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  • #91
    I'm curious as to why you wanted to change the helium crossover since you are using those drivers. Learning exercise?

    The little peerless passive radiator has basically just the right mass for this driver/enclosure combination. Adding weight as you know wouldn't be easy as you'd have to glue it on somehow.

    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


    • #92
      Originally posted by tomzarbo View Post
      I'm curious as to why you wanted to change the helium crossover since you are using those drivers. Learning exercise?

      The little peerless passive radiator has basically just the right mass for this driver/enclosure combination. Adding weight as you know wouldn't be easy as you'd have to glue it on somehow.

      TomZ
      In hindsight, that's a great question about the crossover. Initially, I just wanted to reduce the parts count and do a simple first-order crossover to save cost and space, but a simple first-order design didn't really work nicely with the output-level of that tweeter. As I kept adding to it, it morphed into a second order design, and what I tested it with yesterday, I note that my final crossover is functionally very similar to the original Helium, and the added parts are not expensive, so there's really nothing to be saved by trying to alter the original crossover design. So in the end, I completely agree that using the Helium crossover is the smarter way to go. (I hadn't noticed that I ended up with essentially the same or at least a very similar crossover, until you mentioned it here.) I will say that nothing really beats the experience of tweaking it with your own ears (provided one has reasonably undamaged hearing to begin with!). I would have never imagined how much a 1uF change made such a difference in the tweeter output, for example.

      I had thought the Peerless passive radiator had a threaded hole in the back of its metal pole piece, but as I examine one, it appears that it's just an unthreaded hole after all. If for some reason the design needed added mass, I'd tap threads in that hole so I could add a bolt and washers as weights.

      Comment


      • #93
        Here are photos of the first completed assembly, although I'm actually waiting on parts to complete the crossover. I assembled this for photos:




        It's a good thing that passive radiator mounts externally, as the opening for it is the only way to install the main speaker mounting screws into the backside of the assembled front of the cabinet!


        I really like the look of the main speaker rear-mounted with a roundover on the hole opening on the cabinet.

        Comment


        • #94
          Those came out nice! Yeah, it's interesting how some combinations of drivers just lend themselves to a certain type of crossover and or crossover points.

          Since you've rear mounted the woofer (looks good!) You would likely have to tweak the values a bit anyway.

          That's sharp!
          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


          • #95
            Thanks. I've been really happy with the results I get from Rustoleum High Performance Enamel spray paints. I did my Overnight Sensations in their flat black intending to clear poly them, but liked the results so much I chose to leave them flat. For these speakers (Bantam-Heliums), I used the white gloss over Zinsser 1-2-3 spray primer also in white. LOTS of wet-sanding with either 600 or 1200 in between coats, and a bit of spot-putty to fill any minor gaps. The sad truth is that the more time you spend with wetsanding, the better finish you get, if you're going with a paint finish.

            I have two more Denovo 0.04 knockdown kits, and plan to make 2 more pair, in a different finish (probably black). I just wanted to build one and test it to see if I liked it before buying drivers for the other two pair. I think I'm going to like how these come out!

            Comment


            • Steve Lee
              Steve Lee commented
              Editing a comment
              Your paint job and finish work concerning your methods are quite impressive.

              You gave me some less expensive tips than getting into a compressed air method - thanks for posting that.

          • #96
            You gave me some less expensive tips than getting into a compressed air method - thanks for posting that.
            Thanks! It starts with good sanding to start with. The MDF of these Denovo cabinets is a wonderful material to work with. It behaved very well on the table router to round-over the main speaker openings, and I sanded all of the joints with a random-orbit sander using 100-grit to flatten the joints, and finished with 220 grit. They needed nothing more than a damp wipe to remove dust before spraying the assembled cabinets with the 1-2-3 primer. I wet-sand all of the primer coats, as it really exposes any gaps that need filling and knocks off any paint texturing. A couple wet sanded primer coats and some spot putty to fill any caps or pinholes, covered by more spray primer coats wet sanded out with 600 should give you a nice uniform and perfectly flat surface that actually looks really good on its own.

            Painting is more of the same, with light coats of the Rustoleum High Performance Enamel, wet sanding each coat, typically with 1200, but if the paint textures at all (especially first coats) I knock it back with 600 wet sanding. Somewhere around the 3rd to 4th coat, you get a nice smooth finish and you just know you're done. If you want, you can rub it out with automotive polishing compound and even wax them if you want, or you can apply a top clear coat, but for these speakers I'm really happy with just the top paint coat with no additional clear coating needed.

