That’ll work on a huge Lacroix deck… Very similar to the box I made. I tried skating with it on a smaller deck (Landyachtz Switch 40) and either it hung off the deck sideways, or my ankles were practically touching it lengthwise. Either way, I found the sound, firing up at my crotch, to be lacking. Finally, with a single 6.5in rather wimpy subwoofer, the box performed more like a stiff bag… It audibly vibrated until I reinforced the back with a piece of wood, and even then, it wasn’t particularly rigid. I still use it for camping trips, but it just didn’t quite make it on a board. I’m addicted to bass guitar-heavy doom / sludge, and it simply isn’t fun to listen to w/o a decent subwoofer.
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haha how did you know it was going onto a lacroix
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Cnlinko jack is a dead giveaway. Nobody else uses that plug/jack.
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You might tame the box resonance a bit by stuffing it… I’ve been using plastic shopping bags rolled into sausages to stuff outdoorsy speakers with good results.
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Good call, I was going to use a bunch of foam padding. Thanks
I did the thing
How cheap is on the cheap?
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Lets say Below 150$ without batteries.
Here’s where I’d start.
Of all the Chinesium bluetooth amps I’ve messed with, this is the one I’ve liked the most.
You can find them on Amazon and Ebay too, IDK if the QA is any better through parts express or not.
Its a 2.1 amp, so you can drive the sub on its own channel, without any other hardware.
Next what I’d do is go to their page of Sub drivers.
https://www.parts-express.com/speaker-components/hi-fi-woofers-subwoofers-midranges-tweeters/subwoofer-drivers
And start sorting by the diameter and enclosure size you’re going for. You don’t have to worry so much about the details of how to design the speaker box for the speaker if you can just find one that works good for the size you’re going for, and just use the MFGs recommendations instead.
From there, you’ve got the main speakers to worry about, that gets more complicated.
Its definitely easier to get full range sound by pairing a main driver and a tweeter, but there’s more design elements to consider, and a higher parts list.
The last build I did was just using a couple of full range drivers, and you can see the specs on the driver page, you can look up graphs of the frequency response on the mfgs site, make sure the low end of your main drivers can reach the high end of your sub. Ideally they’d have good response down to where you want your crossover frequency to be, otherwise you may not have as much control over the bass as you’d like. Hard to do all that and keep it easy and cheap.
My last build had this for the sub:
And two of these for the R/L channels.
Not the greatest sound in the world ever, but the best sounding cheap thing I’ve made so far.
You can see the cost adds up quick.
Another option, if you want to go super cheap that can actually have some surprising good sound.
Find some bookshelf speakers from a decent brand at a thrift shop, copy the internal volume and vent dimensions, etc, and repackage them in the form factor you want adding in the bluetooth amp and power. Take advantage of the design work put in by a reputable company, and let the economy of scale work for you.
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Thanks man, as I thought, this is a complicated hobby to start 
.
I’ll look into the parts you suggested.
I’ve blown much more than $150. My goal was under $500, under 10lbs, equal the performance of a top-tier bluetooth speaker in a form that actually fits on the board.
BOM:
Closeout Nakamichi 100W 6x8in powered subwoofer $175
TPA3255 4-ch 50V amplifier board $70
Earstudio ES100 Bluetooth/DAC/Headphone amp $80
2.5mm TRRS cable $5
Gallo Nucleus Micro (used) pair $90
PVC pipe fittings + hanger straps + speaker mounting fasteners $20
Amp enclosure $12
(3) Neutrik NL4 plugs + jacks $15
48V to 12V 20A DC-DC Buck converter $20
12ga, 14ga, 16ga, 18ga silicone insulated wire + braided sheath + ring terminals $30
Rubber feet, amp mounting hardware & straps $20
Sub-Total: $537
I flunked my weight goal by about 2lbs… I think the whole kit weighs in at about 12lbs.
The 12S 20Ah baking pan battery cost me about $100 to make, all-in, and weighs about 11lbs.
I just got the system singing a couple nights ago, and am a few fasteners away from actually mounting it to the board.
There are many things not to like about this rig… It’s heavy, expensive, and there’s no good reason the subwoofer needs it’s own amplifier, let alone 12V-powered. I’ll eventually drive the subwoofer with the 2 unused amp channels of the main amplifier. This will trim about 2lbs from the system by eliminating the redundant 12V buck converter and a goodly chunk of the wiring harness.
