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The Bantams Micro Speaker System

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  • #76
    The AMT Tweeter body is round...you can cut the hole for the tweeter any size you want, it all depends on the method you use. I used a Fostner bit that was close to the tweeter barrel size as the set I own didn't have one that was exactly the same size. On the first set I built, I used foam sealant to mount the tweeters. That proved to be difficult to mount, so for the next few sets, I made the hole slightly smaller and used a few wraps of electrical tape to make the fit tight. Ultimately, sealing the tweeter to the baffle with silicone really does a fine job of securing it, as well as sealing it, at least on the 6 Bantam-themed projects I've done so far.

    If you can make the tweeter opening basically the same size as the tweeter barrel, than that's less work you have to do. I just didn't have an exact match for it, so that's why I used the 'build up' method with foam and tape. On occasions where I've made an opening smaller and tried to sand a perfect circle uniformly to get a slightly larger opening, it usually seems to be difficult to pull this off and you end up going from "It doesn't fit yet" to "heck, well now it's a little loose" in one sanding step. Often a "Press-Fit" tweeter will be spec'd to mount in a 'standard' size opening and be designed with a slightly tapered barrel so it "snugs up" slightly as you press it in the cabinet. These, being stand-alone automotive tweeters are not built that way.

    Regarding sealing things up... yup, Wolf's got it, I was speaking of where the wire exits the plastic housing.

    Here's a pic of what I'm talking about...

    Click image for larger version

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    The tweeter being designed as an automotive type driver doesn't need to be sealed up if used in an automotive environment... it was never intended to be used in a speaker cabinet, just 'taped' to an A-pillar in a car. The pressures inside a speaker cabinet will likely act on the tweeter, causing unwanted vibrations of it's diaphragm of some type... that's why I sealed up where the wire leaves the plastic tweeter body.

    TomZ
    Zarbo Audio Projects Youtube Channel: https://www.youtube.com/channel/UCEZ...aFQSTl6NdOwgxQ * 320-641 Amp Review Youtube: https://youtu.be/ugjfcI5p6m0 *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
    *Part 2 *Gluing multiple curved laminations of HDF

    Comment


    • #77
      I like to template any hole I need to make. If I make a hole that is slightly oversize, I will put heatshrink on a flush-trim bit's bearing so that the copy is slightly smaller. Varying the number of layers of heatshrink can really zero in on the right hole diameter. I use scraps of 1/2" for this and then label the scrap piece to what the hole is for.

      I did this recently to make rear mounts for 1.25" PVC vents and it worked very well.

      Comment


      • #78
        Dukk,
        That is a nice trick. I went lazy, there was no way I was breaking out the circle jig when I had a fostner bit that was 'close enough'
        TomZ
        Zarbo Audio Projects Youtube Channel: https://www.youtube.com/channel/UCEZ...aFQSTl6NdOwgxQ * 320-641 Amp Review Youtube: https://youtu.be/ugjfcI5p6m0 *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
        *Part 2 *Gluing multiple curved laminations of HDF

        Comment


        • #79
          Hi TomZ,

          First of all: Thanks for your development and the time and efforts you put in documenting it!

          Since I'm located in Germany it seemed unreasonable to get the necessary parts directly from Parts Express due to pretty high shipping costs. Thus, I ordered from a company located in the Netherlands (Soundimports). Luckily, I found all parts as listed - except for one: Instead of the air coil from ERSE I got one from Mundorf, which has a 0.01 higher DCR, see here. Does that matter? (Sorry, if this a complete noob question ...)

          Unfortunately, I have to wait until the middle of August before the parts are delivered. But as they say: Anticipation is the greatest joy ...

          I'm super excited to see, I mean hear how the Bantams will perform against the Microspeaker µ from Quint, which I built not too long ago - both speakers have pretty much the same size ...

          Audio Novize

          Comment


          • #80
            That difference in DCR is negligible.
            Wolf
            "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
            "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
            "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
            "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

            *InDIYana event website*

            Photobucket pages:
            https://app.photobucket.com/u/wolf_teeth_speaker

            My blog/writeups/thoughts here at PE:
            http://techtalk.parts-express.com/blog.php?u=4102

            Comment


            • #81
              Great, thanks for the quick answer!

              Comment


              • #82
                Just a quick update: I finished building the Bantams & I am super happy: They are amazing!