            I don't have any special facilities for any of this. I spray in a garage using a large cardboard box as a spray booth. The key for me is wet sanding every coat of primer and paint with a light touch to keep everything super-smooth.

            Comment


            • #97
              I finally completed this build today, after the capacitors for the crossover arrived. Here are the completed speakers:


              I copied that idea of building the crossover on the back of the passive radiator. Test fitting showed I could stack two layers, so I made pontoons out of the resistors and bridged them with the coil and the caps. The resistors are spaced to not interfere with the pole of the passive radiator if it should experience massive excursions. Here's the crossover on the passive radiator:



              I added a little polyfill stuffing inside the speakers, and my build has a T-nut mounted inside one side to facilitate mounting from the kitchen cabinets over my wife's desk. (I'll get a photo of the install when it's done.) Then I tested the little buggers. They're VERY impressive. I drove them with the Parts Express #320-699 class-D amplifier module powered by a very clean 18V power supply. As discussed previously, my crossover is nearly the same as the Helium crossover, and I would recommend using that if building these with the ND16FA-6 tweeters, as I did. These are the first speakers I've ever built with a passive radiator and it really does work. I'm very impressed with it. These speakers sound huge. I will say that I was able to exceed the speakers' capabilities driving them with more bass than they could handle. It took the right song with the right track to do it, and I'm not bashing these little speakers at all; there's only so much you can expect from very small drivers. Nick Campbell's bass at the beginning of this track made the speakers vibrate and flutter (it sounded like they were farting):
              https://www.youtube.com/watch?v=UwoT271WBD8
              It seemed to be a combination of both the ND91-4 and the passive radiator both vibrating and fluttering. I made sure the screws fastening them were good and tight, but I was definitely driving them beyond their limits. I compared the same track using my Overnight Sensations build, and they handled the track fine. To be clear, I was playing them loud intentionally to find their limits. Don't DJ a dance club party with these, but definitely play the hell out of them. Just don't expect to blow the windows out of your house with them. They can play loud; just know that there are limits to small drivers. These are the best speakers I've heard at this size and they're super useful for lots of applications. This pair that I built will make excellent computer speakers for my wife's desk in our kitchen. They'd be equally good in a bedroom or on a bookshelf. I have two more sets of the knock-down cabinets, and will be building two more sets for my kids' desks in their rooms.

              Comment


              • #98
                Hi Everybody!

                I would like to introduce my "desktop enhanced" version of the Bantams.

                Since I am lacking knowledge & experience with respect to electrical and acoustic-specific aspects of developing a speaker, my enhancements mainly relate to the built of the speaker case. Yet, as my listening experience was significantly improved, I hope it's worthwile showing these improvements here.

                Before I start, let me thank Tom for his support in my "improvement endeavors" - I surely tortured him with a lot of noob questions ...

                As to the background: I have built the "original" Bantams already (see as of post #79), but for a family member. So the Bantams I built are leaving me in the forseeable future (after Corona ...).

                When I listened to the Bantams for the first time it made "click" and I instantly knew: I have to built them for myself!

                (Even though I was actually happy with the desktop speakers I had built before, the Microspeak µ and Microspeaker S... but I was intrigued with the concept: passive radiator and AMT in such a compact format ...).

                To cut a long story short: To me they are the best sounding and overall most practical desktop speakers I have listened to so far (in my room in combination with a subwoofer).

                So I could have just built them - and be happy with them. But even though my DIY knowledge and experience is limited, I wondered if anything could be done "better" or more "practical", notably when building your own speaker case.

                After quite some research (due to my limited knowledge) and with the support from Tom and the DIY community in a german hifi forum the following ideas were born:
                • slightly thicker/different material (plywood birch, 15 mm / 0.6 inch, instead of MDF in 0.5 inch)
                • damping of inner case walls (with self-adhesive Damping 10) and of the top (as in the original but with convoluted foam)
                • inner bracing (with MDF 8 x 16 mm / 0,3 x 0,6 inch incl. "suspension" through mounting glue; regarding the "suspension" see this post from Donhighend regarding the "Little Yellow Cab" [in german])
                • enhancement of front baffle (21 mm / 0,8 inch, rounded edges, chamfers; regarding the chamfers see this post from Donhighend [in german])
                • increasement of weight (extension of case incl. quartz sand / crossover compartment; regarding the quarz sand see this post from trilos [in german])
                • optimized set up (tilted at the front through spikes so that the chassis face listening position; regarding the tilted position see this post from Donhighend regarding the "MI-6" [in german])
                • decoupling from desk (via gel mat stripes that are intended for DIY motorbike seats)
                • upgrade of capacitators (to Precision Audio Grade)
                To cut a long story short: I pretty much built it like this - and it was all worth it!

