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12" Sub Build With BMS12N630

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    Posted: 05 August 2021 at 9:03am
The goal for this project was to make a 12" sub for home HiFi, home DJ use, and home studio use.

Happy to provide the Fusion 360 CAD file to anyone for non-commercial use and a paired cut-list + DXFs.

Driver is BMS 12N630.

Amp for testing was a bridged Hypex FA122 (250w 4ohm bridge) - I usually have this in a studio monitor with a 6" woofer and small HiFi tweeter, to put it in perspective, this is a small power plate amp)

Amp for ongoing use will be Hypex FA252 (500w 4ohm bridge).

This driver seems to soak up a lot of power, if I was using it for PA use I'd pair it with an amp capable of good 1200w peaks - this design would be better and much cheaper passive but it will get used by friends of mine who don't want to stuff about with external amps and processing, so Hypex FA is it. The FA502 bridged into 8ohms would give this sub 1000w peaks and I think that would be about right.

I tried various port lengths to find optimal tuning.

- 2x450mm x 90mm for a 35hz simulated extension
- 2x380mm x 90mm (no simulated, only measured)
- 2x300mm x 90mm for a 37hz simulated extension (This is what I think I will go with as it seems to be the best trade off between low end extension and overall gain.)
- 1x300mm x 90mm to test to ensure the port tuning was raising low end gain

Port ends flanged and rounded with a 12mm rounding bit to reduce vent velocity.

I also measured with and without a layer of 90mm Earthwool R2.5 rated density across the rear wall. There was about a 1db gain on the low end and a 1db reduction from 42hz upwards.
I think I will keep the wadding in this enclosure, it subjectively cleaned the cab up soundwise and made it sound less "ringy".

I measured with REW in the backyard with the sub facing front to the sky and the measurement mic hung 30cms or so from the centre of the cone for all measurements.

The top of the enclosure was not glued shut (only clamped) which allowed changing the port lengths and internals and then re-measuring.

In a subjective test against another 12" sub I have in the same room (Yamaha DSX12 MK2 Bandpass) this ported sub with the BMS driver goes far far deeper - the Yammy doesn't have much below 55hz but goes far far louder at 90hz which is where they seemed to have tuned it for most SPL, rather than extension.

The Yammy has a 1000w amp so hits the peaks much better at the moment.

If I was planning to use the BMS12 outside I'd get a Hypex 502 bridged into it to give it 1000w at 4ohm but I think the 500w FA252 should be enough for home listening, DJ, and studio work.

This sub will get used at small house parties most likely so I can report back after a few nights of giving it stick over the next 6months or so.





















38hz tuning with no smoothing, 24db LR HP 120hz 24db LR LP



38hz tuning with psychoacoustic smoothing, 24db LR HP 120hz 24db LR LP The sub below is the first prototype and does not have the extension at the front for a grille or the grille bracing for mounting like the updated CAD version does.


Edited by vertx - 05 August 2021 at 9:42am
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Post Options Post Options   Thanks (1) Thanks(1)   Quote JonB67 Quote  Post ReplyReply Direct Link To This Post Posted: 05 August 2021 at 4:40pm
Nice work. They're great little drivers. 

Loving the bracing too. Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vertx Quote  Post ReplyReply Direct Link To This Post Posted: 07 August 2021 at 11:56am
Added the binding posts between plate amp enclosure and the internals today, plus sprayed the ports black.


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Post Options Post Options   Thanks (1) Thanks(1)   Quote fat_brstd Quote  Post ReplyReply Direct Link To This Post Posted: 08 August 2021 at 2:06am
nice work
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vertx Quote  Post ReplyReply Direct Link To This Post Posted: 09 August 2021 at 9:08am
I've got a DATSv3 on the way so will be able to confirm tuning before I seal up the enclosure/ports!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vertx Quote  Post ReplyReply Direct Link To This Post Posted: 11 August 2021 at 5:45am
DATSv3 arrived!

Look like measurement of impedance shows tuning same with or without wadding.

It also looks like FS and Qts drastically change but I'm not sure if using the "Free Air Parameters" settings is useful for when a driver is in the enclosure for anything other than impedance?




and again with the 90mm wadding removed from the back wall. A few resonances show. I'm guessing some of these may also be due to the top not being glued shut and temporarily clamped.

Interestingly the impedance is higher overall in the measurement without wadding... especially the second one at 54hz.



The FA252 showed up today too so plugged that in and gave it the 500w. The FA252 has much more control than the FA122 that was on temp duty before. Next time I would stretch for the FA502 and get a bridged 1000w into it to really do the driver some justice.

Matching the imdedence graph to the FR frequency graph seems to show the blip at 372hz in imdedence might be some sort of standing wave thats cancelling out.

The bump around 602hz might be the port pipe resonance which is close to where the WinISD sim has it. This might be reduce when I add further port flanging/rounding to the port exit inside the enclosure.



Update: 12N620 free air parameters (taken with top off enclosure)





Edited by vertx - 11 August 2021 at 9:45am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vertx Quote  Post ReplyReply Direct Link To This Post Posted: 11 August 2021 at 7:46am
This is another BMS12N620 in free air:




Published TS specs:




Setup:


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Post Options Post Options   Thanks (0) Thanks(0)   Quote vertx Quote  Post ReplyReply Direct Link To This Post Posted: 30 August 2021 at 11:59am
Got the port flanges for the inside added, then glued on and rounded over the top.

Remeasured with the DATS and found a lot of the 100 - 350hz imdedence ripples/cabinet resonances were now gone with the top glued on.

Tried also with R1.7 rockwool but preferred the R2.5 Earthwool which I got covered up in fabric.

Gave it a propper run-in over the weekend, two 12hr sessions, 6 hours of which the clip light blinked every now and then. Safe to say it's a great sub and much better than the Yamaha in the same room.

If I was upping the amp to 1000w The ports would need to be redone to vent more air, with my ear to the port at full tilt I can hear some minor vent turbulence.




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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greg32 Quote  Post ReplyReply Direct Link To This Post Posted: 13 September 2021 at 10:36am
Nice compact cab well done. where did you order the bms from? Ta
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vertx Quote  Post ReplyReply Direct Link To This Post Posted: 13 September 2021 at 11:38am
Thomann Ships the BMS to Australia via their online store.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vertx Quote  Post ReplyReply Direct Link To This Post Posted: 13 September 2021 at 11:45am
Couple more pics after a few coats of poly

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Post Options Post Options   Thanks (0) Thanks(0)   Quote JulianDA Quote  Post ReplyReply Direct Link To This Post Posted: 13 September 2021 at 12:48pm
Very good work! I really like the additional pieces of wood on the front. They give the whole cab a much more interesting look Clap I think just a black grille without foam will look superb on this little sub Thumbs Up

PS: I also had the idea of the recessed reflex ports with routered ends in my head for a while...your build convinced me to definately use this technique in my next cab! 
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