So my new thing is lamps. Lamps are lit. Actually, I’m into plants, but it’s a whole thing and someone said recently “like, isn’t everyone into plants now? But lamps are underrated”. I think you once told me—or gushed, most likely—that you had plants. I don’t remember, but I can recognize the presence of plants by plant-shaped gaps in my memory, but I can’t remember the actual instances of plants themselves. Plants were something that I did not pay attention to at all until I was beguiled by their verdant wiles. But I think it was fated. When I was 6, my parents had given me my first disposable and I ran outside into the sunny Stanford afternoon and took, in rapid succession, 26 blurry photos of a bush; I wanted pictures of it growing.
Plants are beautiful, delicate, and mute repositories of life and they absolutely bustle. Quitely, they bustle. Sometimes I look at them and imagine how imperceptibly they are growing, with fragile inevitability. Even if I can’t see them grow, they are, without doubt, growing. They even represent sort of perceptual paradox for me: having observed them quite often, I am required to conclude that they are growing day over day, but I can never see them grow. Only when I am not looking. It fascinates me.
What’s cool about plants is that they act as a reciprocal canary-vessel for self-care. Vessel: as they bring me oxygen and joy, taking care of them benefits me, and in the time I set aside to tend to them, I am required to chill the fuck out for a second. Canary: if I don’t chill the fuck out and tend to them, they wilt, which gives me an easy visual representation of my fraying sanity. In this way they embody and promote good vibes all around, which is dope. Plus, girls love plants. Basically, plants are lit.
But plants take like fooooorever to grow and while, yes, the last paragraph is all about the mindfulness of the green goobers, didyouknowplantsgodormantinthewinterwheretheymightnotgrowatall? That’s dumb. After some careful questioning of the local college kid who staffs the overpriced ~vibey~ nursery by my house, I figured out that the dormancy of the plants is only dependent on 3 factors: heat, humidity, and light/dark cycles. It wouldn’t feel right to engage in mindfulness without a little bit of optimization, right? And that’s how I got into making lamps. Plants need light. Loads of it.
So the commission for this was a rescue grow lamp for a Pothos stranded in a corner of a sterile-lit house my friends built themselves. Their house includes a lot of warm tones, light wood, and minimal design accents. Therefore the key aspects of the lamp were: minimal, modern, super-warm bright but indirect lighting (plants love bright-indirect) in the >800 lux region with a >1 foot light dispersal area.
I’ve seen a lot of halo lamps for grow lights; the circular arrangement is actually quite efficient for even light dispersal over a large area, but they always look a bit Christmas-kitch to me. I needed something to break up the IG lowest-common-denominator design and root it solidly in minimal post-modern, so I slapped some emergent complexity on the halo with easy-to-fab rectilinear slats.
My major innovation in this space is using an infill-only slicing (0-wall gyroid infill support block @ 11% infill, thanks to Cura’s easy slicer interface) to create a fully solid yet translucent PLA shade.
I paired this with the very warm-toned and very exciting fully compostable NonOlien PLA from Filamentum, printed hot (189°C) on the Ender 3 V2 (super affordable entry-tier printer, very easy to use). It came out smashingly, although at this temperature, the flow compensation and print accuracy was poor, so I had to undersize the zero-clearance interfaces by a whopping 370µm on each side. 5 hours of printing later, though, I had exactly what I had hoped for:
The slats are 3 strips of 1×5″ poplar with the middle slat cut down to a 1.5″ relief, laminated longitudinally and then cut in 8mm strips transversely. I finished the poplar with 4 coats of Waterlox (soft wood is super thirsty) and a finish coat of semi-gloss Polycrylic, slapped some super warm high density 2700k LED strip lights in there and added a 2.1mm barrel connector for an easy 12V connection to an affordable 2A power supply (due to the 1.5m of installed LEDs). The results:
What’s the right wedding gift with 30 days of lead time when your friends are stranded across the Canadian border because of a global pandemic but they’re willing to risk it all for love and get married in a DMZ? I went with an Ikea cutting board. Well—to start.
