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Helium - a true micromonitor

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  • Doom, check out post #273 for construction photos. I started with the .04 cu ft enclosure from parts express.
    Denovo Audio Knock-Down MDF 0.04 cu. ft. Micro Bookshelf Speaker Cabinet PairWhen it comes to designing desktop computer speakers, surround sound speakers, and micro bookshelf speakers, the hard work has been done for you. With this 0.04 cubic foot speaker cabinet pair, you get CNC-precision cut cabinets without having to own or operate a CNC!During the manufacturing process, dadoes are cut into the top, bottom, and rear of the side panels to ensure a tight, secure fit, maximizing the gluing surface and making assembly that much easier. The front baffle features roundovers on the sides for a professional look while minimizing diffraction, and the entire cabinet is made of MDF for an acoustically inert effect on speakers.The end result is a speaker cabinet that assembles in no time flat—all you need are wood clamps, wood glue, and about five minutes; no screws needed.Note: Panel dimensions and a 3D SketchUp model are included in the Manuals/Resources section. To open and use the 3D model, you need to download and install a program to unzip the file (7-Zip is free and recommended) and then download and install SketchUp to open the .skp file.Specifications: • Panel thickness: 1/2" • Panel material: Medium Density Fiberboard (MDF) • Finished cabinet volume: 0.04 cubic feet (70 cubic inches) • External dimensions: 6.5" H x 4.5" W x 5" D • Internal dimensions: 5.5" H x 3.5" W x 4." D • Made in the U.S.A.

    Then I swapped the mdf baffle For the walnut baffle. That's an abbreviated version.
    Like my Dad always says, "I know enough to be dangerous!"


    • Originally posted by jwjarch View Post
      Thanks doom. This was my first real speaker project. But I have years and years of woodworking experience.
      Very nice. The woodworkers have all the fun


      • I heard some chuffing tonight while listening to Muse -Madness on vinyl with the volume knob a little past 12 o'clock. Definitely a test for these little guys. I think my port design could use a little improvement but the baffles are glued on for good. Oh well! A thin sock stuffed in each port and problem solved! I actually think it improves the dynamics of the mids on some tracks. And I don't need that much bass in our bedroom anyway. Love listening to these. They get better and better.
        Like my Dad always says, "I know enough to be dangerous!"


        • Hi Just started my own build of theses speakers. First speaker build ever, something I have wanted to do for a while. I bought the PE 1” port tube so I could just use the nice flange which I have glued to a 3/4” ID pipe. The speaker and port will all be mounted on the baffle face. Do I estimate the port length as the distance from the baffle along the pipe centre line and make it 6.5-7” long. I think this is correct but just double checking. If anyone knows the correct port volume it might be easier to to size it correctly using water. The terminal cups I bought are almost half the size of the back panel. I don’t think they will look too good. I found a 3” round version on eBay but the 55mm push fit ones on PE look like a good solumtions (but too expensive to get shipped over by themselves). What have other people used? Is 24 AWG light duty speaker wire sufficient for internal wiring? It has 0.026 ohms /ft resistance. For a 5ft run of twin core that would be 0.26 ohms. I read that the rule of thumb is to use cable with resistance that has less than 10% of the speaker nominal impedance (4ohms). So this should be OK. But then again I just found some 18AWG in the scraps bin. Cheers.
          Originally posted by scottsehlin View Post
          Re: Helium - a true micromonitor The port is 3/4" pvc. There are two straight sections and an elbow (which barely fits in the box). I'll check the length of the straight sections tonight, but the tuning frequency should be between 65 and 70 Hz. Total length is about 6.5"-7". The project can be built as posted, but lately, I've been listening with an added 40 ohm resistor across the terminals of the tweeter, which knocks down the highs by about a dB and like that a little better. Dayton has a 39 ohm 5 watt Xicon resistor that would be a good choice for that addition.
          Last edited by Dunk_c; 02-10-2018, 08:20 PM.


          • Actually, I think I might do away with bulky terminal binding plates and directly connect the speaker cable through the back panel. Length will only be about 4-5 ft. Can always be changed later if ever needed. Can anyone see any problem with these crossover assemblies? I will mount them with glue to the inside. The heavier inductor on the floor, the other at right angles on the wall (assuming it will all squeeze in). I will make the wiring connection using the same wire. The franken-ports came out like this. Could have been better but I probably won’t notice after a while if they sound good. I chose to glue the baffle on and screw the rear. Started painting them in satin enamel with a sponge roller to try and get a little texture. Will post picture when completed.
            Last edited by Dunk_c; 02-10-2018, 06:07 PM.


