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Floorstanding mid-bass cabinet from Denovo subwoofer flatpack kits

gy-k

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Oct 25, 2021
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Maybe I can put this out here as a thread, I brought this up previously in the Directiva r2 thread.

The idea is that a floorstanding cabinet could be constructed from two Denovo 1.0 cu. ft. subwoofer kits (or maybe also three 0.67 cu. ft. kits) by gluing or bolting them together. The combined internal volume would be more than 56l based on the specs. The external dimension would be HxWxD: 28.5"x14.25"x15", 724mm x 362mm x 381mm. (For a size comparison I'm going to pick the Revel F208, HxWxD: 46.5"x11.8"x14.8", 1182mm x 300mm x 375mm.)

I've found that the Beyma 10iX driver models nicely in a 56l ported cabinet: "https://imgur.com/lU5vX2F" Here tuned to 31Hz and at an SPL making use of the large Xmax/Xmech. If the response looks like there's a hump at 40Hz, that goes away and the response gets smoother overall by reducing Qa to 50 (absorption inside the box) and primarily by reducing Qp from 100 to 10 (case of absorption inside the port?). The response the looks like this: "https://imgur.com/Agggoe8" and f3, f6, f10 are: 34.6, 30, 25.9 in this example.

I guess absorption inside the port would be a good idea in any case as the port length of 35cm for this tuning is rather long, with pipe resonance around 500Hz. Actually this 4" port wouldn't even fit inside, but two 3" ports (slightly larger overall diameter) would probably fit vertically, so this would be a bottom ported cabinet. Having the ports on the bottom would probably help reducing the port length a bit, this could be modeled with Akabak. (Having cardioid vents could also help by "letting out" sound that would excite the port?)

Looking at the FR of this driver, it looks like it might be nice used as a mid-bass up to 1kHz. Personally I think this is interesting, because it could be part of a 2-way system as well, maybe even a passive one.


Another driver I looked at is the Beyma 10G40. This driver looks quite affordable right now in Europe. Half the excursion specs, but around half the price or so. I wondered if two of them could be used in a "1.5-way" configuration. But this requires a large coil (20mH in this example) for the second (bottom) woofer to roll it off around 100Hz and another large coil and large capacitance (15mH, 270uF) to flatten the impedance peak for less interaction with the low-pass coil. The parts are quite costly, the combined cone area of two 10" drivers below 100Hz would be nice though. Otherwise two DSP and amplifier channels would be needed for bass. This example relies on DSP nevertheless. It's two separate sealed boxes with Linkwitz transform and some EQ fixup. (But two of the four filters are for an example LR4 crossover at 1.1kHz. A passive system might be possible, one that relies on global DSP that implements the LT and some EQ.)

"https://imgur.com/a/2u6BB91"

The magenta line is a target response of a 30Hz 3rd order low-end roll-off and an example LR4 crossover at 1.1kHz. The microphone height is at 1m. The driver level has been increased so that the drivers just hit Xmax at 25Hz. The amp power there is 175W. The SPL is at 2m, it's 92 at 50Hz (though note this is when two 10" hitting Xmax at 25Hz), f6 is at 24Hz.

So this one would be like just two sealed boxes on top of each other and some passive parts (and DSP). There's also a version of the 1 cu. ft. subwoofer flatpack kit with a driver cutout.
 
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gy-k

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There's also a version of the 1 cu. ft. subwoofer flatpack kit with a driver cutout.

On the product page in the Q&A section it is stated that the cutout for the driver has ID: 9.25" and OD: 10.47". Based on this both drivers named above would fit just right: "https://imgur.com/a/FQqpQAC" so no woodworking would need to be done for the driver cutout. In the case of the sealed "1.5-way" idea it would be just two of these boxes on top of each other, the internal volumes need not to be unified. The cost of the drivers and crossover parts would be around $500 plus $200 for the flatpacks, per channel. So not a very budget plan. (The European prices for the drivers are probably better though. It would also need DSP, but probably one global DSP channel could do.) The passive ported version would be around $100 less expensive, per channel. I imagine cutting holes on the tops/bottoms and joining the two boxes wouldn't be very hard to do. (Though there's is no going back to separate boxes after that.) The challenge is to work out a nicely behaved port.
 
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