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Another Sprite Build - My Oak and Applewood Hippie Boombox

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  • Another Sprite Build - My Oak and Applewood Hippie Boombox

    Last edited by stellarelephant; 11-13-2017, 08:57 PM.

  • #2
    After I finally buttoned up the box, I again connected my old iPod Video (on which I run the awesome Rockbox OS) and began listening to different albums in FLAC format. The first things that struck me were the clarity of the midrange and the absurd depth of the bass coming from these small speakers. I also detected an annoying mid-bass resonance from the cabinet, somewhere in the neighborhood of 100 Hz. --edit: much of this resonance was caused by the wall behind my Sprite! With foam added, the boominess disappeared completely when I moved the Sprite out from the wall-- As a result, I spent the next week or so trying out different stuffing strategies. I had some free foam on hand, that actually came packed inside a pair of tall boots my wife bought online when they were shipped. It's a bit denser than mattress topper foam, so I figured it would do the trick. Indeed, I noticed immediate (though incomplete) improvement after covering the back walls of the cabinets.



    I added other bits of foam in other places (using hot glue) until the response evened out. At one point I added too much foam, and perhaps because it was too close to the drivers, or because it was against the inside of the baffle, I definitely heard the higher frequencies begin to sound muffled. So I removed that bit, and in the end, I feel that I struck a good balance.



    Here's what the boxes look like inside now. Note that I caulked everything like a madman. I did not use gasket tape around the drivers, since they were rear-mounted and the flat lip of the NS3's rubber surround provides something of a seal against the baffle already. I caulked them too just to be sure of the seal.



    xxxx

    ..............THE SOUND

    My Sprite lives in the kitchen, and it has made doing dishes infinitely more enjoyable. It fills the roughly 250 square foot room easily, with the iPod signal coming in at line level and my Sprite's volume pot normally up around 70% or so. I sometimes listen to the system at full volume and the sound remains crystal clear at this level unless the material is extraordinarily bass-heavy, which overwhelms the NS3s. I am pleased with their output level for my use.



    And how does it sound? To my ears, quite nice. A little background: I have been a Tripath amp fan for several years. The signal chain of my main listening setup is my Mac Mini, through an Echo Audiofire2 DAC, through a Topping TP-20 (which uses the slightly more powerful 2x20 watt Tripath TA2020 chip), to Axiom M3 bookshelf loudspeakers, which use a vented aluminum cone woofer--another similarity to the Sprite setup. So in some ways, with the Sprite, I'm getting more of what I've already grown accustomed to, in a tiny package. In the bass department, the Sprite keeps pace with the 6.5" drivers of my bookshelf speakers, up to a certain volume level. That was a shock to me. They move a serious amount of air, and sound good doing it. I would also call the Sprite accurate and revealing, at least for on-axis, nearfield listening. I hear great detail in the midrange, and the sound is not fatiguing in the least.

    On the downside, these drivers definitely beam the higher frequencies into small sweet spot--an issue I expected from a full-range design. Still, I wonder if rear-mounting my NS3s against the inside of the baffle, perhaps along with my router beveling, exacerbates this effect by horn-loading the drivers a little bit. Can anybody weigh in on that notion? Is that possible? Speaking of the sweet spot, I have also noticed how much the sound changes as I move around the room--an effect I don't notice with one speaker disabled. I presume I'm hearing phase cancellation in the stereo signal, caused by having the speakers so close together (in my Sprite, they are 14.25 inches apart, center to center). This is likely an issue with all boom boxes. Even with these idiosyncrasies considered, it sounds very good. Boom boxes aren't exactly intended for critical listening, are they?




    Sometimes I wish my Sprite had tweeters, even though I absolutely enjoy the sound of these full-range drivers alone. I'd say my Sprite has helped me appreciate the top end detail and sparkle that tweeters provide in other systems. I almost never use EQ, but with the Sprite, I have been using Rockbox's EQ controls on my iPod to add 4 dB of treble gain via a high shelf filter set at 3500 Hz. To my ears this yields a more natural response in the upper registers that balances the powerful bass of the NS3. My perceived need for this treble boost came after I damped my cabinets with enough foam to tame the 100 Hz midbass resonance I described earlier. --edit: I was overcompensating with foam for a boomy room response. I just needed to move the Sprite out from the wall!-- Can anybody else confirm this phenomenon when stuffing the cabinet of a full-range driver? Everything I read online about stuffing cabinets dealt with 2- and 3-way designs, where the tweeter is sealed and treble frequencies therefore unaffected. With my Sprite, I'm pretty sure I ended up with audible attenuation of the treble frequencies after using what I felt was the minimum foam necessary to tame the midbass hump.

