Reasonably compact sub design?
I've spent quite some time designing a reflex sub, which is both compact yet reaches low enough while keeping a good sensitivity, which should be adequate for smaller parties.
The main 3 goals were:
- Under 200 L external (and light), 1 man portable and dimensions for 2 to fit in the trunk.
- Go flat to 40 Hz (ish) with sensitivity of minimum 94 dB
- Cost under 500 euros for the entire thing
It's designed with 9 mm baltic birch in mind using finger joints for easy assembly.
The driver of choice right now is the Faital Pro 12FH500 4 ohm, since I want 2 ohm resistance to be able to draw all of the power of the MA12070 amp, and the driver simulates pretty well.
Fusion360 simulation shows the first modal frequency at 285 Hz, well out of operational passband. I've attached some pictures, both of the design and from WinISD simulations. Group delay peaks at 36 ms at 37 Hz.
Are there any big issues, that I have overlooked, or any good recommendations regarding design?
I've spent quite some time designing a reflex sub, which is both compact yet reaches low enough while keeping a good sensitivity, which should be adequate for smaller parties.
The main 3 goals were:
- Under 200 L external (and light), 1 man portable and dimensions for 2 to fit in the trunk.
- Go flat to 40 Hz (ish) with sensitivity of minimum 94 dB
- Cost under 500 euros for the entire thing
It's designed with 9 mm baltic birch in mind using finger joints for easy assembly.
The driver of choice right now is the Faital Pro 12FH500 4 ohm, since I want 2 ohm resistance to be able to draw all of the power of the MA12070 amp, and the driver simulates pretty well.
Fusion360 simulation shows the first modal frequency at 285 Hz, well out of operational passband. I've attached some pictures, both of the design and from WinISD simulations. Group delay peaks at 36 ms at 37 Hz.
Are there any big issues, that I have overlooked, or any good recommendations regarding design?
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Consider extending the center brace for the port to the back of the cabinet. That should provide additional front to back bracing at the centers of the baffle and back panel.
+1 and at nearly 41 ft of delay [~28 Hz] seems excessive based on a [now obsolete?] 1.0 Hz limit = ~27 ms/37 Hz.
That EQ at 60Hz will cost you 2dB of overall headroom, and that is where the kick is situated.
Do you operate the amp with battery, or why is it so flimsy?
I would have preferred bms-12n630 woofer
Do you operate the amp with battery, or why is it so flimsy?
I would have preferred bms-12n630 woofer
I know I'm giving up some headroom with the EQ, it was done to achieve a flat response.
Yeah, I forgot to mention that this is a battery powered system, so the sub will probably never see more than 120 watts. That's also why I've mainly looked at drivers with relatively low mms and high motor strength in order to keep a good sensitivity.
The BMS 12N630 driver looks nice, simulations however show no significant improvements and the cost is 100 euros higher compared to the 12FH500.
Yeah, I forgot to mention that this is a battery powered system, so the sub will probably never see more than 120 watts. That's also why I've mainly looked at drivers with relatively low mms and high motor strength in order to keep a good sensitivity.
The BMS 12N630 driver looks nice, simulations however show no significant improvements and the cost is 100 euros higher compared to the 12FH500.
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But neither fulfills my criteria of cost under 500 euros for the entire box nor the criteria of sensitivity above 94 dB
A Reflex sub is a box with a tuned port. Any properly tuned combination of volume & port will work - But what makes one reflex cabinet better than another?
The ports can be big enough to reduce compression effects.
Ports can be postioned to allow convection heat to escape. i.e top & bottom.
Boxes can be made more stiffer & use cross braces to couple opposing walls
There are other improvements but those are the fundamental ones that make one box better than another for high power use, without increasing costs!
The ports can be big enough to reduce compression effects.
Ports can be postioned to allow convection heat to escape. i.e top & bottom.
Boxes can be made more stiffer & use cross braces to couple opposing walls
There are other improvements but those are the fundamental ones that make one box better than another for high power use, without increasing costs!
Given 2 woofers, you could gain a lot in terms of keeping th ecabinet light and efective would be to mount the drivers push-push. 9mm might do the job, the bracing if you are using 9mm material, even w push-push will need to be more substantial.
