Forum Top Banner Ad

Collapse

Ebay Classic organs

Collapse

Announcement

Collapse
No announcement yet.

Converting a Rodgers M13 to a few M10 or M10c

Collapse
This topic is closed.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Converting a Rodgers M13 to a few M10 or M10c

    toodles, uploaded the Rodgers M10 brochure in a recent subwoofer thread. That was helpful to see.

    In addition to my M10, I also I have an M13 that is far too big for my living room. It has many 6x9 and some of the JBL ring radiators (like the RW3). it occurred to me that I could dismantle the M13 and create a few M10 or M10c style cabinets that I could more conveniently place in the room -- perhaps even less noticeable than the present speakers.

    Quick questions:
    1. The M10 have no back. In a living room, would it be appropriate to place these flush against a wall, a distance away or should I enclose the back?
    2. My M13 (and even other M10 that I have include the same JBL ring radiators as the RW3. I think in one of your posts you mentioned these may be too harsh for a small room. Would you recommend I remove them? I also have some small plastic horns that could be used.
    Eric Mack
    www.ThisOld340.com
    Rodgers 340 S/N 34341
    Los Angeles, CA

  • #2
    You probably cannot place the M10 or M13 close enough to a wall to matter, as you won't get an acoustic seal without a serious effort to do so. "Play it by ear" as to placement.

    A better option than converting to the M10 design would be to copy Walker's TP3 design--it used two 6x9 drivers and a phenolic ring tweeter in a small sealed cabinet. You can see them on this page, and get their dimensions: https://buchorgans.com/peripherals/

    This would be an appropriate tweeter for that purpose: https://www.parts-express.com/grs-pr...8-ohm--270-252

    Your plastic horns are probably piezo tweeters, and I can't recommend those except to create noise.

    Comment


    • Eric Mack
      Eric Mack commented
      Editing a comment
      That is a creative solution. And, thanks for the link to the tweeter. That's certainly a possibility for reusing what I already have. My goal is to get my system to a good point, where it sounds as good as it will with what I own, and then shift focus to learning to play. The only TP3 details I have found so far are the dimensions on the walker site: 24″ long x 8″ wide x 6-1/2″ deep, and a discussion thread on OrganForum that you also responded to about using the TP3 and a subwoofer. Understanding that my goal is simply to make better use of what I already have, I wonder if building a few TP3 boxes and perhaps turning one RW3 into my pedal channel would do better than what I currently own
      .

    • Eric Mack
      Eric Mack commented
      Editing a comment
      toodles, I built my first T3 prototype and, to me, it sounds very nice. It is lower in volume than my RW3 (testing by simply swapping speaker's without power adjustment) so I guess that is an issue of efficiency.

      I plan to do more testing between the speakers that I own and I will do that using the FLUTE stop as you advised earlier today.

      Can you speak to whether I should test with the T3 facing the listener or to the wall (as we do with the RW3) and why one way over another? I'm not clear if that is a function of the size of the driver, the design of the cabinet or some other magical quality. Thanks.

  • #3
    I like toodles suggestion about building some Walker-style cabinets out of these 6x9 drivers. I've heard a number of Rodgers organs with this type speaker and found them quite impressive. There is even a large custom all-Walker digital organ in our town (I talked about it years ago in a thread) with close to 30 audio channels. All the manual audio channels use these TP3 cabinets, and the organ sounds positively magnificent. Totally pipe-like and believable. I'd judge these Walker boxes, while built with common components, to be far superior to the Rodgers M13 or M10 or any other typical Rodgers manual cabinets.

    BTW, toodles -- do you have a schematic of the TP3 that shows the crossover design? I haven't seen the inside of one, and I wonder what they did to make it sound so nice. And whether the two 6x9's are 8 ohm or 4 ohm, series or parallel.
    John
    ----------
    *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

    https://www.facebook.com/pages/Birds...97551893588434

    Comment


    • Eric Mack
      Eric Mack commented
      Editing a comment
      Checking in to see if toodles or anyone else has any additional Walker TP3 cabinet info. So far, the only TP3 details I have found so far are the dimensions on the walker site: 24″ long x 8″ wide x 6-1/2″ deep. I am assuming there is a crossover circuit inside, as mentioned by jbird604 above. Any other thoughts? I assume I would put a bag of synthetic fill inside as well. This would be my first speaker build. :-)