It turns out that in places where border boundaries are blurred the acoustic offerings are slim. Without loud music (and strong drinks) no party is bompin, and without a bompin party, it’s not a wedding, so there was really only one thing to do: make a matching & linkable set of portable, hi-fidelity bluetooth speakers:
Cost of parts: $150 (ea.) Loudness: 96dBSPL, 1m, @ 10% THD, A-weighted Frequency Response: 50Hz to 20kHz ±5dB (but look at the curves down below) Connectivity: Bluetooth 5.0 Battery: 3S Lithium-Ion, 37Wh Runtime: 10 hours at “half volume” input (92dBA output) Amplifier: 2x50W TPA3116D2 running @ 24V Difficulty of Build: Dummy high—approx 120hrs from start to finish, requiring 2 CNCs and a 3D printer
In a lot of ways, this was a 2020 capstone project for me: to make something that’s loud, compact, and full of deep bass, with a 30-day conception to finish timeline, I had to pull out at least half of the dirty tricks I’ve learned over the last six years. Here’s how it went down.
When it comes to compact loudness with a lot of bass, excursion and efficiency are the belles of the ball, and although I simulated almost every 2-4″ driver I could find, the Dayton ND91-4 drivers (descended from long-gone AuraSound’s Neo-Radial IP) are nearly unbeatable when you factor in magnet strength, Fs, Xmax, price and weight. E.g. Peerless SLS-85S25CP04-04’s (catchy name huh) are potentially 1dB louder for a similar box size but weigh 285% more, while the Fountek FR89EX win for Xmax but need too much back volume and are 2dB less efficient…etc and so on. Just trust me on this one. In a 1.5-2.5 litre box: ND91-4, tuned low.
Tweeters are a fair sight more efficient, so down selection should be mostly driven by crossover frequency, dispersion and ease of integration. The ND91s break up right after 3kHz:
While the ND16/ND20 tweeters are truly amazing, they have to be crossed higher, and they come with a bunch of extra plastic, which clashes with the ultra compact layout I pushed. LaVoce’s TN100.70 did the trick and can be crossed over at 1.5kHz, which was perfect—the lower a tweeter can be crossed (disclaimer: within its volume displacement limit), the better. Finally, the TN100.70 dispersion is on par with the ND20FA tweeter @ 20kHz (-15dB):
As for the port, in order to maintain compactness and b-b-bass, I had to fit 250mm of port into a 2.5L box while keeping a holdable 4-inch width so I folded it around the ND91 and then crushed the port geometry until it fit in between the driver and borders of the speaker. Tweeter in green, port/body in pink, and woofer in yellow below:
Driving the woofer and tweeter is a 3S 3500mAh battery pack (I use LG 18650s that I order B2B from the factory) paired to a 2x50W Class D TPA3116 D2 amplifier through DC-DC step up converter for maximum power delivery. WONDOM makes a wonderful TPA3116 board with the DSP integrated, which merges with their 3S MPPT Battery Management Board, although to my late-stage chagrin neither of the boards have a step up to power the TPA chipset at an adequate 24V.
With the acoustic design tucked away 15 days from the deadline, it was time to build. The octagonal outer shell is just a set of 22.5° mitres, tape-clamped, with the patent-pending dual-bevel 8th wall precision cut to match:
The front face was a 2 sided CNC operation, which required calibrating features for aligning the Shaper Origin I used.