                But what did I do wrong: Are the Bantams supposed to play as of 40 Hz? Seriously, there almost seems to be a glitch in the matrix: How can (passive) speakers of that size produce such a low bass at full volume?

                If someone is interested, I documented (and am still documenting) the build in a German forum - of course, it's in German, but I also included a fair amount of pictures: http://www.hifi-forum.de/viewthread-205-1138.html

                TomZ: Thank you again, what a great little speaker you have developed!

                Comment


                • djg
                  djg commented
                  Editing a comment
                  Well, the pictures aren't in German. Nice writeup (I assume) and pics.

              • #83
                For certain aspects regarding the build of the Bantams, I chose a slightly different approach. Maybe some of them are are helpful for others:

                The cutouts for the chassis I did with the help of a circle hole cutter (that attaches to a regular drilling machine):
                Circle Hole Cutter

                To prevent the screws from getting lose over time in MDF (or if installing the chassis multiple time) I glued little MPX pieces on the back of the front baffle:
                MPX pieces for screws

                For the sealment of the tweeter I didn't use glue or silicone, but instead a kneading mass (which allows easy removement of the chassis if necessary; it also allows for installing the tweeter after completely building/glueing the speaker case):
                Sealment Tweeter

                Instead of using a terminal - and since space is limited - I used press-in sockets:
                Press-in Sockets

                With respect to damping I chose 4mm of felt for the sides as well as the for the top and bottom of the speaker case. Also, I added one "sheet" of damping between the chassis and the cross over:
                Damping

                Comment


                • #84
                  Great job, they came out nice, the stone look is great for a small speaker like this. I'm glad you like them.

                  The flexible putty you used for the tweeter is a nice way to seal it up as well. These tiny speakers sure are interesting to get put together.

                  Just curious, did you see this design in the AudioXpress magazine or just online somewhere?

                  TomZ
                  Zarbo Audio Projects Youtube Channel: https://www.youtube.com/channel/UCEZ...aFQSTl6NdOwgxQ * 320-641 Amp Review Youtube: https://youtu.be/ugjfcI5p6m0 *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                  *Part 2 *Gluing multiple curved laminations of HDF

                  Comment


                  • #85
                    Thank you!

                    Regarding your question: I was actively looking online for small-sized speakers for my desk - and "somehow" I found the Bantams. And I am very happy I did!

                    Comment


                    • #86
                      I'm doing a kind of crossover between a Bantams and a Heliums build. I'm using the ND16FA-6 tweeter from the Heliums, the Peerless 830878 passive radiator from the Bantams, and the ND91-4 full range 3.5" speaker from both. I'm using a simpler crossover with just two capacitors, one inductor, and two resistors to keep things simple and keep costs down. I used slightly different construction for the cutouts that I wanted to share in case it benefits anyone else.

                      -I used a 3.5" hole-saw to cut the hole for the passive radiator. That left a little more "meat" around the sides of the back piece of the Denovo 0.04 cu. ft. cabinet. Now a 3.5" hole isn't quite big enough for the Peerless passive radiator, because its frame angles out at the four corners. What I did is swap in a 2" hole saw and took an extra 1/8" bite from the diagonal corner edges of the hole. (If holes had corners, which they don't. See the photos if this isn't clear.) That left a hole with eight "lobes" that actually fits much better around the passive radiator.

                      -I used a 3" hole saw to cut the full-range speaker cutout from the front panel, then rounded-over the edge with a 5/8" roundover bit on a table router. I will be back-mounting the full-range speaker rather than front-mounting. I centered the full-range hole 2.5" up from the bottom of the Denovo front cabinet panel.

                      -For the ND16FA-6 tweeter I bored a 1.25" hole using a Forstner bet. You must be careful using a Forstner on the Denovo cabinet material. I recommend drilling a small pilot hole, perhaps 1/8", then drill from the backside with the Forstner about 1/8" deep, then flip the material over and bore the hole through from the front. Otherwise, if you just drill from the front, a big chunk off the back will spall off around the edge of the hole. I centered the tweeter hole 1.25" down from the top of the Denovo front cabinet panel.

