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Yet another Overnight Sensations build

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  • #16
    If you use a larger diameter port, you need to INCREASE the length to get the same tuning!
    Don't worry, if your parachute fails, you have the rest of your life to fix it.

    If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

    Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

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    • #17
      looks like your enclosure is tuned to about 68 Hz whereas the original Overnight Sensations are tuned to about 53 Hz

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      • #18
        Originally posted by thekorvers View Post
        If you use a larger diameter port, you need to INCREASE the length to get the same tuning!
        I apparently did not know this. I presumed if the air volume in the port was the same, it would have the same tuning, but that appears to not be the case.
        Looking this up now, increasing port diameter raises tuning frequency, while increasing port length lowers tuning frequency, with an equation that relates both of these and cabinet volume with tuning frequency.
        Discovering this now, I can't recommend others use the same port tubes I used for front-porting, which need to be around 8.6 inches long for the same tuning. Part 260-472 is a 1.125" diameter flared port with a 6" length that could be cut down to around 3.9 inches in length for similar tuning.
        I'm not sure what I'm going to do at this point, considering the cabinet is already cut for the 1.625" inside-diameter port.

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        • #19
          Congratulations on a very attractive pair of speakers and in devising a way to meet your fabrication and application constraints.
          I see three possible solutions, one of which should be acceptable. Build a small powered subwoofer, or just play them like you stole 'em. Play them as-is, I doubt you had any complaints until you decided they are flawed. Your kids will not likely notice the lack of lower limit bass; they are still very attractive speakers which meet your fabrication constraints. Just my 2 cents...
          Worst case, you can send them to me where they will have an honored place and frequent use.
          If life were fair, Elvis would still be alive today and all the impersonators would be dead.
          ~ Johnny Carson

          Bungelow Ed's Photo Album http://techtalk.parts-express.com/album.php?u=8594

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          • #20
            Originally posted by bungelow_ed View Post
            Worst case, you can send them to me where they will have an honored place and frequent use.
            Thanks very much for your kind words! I'm leaning towards just letting my kids use them as-is. I originally intended to build these for myself, for my computer desktop, but the practical need for a speaker system for my kids drove me to finally construct them. I expect I will buy another kit and build another set for myself, where I may use the 260-472 port tube for front porting, and see how that goes.

            One aspect of this build I'm most pleased with was the construction of the crossover. Making an eyelet board made for a very tidy board. If I ran the speaker wires and terminal cup wires directly to the eyelets, it would have been a very clean, jumper-less design. I hope other people will feel free to make use of it. That's why I posted a full-scale layout for it. I do like the wire-terminals that I used, as it made connecting and disconnecting things easy when I used wires that were too short for the midwoofer that didn't allow me to rotate it so that the tiny print on it was vertical. I was able to quickly disconnect the midwoofer and run longer wires.

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            • #21
              Lucky kids, and now you have an excuse, uh reason, to build another pair.
              If life were fair, Elvis would still be alive today and all the impersonators would be dead.
              ~ Johnny Carson

              Bungelow Ed's Photo Album http://techtalk.parts-express.com/album.php?u=8594

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              • #22
                Can you get the correct diameter, length, port and mount it inside the 1.625" port. A piece of 1.25" pvc would have the correct inside diameter, but the OD would be a little big.
                Do you have a way to turn it down about .035 per side. You could even sand it, would be a lot of sanding. I could do it if you want, I have some 1.25 laying around.

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                • #23
                  Originally posted by Dewmiester View Post
                  Can you get the correct diameter, length, port and mount it inside the 1.625" port. A piece of 1.25" pvc would have the correct inside diameter, but the OD would be a little big.
                  Do you have a way to turn it down about .035 per side. You could even sand it, would be a lot of sanding. I could do it if you want, I have some 1.25 laying around.
                  They actually sound fine for my kids' room purposes. But your idea spurred a thought of another alternative: Ports can have a non-constant cross-section. This makes it more complicated to calculate their tuning frequency, but the idea would be that in theory, one could turn a piece of 1.25" pvc to fit the inside diameter, and then turn the *inside* of the PCV so that it's cone-shaped at least at the end that meets up near the flared opening of the existing tube, then chokes down over a short length (maybe an inch or two) to a constant smaller diameter for the rest of its length inside the speaker box. That would probably work pretty well, but it's a crap-ton of work for a very minor amount of tuning. There's around one to one-and-a-half octaves of useful audio below the tuning frequency that my existing ports tune to, and it would probably just annoy my kids anyway.

                  My plan is to build another set for myself, also front-ported, but use the flared 1" diameter port tube, where a length of around 4-inches ought to be about spot-on. I just wonder if there will be audible chuffing noises from such a small diameter port.

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                  • #24
                    Word of caution, if I may, OS's work well with the port specified. Remember the KISS rule and ask yourself why you want to change Paul's design. Why mess with something that's not broken?
                    If life were fair, Elvis would still be alive today and all the impersonators would be dead.
                    ~ Johnny Carson

                    Bungelow Ed's Photo Album http://techtalk.parts-express.com/album.php?u=8594

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                    • #25
                      You might be able to retrofit. Marry a port of the correct size inside the existing port.

                      Or perhaps1 1/4" PVC may fit inside the existing port and provide nearly the exact inside diameter of the original port. Maybe set it back from the front - paint it - round over the front edge, etc. All a lot of handy work. And you'll likely need to fine sand down the outside diameter to fit in the existing port.

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