Merging the two pieces with the speakers and the front mounted the port was rather easy except for some minor mishaps with a few missing microns; the t-nut I planned to use to rear-mount the woofers were exactly 300 microns short of the planned front face thickness, so after sanding I had two t-nut holes showing on the front face. The port itself had to be printed in 3 pieces because of the complexity of the geometry to fit it both on the border and between the woofer and the back panel:
With space at a premium, but also for aesthetics, I used an LED array for status lights and integrated the on switch into the potentiometer. With that in mind, I also fabbed an ultra slim 6mm bracing/sealing ring for the rear panel mounting, as a butt joint would’ve been ugly but the shell was too thin/weak for threaded inserts. Those loose microns got me again and the flange on the port interfered with the built dimensions of the rear panel, so I slotted that out, but after some truly painstaking finagling of circuit boards, 5 days before the wedding ship date, I was ready for sound test.
That’s when I realized neither the BMS nor the Amp was using a boosted rail which was causing very noticeable voltage clipping, so I had to rip everything open and shove not only a DC-DC buck converter but a giant LC ripple filter (1.3mH L and 100µF C) onto the voltage rail. The only DC-DC buck converters I had in house were straight outta Hua Qiang Bei which means the were both cheap and poorly designed. Buck converters are in general awesome, and about as efficient as one could hope (for 12 to 24V boost, I saw ~85% efficiency depending on load), but the switching causes a lot of load-dependent ripple, which adds both noise and intermodulation into the signal chain. But with that bullet bitten, and with 1 day until ship, it was time to tune. And boy does this design sound good. Sparing the details of the tuning, here’s the final frequency response with a -3dBFS sine sweep @ half input “volume.”
The 2nd harmonic distortion looks pretty high @ 50Hz but this is mostly due to the aggressive non-linear processing I added in for extra kick; a more reasonable measure of THD in this scenario are the 3rd order harmonics, which I kept below 8%. The dips in the mid band (400Hz, 800Hz) are regrettable from a data standpoint (probably due to product baffle dimensions) but overall, these speakers deliver supple bass, smooth vocals, crisp treble, and excellent definition from 50Hz all the way to 20kHz. I added a little bit of level-dependent EQ, so at maximum volume these speakers are loud enough to kick off a backyard party, and at reasonable volumes they deliver a little extra extension for a very full, deep, frequency response. In my book, a thermos-sized speaker that can fill a room down to 50Hz ticks the “bigger than it looks” box; even from another room I found my self saying “damn, these sound good.”
There are far more than five senses available to you in this awful wonderful human sensorium and one of them is the sense that You Could’ve Done Better. But this was not one of those times.
You ever see something and think “I bet I could make that, but better, and more cost-effective”? You ever think “I could make a portable, hi-fi, PA speaker with shit-your-pants bass, noise-complaint SPL, and art-gallery looks”? You ever sit at home and wonder “what if I went all out? What if it was way too big and way too loud and way too pretty?” Yeah, me too. This time I did it.
This was probably a time that I should’ve done less, but didn’t. In scoping out a project on commission I usually discuss
The discussion should and usually does occur late at night over libations which contributes to some amount of scope creep—in a good way—and in this case we started at:
Loud enough the neighbors want to come to the party too
I was thinking of a very reasonable design—1 cu ft, 36V battery, maybe 2 W6-1138 (but with Neo woofers for weight). But then something terrible happened. I saw a targeted Facebook ad for the Soundboks 2; it was was full of shitty marketing claims and absurd dBSPL/battery life statements and poorly mixed dubstep (like, dubstep is fine, just don’t mix it badly or use it to tout sound quality). Here are some reference claims:
I’m not an acoustic engineer, but—wait, no, no I am. These are bullshit metrics. What kind of half-assed sound company specifies a “dB” value but no reference for the units (SPL? Re?), distance, or weighting (A? K?). I could fart at 122 “dB” for a battery life of 40 hours if I’d put the mic by my arse.
For the un-initiated this is the equivalent of saying “Oh yeah my car is really fast, it’ll do 120.” 120…what? MPH? KPH? Like when you drive it? Or when you throw it off a cliff?
