Burning Man Bike Sound System - taking it semi-seriously

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So I'll be going to Burning Man this year for the first time and I want to have a sound system that can be put on the back of a bike using a cargo rack of some kind. The foremost goals are SPL and sound quality, roughly equally weighted. Bass extension is taking a backseat here because fitting a 4 cu ft cabinet on a bike is just not OK. Bonus is that these speakers will be able to be used normally after the Burn is over.

From early on I was thinking of using the SEOS waveguides but after more research and trying to fit everything into my budget, I've come up with the following build. I feel like I've figured out most of it but I have a few questions that will come after I list what I have below.

2x 10" 2 way speakers, internal net cabinet volume ~.72-.75 cu ft, using:

Biamplified using a miniDSP and two of these Sure 2x100W TDA7498 amp boards, powered through this chain:

2x 12v12Ah SLA batteries I had lying around -> 400W power inverter -> Mean Well SE-200-36 36v power supply.

The cabinets have outside dimensions of 18.5"H x 13"W x 9"D and will be made with 3/4" Baltic Birch. Here are some images (album if they don't load right) of what each cabinet will look like:
Back view:
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Side view:
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Front view x-ray:
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Front view opaque:
mBCuNiZ.png


Here are the simulations for the woofer (album if the images don't look right):
Transfer Function:
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SPL for both at the same time with 75 watts each:
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Excursion with 75 watts:
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Port air velocity with 75 watts:
PzrzhPG.png


The few concerns I have about this are mostly related to the sound quality. I'll be using a miniDSP as an active crossover since I'd rather avoid the headache of building passive crossovers and then re-tweaking a bunch of times, etc... but since the compression drivers are so high sensitivity, should there be a resistor in series with the compression driver (maybe an L-pad if the high resulting impedance messes with amplifier frequency response) to avoid noticeable noise coming from it? I'm already going to use a cap in series so they're not accidentally destroyed with turn on thumps and the like.

Also does anyone have experience with the Dayton waveguide? The SEOS-12 looks realllllly nice but I don't know if it's worth the extra $18 per speaker to upgrade. I see that the Dayton has been used in Econowave builds which people seem to think sound fine. The sharp corners at the end of the waveguide kind of scare me though because of the possibility of diffraction and the resulting frequency response artifacts, though I'm not sure if anyone including myself would even notice in the end. The horizontal dispersion on the Dayton waveguide is slightly narrower than the SEOS as well (by 5-10º) but that's a compromise I'm willing to make if the sound is practically the same for much cheaper.

The total weight of everything seems to be coming in around 90lbs so putting this all on a bike may be a bit difficult but in the worst case, my neighbor has a welder and brackets can be made! :D

For the woofer section, I made allowances in the simulation for light stuffing of the back and sides of the box (set Qa = 18 in WinIsd) to attenuate reflections inside it. Worst case I end up using the miniDSP to make a high-q notch and attenuate any resonances like the port that may remain after lining the box.

If you've gotten this far in my post (congrats lol ;) ) you may be wondering how people will get dancing with bass extension that barely goes to 70hz. Luckily I snagged an old-ish (early 2000's) Waves MaxxBass 102 extender off of ebay. They don't make them anymore for cheap, now it's all several hundred dollar rack mount units, this one is 1/2 rack width and not deep at all. It's a glorified distortion generator but will be used tastefully to fool people with the impression of sub-70hz bass. With my tests so far it performs satisfactorily, it will probably end up going before the miniDSP in the signal chain so the compressor/limiter in the DSP catches any peaks that it creates.

Having a pair of high fidelity loud speakers after Burning Man is also a goal here, so if you guys think that the SEOS upgrade would be worth it please say so. I also made the port big enough such that each speaker can handle 150 watts (instead of the 75 I'll be using at BM) without going much above 17m/s peak air speed.

Is there anything I may have missed here? I'll update the thread in a month or two after I start gathering parts and building stuff; waiting on my internship to start so I can get some $$.

Cheers,
--amddude
 
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I think your idea is fun but your trying to make it too universal. I think HiFi, PA, and portable are all very different compromises.

What are you thinking about, is this to entertain you, or to make a mini soundsystem for DJ's and many people to dance to?

If you are just to entertain your self, I would suggest some thing like a "UE Megaboom" as its no work, fun and super portable.

If your doing a sound system have you considered that you could go a lot cheaper and with pizo tweeters, and open baffle midrange?

By a bike do you mean a human powered bike or a motorbike? Is the system stationary once assembled or going to sit on the back of the bike as you move around?

Are you trying to do stereo or would mono be enough?

You could use relatively cheap 18650 cells and keep the weight down. You can get these out of old laptop power supplies and typically just one in a laptop power supply is dead.

If all the parts are to be reused in other places, and wood is your plan, when sealed boxes would be smaller and easier, why make bass reflex?

Do you need 70Hz? It is really low for outside, targeting -3dB at 140Hz seems reasonable to me and makes a lot more design options, have you checked you really need this low bass?

If DIY and creating a sound system that is highly portable why not go foam core for your enclosures.

http://www.diyaudio.com/forums/full-range/223313-foam-core-board-speaker-enclosures.html

If your targeting just stationary midbase, (and mono) and size is less important, have you thought about doing a mid bass horn, it could be made of sections that fit inside each other, and with foam core it could be very light.

The best outdoor PA systems I have ever heard have been Giant Horn systems, pa DIY construction at Fusion Festival (Germany).
 
