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  • PTmini-6 in large groups....

    There is a long discussion about this planar in the archives. Basically, while PE says that they can be crossed at 4000hz, with a 12 db slope, most people here believed that it needed to be higher to avoid distortion.

    In the current design of my new line arrays, I plan to cross them at 5500hz, with a 24 db L-R slope. Additionally, each channel will have ten of them, so each one will only be handling about 10% of the total volume. From my reading, it appears that the distortion comes into the picture when they are pushed too hard and the film is forced to move too much. And of course the movement is greater at lower frequencies.

    Since they have been around here now for almost 3 years, does anyone have any new comments, or comments on my proposed usage of 5500, 24 db L-R, using 10 per channel.

  • #2
    I not as thrilled with the use of these drivers as you are.

    First, the active membrane for each one is tiny--only 2.375" long for each element. Thus you need a bunch to create a long array.

    Second, as they are planars when vertically arrayed their sound fields really don't overlap thus no array gain for the bunch. The vertical dispersion for these units is limited to their height so their dispersion vs. frequency trends toward the height of each active element.

    Third, I don't understand how/why you plan to wire up 10 of these in a vertical array. Nine (in 3 series x 3 parallel groups) yield a 6 ohms impedance while if you use more (say 16, 25, square numbers for 4, 5, etc) you can create longer arrays but still no gain in sensitivity. The only way to get a gain in their sensitivity is to reduce their arrayed impedance so a 3 ohms connection will gain you 3 dB.

    Read my NFLAWP for more stuff on line arrays.


    http://www.audioroundtable.com/misc/nflawp.pdf

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    • #3
      Jim,

      You may not recognize my name here, since we have recently communicated by PM on the DIY Audio site.

      I'm not enamored of them. But I'm also not made of money. Last time, I built a set of 32- ND20FA's with the flanges cut(per side) so that I could have a one wave length above 16,000 hz. But they were about 4 bucks a piece then. Now they are more expensive than these planars, and so 64 of them would cost me $768, just for the tweeters. Considering that I also need the mid ranges, the crossovers, the amplification, and the other stuff, spending 3/4 of the money on tweeters is simply not an option---with the WAF already balking at the cost for this retired couple. She watches TV in her $1600 55 inch large screen, and doesn't get that I have as much need to listen to Vivaldi as she does to her movies.

      In the previous array, the tweeter line was only 32 inches and the mid range line was floor to ceiling. This time I have more of the WAF to contend with since this is in my living room not the "man cave" downstairs. In any case, the ribbons will be also 32 inches. That seemed to work fine then with the same setting hearing distance now as then, where the major coupling was with the midrange. Then I was crossing at 2230, but this time I will be crossing at 5500, since the mids are smaller and the CTC is smaller, and so the coupling will be the four full octaves of the most sensitive human hearing---600-5500 hz. Previously I lost one whole octave and it still worked great. I read some where just this morning(and now I cannot find the reference) that the coupling length of the tweeter array is less that the 70% that you indicated in your paper, because coupling at the higher frequencies doesn't require the same length as at the midrange frequencies. I wish I could quote the source.

      The vertical dispersion of the domes was also limited to the height of the domes. I could hear a loss in high frequencies when I stood up(I'm 6'4"), but my wife at 5'7" could not. I suspect the same would be true. The coupling with the floor and the ceiling in the higher frequencies, in my experience with the past array where the mids stopped at 2230, did not seem to be an issue. This time while the mids won't go to the ceiling, they will be above the 70% of the height from floor to ceiling that your white paper specifies as the minimum distance to couple.

      A 4, 4, 2 will give me an impedance of 5.14, easily within the range of the amps. Of course I don't have to deal with impedance issues that passive crossovers bring, since the speakers are wired directly to the amp, and the amp for the tweeters is 150/ch at 4 ohms. I will have to dial them back in the crossovers(Behringer Active), but more of them will increase the power handling which helps when using an amp that powerful. I can also individually control the power of the 6 amps(and 6 separate power supplies) too. Sensitivity increase is of no real importance in an active crossover, as you know. The real reason for having more, is to reduce the stress on the planar so that only 10% of the sound has to go through each one per side, as described above. My research on these planars and on ribbon planars in general, suggests that the lower the frequency, the more they have to physically move in vibration, and this is what tends to cause the greater distortion. Also, the more I have, the softer they can each play, and the less the kapton membrane has to move.

      Certainly having a floor to ceiling array of tweeters is ideal, or at least the 63 inches of the mids, but that is simply beyond my price range. I have proved in the past that it is possible to build a line array for under $900 including electronic crossing and Quad Amping, that will blow away nearly anything. I have no reason to believe I cannot do it again.

      Eric
      Last edited by malboro2; 10-10-2017, 12:35 PM.

      Comment


      • #4
        I've used the PTmini-6 and while it looks cool, when crossed at 6K it doesn't have the planar sound/ detail I like. I think your plan will work and the distortion will be reasonable, I'm not sure I'd use it over any other tweeter.
        John H

        Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

        Comment


        • #5


          I agree. Like I said to Jim, I'm not enamored of it. I would actually prefer something else, but in a line array where I need a line of 30 inches, the options are not as easy in the price category as they were 11 years ago.