Anyway fair to say this bothered me slightly and the new goal was to make a speaker that was better than the Soundboks 2. A portable party in a box. My specific objective goals were:
122dBSPL (Re) @ 1m in the passband
Passband 40Hz to 20 kHz
f3 @ 38 Hz
Directivity controlled ± 4 dB up to 15 kHz
*For the sake of clarity, if not otherwise specified, all dB numbers in this document will be dBSPL @ 1m relative to 20 µPa.
On the spectrum of “large/efficient” and “small/inefficient” for a constant bandwidth target, there are three main real-life ways to achieve this in the range of “reasonably portable.”
“Pro” speakers in a large box, i.e. lots of magnet, low moving mass, stiff surround. Think FaitalPro12XL
+ efficient as hell
– generally 8 ohms
– Fs is often quite high
“Tang band” style in small box, i.e. lots of magnet, lots of coil, tons of moving mass, allowing for really low free-air resonance and massive linear excursion space.
+ always impressive for size
– low efficiency
“Dayton Audio” style in a medium box: Medium BL, medium mms, heavy magnet
+ pro-sumer design means well controlled directivity, well designed in-band response
+ reasonably efficient
– has potential to be “worst of both worlds”
Here’s a quick comparison of the three designs plotted at a very reasonable 100Wrms:
The Iron Law clearly demonstrated here: The Dayton design is in the middle for sensitivity but sacrifices on size to get extra bass. The Tang Band, which will never have the sensitivity of the DA or the FP design, loses a little bass to be small, but has overall good LF extension. The Pro design is huge and efficient but loses on LF extension. But wait! This is battery powered! We’re voltage limited! How do 2 4 ohm drivers shake out against 1 8 ohm driver?
The Dayton Audio design clearly wins out (dotted lines are theoretical response vs Pmax/Xmax limited response). The final question: can we kill the Soundboks? If we disregard all concerns for safety, in theory—nearly:
At 1100 Watts of input power (rms), 2 DCS205s are capable of outputting 121.2 dBSPL @ 1m @ 100Hz. The Xmax limitation cuts heavily into the bass output below that. But this design will sound better, look better, and be smaller, so DCS205 it is!
The final choice for bass—sealed, ported or passive? A simple one; sealed sucks for battery-powered. The port would’ve had to have been huge to handle the requisite volume velocity with grace, so after modeling every single DSA, I opted for 2x DS315 12″ PRs + 100g to tune to 38 Hz. These are quite wonderful passives—huge xmax, Rms for days, low enough Fs, and their ID matches the DS205s.
Knowing that we’re in the neighborhood of 115 dBSPL@1m @ 50V input makes things a bit tricky from 300Hz to 20kHz. Pro sound options are mainly focused on output efficiency, with the sacrifice being directivity and flatness of response (DA PK165-8 below, which had neither the efficiency nor the response I was looking for):
which would essentially demand that you cross it over at 2kHz—untenable for a tweeter capable of 115 dBSPL.
Luckily, there weren’t that many options, and when one can’t sacrifice loudness, quality, or size (i.e. directivity), you must pay a lot of money. I landed on the beautiful and beautifully expensive FaitalPro M5N8 which measures like:
Their claimed efficiency of 99dB @ 1W/1m is a little short of the truth (95dB@1W/1m) but they manage an easy 117 dBSPL with xmax and plim constraints:
Throw it in (a 3D printed back volume to separate it comes in later):
There was really only one option: the Peerless by Tymphany BCS25SC08, a silk dome tweeter + a (small) horn for efficiency. 98 dB, 100W of power handling (they get ragged before that, though), and the horn rather small so the directivity actually rather pleasant (this is in 30 deg intervals compared, the midrange plot was at a 45 deg intervals).
There are far more than five senses available in the bleak sensorium of human existence, and one of them is the sense that you could’ve done better. Could I have done better? Let’s find out.
