Dipole or Monopole?

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  • Hank
    Super Senior Member
    • Jul 2002
    • 1345

    Dipole or Monopole?

    Rats, the BIG thread is locked. I had a small amount of pride in thinking I kept the thread going so long and I was honestly just trying to learn. I think that the late-arriving "controversy" was short-lived and we could have continued on with the thread with no further hard feelings.

    That said, here are my observations, and please correct any mistakes. Thomas is saying the "best" sounding line array is dipole, for the tweets (ribbon) and woofs, correct? Jon probably argrees, correct? Thomas prefers to do the woof-side baffle angled in, bottom to top, correct? Jon is going to build a straight-sided, monopole line source using a B-G RD50 and MCM 6.5" woofs, as a "baby" or "value" priced line source.
    I see my decision points as cabinet width and amp power considerations. I was wanting to do an outstanding sound line source with less size and bulk than you-know-who's. What I've read here is that best sound = dipole array and smallest cabinet width = monopole. Also, I see that dipole woofs would require quite a bit more amp power than monopole.
    How much better sounding will a dipole implementation be than a monopole? For that better sound, how much wider cabinet will I need? Also, how much more power would the dipole woofs need?

    I'm out of questions (for now) and think I'll monitor Jon's progess on his "baby" line source project. Do you two non-professional rank amateurs think there should be two threads - one for monopole and one for dipole? BTW, I don't mind being talked down to, since I'm fairly ignorant.
  • ThomasW
    Moderator Emeritus
    • Aug 2000
    • 10934

    #2
    Hi Hank

    It's really an apple vs oranges situation. Neither is in reality 'better', they're just different.

    My personal preference is full dipole. I really like the way dipoles load into a room and give an added feeling 'space/depth' to the music. But using a dipole baffle means a big wide baffle to obtain any adequate LFE output. The prototype black baffle is 31" wide at the bottom. The next prototype will be slightly narrower since I'm going to 'nest' the planar against the woofers. The black baffle had a wide baffle area just for the planars. That was deliberate in the design because the original intent was to use a 250Hz XO. With the change of the XO point to 530Hz + or higher the planar baffle can be narrower.

    I'm also getting more and more lazy in my old age. So whipping up a simple dipole is quite appealing

    The monopole approach allows the user to 'tune' the bass output and have a significantly thinner baffle.

    Monopole construction while of course not actually complex, is certainly more labor and material intensive compared to dipole.

    I'd use the same amps for either design.

    Regardless of how sophisticated the design, placing drivers in a box creates a 'box' sound. With a dipole you hear the driver, the baffle and it's interaction with the room. With monopole you hear the driver, it's interaction with the box, the baffle and the room.




    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

    • JonMarsh
      Mad Max Moderator
      • Aug 2000
      • 15209

      #3
      Hey, speaking as one of the "avid" amateurs (not to be confused with "Rabid" amateurs, though that may be closer to the mark), here's my take.

      The dipole setup has a figure 8 radiation pattern, and cancel's the bass through lower mid range. This removes a lot (not all) of the room interaction- at least it really lowers the side wall affects. This removes a significant part of what is sometimes called "box sound" - it's really room sound.

      As discussed in the long thread, for a conventional box, with a given LF alignment, there is a calcuable location in the room which will give the correct LF lift and not induce other peaks and notches. MOST other locations will have one or more problems. This still applies to monopole line sources, though obviously the vertical height from the floor is not an issue for this calculation anymore, just the side and rear wall spacing.

      In general, for a smaller room, I think the monopole line source will be easier to setup, and require less "space"; the dipole should have the ability to "diappear" more into the room, without as much special room treatments.

      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
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      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

        #4
        Originally posted by ThomasW
        I really like the way dipoles load into a room and give an added feeling 'space/depth' to the music.
        Added feeling of space/depth is, to me, "better" sound.

        Originally posted by ThomasW
        The next prototype will be slightly narrower since I'm going to 'nest' the planar against the woofers. The black baffle had a wide baffle area just for the planars. That was deliberate in the design because the original intent was to use a 250Hz XO. With the change of the XO point to 530Hz + or higher the planar baffle can be narrower.
        Okay, I understand both reasons for the next generation baffle being somewhat narrower.

        Originally posted by ThomasW
        The monopole approach allows the user to 'tune' the bass output and have a significantly thinner baffle.
        Do you mean "narrower" baffle?

        Originally posted by ThomasW
        Regardless of how sophisticated the design, placing drivers in a box creates a 'box' sound. With a dipole you hear the driver, the baffle and it's interaction with the room. With monopole you hear the driver, it's interaction with the box, the baffle and the room.
        Good capsulization of the difference between the two. I assumed from the long thread that a dipole woofer stack would require lots more amp power, but you say same amps for either. That removes one of my two major concerns about dipoles.

