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  • Portable Table Radio Build

    I’ve had this build on the back burner for a few months now due to supply chain issues. Now that the parts are in stock, it’s time to start building!

    The goal is a (yet another) relatively compact table radio with battery power and Bluetooth with an F3 ~55Hz. This is for a family member that doesn’t have a very good ear, so I’m not aiming for super high fidelity, but just something that sounds pleasing for rock and country and low volumes (~60dB @ 1m). Kind of like a DIY stereo Sonos One.

    The drivers I’ve chosen are:

    ND91-4
    ND16FA-6
    ND90-PR

    Outside dimensions are about 12.75”x6”x6.5” WHD. Separate enclosures for left and right channels, plus a separate enclosure for the batteries and amplifier that will have some air ventilation.

    I’ve also ordered measurement equipment so I can get the specs and responses of the actual mounted drivers.

    In WinISD I’ve modelled an F3 of 55Hz with 1.5L for each woofer and 17g added to the PRs, plus a sharp EQ and high pass. The intention is to roll off the EQ as the volume increases to protect the drivers.

    Some questions I have for folks here:
    1. For those who have listened to the ND91-4, how do they sound when they go past Xmax? I figure since their Xmech is so heavily advertised it must be somewhat usable. I’ve opted for tuning for more excursion on the woofer than the PR for this reason.
    2. Some sims in VituixCAD show a pretty strong directivity mismatch between the woofer and tweeter when the cross anywhere between 3.5K and 5K. Given its intended use, how much should I be worried about it?
    3. Since I have it on hand and I’d like the speaker to stay compact, I was thinking of using some 3/8” G1S plywood I have. I’m not sure about voids and how resonant it will be. Should I switch to laminating multiple layers of 1/4" or 1/8" MDF / hardboard? Or would the on-hand plywood be okay? I’d be open to trying a CLD approach if it's worthwhile.

    Power handling admittedly isn’t great - the woofer hits Xmax at 2.5W and 87dB. With 6.5W the PR hits Xmax and the woofer has 7mm peak excursion. My thinking is between the low listening levels, the adaptive EQ, and the generous Xmech that it should be okay. If it’s flawed thinking I’m all ears!

    Note the CAD model is missing the top and bottom panels to see the internal structure. I'm planning on making the bottom panel removable for servicing the components.

    Build updates to come as I chip away at this project.

  • #2
    You have to use 2 pr per driver

    Comment


    • #3
      Jonathan,
      that looks to be a pretty cool little project.
      I haven't used the ND90 PR, but I have used the ND91-4 in a few things and it's a little bugger of a beast. It doesn't sound too bad when driven past it's X-max. One of the projects I've made with the ND-91 is the Bantam speakers. They are my daily use speakers combined with a 8" powered sub. I BEAT on these things, they just almost have no limit for a small speakers. I crossed my project around 6,500 Hz (I know, really high!) to a AMT tweeter (that's why) and there really are not any issues with crossing high to my ears, and others who have heard it as well. I think you could cross higher than you normally would with a 5.5" woofer easily if it helps to avoid issues.

      It lists 4.6mm as a one-way Xmax figure, but it has 12.5mm one-way as it's Xmech figure, (as listed on it's PDF product page 290-224--dayton-audio-nd91-4-3.5-inch-aluminum-cone-full-range-driver-4-ohm-specifications.pdf (parts-express.com)) and it's possible to use pretty much all of that if you start cranking things up because of it's fairly clean output past Xmax (to my ears, graphs notwithstanding). If you high pass the low stuff out of the equation, you may be okay with that one ND90 PR, but figure on 8-10 mm of one-way excursion on the driver and see what excursion is on the PR then. You may be fine, but it still may be possible to over-drive the PR's if you get too crank-happy.

      I've used baltic birch and 1/2" MDF with no issues, but not plywood. I like multiple layers of HDF though. I'm working on a sub project with 4 layers of 1/8" HDF to make 1/2" thick 10" x 10" panels that are less resonant than regular 1/2" MDF.

      P.S. I've made a bunch of these little radio things in various varieties, and they all have some noise issue or gremlin that has to be worked out. My friendly suggestion would be to wire it up outside the box if possible and work the issues out there as buggering with things in a tiny space can be maddening! One more thing... having some 'wire connector plugs' like these can help to make life easy with this small stuff. The 'Zon' sells two and three conductor (and more probably) versions of various gauges to make hooking and unhooking stuff easy.

      Click image for larger version

Name:	Wire Connectors.JPG
Views:	133
Size:	17.1 KB
ID:	1478997

      I don't know what level of experience folks have with this stuff and I don't want to sound like I'm talking down to you at all, just wanted to offer some suggestions that may avoid pesky issues that can be frustrating. I've had a few of those.

      Please post pics as you go, I'd love to see what you come up with. The angles on the front alone give it a unique look. Looks like a pretty cool project!