Obligatory finished product first:
I think the journey began confidently over beers, but the tolerances involved in interpreting what someone means by “portable and loud but doesn’t have to be too loud but also make it look really cool” can allow for a lot of design doubt (by no fault of their own–it’s just hard to gauge what reference points people have for “small” and “loud”), and so by the time I packed the Tesselator out, I had built 6 separate designs, each one but the last dusted in a fine sheen of “not-quite-good-enough.” This is their story (dim the lights).
ROUND 1: TOO BIG
Try 1 was actually pretty awesome. Basically, I wanted to see what the hype was about with the HiVi B4N’s. Ports in small boxes often of chuff me the wrong way and the client wanted “big circles on the front,” which I interpreted to mean speakers. Plus, I go for passive radiators when I can…and so I went for a passive radiator design. I had been having luck with asymmetry, and I wanted to carry a “T” motif through the design.
The problem with the B4N’s that all the fanboys won’t admit is there’s an insanely high Q 15 dB break up mode right at 3kHz, and it likes to jump around depending on boundary conditions, air temperature, zodiac sign, etc. [For the uninitiated, basically the B4N is the classic DIY beginner speaker design because it sounds and looks good, is cheap to make, and because so many other people have built it. However, the all metal cone it’s based around tends to “ring” like a bell at annoying frequencies]. So I wanted to be at least 15 dB down by 3kHz which meant a tweeter that could hit 1.5 kHz, and for directivity reasons, I decided on a 500 Hz crossover, which obviously meant I was going to use the Aurasound NS1s.
Then I found a sweet spot of plywood that I could waterfall from top to front face to edge, cut with confidence, laid out some paper circles for test fit, and very poorly lock-mitered the shit out of the wood.
Lock miters as promised:The separated volume is for the electronics–lesson learned from previous projects is when trying to attain a good seal, either get better at electrical engineering, or compartmentalize your bad work.
Of course, I still overestimated my abilities and placed the batteries in the acoustic chamber for space reasons. The white boxes are the enclosures for the NS1s.
I also had the idiotic notion that using banana plugs as pass-throughs would be simplest, but not only did I get the polarities wrong, it turns out banana plugs are super expensive and take up tons of space:
I didn’t manage to fuck up the miters too much and the face is perhaps lovable by more than it’s mother:
I cut out some purple heart and embedded some glow in the dark for the volume knob:
With all that shit sorted, it was time to make an absolute mess of the ASP. The signal chain starts with a power-source isolated bluetooth chip, which is split by an op-amp active crossover, the low frequencies going to a china-market bought TDA7492 class D amp and then to the B4N’s while the high frequencies are padded down by potentiometer and sent to a similarly procured TPA3118D2 amp. The TDA7492 is rated for 40W into 8 ohms @ 25V @10% THD, which works reasonably with the B4N’s 25W RMS rating. Typically it’s better to spec an amp with more headroom (@ less THD) over the continuous power rating of a woofer in order to match the crest factor of music, but I didn’t think of that at the time.
This is the last build I used analog signal processing on, partially because of the above mess of wires. Here’s the terrible wire management in context:
I opted for a glow in the dark, 3D printed, inset handle to preserve the form factor, and then slapped some spar varnish all over that bad boy and called it a day.
ROUND 2: TOO QUIET
Sometimes things come together, and sometimes they come together perfectly. This was not either of those scenarios; the “Tesselator” it’s actually just a decent name pun. Honestly, I was pretty happy with Round 1, but it was just not quite there. It was a little too big, and the lock miter bit I used for the edging was one of those cheap amazon finds that reflect their pricing in their quality. So, I started completely anew…by taking an old project that had been called into half-hearted existence with 3 other siblings in a similarly iterative process that finally yielded the Krump Kanon and cutting it in half. In general, this approach is poor.
It sucked for multiple reasons, some of which were that it was ugly and sounded bad and was still too big. Essentially, it failed to meet any of the criteria laid forth.