        Comment

        • Hank
          Super Senior Member
          • Jul 2002
          • 1345

          #5
          Originally posted by JonMarsh
          The dipole setup has a figure 8 radiation pattern, and cancel's the bass through lower mid range. This removes a lot (not all) of the room interaction- at least it really lowers the side wall affects.
          In general, for a smaller room, I think the monopole line source will be easier to setup, and require less "space"; the dipole should have the ability to "diappear" more into the room, without as much special room treatments.
          Yes, easier to set up a monopole in a smaller room and part of the reason commercial line arrays are mostly monopole. Interesting comment on room treatments which affects the economics. In a larger room, you'd have the less expensive cabinets of a dipole plus less costly room treatments. Therefore, dipoles, given a decently large room, are "cheaper"

          Okay, I'm zeroing in on this. "Space/depth" are important to me. I have listened to Maggies, and my line source quest began as a way to, dare I use the term, "klone" the space/depth of the Maggie sound. Building a line source will be affordable, as opposed to buying a pair of large Maggies. Dipole is tempting, but maybe I should stick with a baby line source with an RD50 and a stack of inexpensive woofs. I know from experience that a stack of 6.5" woofs delivers the SPL's. Hmmm...what's the effective piston area of twelve 4"ers... I could always recyclye the RD50's.

          Comment

          • ThomasW
            Moderator Emeritus
            • Aug 2000
            • 10934

            #6
            Hank

            One of the reasons I fell in love with my Accoustats (actually big planars, big ribbons, big leafs in general) and have forced them to evolve for so long is what they do in the room. IMO no 'box' design is capable of this effect. Actually a more correct statement would be after a total of 40yrs in audio, I've never heard a box design that could do what a dipole does.

            Now the fact that they (generic reference to all planars) usually have square feet of radiating area resulting an extremely low workload per square inch = extremely low distortion, doesn't hurt either.

            You've heard the output of an array of 6.5" drivers with box loading and tuned to a specific frequency. Taking those same drivers and mounting them in a dipole baffle is a complelely different kettle of fish

            FWIW, while constructing the black dipole prototype (Eton 8"s) I was concerned that the cone drivers might not have adequate output for the RD-75's. Fortunately for me ,they are more that loud enough and are actually turned down slightly in comparison. But for dipole use anything any smaller than a 6.5" probably isn't worth the effort.

            Oh BTW, as I write this Jon is jetting away to Seattle. He's meeting with the people at Intel through thurdsay (power supply design issues of course) so his posts will be sparce until at least Friday.




            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

              #7
              OK Tom, thinking in terms of my room again....

              Can dipoles work effectively with the pile of hardware that I have that would be right next to them (actually they'd be in front of the pile some, but not much, ~1')?

              Pete
              Birth of a Media Center

              Comment

              • ThomasW
                Moderator Emeritus
                • Aug 2000
                • 10934

                #8
                Pete

                Let's see your place is the standard HT nightmare.



                If it were mine I'd move everything to the right centering it in the room and walk around the right side speaker when entering and exiting the room That from an acoustical standpoint would make life easier. But that's probably not a SAF acceptable option, right?

                As far as any speakers are concerned the idea is to at least attempt to equalize the effects of boundry loading. Having the speakers centered in the room will equalize the loading from the side walls. Obviously there's nothing that can be done about the hallway. As a result the further out from the backwall that any speaker can be placed the better the performance.

                Regarding the gear some of it will act as a diffuser the rest will reflect the rear wave. I can't be more specific than that. The biggest problem other than room placement is the large RPTV. I'd get a wool rug or make something to cover the screen when it isn't in use. The screen is highly reflective to sound. That causes comb filtering effects= muddy sound.

                BTW, the cool thing about making dipoles, is that a pair can be made in a weekend for test purposes. If they don't work then build a box and use the same speakers as monopoles




                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

                • JonMarsh
                  Mad Max Moderator
                  • Aug 2000
                  • 15209

                  #9
                  Well, it's pretty beautiful in downtown Seattle tonight- tomorrow is the Intel Power Delivery Workshop, and the next two days are the Intel Technology Symposium.

                  Hopefully I'll have a little time in the evening to stop by HTGuide and look over everyone's shoulder.....

                  On Friday I fly to the UK, and won't have much access, unless Yvonne's cousins have decent net access- but then he's supposedly even got some kind of posh (by UK standards) Home Theater setup, so perhaps I can turn him on to HTGuide as well as drop in here.

                  Hi Pete,

                  In general, I'd say you do want to have a bit of breathing room behind any speaker; this is certainly true of dipoles, also.

                  Even my little M8 "boxes" (which I'm still listening to in the living room) are about 2 meters out from the back wall, though there are some things closer to them, nothing much closer than a meter. That's not a positioning that all people can be comfortable with, but they do disappear pretty nicely, and as Thomas has said, they don't sound like box speakers. Placement is a big factor in addition to the basic design.

                  Geeeezzz, I'm tired! No more creative thoughts from this corner tonight, going to go tuck myself in! (I've been up before 4AM the last 8 days in a row... too much!)