      TomZ
      Last edited by tomzarbo; 11-19-2021, 06:41 AM.
      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


      • #4
        Scarface1 it looks like your Mini Daytons build is pretty similar to this one! I modelled a bunch of 3.5"-5" PRs and I found a pretty wild response difference depending on their specs. When I modelled two ND90-PRs per woofer the excursion load went to the PRs instead of the woofer at low frequencies, so I opted for one instead because of the Xmech on the ND91. One ND90-PR seemed to be the best balance, at least in modelling.

        Comment


        • #5
          tomzarbo thanks for the input! I don’t feel you’re talking me down at all, this is my second foray into speaker building and you’ve built many a speaker, especially table radios. Good to know the ND91-4 still sounds reasonable at high excursions. As mentioned, when I modelled two ND90-PRs there was less excursion on the woofer but more on the PRs, but we’ll see what actually happens when it’s put together. The more I think about it the more I’m inclined to go the multiple layers of 1/8” hardboard. And good tip about testing everything outside the box - I’ll give that a go when the parts arrive.

          Comment


          • #6
            Originally posted by JonathanPenner View Post
            Scarface1 it looks like your Mini Daytons build is pretty similar to this one! I modelled a bunch of 3.5"-5" PRs and I found a pretty wild response difference depending on their specs. When I modelled two ND90-PRs per woofer the excursion load went to the PRs instead of the woofer at low frequencies, so I opted for one instead because of the Xmech on the ND91. One ND90-PR seemed to be the best balance, at least in modelling.
            Maybe you can use the bottom erea of the backwall to ad to the nd91 chamber and use an nd105 passive or even an nd105 passive..

            It looks like a big build on paper but it is really small with those nd91, those are my favorite speakers because they have it all ( a lot of benefits) .. curious how the table radio going to be

            Comment


            • #7
              https://www.parts-express.com/Passiv...-Pair-300-7148

              https://techtalk.parts-express.com/f...ve-aggressives

              Comment


              • djg
                djg commented
                Editing a comment
                Easy button alternative. I built a pair before kit was available. A really excellent speaker. You'll never overdrive these with a small battery powered amp.

            • #8
              Originally posted by JonathanPenner View Post
              I’ve had this build on the back burner for a few months now due to supply chain issues. Now that the parts are in stock, it’s time to start building!

              The goal is a (yet another) relatively compact table radio with battery power and Bluetooth with an F3 ~55Hz. This is for a family member that doesn’t have a very good ear, so I’m not aiming for super high fidelity, but just something that sounds pleasing for rock and country and low volumes (~60dB @ 1m). Kind of like a DIY stereo Sonos One.

              The drivers I’ve chosen are:

              ND91-4
              ND16FA-6
              ND90-PR

              Outside dimensions are about 12.75”x6”x6.5” WHD. Separate enclosures for left and right channels, plus a separate enclosure for the batteries and amplifier that will have some air ventilation.

              I’ve also ordered measurement equipment so I can get the specs and responses of the actual mounted drivers.

              In WinISD I’ve modelled an F3 of 55Hz with 1.5L for each woofer and 17g added to the PRs, plus a sharp EQ and high pass. The intention is to roll off the EQ as the volume increases to protect the drivers.

              Some questions I have for folks here:
              1. For those who have listened to the ND91-4, how do they sound when they go past Xmax? I figure since their Xmech is so heavily advertised it must be somewhat usable. I’ve opted for tuning for more excursion on the woofer than the PR for this reason.
              2. Some sims in VituixCAD show a pretty strong directivity mismatch between the woofer and tweeter when the cross anywhere between 3.5K and 5K. Given its intended use, how much should I be worried about it?
              3. Since I have it on hand and I’d like the speaker to stay compact, I was thinking of using some 3/8” G1S plywood I have. I’m not sure about voids and how resonant it will be. Should I switch to laminating multiple layers of 1/4" or 1/8" MDF / hardboard? Or would the on-hand plywood be okay? I’d be open to trying a CLD approach if it's worthwhile.

              Power handling admittedly isn’t great - the woofer hits Xmax at 2.5W and 87dB. With 6.5W the PR hits Xmax and the woofer has 7mm peak excursion. My thinking is between the low listening levels, the adaptive EQ, and the generous Xmech that it should be okay. If it’s flawed thinking I’m all ears!

              Note the CAD model is missing the top and bottom panels to see the internal structure. I'm planning on making the bottom panel removable for servicing the components.

              Build updates to come as I chip away at this project.
              I used the nd90's (2 of them) with my phantom clone and they sounded great, I had it with a nd65-4 though.

              Comment


              • #9
                Thanks all! I'll give it a shot with the 1 PR per driver for now, but I'll keep in mind I might need to order a couple more. In WinISD if I shape the EQ to be more like the response of the Passive Aggressives I get much better power handling (~15W), so I'll try transitioning to that response as the volume increases. This weekend I'm hoping to actually make some progress on the build.

                Comment


                • #10
                  Slow progress was made. Prep work took longer than I thought. Since my last build I bought a house, had a baby, and bought an old table saw, so the little time I had this weekend was setting up a workbench in the garage and tuning up the saw. Next up is cutting and laminating the 1/8" hardboard.

                  Comment

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