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  • Bamboozled

    I'd like to introduce my latest project. This is my most ambitious and expensive project to date. I had obtained several high end drivers on sale, and always wanted to build a dipole, and this is the result.

    Design:
    I always wanted to try and build a full dipole system, similar to what John K has done, but the cost of a fully active system and needing 4 large woofers (pair per side) had me at a disadvantage. After some research I decided to build a dipole system that utilized a monopole woofer, needing only a pair of woofers (1 per side) to make the desired SPL. I also decided to use a DSP plate amp, utilizing 1 channel for the mid and tweeter, and 1 channel for the bass range. A basic passive crossover is utilized between the midrange and tweeter, with response shaping applied by the DSP.

    Driver Selection:
    The woofers are Peerless XXLS 830847 10" subwoofer. These were chosen as I purchased the last few available at Solen, which were on a significant discount when the driver model was discontinued. They offer low distortion, relatively high sensitivity considering the xmax, and a healthy xmax and power handling.

    The midrange are Peerless HDS Exclusive 6.5" 830883. These were purchased from the swap meet forum at DIYAudio several years back. I had used them in a centre channel for a few years, which was later dismantled. They are a excellent driver and found a very nice home in this speaker.

    The tweeter is the Dayton AMTPRO-4. These were purchased from a forum member via the classifieds here. They are the model with a removable face plate, different that the faceplates currently sold. I originally had the thought to remove the face plate and mount the tweeter directly to the baffle, but eventually decided against it. These came with an ugly "veil" over the tweeter which was removed. These are a truly high end product, and are a fully dipole capable tweeter, the rear wave can be easily damped as well by adding felt (included with the tweeter).

    Baffle Detail:
    The baffle is a 1.5" thick bamboo counter top from Lowes. Originally I was going to use baltic birch plywood, but I liked the look of these boards more and the price was right so here we are. The baffle shape is optimized for dipole operation, and the shape was cut by CNC. I was fairly disappointed with these boards after cutting them, as there were significant gaps inside that needed to be filled. The gaps were filled with sawdust, then epoxied over top and sanded down. The round-overs were completed by hand.

    Finish is Circa 1850 Tung oil. As far as I know this is straight tung oil with only thinner added (no varnish). I really liked using it for another project, and I am not disappointed here either. 4 Coats were applied, with a rub down using super fine steel wool in between coats. What is left is the natural wood lustre with a nice sheen. Some scratches and dings are visible up close, but I am real happy with how these turned out.

    If I was doing this again, I would add a small brace in the middle of the port, as the bottom of the baffle does have some flex to it.

    The baffle is 14" wide by 42" tall, which puts the tweeter at face height when sitting down. The baffle will not be glued to the cabinet, it is held on by steel angle brackets (standard hardware store materials) and a foam gasket prevents air leaks. The brackets are screwed in from the inside of the cabinet, it is awkward but they are all accessible through the woofer hole to remove the baffle if needed, or reaching my arm through the back by removing the plate amp.

    Cabinet Detail:
    The cabinet is simple 3/4" MDF with 1/2" round-overs. The finish here is White Duratex, applied with a foam finishing roller. This created a very fine texture, much finer than when using the standard Duratex rollers. It was tougher than the normal application to get the roller marks to not show, but I settled after 4 coats. It looks great next to the natural Bamboo colour.

    The cabinet if I recall is 60 Litres, tuned to 30Hz.

    Crossover detail:
    The crossover is a hybrid design, utilizing both DSP and a passive crossover. I got this idea after looking at another project doing just the same, using a Seas Subwoofer and a Seas Excel coax (Seas KingRO4Y).

    A simple passive crossover is used between the midrange and tweeter, that provides the necessary transfer function to cross over as well as attenuation of the tweeter. The passive crossover does not apply any other response shaping such as BSC or dealing with the rising response of the tweeter. This was tamed using the DSP as well as any other response shaping to suit the room and listener. The passive crossover is electrically a 2nd order on the midrange, a 3rd order on the tweeter, and a single 3 Ohm resistor in series with the tweeter provides attenuation. Crossover frequency is 1500Hz.