                  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

                    #10
                    Well, Tom, It's worse than you think!



                    Centering in the room is impossible. That's what sparked my interest in dipoles. I kept hearing they could make room interaction less of a problem.

                    What do you think now? I will do a dipole first, as you suggest, but off the top of your head, monopole or dipole for this room?

                    Pete
                    Birth of a Media Center

                    Comment

                    • ThomasW
                      Moderator Emeritus
                      • Aug 2000
                      • 10934

                      #11
                      What do you think now?
                      The solution is to use dynamite!!! :B

                      I'd try reversing the placement of the HT in the room. I assume that the current listening position is a solid wall opposite the current speaker/RPTV wall? If so I'd move the listening position to where all the gear is now located and put the gear across the solid wall.

                      I can't speculate about the best design for the room. Regardless of how the room ends up being set up, I'd whip up a quick and dirty pair of prototype dipole panels to audition. If they don't workout then make a set of monopoles.




                      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

                        #12
                        Not an option.



                        The built-ins wrap around three walls. I went for the "diffused back wall" idea. Also, behind the current location of the gear is a laundry room that has the heater and air conditioner blower in it. My neighbors have the same model, with the furniture reversed, and it's quite distracting when the unit is on.
                        Birth of a Media Center

                        Comment

                        • Hank
                          Super Senior Member
                          • Jul 2002
                          • 1345

                          #13
                          Pete, before I saw Thomas' reply, I swear the word "dynamite" came to mind, BUT, I was going to be nice and not suggest that Could you at least get rid of the equipment rack by building an in-wall cabinet that extends into that utility room? Same size as the rack, but about three feet off the floor. That would simplify the adjacent surface problem a bit, then you could deal with the RPTV as Thomas suggested.
                          If you do an experimental dipole, keep us posted.

                          Comment

                          • Jack Gilvey
                            Senior Member
                            • Aug 2001
                            • 510

                            #14
                            I assumed from the long thread that a dipole woofer stack would require lots more amp power, but you say same amps for either. That removes one of my two major concerns about dipoles.
                            It doesn't take all that much power to get dipole woofers to reach Xmax, it's just that the output is greatly reduced by the front-back cancellation. I'm using a pair of Adire DPL12's on a 2'x4' marine ply baffle w/ 8" "wings" and the excursions are enormous for fairly moderate output. Still, the sound quality is such that it's well worth it, really quite extraordinary. As soon as I can get some BB home, I'm doing a bigger baffle to accomodate all four, and eventually I'll try a push-pull arrangement (like SL's Phoenix) to cancel the reactive forces which are very much in evidence when my simple baffle is in operation (I'm sure this resonance is coloring the sound). I won't soon revert to a monopole sub for music, although a PR'd Tumult is in the future for HT hijinx.

                            Comment

                            • PMazz
                              Senior Member
                              • May 2001
                              • 861

                              #15
                              That's it! I'm never posting pics of my room again.

                              Hank, actually, it'll get worse. I have plans to enclose the RPTV and the gear with an entertainment center. The speakers will sit in front of the whole thing, but only by a foot or so.

                              Hmmm.....dynamite.......insurance would cover the rebuild......I could do that underground IB I've always wanted......all new gear......

                              Moving would be easier!

                              Pete
                              Birth of a Media Center

                              Comment

                              • ThomasW
                                Moderator Emeritus
                                • Aug 2000
                                • 10934

                                #16
                                The solution to the room problem is

                                HEADPHONES :B

                                Jack

                                Don't be dropping in here and changing the subject to some speaker building project. We're here to give Pete a hard time about his room




                                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

                                • Brian Bunge
                                  Super Senior Member
                                  • Nov 2001
                                  • 1389

                                  #17
                                  My dad's actually finishing up a project where he built a wall between his dining room and living room and enclosed his Pioneer RPTV and all his equipment into the wall. There are folding doors on the dining room side for easy access to the equipment. I'll have to post some pics when we get his new speakers and stands finished as well.

                                  Brian

                                  Comment

                                  • Hank
                                    Super Senior Member
                                    • Jul 2002
                                    • 1345

                                    #18
                                    Speaker building projects?! I'm here to learn about redheads!

                                    Comment

                                    • Jack Gilvey
                                      Senior Member
                                      • Aug 2001
                                      • 510

                                      #19
                                      Opps, sorry.

                                      Pete, my man, that room sucks.

                                      Comment

                                      • ThomasW
                                        Moderator Emeritus
                                        • Aug 2000
                                        • 10934

                                        #20
                                        Pete

                                        I think that you need to forget using a dipole baffle. They're going to be too wide for your room.

                                        Going monopole with the narrowest baffle possible is the only way to fly!

                                        Everyone else

                                        Now I'm going to put a fly in the soup so to speak (yea like what else is new Thomas?)

                                        My personal opinion is that all the B&G planars need supertweeters. I tried running the RD-75 without them in the HT. And found that there was something missing. When I put the tweeter array back in the system life was good again.