                      -I used 1/2" (rather than a 3/8") Forstner bit (again with a 1/8" pilot hole and again drilling a shallow depth from the backside before drilling through from the front) to drill the holes for the speaker jacks. I'm using the same speaker jacks as the Bantams guide. I used the exact drill location for the cabinet back as the Bantam dimensions, and when assembling the cabinet I see a tiny bit of the holes are blocked by the bottom cabinet piece. I will follow up with whether there are any clearance issues with getting the jacks installed.

                      Front and backs after drilling and roundover:


                      Closeup of the fronts:


                      Overhead shot of the fronts and backs that better shows the 8-lobe passive radiator cutouts:


                      Simpler crossover design:



                      [EDIT: As others point out, this design is not good. The 100uF cap for the tweeter does essentially nothing. In the end I used 3.3uF caps for both the tweeter and the main speaker, and as Tom pointed out, I really ought to have just stuck to the Heliums crossover, since I'm using the Helium driver combination. But for posterity's sake, here is the first attempt at a design I came up with, faulty though it is:]


                      I'll post updates as my build progresses.
                      Last edited by Bugsi; 12-17-2020, 03:08 PM.

                      Comment


                      • #87
                        Hmmm, a pair of "Bantiums" (Ban/tee/ums)

                        TomZ
                        Zarbo Audio Projects Youtube Channel: https://www.youtube.com/channel/UCEZ...aFQSTl6NdOwgxQ * 320-641 Amp Review Youtube: https://youtu.be/ugjfcI5p6m0 *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                        *Part 2 *Gluing multiple curved laminations of HDF

                        Comment


                        • Bugsi
                          Bugsi commented
                          Editing a comment
                          Maybe we should just call them "Byzantiums".

                          -There are no clearance issues with the holes for the speaker jack.

                          -There is a bit of an issue with figuring out how to attach the front and mount the full-range speaker from behind, and still being able to paint the cabinet. Amazingly, the 8-lobe passive radiator is *just* big enough to slip the full-range through to the inside, so I'm planning to pre-drill mounting holes, and I think I can get 1/4" sheet metal screws in to mount the full-range with a dab of glue on them, and do all that through the passive radiator opening. That way I can finish the cabinets without any speakers mounted. These speakers are for my wife's computer desk, and will be mounted horizontally on the underside of a white cabinet, so I'm planning on finishing them entirely in white. White cabinets are not a thing I'm really terribly fond of, but for this set of speakers it will be the right choice. I think I lucked out that there's *just* enough access to get screws in to mount the full-range though the passive radiator opening!

                      • #88
                        Byzantiums is taken, a build by Pete Schumacher.

                        I don't think a 100uF cap is going to protect your tweeter well. That is WAYYYY too large.

                        Later,
                        Wolf
                        "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                        "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                        "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                        "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                        *InDIYana event website*

                        Photobucket pages:
                        https://app.photobucket.com/u/wolf_teeth_speaker

                        My blog/writeups/thoughts here at PE:
                        http://techtalk.parts-express.com/blog.php?u=4102

                        Comment


                        • Bugsi
                          Bugsi commented
                          Editing a comment
                          Oh wow! You're right! I'll have to change the design.

                      • #89
                        What Wolf said.
                        What Wolf said.

                        100uF series cap will just about do nothing - as a high pass filter on that tweeter.

                        Comment


                        • Bugsi
                          Bugsi commented
                          Editing a comment
                          Thank you. I will have to re-engineer the design of the crossover. Good catch!

                      • #90
                        Okay, my build is nearing completion. I installed the drivers today and ran the wires out the holes for the speaker jack module, then installed the passive radiator, so I could test with real-world tweaking the crossover components. My oh my, that ND16A-6 is a bright little tweeter. After a bunch of modeling and actual testing, the only modifications to my crossover is to replace all of the capacitors with 3.3uF caps. That pushes the crossover point up to around 5K. There was an audible difference on the tweeter level between a 2.2 uF and 3.3uF capacitor. At 2.2 it was dull and at 3.3 it woke up. At 4.7 it was too bright. The passive radiator will wake up more when the holes where the speaker jacks go are covered by the speaker jacks, but it definitely works. I was wondering if anyone found any need to tune it by adding mass, or if it works best in this cabinet with the ND91-4 as-is without adding any mass. I'll get some photos up once the build is complete. They're finished in white, which is not my favorite finish, but this pair will be mounted below white kitchen cabinets, When this set is done I'll be building at least two more.

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