                I can not say which of those measrues contributed to which extent to the overall improvement. But there is a significant overall improvement in my hearing experience, notably with respect to the "immersiveness", dynamic and clearness, which is accompanied by a super dry bass - all the way down to the octaves reserved for the sub (the transition to the sub is just flawless). I know that any description of a hearing experience is inherently subjective (not to speak about the room influence ...). So I just repeat myself: In my ears and in my setting it is an outstand listening experience!

                Enough talking, here we go with the pictures (of which you can only integrate 5 per post, so I am going to split up the post) ...
                Last edited by Audio.Novize; 01-09-2021, 07:01 PM.

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                • #99

                  The first draft (with SketchUp) was based on the built of the Microspeaker µ, which incorporated an external crossover box. The modifications of the front baffle were based on simulations in VituixCAD (and after checking back with Tom):

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                  After checking back with the DIY community in the german forum I decided to increase the speaker case to a) add more weight, b) integrate the crossover into the case and c) create a compartement for both the crossover and quartz sand for additional weight and as absorbtion material against case resonances. So the design changed accordingly:

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                  The built started with the cutouts:

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                  Last edited by Audio.Novize; 01-09-2021, 05:41 PM. Reason: Updated pictures

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                  • I generously gave both the ND91-4 and the passive radiator room to "breathe". For that purpose I not only worked with a router but also a Dremel-like tool (not the prettiest work, but inside it's more about function than form ... ​​ )

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                    Last edited by Audio.Novize; 01-09-2021, 05:46 PM. Reason: Updated pictures

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                    • Speaker case glued, sanded and with rounded edges (incl. damping and inner bracing):

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                      Last edited by Audio.Novize; 01-09-2021, 05:50 PM. Reason: Updated pictures

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                      • Cutting the chamfers was a challenge, I have to admit. It was my first time and I guess I was a little bit too cautious and unexperienced with the dimensions. Thus, I only sawed off a little piece of the corner and had to sand quite a bit by hand. The result though pretty much turned out as hoped for (considering I did it the first time):

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                        Last edited by Audio.Novize; 01-09-2021, 05:55 PM. Reason: Updated pictures

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                        • As the speakers are integrated into an office environment (on black desks), the speakers were customized accordingly: color-wise, but also regarding the surface. I used black stain and resin, which creates a matte, deep black appearance that pretty much looks like a switched-off LED monitor with interesting gradiations due to the chamfers and rounded edges:

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                          Testing and Installing the crossover and finally filling up the "quartz sand" compartment, which increases the weight of the speaker by nearly one third (= approx. 720 g / 1.6 lbs; altogether per speaker approx. 2,8 kg / 6,2 lbs):

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                          Last edited by Audio.Novize; 01-09-2021, 06:02 PM. Reason: Updated pictures

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                          • The goldish-yellowish color of the AMT inspired me to add another little "color sparkle": I added gold plated inside angle bolts and yellow gel mats (which are acutally used for DIY motorbike seats). Sorry for the bad image quality, but at some point it was dark and priorities pretty quickly changed to: Now, I want to listen! ... ​​ ):


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                            (In this picture still with "Iso-Pads" and Basotec for the tilted stand)​​

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                            (In the final setup the Bantams only rest on 10 mm / 0,4 inch gel mat stripes in the front and back of the stands, which helped to reduce the vibrations of the desk to a minimum).

                            If anyone is interested to see the ND91-4 in action and slow motion: Here you go ...


                            P.S.
                            A lot more details can be found in the respective thread of the german hifi forum [but only in german ...]

                            P.P.S.
                            Originally posted by Bugsi View Post
                            Nick Campbell's bass at the beginning of this track made the speakers vibrate and flutter ...
                            Not in their enhanced speaker case ...
                            Last edited by Audio.Novize; 01-09-2021, 06:14 PM. Reason: Updated pictures

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                            • Originally posted by audio.novize View Post
                              p.p.s.
                              Not in their enhanced speaker case ...
                              nice!

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