  • #4
    I'll throw out a few suggestions, though I don't have access to any Walker speaker cabinet schematics. I did once draw out the schematic when I had a large Walker cabinet opened up to replace drivers, but it was quite odd. I'd think the crossover you need to use will depend somewhat on the drivers. The two 6x9 drivers are not capable of handling a lot of bass, so you might want to insert about a 30 to 60 mfd cap in series between the amp and these drivers. They might not need anything else at all in their circuit, although good practice might call for a choke of some kind, maybe about .5 mH, also in series between the amp input and the voice coils. I suppose the two 8 ohm voice voices should be wired in parallel, giving the cabinet an impedance of 4 ohms. That's probably good for an application where there is only the one speaker cabinet on a channel, but you might not be able to have two cabinets on the same channel, as that would present to the amp as a 2 ohm load, quite low. If you want these new cabinets to be used in pairs on the same channel, or to supplement an existing speaker on a channel, you might consider wiring the two coils in series, for a 16 ohm impedance.

    The high frequency driver would of course require a small capacitor in series with its coil to prevent the bass frequencies from burning up the coil. A single cap crossover for a typical tweeter might be as small as 1.0 or 2.0 mfd, or as large as 5 or 10 mfd. Different values will give different output levels for the highs, but too large a cap risks damage to the coil. You might just go by the cap that Rodgers used in the W3 design, though you could also consult an on-line crossover calculator and build a little circuit to cross it over around 5 kHz (since the driver's specs say it goes down to 2.5 kHz, but you must have your crossover somewhat higher than that).

    Higher end speaker cabinets may also have a choke coil ACROSS the tweeter coil to further roll off the bass (actually to give it a steeper roll-off curve). But you'd need to use a crossover calculator program to get the right value for that coil and cap, if you want to use a circuit that elaborate.

    Filling the cabinet with polyester fiberfill or some such material is good practice, helping to prevent ringing and cavity effects. It also tends to lower the resonant frequency of the box, which might give you just a tad more body in the sound.
    John
    ----------
    *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

    https://www.facebook.com/pages/Birds...97551893588434

    Comment


    • #5
      I do not currently own any TP3's so I can't check, and I do not have the crossover schematic. However, it is probably very simple. Here's a link to a crossover calculator. https://www.diyaudioandvideo.com/Cal...akerCrossover/

      Depending upon the tweeter, you might want to use a 1st or 2nd order filter, and the crossover frequency depends on the tweeter. If you use the phenolic ring tweeter I suggested, it has a resonant peak at about 1100 Hz. The peak is high enough, that I would cross over at least 2 octaves above that frequency (4400 Hz) especially if you are using a 1st order crossover (just a capacitor). This is an appropriate capacitor for that purpose: https://www.parts-express.com/dayton...citor--027-419

      If the highs are too prominent, you can add an L-pad on the tweeter. https://www.parts-express.com/speake...8-ohm--260-250 The L-Pad on the tweeter doesn't have to have the same power rating as the amplifier, because about 90% or more of the power goes to the woofer.

      You could use that tweeter with a lower crossover frequency, but then you should go to a 2nd or 3rd order filter, or add a series notch filter to subdue the resonance--all of this costs more (sometimes significantly) so I'd just stick to the capacitor.

      I would first try the design without any crossover on the 6x9 speakers and see how they work. Adding acoustic dampening material is probably a good idea--it makes the box volume act larger. You can use household fiberglass insulation (remove the backing paper if it has any), but it's a pain to work with. You can also use dacron polyester batting (the kind used to stuff pillows or teddy bears) which is nicer to work with, since fiberglass breaks off and is hard to remove from clothes and skin.

      Note that the speaker enclosure needs to have air tight joints--builders often use silicone caulking on the inside along the wall panel joints to do this.

      Comment


      • Eric Mack
        Eric Mack commented
        Editing a comment
        I wrote to Walker and asked about a TP3. A very helpful person responded within 3 hours -- on a Sunday. I will attach to the bottom of this thread. Great company.