                                        The black dipole baffle doesn't have them because it's just a prototype to checkout baffle loading for the cones and the big B&G planars. When that system is finshed it will contain super tweeters.

                                        Those that have heard the A***a system have some idea as to what the top end of the little planars is. The big planars are basically the same.

                                        I realize that almost none of the commercially built system using B&G planars use supertweeters. But I think it's important before people invest the big bucks these drivers cost to understand that they start rolling off around 15Khz and actually start beaming around 7Khz, So if you go without super tweeters you must be directly on axis to hear the what high frequencies they do reproduce.

                                        I meant to discuss with Jon the idea of adding a single dome tweeter placed in the center of the cone line array running only as a supertweeter. But forgot given his hectic schedule. Perhaps he'll have time to read this and reply before leaving for merry old England

                                        Another possibility might be to put a separate dome on top of the monopole cabinet ala the B&W designs. Now I have no idea how this would sound. So again a prototype would be necessary to test the concept. I'll see if I can attach one to the top of the black dipole to see what happens




                                        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

                                          #21
                                          I still have to try a dipole setup first. We've talked too much about it to not have a listen, at least.

                                          Super tweeter, huh? I was hoping maybe some EQ on the top end would do it. AArgh!

                                          That'll be a wait and listen decision for me. You talking something like the Neo 3?

                                          Pete
                                          Birth of a Media Center

                                          Comment

                                          • ThomasW
                                            Moderator Emeritus
                                            • Aug 2000
                                            • 10934

                                            #22
                                            Pete

                                            I'm think you'll like the sound of the dipoles but you probably won't like living with a pair of baffles that are no less than 18"+wide. That's what's going to be needed to get the smoothest response.

                                            EQ isn't recommended for planars where to top octaves are rolling off. I chatted with Jon about this since it's a favorite topic on other forums. He says it's 'not a good thing Martha'

                                            The little Neo-3 might work (the FR plots aren't all that impressive) and it's a line source so are you willing to make a line array with them and use an even wider baffle?

                                            I have a stash of various leaf/planar tweeters I bought in the mid 80's at wholesale pricing. Some aren't so great, others are pretty nice. I'll play around with the cheap ones first. I may pop for a short array of Raven 2's IF Santa's good to me this year......




                                            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

                                            • Dennis H
                                              Ultra Senior Member
                                              • Aug 2002
                                              • 3791

                                              #23
                                              EQ isn't recommended for planars where to top octaves are rolling off. I chatted with Jon about this since it's a favorite topic on other forums. He says it's 'not a good thing Martha'
                                              Hi Thomas,

                                              Could you explain your (and Jon's) thinking on why EQ is a bad thing? Is it the width of the ribbon or some other factor?

                                              Comment

                                              • ThomasW
                                                Moderator Emeritus
                                                • Aug 2000
                                                • 10934

                                                #24
                                                Dennis

                                                I'll leave the techinical explaination to Jon

                                                The larger stock B&G planars start beaming at 7khz and run out of gas starting at 12-13Khz and die around 16-16.5Khz.

                                                The B&G planars used in the Wisdom Audio speakers use a special plastic membrane (higher temp tolerances) and 2 additional radiating elements specifically designed for the highest frequencies. As a result they can handle the EQ used to flatten the FR in the top end.

                                                The stock B&G planars (the only one available to DIYers) don't have the additional elements or the high temp membrane and as a result it's not a good idea to try and force them to play that high. Doing so will impact the SQ of the rest of their passband.

                                                The stock elements can run slightly higher if the recommended 5Khz notch filter isn't utilized. But to my ears the filter is absolutely necessary.

                                                Here's a nearfield, fullrange, on axis plot of RD-75 without the 5Khz filter. This plot was done with the driver in a test baffle. We haven't had an opportinity to measure it in the new prototype black baffle.



                                                Also we're just not fans of active EQ in general. If it's being used to 'cut' a peak that's usually ok . But using boost is something to avoid. I know lots of people use EQ we prefer not to use it.




                                                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

                                                • Hank
                                                  Super Senior Member
                                                  • Jul 2002
                                                  • 1345

                                                  #25
                                                  Whoa, Thomas! First you mentioned a dome tweet in the middle of the woof line. Next post you said maybe the NEO 3 and asked Pete if he's willing to live with a line array of them. Next sentence you say you may try a line of Ravens! Man, when you start thinking, your driver cost possibilities escalate in a geometric progression. 8O Let's get back to that dome tweet - how about a Vifa - just a tad less expensive than a line of Ravens.

                                                  Comment

                                                  • PMazz
                                                    Senior Member
                                                    • May 2001
                                                    • 861

                                                    #26
                                                    Should the xover take place at or below 5K to avoid the notch filter, or just have it up ~ 10K to just "top off" the B&G?