ROUND 3: TOO LITTLE BASS
I then tried a new design that was basically Round 1 but with half the stuff in half the space. It also sucked. I was convinced that it wouldn’t because of my experiential lesson on KK Round 2–“efficiency is king”–but it turns out that only works if you have a pleasing natural response or some good DSP.
It was doubly a shame because the wood that went into the box was beautiful, but for some misguided reason, I used the cheap lock miter bit from Round 1 and, completely to my surprise, it didn’t work well the second time either.
ROUND 4: TOO HAMMERED
I then decided that everything I had decided was wrong, that efficiency wasn’t king, and it was all about extension. I went back to some of my “super-compact design” notes and decided to drag some micro-subwoofer Tang Bands into wretched existence. The only problem is that tuning a small box to subwoofer frequencies requires a long-ass tube (because the air spring in a small box is relatively stiff, you need a lot of acoustic mass in the resonating port to get a low resonance frequency), and long-ass ports are very inconvenient to fit into small boxes (not a problem encountered in my daily life). I had a minor stroke of brilliance stroke and decided to make a port that was both a long-ass tube AND a handle, therefore circumnavigating this issue. Here is the relatively tiny box, which looks shitty because I had also come up with the terrible idea that I’d wrap the whole thing in carbon fiber once assembled:
And the incredibly sleek and not at all awkwardly protruding port/handle design.
I set the thing up, hit play and was, for the first time in a long time, pleasantly surprised. Here’s a casual video of it in a living room (turn ya sound up and throw on some head phones to appreciate the FIDELITY that’s SPEWING out of this BOOMBOX).
For such a tiny little thing, it was really moving air. It had real potential until I hit it with a hammer.
ROUND 5: TOO UGLY
Not really much to go on about here. It was ugly. I underestimated how weird it would look to have the speakers sticking out of the face instead of flush mounted, and the thing looks like a damn bug-eyed pug.
ROUND 6: NOT BAD
In a surprisingly reflective and narratively satisfying moment, I decided to combine the lessons of the last 5 iterations. I drew up a plan for a small, relatively efficient boombox with precise waterfall miters, inset speakers, DSP, and a port handle. And no fucking carbon fiber.
On to the even more boring stuff. Yes, yes, I know the stereo image is going to be ruined by placing the “tweeters” on top of each other. But it looks cool, and there’s no point in attempting to get stereo width out of a box narrower than one’s head.
Anyway, it’s got 2x TB W3-1876 in a mono “sub” configuration, sitting in a 3.7L box stuffed with light polyfill, tuned to 48 Hz with a 12″ long by 1.2″ diameter port. This theoretically gives an f3 of 42 Hz. The port is a 3D printed 3-section design that was epoxied together for surface finish and adhesion. It’s flared on both sides equally for symmetry. The “tweeters” are 1″ W1-1070SH, which are sitting in a 0.1L box and crossed over in a 48 dB/oct LW DSP crossover at 500 Hz. The outer dimensions are approx 4.5″Hx4.5″Dx14″ and the 80Wh battery supplies 24V (nominal) to a China Black Market TDA7492 (to run the woofers) and a CBM TPA3118D2 (for the tweeters) for about 8h of quite listening and 4 hours of TURNT listening MiniDSP 2×4 runs the tuning, and the bluetooth is run by an APT-X Bluetooth 4.0 chip. The advantages of this chip are high quality transmission with surprisingly low radio noise, but by some trick of China-blackmarket circuitry, it manages to clip it’s output stage at maximum source volumes. I suspect they added a NE5532 output buffer but didn’t manage the gain properly. The numbers on the edge display battery voltage, which is my lazy solution for a battery gauge.
The wood itself is is 1/4″ maple ply, reinforced on the interior with another 1/8″ of ultra-stiff epoxy and some bracing. I finished the wood Water-Lox high gloss finish, which I enjoyed for the simplicity of use and quality of finish. It brings out the grain and luster of the wood beautifully, and it dries quickly into a reasonably durable exterior finish.