    • #6
      Thank you toodles and jbird604. A few thoughts/questions in response to your comments.I will post each as a separate comment to keep threads easier to read, no and in the future.
      Eric Mack
      www.ThisOld340.com
      Rodgers 340 S/N 34341
      Los Angeles, CA

      Comment


      • #7
        #1. Do we really need to keep low frequencies from the 6x9 drivers?
        The Rodgers 340 analog organs, like the 340, already route all low frequencies to a dedicated pedal amplifier channel which has its own speaker (as we are discussing in another thread). For that reason, I'm not sure I would need to have a crossover to keep low frequencies from the 6x9 speakers. As it is, the M10 speakers (which are just a bunch of 6x9) are connected directly. The only crossover in the M10 is when it also has the JBL 075 Bullet Tweeter. So, that is my understanding. Does it make sense, then that I would not need a crossover to keep low frequencies out of the 6x9?
        Eric Mack
        www.ThisOld340.com
        Rodgers 340 S/N 34341
        Los Angeles, CA

        Comment


        • #8
          #2. Would there be any value in reusing the tweeters from Allen HC12 for the new Walker T3 Style cabinet builds? (or to replace a JBL 075?)

          toodles, before I order the parts you mention, I wonder if you or jbird604 think the HC12 Tweeters would be of use.

          A few years ago, I was given the crossovers and tweeters from four Allen HC-12F speakers. They are in excellent condition. I understand I cannot reuse the crossovers because they are unique to the Allen design; however, I wonder if you think the tweeters from the HC-12 would be an improvement to install in the either
          • The new "Walker T3 Style" cabinet that I will build using 6x9 drivers from the M13
          • My existing M10 speakers in place of the JBL 075 Bullet Tweeter
          Eric Mack
          www.ThisOld340.com
          Rodgers 340 S/N 34341
          Los Angeles, CA

          Comment


          • #9
            The tweeters from an HC-12 would be OK to use, but Allen used several different tweeters over the years. I think Allen crossed these over at about 5 or 6 kHz, so that frequency will be safe. They used a 12 dB per octave crossover.

            As to keeping bass out of the 6x9's--I suggest trying the cabinets without incorporating that. If you get distortion on low notes, you'll know you need to add that filter. For a 16 Ohm load (2x8 Ohms in series) use 165 microFarads, for 8 Ohms (2x4 Ohms in series) use 330 mF, and for 4 Ohms (2x8 in parallel) use 660 mF. You'll need to use non-polarized electrolytic capacitors. Those values will filter out frequencies below 60 Hz.

            I recommend trying it without the caps first because the caps will be relatively expensive.

            Comment


            • Eric Mack
              Eric Mack commented
              Editing a comment
              Thanks for sharing the values and type. I was confused, because an earlier Parts Express link you gave me was for a polypropylene capacitors, vs non-polarized electrolytic capacitors. Is there a difference in performance?

              When you order your crossover caps, what minimum voltage value do you normally specify?

          • #10
            Thank you toodles, jbird604, for your helpful responses and component suggestions. I have been rereading this thread to think about and research the concepts or products I was unfamiliar with.

            In comment #2 and #3 above, you both spoke highly about the Walker TP3. (When it stops raining and I get the time in the shop I planning to assemble one to test.) Meanwhile, I'm curious to understand what, apart from physical size, would be the difference between these options:
            1. Enclosing the back of my existing M10 speaker with 3/4" plywood, center braces and caulked airtight. (This M10 has six 6x9 drivers and no tweeter.)
            OR
            1. Building 3 Walker TP3 style enclosed cabinets using a two of the 6x9 drivers removed from my open back M10 .

            Note: In both options above, I would install a new Phenolic Ring Tweeter and appropriate crossover.

            Forgive my ignorance about speaker design, but I am curious to understand, when looking the above two options, where the greatest improvement comes from. Obviously the TP3 is smaller and with three I could spread them around, but let's say for this illustration, they are side by side. Would they still be better than an enclosed M10? If so, please help me understand why. Is it the volume of the TP3 box, the new tweeter, or other magical properties I do not yet understand?


            Eric Mack
            www.ThisOld340.com
            Rodgers 340 S/N 34341
            Los Angeles, CA

            Comment


            • #11
              Any speaker driver radiates in 360 degrees as long as the wavelength of the frequency being produced is longer than the diameter of the driver--yes, a driver will radiate behind itself (even in an enclosure), though there is a "sound shadow", so to speak, directly behind the driver where the volume is reduced--think of a wave arriving at a beach, splashing over and around a small rock, and then the wave recedes--there's no lack of water directly behind the rock or in front of it. Sound waves work similarly.

              Since the speed of sound at room temperature is about 1125 ft per second, a frequency of 1125 Hz has a wavelength of about 1 ft; thus, a 12 inch diameter woofer will radiate to about 1 kHz in all directions; a 6 inch wide driver will go to about 2250 Hz. The TP3's narrow footprint (with the 9 inch dimension oriented vertically) gives a good, even radiation pattern to, approximately, 2 kHz. This orientation limits the vertical radiation pattern, which helps eliminate floor and ceiling reflections--often a good thing.