    The DSP crossover is used between the midrange and woofer drivers. This arrangement makes the best use of the available amplifier power, and the crossover here is 300Hz. The availability of the DSP allows any further system tweaking to by applied on the fly.

    The DSP amp is a Hypex AS2.100D purchased from another forum member in the classifieds here.


    Completion
    So far I am absolutely amazed with the sound. The clariy through the entire midrange up to the trebel is astounding, and I felt the impact of the bass was very nice, it should need only small adjustments with the EQ. There is something special about the dipole arrangement I think, the stereo separation and spaciousness is like no other speaker I've built.

    Photo album is available on Google Photos below. There is a description available in most photos, just press the little "i" button.

    https://goo.gl/photos/ACvpPpDDFTTUMypM9
    Last edited by dcibel; 04-25-2017, 05:10 PM.
    Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

  • #2
    Wow that countertop turned out FANTASTIC!!

    Excellent job and nice looking drivers! Look forward to seeing completed pics!

    Comment


    • #3
      Thank you Scott! I agree, this one is turning out very nice, but just the same I have put a lot of work into it. I don't think I'll use the countertop again due to the PITA that was all the gaps in the core, however it was a good experience and I really like how it turned out.

      I can't wait to finish it. The last coat of Tung Oil just went on. I may consider buffing it with some wax as well in the future. Hopefully this weekend I can assemble everything and listen to both speakers as a completed pair.

      Just a few more notes that I don't think I explained above:
      The baffle will not be glued to the cabinet, it is held on by steel angle brackets (standard hardware store materials) and a foam gasket prevents air leaks. The brackets are screwed in from the inside of the cabinet, it is awkward but they are all accessible through the woofer hole to remove the baffle if needed, or reaching my arm through the back by removing the plate amp.

      The other note I want to make is that the AMTPRO-4 is an amazing tweeter, with extraordinarily low distortion right down to 1kHz. It does however have quite limited vertical response (albeit wide horizontal dispersion) so it best used only if you can have the tweeter at face height, or in a large room where the vertical dispersion is less of an issue. The benefit of this is that there are no reflections from floor or ceiling in the trebel. This was verified in my acoustic measurements as well, you can get a pretty good measurement of the tweeter response ungated. For this speaker, I have designed the baffle so that the tweeter is roughly at face height, and have been nothing but impressed with the sound from it.
      Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

      Comment


      • #4
        very nice design and execution, dude.

        I have always wanted to use those HDS drivers, they just look SO classy.
        I was most interested in:
        re: "The clariy through the entire midrange up to the trebel was astounding"

        That's what I'm looking for, and haven't found yet.
        Since you used those 830883 mids in a CC previously, can you comment how much of the clarity is
        the driver vs the drive used open baffle?



        I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
        "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

        High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
        SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
        My Voxel min sub Yet-another-Voxel-build

        Tangband W6-sub

        Comment


        • #5
          I've used both the 830883 and 830884. My centre channel design used the 830883 with the Fostex FF85K which I couldn't get to sound right, so it was eventually thrown out.

          This is my first dipole/OB experience, so I don't think I can really make a fair comparison and justify the difference in sound based on it being an OB. There is just too many differences between my designs using the 830883. If I had to say for certain, I would nail down the clarity to the AMTPRO-4, taking over a crossover frequency of 1500Hz the upper midrange and lower treble benefits the most in the perceived midrange sound.

          I wouldn't hesitate to use the 830883, it is truly an excellent driver. But for the utmost midrange clarity, look for low distortion and smooth power response from 800Hz through to 5kHz. Before this speaker, the nicest midrange performance I found was from the use of a DE250 in SEOS12 waveguide, crossed to a 12" woofer. The constant directivity through the midrange makes a real difference IMO.