                                                    Pete
                                                    Birth of a Media Center

                                                    Comment

                                                    • ThomasW
                                                      Moderator Emeritus
                                                      • Aug 2000
                                                      • 10934

                                                      #27
                                                      Yup a creative mind is a dangerous thing

                                                      I wasn't the one that suggested the Neo-3's that was Pete. When they were first introduced I hoped they would be the line array suptertweeter of choice. But the original one's had about the same top end roll off as the Neo-8's. Now there's a newer version, they claim goes to 28Khz but IMO the FR plots are a jagged mess.

                                                      If a dome is being use to fill in the top end I'd use a metal dome. There's a Titanium one from Audax that goes to 40Khz for under $30 (they're used for the ambient fill in the real SLAMM's so they're pretty good). I several Focal TC120's around. I'll try putting one on the black baffle to see what it does. And yes will use 10Khz as the XO point.

                                                      If the Ravens 2's are used I'll try a 5Khz or slightly lower XO point to avoid using the notch filter. I certainly wouldn't go that low with a single dome.

                                                      It really a drag that the nice mid buck leafs like those made by Technics aren't available. I've tried to find out who makes the leafs used in the Legacy speakers, but no one seems to know. They are similar to the Technics EAS-400's I use with the big ESL array.




                                                      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

                                                      • Victor
                                                        Senior Member
                                                        • Apr 2002
                                                        • 338

                                                        #28
                                                        This is a very interesting discussion. I would like to raise the lonely voice in favor of the high frequency boost. I have some experience with the high frequency EQ although perhaps not as extensive as what Jon or Thomas brings to the table.

                                                        I played with HF EQ on my Carver Mark IV ribbons and I managed to quite successfully flatten the response to about 17 kHz. I only needed about 6dB of rise past 9.5 kHz in order to achieve that. As we all know Carver planers are very similar to BG’s in construction. Naturally BG product has better response.

                                                        I just finished my new baffles that now house the RD-75 drivers and I intend to repeat the experience I had with Carver’s. Judging from what John Whittaker posted in his study of RG-75, the response of RD-75 driver is better then 1 dB all the way to 15 kHz. So I anticipate that all that is needed is about 3-5 dB of gentle rise starting at about 8.5 kHz and going to about 18 kHz.

                                                        Also I must confess that I cannot hear anything past 16.7 kHz and I am 41, -it is only downhill from here, as we all know… So with all that in mind, is the super tweeter really necessary, particularly considering the cost, complexity and possible (and very real!) frequency response anomalies that such integration will bring about? Is the cure worst then the disease?

                                                        On slightly different note, I noticed from John Whittaker’s plots that the cavity resonance on RD-75 is actually closer to 6 kHz. The graph Thomas posted in this thread seems to support that. Can anyone confirm my suspicion that the notch filter must be at 6 KHz and NOT at 5 kHz? This is important to me as I am deep into active crossover for my new RD-75 ‘wings’ as I call them.

                                                        Regards,
                                                        Vic

                                                        Comment

                                                        • ThomasW
                                                          Moderator Emeritus
                                                          • Aug 2000
                                                          • 10934

                                                          #29
                                                          Hi Vic,

                                                          Welcome to the new thread!

                                                          Part of the issue isn't necessarily getting the flattest frequency response out of the planars. My hearing HF isn't the best either. But not using the leafs with the ESL/RD-75 array resulted in less air and space in the top end of the music. BTW I wasn't the only person to notice this.

                                                          A problem that I think is just as a significant as the top end roll-off(actually maybe more so), is the fact the planars start to beam around 7Khz. and this beaming obviously continues to increase as the frequencies go up. So if one wants to hear the HFE then one must be on axis. If the silver traces of the radiating element can't be seen, they can't be heard. Using EQ may flatten the FR but it isn't going to solve the HF beaming issue.

                                                          In the B&G literature available from the PE website, they state that the cavity resonance is 5Khz-6Khz 'range'.

                                                          The FR plot I posted was made using a $$$$ labratory standard grade B&K 4133. So it's safe to assume it's an accurate representation of the top end of the RD-75

                                                          I use the passive notch provide by B&G for the ESL/RD-75/leaf arrays. I just duplicated it with the newer pair since PE doesn't include them.

                                                          Parallel a 20uf cap, a 0.05mh coil, and a 10 ohm resistor and drop them in the + speaker lead for the RD-75's. Lower the resistor value to 8 ohm for the RD-50's everything else stays the same.

                                                          Regarding the dome supertweeter, That's just an idea I can easily try using the black baffle, 10 minutes of spare time and some parts from the basement. So not much is lost if it's a bust.




                                                          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

                                                          • Victor
                                                            Senior Member
                                                            • Apr 2002
                                                            • 338

                                                            #30
                                                            Thomas,

                                                            Well, beaming is a problem indeed. You are right, the top end EQ will flatten the response but will do nothing to the beaming issue. Come to think of it, I do not think I spent any significant time looking at off-axis response of my EQ’ed Carver’s. But then again, I would park myself in the sweet spot every time I listened or watched a movie and the darned thing sounded just great! At this time I will proceed with an EQ of the top end, however I’ll be very interested to see the results of your test with a super tweeter.