            • Not sure exactly WHAT I'm lookin' at w/that port end/flair? there, but if that's an open "groove" (between a large outer flair, and a separate, smaller inner flair - somehow) I'd be tempted to redo something there, or fill that entire groove in w/bondo or similar. That looks like a chuffer to me (as it stands).


              • OK I have removed the inner lip and repainted it. I can see what you mean. There would have been some turbulence when it was drawing air in. Sloppy work. Thanks.
                Last edited by Dunk_c; 02-11-2018, 03:31 AM.


                • I'm not sure if it's proper etiquette to post derivatives in their own thread or in the "parent" thread. I had an itch to design a crossover and I really liked the layout and size of these, so I designed and built a derivative with the AMT Mini-8 tweeter, I realized after the fact that this is really close to the Bantam as well. Doing my own xo wasn't a judgement on the merits of the original helium at all, but it was an inspiration.

                  To start with, this is my first attempt at a crossover, I've built other boxes and have ample electronics and fabrication experience, but had never done a crossover. I did it based on simulated measurements, as in a tutorial posted by wogg and as outlined by Paul C. on his website. These include 6db of BSC. I have not made actual measurements yet, but I intend to before I glue the baffle on for good, it's clamped on with foam gasket tape now.

                  I've been listening to them for a couple of weeks and have been playing with DSP tweaks occasionally to see if I like any changes, but I keep coming back to no changes. They're paired up with an almost-voxel sub, slightly larger volume, longer port, and 25w plate amp. Currently being run off my PC as an htpc, with equalizer APO acting as the XO for the sub and mains. I don't have the breadth of experience with high quality audio that many of you, but I'm extremely pleased with how these sound, they've pretty effectively reduced my miccas to being speaker stands.

                  Edit: Realized I made a mistake in the XO design, it's quite hot in the 3khz range. I would suggest ignoring me for now, if anyone was interested in building this.
                  Last edited by copper280z; 02-22-2018, 12:25 AM.


                  • Job done. Running them with my TDA7297 diy amp. Got is at about 80% volume so might try bigger amp. Anyway, they sound great! Loud and plenty of base in my large room. Barracuda, Brothers In Arms, Singing Winds,Crying Beasts, Tubular Bells all sound great. Nothing more to say except to thank the s designer. Here is a build picture and finished speaker for anyone considering this worthwhile project.
                    Attached Files


                    • for the crossover on the Heliums, I don't understand such odd resistors are used for the tweeter L-pad.

                      14 in series, then 39 parallel.

                      That gives about 11.5 dB of reduction.

                      Couldn't you could achieve the same thing with 9 ohm series and 8 ohm parallel ?

                      Ok -- I think I can answer my own question:
                      when I play around with the XO in XSim, using -0.25 for the woofer position relative to the tweeter position, the original helium XO gives perfect phase tracking between woofer and tweeter. The 14 Ohm resistor in series is important to keep that phase. Then the 39 Ohm shunt resistor is the value needed to give the desired tweeter output
                      Last edited by ceiol; 02-16-2018, 08:54 AM.


                      • The resistors do more than just tweak the FR, they also manage the impedance. Smidge different in both resistors shapes both curves. Something tells me that the Fs is managed a bit by using the ~40 ohm in parallel with the tweeter, and this can reduce distortion.

                        "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
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                        • Anyone recently compile a parts list for the Helium? I've been going through build logs and trying to piece one together...


                          • Check out the first page of the thread. I have an updated parts list. It was long overdue. Thanks for bringing that to my attention, Matt.
                            Keep an open mind, but don't let your brain fall out.

                            Sehlin Sound Solutions


                            • Originally posted by scottsehlin View Post
                              Check out the first page of the thread. I have an updated parts list. It was long overdue. Thanks for bringing that to my attention, Matt.

                              Thanks Scott! Whoa--47 Ohm instead of 39? I'm calling it the new and improved BOM!


                              • Originally posted by scottsehlin View Post
                                Check out the first page of the thread. I have an updated parts list. It was long overdue. Thanks for bringing that to my attention, Matt.

                                Thanks, so you changed from the 40 Ohm to the 47 Ohm across the driver and are now using a 15 Ohm resistor instead of 14 Ohms?

                                I ask because I placed an order for the parts a couple of days ago and I went with 2 x Dayton Audio DNR-7.0 7 Ohm 10W Precision Audio Grade Resistor so I can wire them in series to get 14 Ohm and Dayton Audio DNR-40 40 Ohm 10W Precision Audio Grade Resistor across the drivers. Should I go and grab the updated design with the 15Ohm and 47Ohm resistors?

                                BTW I ended up getting the 10 Watt versions of the resistors and the 18AWG inductors, not sure if that matters or not. Hopefully I can fit it all in the cabinets.

                                Will post pictures when I get all the parts and assemble.