Subjectively, the thing is awesome. It sounds far bigger than it looks, and with DSP trickery, there are little concerns of over-excursion despite a relatively low tuning for such small woofers and such a small box. It’s a good feather in the cap for extension over general sensitivity, though it seems that the “high-moving mass, giant coil, really strong magnet” combination that Tang Band is throwing into their designs does a decent job of balancing sensitivity with extension, and this design ends up being a good compromise of the two. The stereo image is shit for previously mentioned issues, but it manages to have pretty laid-back directivity, which is all you could hope for from a small source.
Final assessment: can fill a living room with danceably loud music, yet it is small enough to hand carry to a barbecue. Ship it.
Much like worried parents will fuss over a child before sending them off into the world, I fidgeted over the details of this lil guy, attempting to delay the inevitable departure, filled with pride and worry at the rigors he’ll face out in the real world. Unlike most worried parents, I eventually said “fuck it,” and dropped this fucker off at the local Fedex, to be shipped cross country in a large cardboard box.
The details were particularly sweat-able on this build, as this was essentially the third iteration on the concept, starting with a beast of the beats that went to Keith, and then a semi-pro configuration that went nowhere. Here are the vague details of the build:
Obviously, the first detail to isolate is the Lego theme. Legos, by the way, are a fairly mediocre permanent construction material. Turns out the 10-micron precision makes them fairly expensive from a cost/volume stand point (a small enclosure requires a lot of legos). Had my little siblings help me build lego boxes to compare the looks. Turns out rainbow is a crowd favorite
Fast forward a few days, after much designing, some deliberation, and then cutting, I’ve got a wood box to match the lego box. I believe I designed for 4L internal volume for each NS3 driver, which, in retrospect, I feel was too much. However, once the wood is cut…alea acta est. I went for a seamless miter approach on this build, to avoid the ugly “end-grain” of the birch plywood. I wrapped the grain around the “depth” of the box, but the grain of the “face” does not flow into the edges. So far I haven’t figured out a solution to this that works out in our boring 3 dimensional Euclidean / Newtonian universe.
Here we can see the translucence of the 3d prints, pre assembly. Originally, I had not planned for there to be a VU lightstrip in this build, but then I realized that since I built all the electronics off of the wood box, fitting them into the lego box, which had 5/6 faces constrained already, would be extremely difficult. At this point, I also realized I miscalculated the amount of space wires take up. Medusa rears her ugly cable management head yet again.
Now you see what I mean.
Analog signal processor demonstrating that I am the particular type of person that loves neat things but does not love making things neat, and so I live in a constant torment of my own devising. I chose a scheme that allows for a bass shelf at lower volumes, but flattens the EQ towards higher volumes—it’s essentially a loudness compensation circuit, except that since I have no reference for the actual loudness of the output (due to lack of information about source gain, listener position). I call it the “party” compensation circuit, because while one might enjoy deep sonorous extension at lower listening levels, once your friends roll through, 14 beers deep each, you’re cranking that fucking volume knob. And while the NS3’s have a lot of allowable excursion before crashing, the garbage bass lines that litter the hip hop soundscape are essentially glorified sine waves that will fuck your shit up. The obvious and simple solution to this is a simple dynamic gain-tied or signal-adaptive high-pass for excursion limiting, or a multi-band compressor. I leave these endeavors as an exercise to the reader until I have the time to implement them on the next build.