When i saw compact i thot 20 litre or less, 200 litres is not small.
dave
When i saw compact i thot 20 litre or less, 200 litres is not small.
dave
I would consider recessing the baffle (about 5 cm) to physically protect the drivers, in this recess you can also add a grill with acoustically transparent foam to protect the drivers against the weather.
I would also consider handle placement at this point as they might best go at the place where your bracing currently is. If you use 'wooden handles' you can make a wooden cap, that acts as bracing or easily can be made a part of it.
Example of wooden handle with cap: YouTube
If cost (and weight) is an issue you might like the B&C 12CL64, if it's just the cost consider the Thomann 12-280/A.
Johan
I would also consider handle placement at this point as they might best go at the place where your bracing currently is. If you use 'wooden handles' you can make a wooden cap, that acts as bracing or easily can be made a part of it.
Example of wooden handle with cap: YouTube
If cost (and weight) is an issue you might like the B&C 12CL64, if it's just the cost consider the Thomann 12-280/A.
Johan
The Fane 12-300 is value for money, even the cast frame PRO version is not that expensive.
I'd prefer using 15mm ply on a box this size, but 12mm should be okay too, still need a bit of bracing but much less. 9mm might need a lot of bracing, so not sure how much weight you save on that compared to 15mm or 12mm.
I'd prefer using 15mm ply on a box this size, but 12mm should be okay too, still need a bit of bracing but much less. 9mm might need a lot of bracing, so not sure how much weight you save on that compared to 15mm or 12mm.
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I have extended the center brace and re-run the nodal simulation without pinning the entire side of the speaker down. Results now show a very small area with resonance at 200 Hz, which I would consider benign. Next resonance is at 300 Hz, so I expect this to be good enough for the amount of power I'm going to use.
I've thought a lot about push-push driver configuration (already have one designet actually), but this box is going to be used in many different configurations, so can't guarantee optimal placement. For that reason I'm going to go with the old faithful front drivers and front port.
I've simmed alot of the driver recommendations, the CL64 is a nice driver, however the 4 ohm version (which I only found on toutlehautparleur) is out of stock for at least 114 days, so I'm sticking with the 12FH500-4.
Handles, flange and speaker grill has already been added, the grill is just very resource intensive for Fusion360, which is why I'm not showing it. Handles are placed right smack in the center of mass.
So far Fusion360 estimates total weight including drivers to be 16 kg, my goal was under 20 kg. External volume is 158.7 L and net volume is 141.5 L.
I've thought a lot about push-push driver configuration (already have one designet actually), but this box is going to be used in many different configurations, so can't guarantee optimal placement. For that reason I'm going to go with the old faithful front drivers and front port.
I've simmed alot of the driver recommendations, the CL64 is a nice driver, however the 4 ohm version (which I only found on toutlehautparleur) is out of stock for at least 114 days, so I'm sticking with the 12FH500-4.
Handles, flange and speaker grill has already been added, the grill is just very resource intensive for Fusion360, which is why I'm not showing it. Handles are placed right smack in the center of mass.
So far Fusion360 estimates total weight including drivers to be 16 kg, my goal was under 20 kg. External volume is 158.7 L and net volume is 141.5 L.
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Better box than previous revision, but what does "but this box is going to be used in many different configurations" mean?
What I meant was that the sub would be used in a lot of different settings. From on festivals, in small apartments and for garden parties. I could imagine placing the box up against a corner in several occasions, which isn't possible when doing a push-push configuration. At least not in my head, but I'm ready to be proven wrong 😀
Thanks for that. Didn't want to misread/miss requirements for intended application(s). It's clear you've worked hard on it, the question is how much optimization you want (and how sick of working on it you are).
I'm always ready for a bit of optimization, changing the 3D model is a lot easier than redoing the real box, haha. I'll be laser cutting it, which is also why I don't do angled cuts.
As for powering it, the electronics will get its own 3D printed box. Battery is 20 Ah LiFePO4, amp is 2x MA12070 and ADAU 1701 for processing. It's on my to do list, but shouldn't total more than 6 kg, including a charger for the battery and some fans and low power cut off. Going for as compact as humanly possible here.
Top will be 3D printed synergy horn designed by bwaslo.
As for powering it, the electronics will get its own 3D printed box. Battery is 20 Ah LiFePO4, amp is 2x MA12070 and ADAU 1701 for processing. It's on my to do list, but shouldn't total more than 6 kg, including a charger for the battery and some fans and low power cut off. Going for as compact as humanly possible here.