                                                            So, the notch must be somewhere between 5 and 6 kHz. I guess I’ll go for the 5.5 kHz, thanks for clearing this up.

                                                            Vic

                                                            Comment

                                                            • Dennis H
                                                              Ultra Senior Member
                                                              • Aug 2002
                                                              • 3791

                                                              #31
                                                              Beaming and EQ.

                                                              Here's one I experimented with briefly a while back before I had to pack up my DIY stuff and concentrate on other things. It showed some promise but it needs a lot more testing. I was playing with a Monsoon panel but a BG Neo should work about the same way. The big BGs would be more problematic because of the metal "horn" on the front. Anyway here goes.

                                                              Premise 1: if you're using an active notch filter or an active crossover, you're already EQing so a little more won't hurt.

                                                              Premise 2: side by side lines of HF drivers are a "bad thing" for all the obvious comb filtering and polar response reasons.

                                                              Premise 3: large amounts of boost above 10K are no big deal for the driver because the actual musical content up that high is very low so there's no danger of working the driver too hard.

                                                              Premise 4: the problem with boosting the HF is the power response; the drivers are so wide they beam like crazy at the highest frequencies.

                                                              Possible solution: use thin tapered pieces of foam (or wool blanket) covering the outer (side to side) portions of the driver. The center 1/2" has no foam so, at 20K, the driver acts like a 1/2" wide tweeter with excellent lateral dispersion. As you get farther (side to side) from the center of the driver, the foam gets thicker. This has the effect of making the driver appear narrower acoustically as the frequency increases. By trial and error, you adjust the thickness of the foam so the frequency response measures about the same off axis as it does on axis.

                                                              Of course, we are absorbing a lot of HF energy from the outer edges of the driver so the frequency response is anything but flat. That's where the EQ comes in. Once we have a polar response we are happy with, we EQ the whole thing back to flat. The net result is a single driver that is flat up to 20K both on axis and off axis.

                                                              Like I said, the idea needs a lot more work but it was showing some promise. With a line array of small panels, you would just use two long strips of foam or wool, carefully tapered side to side, and stuck on the outer edges of the line.

                                                              Comment

                                                              • Hank
                                                                Super Senior Member
                                                                • Jul 2002
                                                                • 1345

                                                                #32
                                                                zzzzzzzzzzzzzzzz....oh, hello! Where is everyone? A big hiatus while we ponder whether or not line source projects are affordable? For myself, If I do the deed, I need a couple of months to save up the scratch to buy drivers.

                                                                Dennis: interesting information you've added here. Did you do testing with instruments as well as ears? If so, do you have response graphs you could share?

                                                                J&T: what do you think about Dennis' info? How about HF boost, like Victor recommends?

                                                                Pete: when/what do you plan to build?

                                                                Comment

                                                                • ThomasW
                                                                  Moderator Emeritus
                                                                  • Aug 2000
                                                                  • 10934

                                                                  #33
                                                                  Hank

                                                                  Ok, ok, gees you youngsters are sooo impatient :B

                                                                  First here's some 'eye candy' compliments of Vic. I'd say he does some pretty nice work 8O







                                                                  Here are both black dipoles up and running tri-amped, each with an array of old not so good leaf tweeters.





                                                                  I have a Symetrix 551 (it's mono) not in use. As time permits I'll remove one of the leaf arrays, and use the 551 to EQ top end of one of the RD-75's. Then I'll A/B it with the other and see what happens.




                                                                  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

                                                                  • Hank
                                                                    Super Senior Member
                                                                    • Jul 2002
                                                                    • 1345

                                                                    #34
                                                                    Nifty! Neat-o! Can I build some, huh Daddy, can I, can I??
                                                                    Vic, great looking work, man! The pics are dark. I'd like to see detail so I can ask questions (who, me?). Do you have "lighter" photos you can post?

                                                                    Thomas, I've very, very interested to read your listening test results. It would be nice not to have to incorporte a line (or even one) of supertweets.

                                                                    Comment

                                                                    • Victor
                                                                      Senior Member
                                                                      • Apr 2002
                                                                      • 338

                                                                      #35
                                                                      First of all, my thanks go to Thomas for posting the pictures of my RD-75 baffle. I realize that the photos are a little dark, but I took them without paying any attention to the lighting at hand. Naturally I can try to do a better job and also I may photograph the close-up details of the baffle. I’ll try to do it later this week.