Pre-wood finishing. After disliking the gumminess and amber tint of marine spar varnish, I chose to use tung oil to bring out the figure. Then I sealed the box+3d printed parts with epoxy (bar top) for strength/durability, and finally, for UV protection and hardness, I finished with a clear gloss polycrylic. Here’s what it looks like finished:
So after all that talk of efficiency v extension, I figured I’d actually build something. It worked out that I ended up building on both sides of the coin, as the “Extension” build ended up being pretty gigantic. But the review of both approaches is in and it turns out that in some regards efficiency is more pleasant; I used the Faital Pro 5FE100 in a ~8L enclosure tuned to about 45-50 hz with a 3 inch x 15 inch port which I 3D-printed. It WOMPS. Sounds great, crisp, powerful. Really pushes the “effortless” bass feeling, until you get below resonance and the woofer starts whacking around. It becomes excursion limited quite fast on songs with a lot of low frequency content, and it sounds pretty alarming. This forces my hand in ASP to put in a high pass around 32Hz-20Hz, adding complexity and heartache. But all in all, not a bad design.
As for the extension, which also sounds good, a different set of issues comes into play. I went with the Tang Band W5-1138SMF ~14L tuned to around 40 hz with a PR, and for starters, the thing is fucking gigantic. Despite the apparent size, 40 hz in 14L is pretty damn good, and it definitely has a presence visually and sonically. It sounds large, powerful, and it’s exceedingly hard to push the woofer itself into distortion. However pushing the low efficiency of that driver is it’s ridiculous excursion capability, which brings an unexpected issue into play: high excursion means a lot of acceleration. A lot of acceleration mechanically means all kinds of shit is moving around, including things coupled to the boombox through the surface it’s on; put the boombox on the counter and all of a sudden the beer bottles on the counter start wiggling around too. Additionally, in the electrical domain, a lot of acceleration means a lot of voltage, which means more batteries.
These factors push the design to seem a lot less effortless than the 5FE100, potentially because the 1138 design seems to promote higher THD. It’s not necessarily a fair comparison, because the ASP, amp, and battery management on the 5FE100 design happens to be a lot better (I built it second, learned from previous mistakes). Normalizing for those factors, though, the smaller size is pretty great as it turns out that there is usually very little content from 40 Hz and below, and because larger boxes tend to be less efficient in terms of materials.
So for the KrumpKanon I’m going with the W5-1138SMF, and for Keith’s, the W6 version of the same driver. Why? Because it has the excursion, Fs, and general specs to have solid bandwidth and linearity at loud volumes. Unfortunately, if you look at the models:
The yellow line represents the optimal ported design, while the blue is the optimal 8″ Dayton Audio PR design. The vented design is more efficient, has higher bandwidth, and requires less box volume. However, for a 4″x2.5″ port, opening I’d need 36 inches of port to get the 12L box resonating at 36 Hz. That’s absurd, and what’s more absurd is that at 50W, the airspeed would be ~40 m/s. That’s 90 mph, and the air has to move 90 mph through a folded port 3ft long. I have low expectations for the laminarity of the air flow in that scenario, but an educated guess tells me it would sound like an elephant farting through a muffler.
PR’s it is. With dual 8 inch passive radiators, I could be pretty near the vented design, but a) that’s a ridiculous amount of radiator area for a 5 inch area, b) that’s 2x the cost, machining, surface area dedicated to the radiator, and c) trying to fit two 8-inch radiators, a 5-inch woofer, and 2 full ranges onto the front of the boom box would be ridiculous. Why not throw them on the back? Well, then the front will look stupid, barren. I want the raw visual and auditory power of a fat fucking 8″ blasting you in the face. But fitting 2 8’s on to the front of a reasonably sized boom box (using the esteemed [boombox name to go here once I find my notes] as a template) would be geometrically dubious.
So at the sacrifice of about 1/3 of an octave of bass, I’m going with a single 8. I hate leaving bass on the table, especially when it’s easy, efficient bass, but given the constraints and my desire for a simplistic design…it’ll have to do. Additionally, and this is the most important part, but, if you look at an analysis of the most popular music being played these days, there’s little content beneath 40 Hz, and therefore, little need for sound below 40. So I guess 40 Hz it is, and we’ll hope it sounds good. There’s only way to find out.