Cube Cubed - A Passive Radiator Build

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  • 123Toid
    Member
    • Mar 2017
    • 30

    Cube Cubed - A Passive Radiator Build

    I have always loved passive radiators, so I thought I would finally do a build log along with all the parts needed. Thanks to Parts Express, I am able to bring one of these Passive Radiator Builds to life. My goal was to make a small subwoofer that would still have high spl, for a smaller room all while keeping the cost of the major parts under $200. As I looked around, I haven't found many great subs in that price range, so I thought DIY work might give the best bang for the buck. Here's a list of all the parts chosen for this project along with links:



    Dayton Audio DCS205-4 8" Classic Subwoofer 4 Ohm
    2 - Dayton Audio SD215-PR 8" Passive Radiator
    Dayton Audio SA100 100W Subwoofer Plate Amplifier
    Harrison Labs FMOD Inline Crossover Pair 30 Hz High Pass RCA

    I didn't have a separate DSP, so I had to go with an FMOD for the High pass to protect the woofer from over excursion. I did test it, and it was an issue. ALthough, if you have a DSP you would not need the FMOD. The total cost with the FMod is $190.

    The Enclosure is a very small footprint sitting at a 14" cube with 3/4" MDF or a 13.5" cube using 1/2" MDF. So it is a great footprint for a smal room.

    Later I'll post the theoretical response before room gain via WinISD. I will say, I have been playing this and it blew me away. I was very pleased with the SPL this thing can put put out, especially for it's size.
    Check out my YouTube Channel on DIY Speakers
    Instagram
  • 123Toid
    Member
    • Mar 2017
    • 30

    #2
    Theoretical Frequency Response with no added mass in a 1 cubic foot cabinet.

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    Theoretical SPL using 100 watt amplifier (106DB)

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    Cone Excursion without a High Pass

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    Cone Excursion with 30hz High Pass

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    When I get it all assembled, I'll post the actual graphs via REW and my UMIK1.
    Last edited by theSven; 30 April 2023, 14:03 Sunday. Reason: Update image location
    Check out my YouTube Channel on DIY Speakers
    Instagram

    Comment

    • 123Toid
      Member
      • Mar 2017
      • 30

      #3
      Finished Pictures: I may repaint it. My wife likes it so much, she wants it in the living room. That means, it'll need to be white. Oh well..

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      Size and Cutouts:

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      Last edited by theSven; 30 April 2023, 14:08 Sunday. Reason: Update image location
      Check out my YouTube Channel on DIY Speakers
      Instagram

      Comment

      • JonMarsh
        Mad Max Moderator
        • Aug 2000
        • 15259

        #4
        Why did you use such a high tuning frequency? Is this your design, or one promoted elsewhere, such as by PE? Was the target just a music system, or HT use too?

        Now, there are always interactions between the primary driver Their/Small parameters, as well as the PR compliance and mass tuning, and you wouldn't be able to get a maximally flat response in that enclosure size with those drivers tuned just by adding mass to the PR's, but you're working with about 1 cu ft, or 28L, and a more extended response than an F3 of about 42 Hz might be desirable for an HT system, even for a music system.

        Did you consider any design alternatives? Please don't take this as criticism of what you've accomplished to date, but as an opportunity for design dialog. (if you're interested). Your budget requirements do impose some restrictions, and it's very good that you're using the inline high pass crossovers. Have you modeled the net system response with those crossovers inserted, too?

        Looking at the FMOD plots on the Harrison web site, I see no justification for claim of 12dB/octave slopes; it looks more like a 6dB/octave RC high pass, with significant impact above the nominal corner frequency.

        Have you measured the net system reponse with and without the FMOD? That would be interesting to see.

        An interesting idea would be to share concepts for a 1 cu. ft. sub, see what we might come up with at other price points in the same volume.

        Unfortunately the Dayton 8" PR, though very attractively priced, doesn't have the design data necessary to do a alignment adjustment on a design basis, as opposed to just a modify and measure basis. Take a look at the Scanspeak and Seas PR's to see what I mean.

        Thanks for your post- it's a good reminder that something useful can be built at a minimal cost. I do tend to look at the sweat equity carefully, though, and sometimes minimizing the hardware cost when you do need to put in a fair amount of sweat equity doesn't give you the best return for your efforts, as to the final results.
        the AudioWorx
        Natalie P
        M8ta
        Modula Neo DCC
        Modula MT XE
        Modula Xtreme
        Isiris
        Wavecor Ardent

        SMJ
        Minerva Monitor
        Calliope
        Ardent D

        In Development...
        Isiris Mk II updates- in final test stage!
        Obi-Wan
        Saint-Saƫns Symphonique/AKA SMJ-40
        Modula PWB
        Calliope CC Supreme
        Natalie P Ultra
        Natalie P Supreme
        Janus BP1 Sub


        Resistance is not futile, it is Volts divided by Amperes...
        Just ask Mr. Ohm....

        Comment

        • 123Toid
          Member
          • Mar 2017
          • 30

          #5
          I did design this sub to be a small subwoofer for a living room/office for a limited budget. I wanted a small footprint that could easily be placed, not take up any room and be pretty fool proof for anyone that wanted to get into speaker building. This is one of the reasons I chose a passive radiator build. It is a lot more forgiving versus a vented system. Secondly, I was asked by many to create a passive radiator system. It seems a lot of people are trying to design subwoofers around them, but do not understand the complexities of what it takes to design it. Although, you could get this sub to tune at a lower frequency, you then run into max SPL problems even while only pushing it with 100watts. Plus, you would then have to make the box 3 times larger with a 4 inch port that is approximately 16 1/3 inches long. That didn't seem to fit what I was trying to go for.

          Image not available

          As far as the tuning at 40hz, that is the sweet spot for this subwoofer. And honestly, I can't think of many 8" subwoofers that really tune much lower than that (Ultimax 8). My main focus on this build was to keep it under $200 in parts (amp and all) to make it a budget friendly subwoofer. Most subwoofers in this range, that are bought from a store have the typical port noise problems or are just bad in general. So i wanted to give someone who was interested in DIY an inexpensive option, they could easily build themselves. And I really think this would be a great budget option for most people. Heck I use it in my Living room connected to a custom soundbar I designed and it is a fantastic experience.

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          As far as the FMOD goes, it is a basic 2nd order PLLXO at 30hz that is encased in an RCA jack. I didn't take measurements without it. However, before I put it on, anywhere past half gain would cause me to hit the mechanical limits of the sub. Since I added it, I have not hit mechanical limits at all. So it does work. Is it a full 2nd order? I couldn't tell you for sure.

          I'll have to find my net data. I do have it, but the subwoofer really isn't broken in yet. I like the idea of seeing what other people can do in a 1cuft box.

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          P.S. I don't take it as criticism. You want to know why I designed it the way I did and what I was seeing and I appreciate that. There are so many subwoofers and amps out there, there are an unlimited number of designs out there.
          Last edited by theSven; 30 April 2023, 14:11 Sunday. Reason: Update image location
          Check out my YouTube Channel on DIY Speakers
          Instagram

          Comment

          • 123Toid
            Member
            • Mar 2017
            • 30

            #6
            I hven't messed with sub crawl. This is a real basic test. I had a suck out at 80hz and I am guessing that is due to the room.
            Check out my YouTube Channel on DIY Speakers
            Instagram

            Comment

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