          I don't know how this speaker really stands up as far as power response / directivity goes, but I have tried to incorporate as much knowledge as possible that I gained from reading the tech info on John K's site. I'll try to take some more detailed measurements once I have completed the build.
          Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

          Comment


          • #6
            Just as a spoiler, somewhere down the road I will be designing a seconds pair of these, using the Morel SCM634 midrange instead for a "Bamboozled Supreme". These will be for a friend of mine who has the same tweeters and woofers, and even baffles cut too. But I've no idea when this build will take place, as he has a newborn and is looking at purchasing a new house as well.
            Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

            Comment


            • #7
              Yes, great looking project, thanks for the details concerning the AMTPRO4, I have a pair but as of yet, have not found the best use for them.

              Comment


              • #8
                Nice project. Good design choices IMO. Could you see the dipole peaks in the raw measurements?
                John H

                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
                  Nice project. Good design choices IMO. Could you see the dipole peaks in the raw measurements?
                  Thanks!

                  The raw measurement are included in the album, the two images from SoundEasy. The tweeter dipole peak was quite pronounced at 1kHz, and I found that I could flatten it out by adding the included felt pads to the back side of the tweeter. I designed my crossover without the felt, and will experiment a bit with rear wave damping and EQ to see what arrangement sounds best to me. The dipole peak for the midrange was less proud, making the midrange response fairly easy to work out.

                  Here's direct links.
                  Tweeter raw dipole response:
                  https://goo.gl/photos/rKAEeCPreov5dNZN9

                  Midrange raw dipole response:
                  https://goo.gl/photos/K3f1whGkgQAaZmBEA
                  Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

                  Comment


                  • #10
                    Thanks, looks good. In your future measurements I would be interested to see how the tweeter performs off axis.
                    John H

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

                    Comment


                    • #11
                      Originally posted by jhollander View Post
                      Thanks, looks good. In your future measurements I would be interested to see how the tweeter performs off axis.
                      Sure, I'll see what I can do. I can tell you without measurements that the verticle axis is a lazer beam on the high end (I assume you are wanting the vertical axis), but it is very wide horizontally, wider than the AMT3-4. I am actually interested to take some measurements to see the horizontal directivity of the AMTPRO paired with the midrange response.

                      I know that you added a small tweeter to use with the AMT3-4, so you can be certain that since this is a larger driver, the verticle axis is even worse than the AMT3-4. I was actually quite surprised when I received the AMTPRO to see how big it really is.

                      No photos, but the last coat of Tung Oil went real well. Nice sheen, and it doesn't seem to matter how closely I go over the boards before finishing, there is still a spot or two that didn't get sanded well enough. Oh well, that just makes it more apparent that this was made by hand. I am an amateur woodworker, so I am happy if it looks even remotely presentable.

                      I'll have some photos of the assembled finished product this weekend hopefully.
                      Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

                      Comment


                      • #12
                        Actually I was more curious to see where the first null ends up. Rear response, baffle, and the driver's directivity don't always sum like you would expect .
                        John H

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

                        Comment


                        • #13
                          Very interesting! Nice router work. Next time I'm in S-toon I'll have to look you up.
                          David

                          Comment


                          • #14
                            Impressive.

                            Comment


                            • #15
                              Thanks for the kind remarks guys!

                              It was a busy weekend but I did manage to get these both assembled and functional. No photos yet as I spent my time breaking in my ears on them ;). I'll have to lug them upstairs to take some photos that aren't in the dungeon, and then lug them back downstairs to take some more measurements and tweak the DSP settings.

                              So far they look and sound real good. Excellent vocal representation, bass had a good blend albeit a bit light, but I did have them far from the back wall so I'm not sure that the low end needs and adjustment apart from some EQ in their final location.

                              I do wish the Hypex DSP plate amp had a cable connection from one amp to the other so I could load DSP settings in both channels with a USB connection to the master amp. As it is I have to load the DSP settings in once side, then move my cable to the other side and do it again. I do like that the Hypex plates will play audio over USB which isn't a feature available in every DSP, and that it has a sub channel so somewhere down the road I can upgrade to a fully active 3 channel DSP system by simply adding a separate amp for the woofer.
                              Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

                              Comment

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