Ideally this system will have multiple purposes, with portability weighted the least. I want to use it at camp where it wouldn't be moving at all, and be able to put it on the back of a (human powered) bicycle, which would require a beefy cargo rack that I'm willing to build. After Burning Man I want to be able to use them for parties and maybe as a hifi if they end up sounding good enough.

I will be making two and using all the outputs of the miniDSP so indeed I would be doing stereo. Worse comes to worst at the burn, I'll just leave one of the two speakers that I'm making back at camp, and just have one battery, one speaker, plus the amp and DSP on the bike to keep the weight down. It would still get decently loud while maintaining the other goals discussed below.

My budget for this system is around 500 dollars so I'm willing to put more money into the speakers and deal with the weight of the SLA batteries I have lying around if that means that they'll sound better, be more durable, be able to be used in other applications later. It seems like I can get close to making this both a party-ish and hifi-worthy system with the budget I have. I wanted to use wood because I have just enough nice 3/4" birch lying around to make two of the speakers I showed in the first post, and because I want the enclosures to be tough and something that I can be proud of.

I like the idea of foam core for experimentation, extreme portability and weight saving but for these I'm willing to tolerate the weight of wood to keep the build quality good and make sure I don't encounter distortion or have the cabinets rattle apart if I turn them up too much.

I want to entertain, lets say 10-20 people people with them, that's why I was going for SPL, and I'm willing to get a slightly bigger box (compared to a sealed design or a tiny ported design, but still less than about 1ft^3 for each) so I can get at least below 100hz. Although I said in the OP that "bass extension is taking a backseat here" I think that my definition of "backseat" is that I'm not trying to get to the 50's range or lower that I've been targeting with the other builds I've done.

I feel like 80hz, is a reasonable goal for extension in a ported system designed to be used outside while also being loud considering that they will be used for a lot of electronic music. Normally for electronic music I'd want a -3db point of at most 35-40hz but using the Waves MaxxBass unit I'll be faking it out with harmonic generation, though the believability and quality of the fake bass is not as good when the cutoff frequency increases. With the design I currently have the fake bass should still sound decent because the second harmonic of most of the lowest bass notes in the original signal will still come through the speakers, whereas if I was going for an f3 above 100hz there would only be third harmonic and above for some notes, which is not nearly as satisfying as the meaty sounding second harmonic.

I hadn't considered cheaping out on the cabinets and tweeters and then just buying/making better other components around the woofers, amps, and DSP later. That could be an option but doing it fully right the first time would probably keep costs down though weight would still be high. I'm not super concerned about the weight anyway because even if it means more resistance pedaling the bike, it's just incidental exercise which isn't bad.

The design I made was inspired by the Fusion waveguide designs from DIYSoundGroup, though I didn't want the weird bass shelf designed for indoor use that I found out those designs had when I did some digging. Turns out the nice flat response graphs they post on their order pages include assumed room reflection gain from being placed near a wall which would be a problem were I to use them outside.

The thing I'm most concerned about still is if the dayton waveguide will sound noticeably worse than a SEOS and if the extra dollars for the SEOS would be worth it considering that I want to use these speakers long after the burn.
 
Have you calculated for power consumption? 24ah of batteries running 12VDC to 120VAC to 36VDC won't last more than a few hours at high volume and you shouldnt discharge more than 50%. Do you have a generator in camp to charge off? You'll need to charge the batteries one at a time, or use 2 chargers, or hook them up in series and use a 24v charger. You'll need to leave your bike in camp while this happens (you won't want to do this) or remove the system from the bike for charging...or bring two bikes.

I run a 15" passive yorkville speaker with ~105db/watt sensitivity using a 200w mono boss amp and a Rolls "Mini-mix" mixer to pre-amp from the mp3.
2x26ah SLA batteries in parallel run the 12v amp, and a separate 12v 10ah battery runs the 12v Rolls mixer and the lighting system. It'e loud and sounds great. I get about 4 hours at full volume and another 4-6 at 80% volume before I start getting close to 50% battery drain. The whole setup is just under 55lbs. Speaker goes on the rat trap, amp behind the seat, batteries either side of the rat trap (put them as low as possible). I modified milk crates and strapped them onto the sides as battery compartments but I've seen ammo boxes used as a prettier version of the same. Mixer and mp3 on the handlebars.
Not audiophile quality I'm sure, but it's more than adequate for a bike and crazy loud. We've been throwing bike parties for years with this setup and none of the DJs or audiophiles have anythijg bad to say about it... plus it lasts all night.
Pulling 90lbs around the playa is going to suck *** so bad. If the ground is soft you might not even be able to unless you have fat tires.
You need bigger batteries or more batteries. I'd recommend a trailer with fat tires so you can detach it for camp charging while you're out doing other things. I'd also recommend a single speaker and a mono output, stereo doesn't matter on a bike. I chose the speaker in part based on the high sensitivity since power (and thereby weight) is the biggest issue. Unless you have a huge budget to buy big lithium batteries...
Admirable sound quality analysis though! I don't know what most of that means 😉
Also PS your bike will be but a grain of sand at the beach, you'll see once you're there. Happy burning
 
Update

So I did end up building the design I initially proposed, and towing 90lbs around the playa did indeed suck ***. I ended up using the system mostly at camp.

The batteries did last pretty long, and we had another car battery that I used while we were at camp.

While it didn't fit the original intended purpose, I'm very happy with how they sound, using the MiniDSP as the crossover, manually tuned from REW measurements. The MaxBass unit was also very good at creating the illusion that the speakers were tuned lower than they actually were.

Pic attached of one of the speakers
 

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