    I was a bit distraught at first to realize that I needed EQ to tailor my Sprite's response to my liking. On the other hand, perhaps I should be glad that I'm not hearing all those cabinet reflections coming back out through the driver, even if it means I have to boost the top end to compensate. --edit: again, room resonance was the main issue!--
    Last edited by stellarelephant; 11-13-2017, 09:04 PM.

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    • #3
      Last edited by stellarelephant; 11-13-2017, 09:06 PM.

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      • #4
        Kudo's. Very nice job and excellent write-up!!
        “I cried because I had no shoes until I met a man who had no feet”

        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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        • #5
          Looks amazing.

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          • #6
            Originally posted by stellarelephant View Post
            ...a handle and volume knob made out of a couple apple tree branches I cut from my tree..
            I save pieces of Apple Wood. It carves beautifully

            "Not a Speaker Designer - Not even on the Internet"
            “Pride is your greatest enemy, humility is your greatest friend.”
            "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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            • #7
              Nice write up on a great looking build... I look forward to seeing what you do with the speedster..

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              • #8
                Very nice build, and fantastic documentation. Welcome to the obsession!

                I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
                "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

                High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
                SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
                My Voxel min sub Yet-another-Voxel-build

                Tangband W6-sub

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                • #9
                  Haha, I love the volume knob......

                  and uh...mmmmmmm....Speedster'sssssssss........LOVE EM. Can't wait to see your rendition there.
                  Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

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                  • #10
                    Thanks, y'all. I appreciate your comments. Yeah, it is an obsession isn't it?

                    I asked a few questions at the end of my initial post. Can anyone weigh in on any of the following issues?

                    1) Is it possible to get horn-loading effects from rear mounting drivers? I am wondering if this exacerbates beaming.
                    2) Any special strategies for stuffing cabinets of full-range drivers? I noticed attenuation in the treble frequencies when I was trying to even out the initial midbass resonance I was hearing.
                    3) Is it worthwhile to do power supply upgrades on Tripath amps? I used the 2000 mA brick recommended by PE.
                    4) Here's a silly one. I wired my potentiometer between my signal source and the amp. Is that the ideal place for it in the circuit?

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                    • #11
                      Fantastic job on the build! Excellent writeup, too. Although I have to admit, I lost it when you glued cubic zirconia to an LED. Could this be a new trend!?!

                      Anyway, so much creativity and hard work went into this, and you should be very proud. Thank you very much for sharing.
                      Isn't it about time we started answering rhetorical questions?

                      Paul Carmody's DIY Audio Projects
                      Twitter: @undefinition1

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                      • #12
                        Originally posted by stellarelephant View Post
                        Thanks, y'all. I appreciate your comments. Yeah, it is an obsession isn't it?

                        I asked a few questions at the end of my initial post. Can anyone weigh in on any of the following issues?

                        1) Is it possible to get horn-loading effects from rear mounting drivers? I am wondering if this exacerbates beaming.
                        It's possible, although honestly beaming is just a natural by-product of full-range speakers. I admit that this is the weakest point of the Sprite. However, the way I use it (background music while doing other things) I often stop thinking about it after a few minutes.

                        I have been asked many times if I'd ever add a tweeter to the sprite. the problem is that this adds to the cost and complexity. The crossover would probably add 3-5 parts. So I decided to just leave it as it is, a simple design that someone could build with minimal fear of messing up the crossover, or investing too much in components.

                        2) Any special strategies for stuffing cabinets of full-range drivers? I noticed attenuation in the treble frequencies when I was trying to even out the initial midbass resonance I was hearing.
                        It's trial-and error for me. I typically use polyfil (pillow stuffing). It's easy to add and remove to taste. It may be hard to attenuate a cabinet resonance, though, without an actual brace. You could experiment with a brace by cutting a scrap of wood and sort of "jamming" it in by tilting it a bit, if that makes sense. This is how I figure out optimal locations of braces. I jam a piece in and knock on the cabinet walls with my knuckles.

                        Eventually, you may just want to let it be, and to parlay these new skills you've acquired into a new build, though. At least, that's why we all suffer this addiction!
                        Isn't it about time we started answering rhetorical questions?