                                                                      The baffle is 76.5 inches tall. It uses a 6-inch diameter half-round from

                                                                      http://www.tapeease.com/2rounds.htm

                                                                      on the slopping edge. The baffle dimensions follow closely the work by John Whittaker, who did a HUGE work-up on RD-75. Here it is

                                                                      http://www.snippets.org/alsr/dbsindex.html

                                                                      The top of the baffle is 12.5 inches and the bottom is 18.5 inches. Then you must add another 3 inches due to the half-round. So overall the baffle is one-sided trapezoid with 15.5 inches on top and 21.5 inches on the bottom. The other end of the baffle, closest to where the RD-75 is, has a 1.5 inch half round. That edge is vertical, i.e. not sloped at all. The back of the baffle is covered by a thin carpet. The RD-75 driver is completely flash with the baffle surface in the front and in the back.

                                                                      I endeavored to design the baffle that has no sharp edges or discontinuities, owing to John Whittaker’s conclusions that it is the only way to mitigate the diffraction effects. That led to this ‘swept airplane wing’ concept, with the 6-inch half-round being the leading edge. The total area of the baffle should support the frequencies into the 200 Hz range and it is only slightly larger that what Mr. Grebner suggested as a good starting point, i.e. flat baffle 15 inches wide.

                                                                      I just finished the active crossover for the RD-75, but I have yet to fire everything up, so I do not know how the sound is. I hope it’ll be fine. The active cross-over has a gradual linear boost of +3 dB from 8 to 15 kHz, and then boost becomes exponential ending up at about +10 dB at 20 kHz. I am hoping that I will have fairly flat response to the limit of my hearing at least on axis. I ended up fixing the notch at about 5.5 kHz. The notch is asymmetrical with a ‘faster’ high frequency edge. The notch depth is 9 dB and its bandwidth (-3dB) extends to about 3.5 kHz and correspondingly 6.5 kHz from the center frequency. All in all, the notch is tighter then the stock passive notch supplied with RD-75.

                                                                      I am now busy building the midrange and the subwoofers. As it looks, the subwoofers will be ‘a la’ Phoenix woofer. I will use 4 drivers (Peerless 830500) per side, - 2 will fire forward and 2 will fire backward. One cabinet will house 4 drivers. The subs will cover up to 70 Hz. The midrange will be 4 units of Scan Speak 25W8565 in a narrow 12.5 inch wide baffle with 3.5 inch ‘wings’, again ‘a la’ Phoenix main baffle design. The midrange section will cover 70-300 Hz range. This midrange baffle will be affixed on top of the subwoofer cabinet and bolted to the subwoofer cabinet for added security. All filters are going to be 4th order L-R.

                                                                      Overall height of the subwoofer-midrange combination will also be 76.5 inches. Both structures, - the RD-75 baffle and the sub-midrange unit, will stand side by side as close as possible. That means that the RD-75 will be about 7 inches away laterally from the midrange array. With the midrange array being directly on top of the subwoofer cabinet hopefully the acoustic centers should be fine.

                                                                      Comments???

                                                                      Regards, Victor

                                                                      Comment

                                                                      • ThomasW
                                                                        Moderator Emeritus
                                                                        • Aug 2000
                                                                        • 10934

                                                                        #36
                                                                        Vic

                                                                        Personally I think they're much better looking than John P's 'wings'

                                                                        Did you make a mockup/prototype, or just go straight for the good stuff?

                                                                        Hank

                                                                        I'll need to do the EQ by ear (bummer ) I don't have a mic around that's accurate above 12-13Khz. The B&K is at Jon's, and Jon is of course still in merry old England.




                                                                        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

                                                                        • Victor
                                                                          Senior Member
                                                                          • Apr 2002
                                                                          • 338

                                                                          #37
                                                                          Thomas,

                                                                          I never did a mockup. However, I did a lot of thinking and even more reading. I realized that there are only so many ways you can do the baffle and Tom P.’s was one of them. His baffle however, did not address the diffraction problems due to the symmetry of he design. Yes, it did curve, but the curve was uniform throughout the shape. It was very evident from John Whittaker’s study that the shape must be asymmetrical, i.e. one-sided in order to mitigate the diffraction effects. And so I went with the swept wing shape. Once the decision was made and all other possibilities were dismissed, I went directly to baffle fabrication.

                                                                          Victor

                                                                          Comment

                                                                          • Hank
                                                                            Super Senior Member
                                                                            • Jul 2002
                                                                            • 1345

                                                                            #38
                                                                            Vic, thanks for the details. You obviously did lots of homework. Interesting idea to use plywood half-rounds. That is indeed a large radius edge. Do you need 3" radius per edge diffraction calculations? Is the opposite edge 1.5" diameter or radius?
                                                                            I'm not convinced to use an RD75 - I think an RD50 is tall enough - it will cover seated listening positions. If I do a line source, I'll put the ribbon and mids in one tower. For me, two big towers per side is just too dominating a room.
                                                                            Again, nice work and I look forward to more photos!

                                                                            Comment

                                                                            • ThomasW
                                                                              Moderator Emeritus
                                                                              • Aug 2000
                                                                              • 10934

                                                                              #39
                                                                              Hank

                                                                              Unless your room is really deep you don't want RD-75's. In the 'family room' I have 2 listening positions one 11,' and another 16'+ away from the black dipoles. At the 16' distance the soundstage is better.