              The horizontal radiation is useful to ensure even response throughout the listening area.

              The M10's design makes the radiation area wider, and thus limits the horizontal and vertical dispersion--so it's easier to get hot spots of sound with it for the part of the range covered by the 6x9's--the tweeter design, though has a different radiation pattern because of the multiple tweeters and the crossovers that Rodger used.

              It will be harder to get an M10 design to sound good compared to the TP3 design.

              You can try enclosing the back of an M10, but I can't vouch for the results. The M10 works OK in a church probably because the distance from sound source to the listener permits a smaller radiation angle to still reach the listeners with relatively even intensity.

              Comment


              • Eric Mack
                Eric Mack commented
                Editing a comment
                I may have to read this a few times over the next few days before I get it. What I do get is there is a and rational difference between the designs, so thank you for taking the time to help me understand. As I said, I may have to reread this thread a few times to get it. Again, thanks.

                You seem to have a tremendous amount of experience, not only with electronics and Rodgers/Allen organs but also with the physics behind sound and sound reproduction. If you care to share, I'm curious to know your professional background. If you prefer not to share, that's OK, too. Either way, thanks for sharing what you know with those of us to are getting started. - Eric

            • #12
              That's a good question! It just seems that Walker's speakers are extra nice, all models. Somehow they turn out to be "more than the sum of their parts" so to speak.

              BTW, an M10 without the tweeters is properly called an M6. Same 6x9 drivers, just no tweeters and no crossover. They were sold as supplementary cabinets to provide a bit of volume boost to the channels without adding any more highs. An M6 is a perfect candidate for adding on a good tweeter, if you just want to experiment. It might well sound very good, though the shallowness of the box is definitely a drawback to the design.

              In part, the TP3 is a better unit because the tweeter is much nicer. The Rodgers M10 uses four of those plastic piezo horns coupled to the amp through a somewhat complicated circuit that serves as an attenuator and to "tune" the sound using some variable inductors. As noble as their efforts were, they just sound a lot more "wild" than a system built with audiophile quality tweeters like the Walker cabinets.

              Beyond the better tweeters, the Walker enclosure is a more optimum size for the two 6x9 drivers, filled with damping material, and sealed. All those factors make it possible for the unit to have a smoother and more extended response. Of course Rodgers sends the lower frequencies into the bass channel, so the M10's can be pretty shy in the low end and it may not matter. And they are extremely efficient, which is in their favor. But they are simply not as smooth-sounding as Walker speakers.

              There may also be a good crossover in the TP3, though none of us seems to have that info at hand. I do remember than the large Walker unit that I dismantled a few years back had a very elaborate crossover with both coils and capacitors involved with each driver. A carefully-engineered crossover, specially tweaked for the specific drivers in a system, can certainly do a lot toward smoothing out the peaks and dips in response, controlling resonances, and so on. So that may be part of it, and will be hard for you to fully emulate.

              But I suspect that just enclosing two 6x9's in a good solid box with some stuffing and a good tweeter, even with nothing but a rudimentary crossover, will sound better than the M10 ever could, no matter what you did to it. The box is too shallow for that many drivers, and will surely limit the output below a certain frequency if you put a back on it, though it's already shy down there due to the interaction between front and rear of the cones.
              John
              ----------
              *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

              https://www.facebook.com/pages/Birds...97551893588434

              Comment


              • #13
                Polypropylene (as well as mylar and polyester) capacitors are much better than non-polarized electrolytic capacitors. But for large values they get very expensive. Thus, polypropylene capacitors are usually reserved for tweeter applications.

                Usually get at least 100V rated capacitors.

                Comment


                • #14
                  I wrote to Walker this afternoon to inquire about the TP3. Within a few hours (on a Sunday!) I got a response and a brochure. How's that for service! See attached. TP3.pdf
                  Eric Mack
                  www.ThisOld340.com
                  Rodgers 340 S/N 34341
                  Los Angeles, CA

                  Comment


                  • #15
                    I wonder why Walker used 6x9 instead of round speakers? Perhaps it was to have a narrower cabinet? With there be any other difference between a 6 x 9 versus a round speaker of similar size?
                    Eric Mack
                    www.ThisOld340.com
                    Rodgers 340 S/N 34341
                    Los Angeles, CA

                    Comment

                    Working...
                    X