Top will be 3D printed synergy horn designed by bwaslo.
What you do depends on what modules & tools you have licenses for and how much of a pain interoperability might be. IMO, there's both (a) some mass left on the table to be had and (b) some better distribution of that mass for two 12" woofers on a 9mm baffle. Vibe modes are important and that's one thing, but if something moves, it's loss, right? (BTW, what is the passband target?) Not talking failure/drop/buckling, just "normal operation" and loss takes some of the bottom off of your LF. If you're fighting for every dB/kg-euro, it might matter to you.
If you have it, suppress the brace holes and cut an optimizer loose on the them for a couple load cases of simple linear statics even, and you'll see where the waste is (and isn't). If you don't, you can get useful results even hacking-up a separate single-body to slam-out a few iterations guided by stress & deflection. It looks symmetrical (is it?) so you can cut it in half and mesh finer if you need to for some of the detail-work. Alternatively, load it as a pressure vessel (both ways) and you can gain insights, too. You don't need all the interfaces and non-linear stuff to get something useful. The problem is thinking-out all the Real loads and choosing what to provide-for. A couple quickies should get you a better box if you have the modules and time/inclination to check. As always, better is handcuffed-to "better for what?". (Yeah, all that an not even any "acoustics stuff", which might matter some) 🙂
It does raise the issue of handling, too, and providing for who you might loan it to. I don't know anything about laser-cutting ply, but my 35 seconds of "research" indicates that those materials aren't weather-coated the same so they don't burn weird and that cores vary? Nonhomogenous materials are always reality, but even qualitative diffs in the sims will steer you (ie, you don't have to bet your tail on quantitative failure numbers in this project). If your friends are anything like mine, things you loan will come-back thrashed (if they ever come-back). Perhaps some pros have input, but I'd plan for the thing to be dropped at a minimum.
Unrelated thoughts/considerations: What about wings/doors for both protection & some sort of "baffle" for 2pi use (like old theater speakers)? What does the synergy-thing on top weigh and can you bank on it always being there)? Where will it be stored when not used (insect/mammal-proofing?)
Might be a little late, but the only thing I can think of for push-push to still work is maybe some kind of slot-loader with push-push "module" like Dennis used push-pull. Having trouble thinking that through--almost "saw it" for a second, but it might acoustically cancel and I think it adds wood 🙂
PS Your printed horn looks beautiful and I'm jealous.
If you have it, suppress the brace holes and cut an optimizer loose on the them for a couple load cases of simple linear statics even, and you'll see where the waste is (and isn't). If you don't, you can get useful results even hacking-up a separate single-body to slam-out a few iterations guided by stress & deflection. It looks symmetrical (is it?) so you can cut it in half and mesh finer if you need to for some of the detail-work. Alternatively, load it as a pressure vessel (both ways) and you can gain insights, too. You don't need all the interfaces and non-linear stuff to get something useful. The problem is thinking-out all the Real loads and choosing what to provide-for. A couple quickies should get you a better box if you have the modules and time/inclination to check. As always, better is handcuffed-to "better for what?". (Yeah, all that an not even any "acoustics stuff", which might matter some) 🙂
It does raise the issue of handling, too, and providing for who you might loan it to. I don't know anything about laser-cutting ply, but my 35 seconds of "research" indicates that those materials aren't weather-coated the same so they don't burn weird and that cores vary? Nonhomogenous materials are always reality, but even qualitative diffs in the sims will steer you (ie, you don't have to bet your tail on quantitative failure numbers in this project). If your friends are anything like mine, things you loan will come-back thrashed (if they ever come-back). Perhaps some pros have input, but I'd plan for the thing to be dropped at a minimum.
Unrelated thoughts/considerations: What about wings/doors for both protection & some sort of "baffle" for 2pi use (like old theater speakers)? What does the synergy-thing on top weigh and can you bank on it always being there)? Where will it be stored when not used (insect/mammal-proofing?)
Might be a little late, but the only thing I can think of for push-push to still work is maybe some kind of slot-loader with push-push "module" like Dennis used push-pull. Having trouble thinking that through--almost "saw it" for a second, but it might acoustically cancel and I think it adds wood 🙂
PS Your printed horn looks beautiful and I'm jealous.