                        Paul Carmody's DIY Audio Projects
                        Twitter: @undefinition1

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                        • #13
                          Thanks for your encouragement and advice, Paul. I respect your decision to keep the Sprite a full-range project, because I probably wouldn't have attempted a 2-way design as a first-timer.

                          Originally posted by Paul Carmody View Post
                          It may be hard to attenuate a cabinet resonance, though, without an actual brace. You could experiment with a brace by cutting a scrap of wood and sort of "jamming" it in by tilting it a bit, if that makes sense. This is how I figure out optimal locations of braces. I jam a piece in and knock on the cabinet walls with my knuckles.
                          Ah! Until now I had only considered the resonance of the entire cabinet cavity. It hadn't dawned on me that each piece of wood in a cabinet has its own resonance as well. I guess I made things a little harder on myself by using oak, which I assume resonates quite a bit more than the MDF most folks seem to use. I doubt I can bring myself to quit working with solid wood, but I may try to use a softer wood, and perhaps also thicker boards, to build my next project. For now, I will try squeezing some little braces into my Sprite and see if I can hear a difference.

                          Glad you got a laugh out of the cubic zirconia. I totally stole the idea from the DiamondBoxx guys...You know, this might actually be the Sprite's big brother. They don't say, but I think the "Two 5.3 inch (135mm) active woofers, aluminum cones, rubber surround, neodymium magnets" look suspiciously like a pair of PE's ND-140 midbass drivers!

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                          • #14

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                            • #15
                              Argh! I blew out the speakers in my Sprite! =( Here's a pic of the damage:



                              It started with good intentions. I run an after school program for 40 kids and we had our Halloween party yesterday. We all dressed up in our costumes and I took the kids into the school gymnasium to play games with the lights out (everyone got a light stick necklace to wear with the intentions of looking cool and preventing kid collisions). I brought out my boombox and hooked it up to my XDuoo X3 player as usual. But darn, it ain't easy filling up a huge gym with sound!

                              Making matters worse, the first song on my custom playlist was "Monster Mash", recorded in the sixties and presenting a very low overall volume level in the mp3 file. To compensate, I made a fateful decision: I connected my Sprite to the X3's HEADPHONE output instead of the dedicated Line Out. If I'd been using my old iPod, it wouldn't have made much difference, but the X3 boasts 250 mV at 32 ohms...about 5x the output power of any Apple device. Surprisingly, the X3 did not overload the TA2024's input, and sounded great, just WAY louder! Mission accomplished...or so I thought.

                              Next on the playlist was "Thriller," the remastered version from Number Ones, circa 2003. As I did my best to lead a game of Zombie Tag in the dark while wearing a giant carrot costume I thought, "Wow, this song is much louder! And..the bass is somewhat farty and distorted. Oh well."

                              Finally, near the end of our game, the Ghostbusters theme song came on. Earlier in the day, I had downloaded the brand new remastered version from the 2016 soundtrack, thinking it ought to be superior to the original. "Dang, this song is loud!", I thought. The kids seemed to love the song as much as I did when I was little, which made me happy, as a ran around the gym, hopelessly trying to keep order while sweating inside my polyester carrot suit. I will say that the vocals in the track sound much clearer than they used to back in the day. But the Sprite really lost its composure with the overly compressed, hard limited track. The bass was ridiculously distorted this time around. I let it ride, thinking that this was the grand finale, and it ought to be a loud one...

                              When I got home last night, I put the Sprite back on the shelf in my kitchen and gasped when I looked at it. Both drivers have the same sort of deformed overall shape in the aluminum cone, and this one I photographed actually has a stress fracture in the center. Dang! Surprisingly, I notice no sound degradation yet. But it looks awful, and I've already ordered two new NS3s. Another casualty of the loudness wars, I suppose. Happy Halloween everyone.

                              Can't resist. Here's a glamor shot from a couple months ago. By the way, Paul, I take back everything I said about the Sprite's cabinet having an impossible-to-damp 100 Hz bass resonance. It was just the darn wall in my kitchen! When I had the Sprite in the classroom in this photo, I pulled that little table out from the wall, and played the Sprite in a big space for the first time. What do you know...everything evened out. I actually quit boosting the treble for the first time. I can now confirm that the Sprite delivers a very even frequency response when not backed into a corner!

                              Last edited by stellarelephant; 02-20-2017, 11:00 PM.

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