                                                                              Also it requires a complete rebalancing of the output levels of the different elements of the line array to get the best sound if I move between the 2 listening areas. I'm thinking that the Avro Pärt design might be a better compromise for my needs in the family room




                                                                              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

                                                                              • Victor
                                                                                Senior Member
                                                                                • Apr 2002
                                                                                • 338

                                                                                #40
                                                                                Hank,

                                                                                The choice for the 6 inch diameter half round was to some degree dictated by the John Whittaker’s work. You see he tested something he called a ‘Compound Shape Baffle’ which appeared to have the least diffraction problems. The curvature of that baffle was in the 6-inch range, although the shape of the baffle was somewhat different. And so it is the size I chose.

                                                                                Close form mathematical solution for the diffraction effects computation does not exist as far as I know. Extensive computer modeling with finite element software must be done in order to gain a meaningful modeling success. I happened to study some aerodynamics about 15 years ago and the shape of the wing that I build resembles in many ways one of the most successful from aerodynamic perspective shape that I had experience with. It also looks somewhat similar to the ME-262 and early MIG-15 fighter jet designs of 1944-50 time frame. Does the aerodynamically well executed shape have any benefit for audio applications? I have no idea, and it would be an interesting study.

                                                                                The opposite edge is indeed 1.5 inch diameter. This dimension is dictated by the actual depth of the RD-75 driver. I cannot comment on the RD-50 as I have never seen one, but I would imaging that the utilization of the 50 model is most likely identical to 75 model as far as baffle construction issues are.

                                                                                Regards,
                                                                                Victor

                                                                                Comment

                                                                                • Hank
                                                                                  Super Senior Member
                                                                                  • Jul 2002
                                                                                  • 1345

                                                                                  #41
                                                                                  Vic, thanks for the clarification. Airplane wing...hmmm...I wonder if there's any relevant relationship between the top/bottom pressure differential of a wing with air flowing over it and the air pressure flow on the front (top) of a wing-shaped baffle. Yes, an interesting study indeed.

                                                                                  Thomas, how did you do your baffle edges, and did you mount your RD's and tweets dipole?

                                                                                  Comment

                                                                                  • ThomasW
                                                                                    Moderator Emeritus
                                                                                    • Aug 2000
                                                                                    • 10934

                                                                                    #42
                                                                                    Hank

                                                                                    The front edges are just knocked off with a roundover bit. When time permits I'll grab a piece of PVC tubing, split it lengthwise and attach it to the edges. This has been my plan all along. I will probably use 3" diameter pipe. Understand that mine are prototypes so there will be a lot of experiments done to them. As built there are quite a few differences between the L and R baffles. And I have several ideas for modifications/tweaks.

                                                                                    Jon's scheduled to be here around Sept 26th. I hope we can do a series of measurements of the baffles so as to compare and contrast.....

                                                                                    Everything but the leafs are dipole. There are no dipole tweeters available for DIY use.




                                                                                    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

                                                                                    • Dennis H
                                                                                      Ultra Senior Member
                                                                                      • Aug 2002
                                                                                      • 3791

                                                                                      #43
                                                                                      Hank, I did a quicky test of the foam bit with a semi-close-mic'd RTA but I didn't save any curves. I'm interested in a monopole line array so I just laid the Monsoon driver on some thick foam to absorb the back wave. Then I played with putting thin strips of foam over the outer edges of the driver until I got a frequency response that was similar on axis and 30 degrees off axis. All my DIY stuff is in storage now pending a move so it's going to be a while until I can get back to the project.

                                                                                      Vic, beautiful looking baffles!

                                                                                      Comment

                                                                                      • PMazz
                                                                                        Senior Member
                                                                                        • May 2001
                                                                                        • 861

                                                                                        #44
                                                                                        Originally posted by ThomasW
                                                                                        Unless your room is really deep you don't want RD-75's.
                                                                                        Tom,
                                                                                        Based on your listening/tweaking, do you think the RD50 will be better for a 10-12' listening distance?

                                                                                        Pete
                                                                                        Birth of a Media Center

                                                                                        Comment

                                                                                        • Hank
                                                                                          Super Senior Member
                                                                                          • Jul 2002
                                                                                          • 1345

                                                                                          #45
                                                                                          Thomas, yeah I thought about PVC for experimenting when I looked up the price of those half-round plywood forms. Keep us posted on your experiment results. I'm not trying to be pushy - it will be a while before I can budget for all the drivers - two kids in new college semester :cry: .


                                                                                          Dennis: When you recover from your move and dig out the DIY stuff (it will be first priority, right? ), let us know. I'm intrigued with evening out the off-axis response with foam. Look how Thomas went wild with felt! If I can come up with a cosmetically acceptable felt or foam (maybe a combination?) application, that would be a heck of an inexpensive performance enhancement tweak.

                                                                                          Comment

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