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  • Dr Pepper Boombox

    Inspired by the Sprite, I set out to make a boombox with the 4 ohm version of the Aura NS-3, aka the Dayton ND90-4. The $5 sale on the ND16FA-6 made the choice of tweeters easy. They're crossed high (8k) just to add some sparkle.

    The box is the knock-down PE 0.23 cubic foot and it's powered by the Dayton KAB amp board. I used the 50w x 2 version, but now after reading the forum, I know better and I'll be using the 30w x 2 version next time due to the issue with the gain. Two of the 18650 3-battery packs are used to give a long playback time. Box is tuned to 55 Hz using the 1.125" x 6" PE ports -- big enough so there's no port noise even at max volume. Port tuning is intentionally boomy at 55 Hz in order to put the boom in boombox.

    Crossover pic is attached. Something simple. Good reverse null. Not perfect, but hey, I'm still learning. Box was veneered and then the baffle was painted gloss black. The three LEDs for the amp board are too bright so I'll have to go back and add some resistors to dim them.

    Sounds great and it was a fun build. What more can I ask for?

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  • #2
    let me know if you need any more detail... or if you have suggestions for improvement!

    I'm always willing to learn

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    • #3
      Looks great. I picked up a pair of those tweeters too and am trying to decide how best to use them. Seems like a good fit.

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      • #4
        Thinking outside the box.

        That looks like the tip of a fishing pole, and with the soda also sitting there it leaves me thinking outdoors and music .. what about a small ice chest instead of the mdf box?
        http://techtalk.parts-express.com/fo...khanspires-but
        http://techtalk.parts-express.com/fo...pico-neo-build
        http://techtalk.parts-express.com/fo...ensation-build

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        • #5
          That looks really great.
          I would love to see the inside details and how you wired up every thing.

          I have been wanting to build a portable boombox for using while doing the yard work, etc. and don't care to wear IEMs and isolate myself from the world.
          My ancient Soundesign boombox from the early 80's still works, but has to be plugged in nowadays and doesn't really sound good at all...

          Thanks, Andy.

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          • #6
            How is the load on the amp. It must be seeing a load lower than the rated minimum 4 ohm. Also, the filter is totally different compared to the 4 ohm filter of the sprite.

            Now, if I wanted to use the same filter as the Sprite for the ND90-8 (I already have the coils and resistors), and cross over to the AMT-8 tweeter at 9000Hz with a 1st order crossover, how / where would I add the 0.15mH coil on the ND90-8 with respect to the BSC filter.

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            • #7
              I don't understand why you think the amp is seeing a lower Z than 4 ohms? The OP also said it's his attempt on something like the Sprite, but not actually a Sprite.

              Later,
              Wolf
              "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
              "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
              "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
              "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

              *InDIYana event website*

              Photobucket pages:
              http://photobucket.com/Wolf-Speakers_and_more

              My blog/writeups/thoughts here at PE:
              http://techtalk.parts-express.com/blog.php?u=4102

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              • #8
                Originally posted by Wolf View Post
                I don't understand why you think the amp is seeing a lower Z than 4 ohms? The OP also said it's his attempt on something like the Sprite, but not actually a Sprite.

                Later,
                Wolf
                Just trying to understand the basics from reading here and in other forums and whatever links are given. These are newbie questions, not to be taken in any other way than a person trying to understand from people who have been there and done that:

                1. My basic understanding from the circuit above is that the two speakers (6 ohm and 4 ohm) are connected in parallel and should be offering a 2.4 ohm load. I would like to understand how the crossover components overcome / change this.

                2. The filter used is different to the Sprite 4 ohm filter. Again, I wanted to understand how this would change the sound signature.



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                • #9
                  Originally posted by bsl100 View Post

                  Just trying to understand the basics from reading here and in other forums and whatever links are given. These are newbie questions, not to be taken in any other way than a person trying to understand from people who have been there and done that:

                  1. My basic understanding from the circuit above is that the two speakers (6 ohm and 4 ohm) are connected in parallel and should be offering a 2.4 ohm load. I would like to understand how the crossover components overcome / change this.

                  2. The filter used is different to the Sprite 4 ohm filter. Again, I wanted to understand how this would change the sound signature.


                  I'm a novice too -- I've learned a lot, but still a way to go.


                  1. the impedance is not a fixed value -- a "4 Ohm" speaker is not 4 ohms at every frequency -- there is a graph that shows the impedance vs the freq,
                  an "8 Ohm" speaker like the ND90-8 is only 8 Ohms for a certain range -- from 150 Hz to about 1000 Hz. Near its resonant freq it is much higher impedance -- look at the graph here
                  https://www.parts-express.com/pedocs...on%20Sheet.pdf

                  so the overall impedance of my Dr Pepper build is around 4 Ohms for much of the range, but then actually much higher impedance for the rest.

                  2. You can't just substitute a 4 Ohm driver for an 8 Ohm driver in a crossover. You have to customize it for each. I used the XSim software and the individual FRD/ZMA files for the drivers and designed my own crossover

                  this sums it up better than I can:
                  https://sites.google.com/site/undefi...iverimpedances



                  Comment


                  • #10
                    I'll over-simplify things a little in order to (hopefully) explain the impedance questions a bit more.

                    Resistors are constant impedance across the entire frequency range. The impedances of inductors, capacitors, and even the drivers themselves vary with frequency. The impedance of inductors increase as the frequency rises, while the impedance of capactors increases as the frequency drops.

                    The impedance varying characteristics of those passive components (inductors and capacitors) are used to direct the various frequencies to the desired driver(s). The low pass crossover in front of a woofer has a very low impedance at low frequencies and a high impedance at high frequencies, thereby directing only lower frequencies to the woofer. In a similar manner a high pass crossover in front of a tweeter has a high impedance at low frequencies and a very low impedance at high frequencies, directing higher frequencies to the tweeter.

                    When you combine the woofer, tweeter, and crossovers (as they are in parallel) the total impedance can still be not much lower than the drivers themselves. This is because the woofer and crossover looks like say, 4 ohms at 100Hz, but perhaps 250 ohms at 5kHz. Likewise the tweeter and crossover looks like perhaps 200 ohms at 100 Hz, but only 6 ohms at 5kHz. So when in parallel, the total looks like 3.92 ohms at 100 Hz and 5.86 ohms at 5kHz.

                    HTH

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