 dB for the MCM. Price is about the same as the MCM driver, which uses a carbon fiber cone and cast frame.
                        Choices, choices!

                        But I've already got 16 of the MCM, so I know what I'll be trying first!





                        ~Jon

                        PS- It's pretty dang hot and humid in Raleigh so far this week, also just had a brief frog strangler. Flying back home tomorrow night.




                        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

                        • Hank
                          Super Senior Member
                          • Jul 2002
                          • 1345

                          #13
                          I should have included specs. Here's Jon's recommended MCM 55-2321:
                          Specifications: “Power capacity: 55W/80W RMS/peak “Frequency response: 30Hz~6KHz “Impedance: 8Ω Mounting specifications: “Required cutout: 5.73" “Mounting depth: 4.12" “Outer frame: 6.40" square (rounded corners) Thiele-Small Parameters: “Fs: 40Hz “SPL: 89dB 1W/1M “Qts: 0.42 “Qes: 0.51 “Qms: 2.59 “Vas: 26.64 liters “Le: 0.73mH “Re: 6.1Ω “Xmax: 3.4mm “Sd: 0.0129m2 “Cms: 1.15 mm/N “BL: 6.62 “Mms: 12.28g Price: $19.95

                          Here's the P.E. Dayton 295-335:
                          Specifications: *Power handling: 50 watts RMS/75 watts max *VCdia: 1-3/8" *Le: 1.15 mH *Znom: 8 ohms *Re: 5.90 ohms *Frequency range: 35-10,000 Hz *Fs: 36 Hz *SPL: 85 dB 1W/1m *Vas: .75 cu. ft. *Qms: 2.15 *Qes: .53 *Qts: .42 *Xmax 4.25 mm Price: $15.89 for 4 or more.

                          The MCM looks more high-end to me with its cast rather than stamped frame and carbon fiber cone, but, as Jon would probably say: the proof's in the listening. :?? BTW, MCM STILL has a photo of a pincushion style frame driver shown as the 2321. Do you get the impression that MCM's web site is low on their list of priorities? :roll:

                          Comment

                          • JonMarsh
                            Mad Max Moderator
                            • Aug 2000
                            • 15259

                            #14
                            Yup, MCM doesn't put a quarter of the effort PE does into their web site, even though they did just totally revamp it a few months back.

                            I also like the way the flat sided frames of the MCM drivers stack, but then I'm also pondering whether to leave a little extra space in their, so if I want to mount a more conventional driver as an "upgrade", I'd have the opportunity to do so. Every now and then I think about how cool a stack of M6a's would look, or even D6.8's, but then I remember how big a stack of cash that would be... :E

                            ~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
                              I ordered 12 of the PE Dayton 7" that Hank spotted, so we'll see how they are. They model pretty good in the sims, and if PE's Clio plots are on, they should work well for me.

                              Pete
                              Birth of a Media Center

                              Comment

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