That said, it SOUNDS wonderful, with more bass than I’ll ever need. I predict a 1/3 range hit with the range-extender battery if I’m rockin-out the whole way. This means my 22mi range w/o the range-extender went up to 43mi, I expect to be back down to ~30mi with the stereo blasting.
There are many ways to skin this cat… I’m quite happy with the way this method turned out.
I’ll post actual skating/listening impressions on Sunday pm. (I’ve got a group ride in Ann Arbor coming up… Will be the maiden skate with this system fully deployed.)
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Nice build. I built a similar boombox w/ a 6S4P battery in 2019, tried skating with it, and tried to use it as a range extender (via a DC-DC boost converter.) I used a pair of 2.5in full-range speakers + a Tang Band 6.5in slim subwoofer. The plastic tactical box flexed like mad… I had to reinforce the inside with wood. I still use it, but wanted something more “solid” for the Nazare… with a LOT more bass. I used a TPA3116 2.1ch amp board for the boombox, as suggested by someone else, but wanted to power this amp directly from the pack, w/o using a buck converter.
Anybody holding onto an “I told ya so” can now let it out… This system failed in many ways to produce the smiles I sought.
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The subwoofer uses a class AB amp, wastes a tremendous amount of power. I’ve yet to figure out how to divorce the preamp circuitry (which I want to use… I need a crossover) from the power amp. It really needs to be powered with a class D amp to make any sense. (90% efficiency or better vs 50%!)
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The BMS board I used for the range extender battery let out the magic smoke under regen braking. With the extender + stereo, I had slightly longer range than stock, and damn near double without the stereo. It only lasted for about 5 skates before the extender fried. Methinks the harshest abuse came from regen braking. I need to use a better / higher current BMS for the rebuild.
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I finally got the speakers solidly mounted (to a pair of PVC pipe fittings strapped to the aluminum amplifier enclosure) but they needs loctite to really stay put.
That’s really it… It sounded divine, but didn’t stand up well to use/abuse, and sucked down a stupid amount of power.
If this shows promise / value in the future, I’ll post revised info.
In the mean time, I replaced a pair of 1400mah Lipo cells (used in parallel as 1S2P) in my Ecostone bluetooth speaker with 4x 3500mah 35E 18650 cells… I’ve left it on literally for 3 days, played it for 12hrs+ at max volume, still not killed it.
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Nothing ventured nothing gained! At least you went for it and tried to build something innovative and cool. I won’t be surprised if you end up with something different in the future with applying the lessons learned from this build… anyone saying I told you so probably never builds anything themselves… besides, no build is every really “done” !
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Unless you’re talking about idle current a class D won’t fix your power drain issues. Turning the volume down will 
Unless your amp is way overpowered?
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Time to add a separate battery pack just for your audio system 
no more magic smoke
I beg to differ re Class D… The best efficiency you can get from a class AB amplifier is about 50%.
Operated upwards of a few watts, most class D amps are above 85% efficiency, many over 90%. I had more inefficiency built into this system with the DC-DC buck converter… Even it that was operating at 90% efficiency, that means my powered subwoofer was drawing 100/0.5/0.9 = 222W to drive the woofer with 100W.
I don’t just want tunes, I want a range extender too. I picked this amplifier board specifically because it could operate at full 12S pack voltage, making my board and audio power source one in the same. This also allows me to eliminate (at least for the “top boxes”) the DC-DC converter and it’s ~10% loss.
Yeah fair enough I thought it was more to do with idle current but looks like it would work well. I’m not that well versed in amp efficiency and power draw other than going for the max lol.
There’s no free lunch here… You can make deep loud bass with little power, but that requires a very large enclosure (tapped horn.) In this thread, I’ve discussed several subwoofers that go low in tiny enclosures, but they are still terribly inefficient. Even the Gallo Nucleus speakers are awfully inefficient. My benchmark is the $400 Ultimate Ears Megaboom, which weighs 13.5lbs, and is about 7.5x7.5x13.5in. That thing lasts 23hrs on a charge, has linear response up to 98db max (at 1m I presume) but doesn’t exactly fit well on my board, in a spot where I can enjoy it. I tried skating with my first home-made boom box firing upward at my crotch, sounded terrible. The “top boxes” need to be pointed at my noggin, at the front of the board, so it’s DIY or bust.