          However, I would suspect that your listening to it has taken place with two singly---one in each speaker. I suspect that it will be quite different when there are 20 of them. Most mediocre speakers have rather flat frequency responses, and low distortion at low volume levels. Its when you turn the volume up that they become whacky. In the case of a line array, this doesn't happen, and additionally in my case, there is also no passive crossover to modify the sound.


          Comment


          • #6
            Originally posted by malboro2 View Post
            Jim,

            Certainly having a floor to ceiling array of tweeters is ideal, or at least the 63 inches of the mids, but that is simply beyond my price range. I have proved in the past that it is possible to build a line array for under $900 including electronic crossing and Quad Amping, that will blow away nearly anything. I have no reason to believe I cannot do it again.

            Eric
            Have you been to any meets with your line arrays?
            http://techtalk.parts-express.com/fo...khanspires-but
            http://techtalk.parts-express.com/fo...pico-neo-build
            http://techtalk.parts-express.com/fo...ensation-build

            Comment


            • #7
              Originally posted by Kornbread View Post

              Have you been to any meets with your line arrays?
              That would be kind of hard to do. Most Meets take place in the Midwest, more than 1000 miles from me up near the Canadian border of New Brunswick Canada. Second, they are not just speakers. Despite the fact that they are 96in x 24 inch x 6 inches, plus two woofer boxes of 30 x 15 x13, I also have three big power amplifiers, a rane crossover, a pre amp, and maybe a cd player. They are not made to travel.

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              • #8
                I'd take the DX20 over the PTmini in a heartbeat, and probably the Peerless OC16SC04.
                John H

                Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                Comment


                • #9
                  Originally posted by jhollander View Post
                  I'd take the DX20 over the PTmini in a heartbeat, and probably the Peerless OC16SC04.
                  The Peerless DX20 cannot be used in a line array in a group due to comb filter distortion. By itself, maybe, by itself. But I'm still hooked on line arrays, since I've had both and no point source for me matches a line.

                  The Peerless OC would require 32 of them per side, or 64 for two sides at $438 for a set---more than I can afford. The frequency response is hardly very flat for $438.

                  But both of them are singly better than the PTmini, for sure. However, I would expect 10 of them would be better than one DX20.

                  Comment


                  • #10
                    I used the PTmini-6 in a recent build crossed 24db/oct at 5K and was very happy with it. I decided to use it because I heard it at DIY Iowa a year or two ago. They're a little tricky to mount but I think an array of them should sound pretty good.

                    Ron
                    C-Note Iron Driver Build
                    The Lydias
                    The Cherry π's
                    The Champs - Iron Driver 2015 Entry
                    My Projects Page

                    The good thing about science is that it's true whether or not you believe in it. - Neil deGrasse Tyson
                    http://www.youtube.com/watch?v=cjuGCJJUGsg

                    Comment


                    • #11
                      Originally posted by Ron_E View Post
                      I used the PTmini-6 in a recent build crossed 24db/oct at 5K and was very happy with it. I decided to use it because I heard it at DIY Iowa a year or two ago. They're a little tricky to mount but I think an array of them should sound pretty good.

                      Ron
                      I notice in your construction you are also using the CE65w-8 which I am also planning to use, but instead of one, I'm going to be using 20 per channel. They look a lot like the Sammi 3.5's I used for my last line array(which I picked up for about $4, and which now cost $12 when you can find them.

                      Comment


                      • #12
                        The CE65w-8 isn't bad for the money. A bunch of them should be pretty good. This is the plot of the individual drivers response from the crossover sim. The tweeter roll off up high is my mic. I don't use a cal file because my mic is flat where I need to use it for crossover design.

                        Ron
                        C-Note Iron Driver Build
                        The Lydias
                        The Cherry π's
                        The Champs - Iron Driver 2015 Entry
                        My Projects Page

                        The good thing about science is that it's true whether or not you believe in it. - Neil deGrasse Tyson
                        http://www.youtube.com/watch?v=cjuGCJJUGsg

                        Comment


                        • #13
                          I noticed that cutting the rectangular hole for the PTmini's seemed pretty labor intensive. I never liked using a hand operated router for that kind of work. And I would have to do it 20 times. Cutting holes with a hole saw is one thing; routing rectangles is something else entirely. Where'd my laser cutter when I need it?

                          Anyways, I'm planning on surface mounting both speakers, but I am covering the outside of the speaker baffle with black 1/4 inch wool felt. Some research suggests that this, combined with the curved edges goes a long way to dealing with edge diffraction. And it has the side effect of not having to route holes for the planars.

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                          • #14
                            The felt needs to be much thicker (like an inch thick) to be effective.
                            Craig

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                            • #15
                              Originally posted by PWR RYD View Post
                              The felt needs to be much thicker (like an inch thick) to be effective.
                              OH NO..... That's distressing. However, I have not been able to find a reference for the density or thickness of the felt required. Perhaps you could share where you got this information so I can get a bigger and clearer picture. Perhaps there is some reference to it in Vance Dickason's 6th edition, but I cannot find it.

                              I do remember that when I built my first line arrays 12 years ago, there was a modeling program that showed that after about 10 speakers on the baffle the increase in sensitivity of the system made the loss due to diffraction meaningless.

                              And doubly distressing that I couldn't even remember what I wrote there in the thread!!!!
                              Last edited by malboro2; 10-12-2017, 10:19 PM.

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