Building The Blanda Sub ~ Big Bamboo Bowl Bass 02Jan24-10Jan24

The near-field 8" Blanda 108s, and even the Blanda Googly Eyes, are excellent but want for bass... they got it! I built a sealed 11" Blanda bowl subwoofer with a 6.5" driver powered by an external 100 watt plate amp which mates with the L/R main bowls well. I'm using a bamboo dog bowl stand to hold this speaker :). The amp is external so as to not take inordinate volume in the cabinet (which it would have). I'll build a box for the amp from leftover Baltic birch probably, rather than buying bamboo plywood... we'll see.

I hoped for a viable 11" sphere subwoofer design that'd get me down below 40Hz, but all those designs needed porting that was very large & long, which could not be done within the cabinet (stole too much volume), and therefore would just look weird ~ like Saturn if wrapped around, or an umbilical coming out of the sphere. Such a port would be about 3.25" in diameter and at least 18" long! Plus, bass ported woofers often sound flabby to me ~ I prefer tighter and more musical bass contributors ~ such as those capable of rendering acoustic bass (40Hz-400Hz)  music well. Therefore, I sacrificed some low end and focused on a sealed cabinet design. As with the L/R main Blandas before, the Blanda sub cabinet is completely fixed to an 11" sphere minus the section taken by the driver, and the driver itself. I looked at a number of round drivers with ~6.5" diameter and needed to find a solid one with an EBP (efficiency bandwidth product) 50-100. Small's rule of thumb is that drivers which yield EBPs above that are only suitable for vented designs, primarily due to their motor's ability to hold court in a completely sealed box. Anyway... from among a half dozen 6.5" drivers I chose the Tang Band W6-2253S with neodymium magnet for the perfect fit without taking too much volume from the cabinet, and it's solid match to task at the low end to 55Hz in a sealed cabinet (Vcab = Vtot - Vsec - Vdrv = 9.14 - 2.3 - .78 = 6.06 liters). It may be meant for walls & doors but it is a solid driver for sealed cabinets like a big Blanda bowl.

The parts arrived and the "the look" is fine and funky.

Fabrication for the sub was nearly equivalent to the original Blanda salad bowl speakers. Again the toughest aspect was cutting the driver hole the correct size with a flat lip to secure the driver nicely - back to the Japanese pull saw for handiwork and then sand clean with a palm sander.

The cut was much more challenging on the 11" bowl than the 8"ers as there was a lot more material to cut through at the bottom of the bowl this time. So much was left over on the flat lip that I needed to sand out a substantial amount to allow the driver to clear... I used a Dremel tool and lots of trial fits. Ultimately it fit like a glove.

I drilled for banana jacks in the "back" bowl, sanded the lips (for glue adhesion), and wired the jacks. I then glued the bowls together into somewhat of a sphere ("somewhat" because the Ikea Blanda bowls are not exactly hemispheres; bowl height is < d/2).

Once the bowls dried I ran a gasket around the driver, wired it, and installed it with wood screws in the "front" bowl. I also installed "feet" on the the dog bowl holder uprights to get some purchase on the speaker, eliminate any rattle, and increase isolation. No wool in the cabinet this time... at least to start. I fired it all up in a smoke test with some Flim & The BBs and got some lowish notes ~ the low rez rudimentary curve looks OK. Who knows if it's right yet, the Blanda 108s are in another town, as is my measurement rig; the setup seems to work well though... no smoke, all jazz. Ultimately I will only pass ~<200Hz to the sub's amp, which despite it having a variable filter maxing out at 180Hz, was still playing higher frequencies.

I listened and measured performance both down-firing and front-firing, mainly to assess whether the carpet absorption or the slot behavior in down firing would effect results. I'm running the sub high enough in the dog bowl holder (4") that I was not worried about compression, and didn't expect slot effects as the sub is a sphere without real slots effecting the driver output. The new Blanda Sub measured the same down-firing or front-firing. Nice thing too as I might well have booted a hole in the driver at my stand-up desk were I to need to run it front firing.

On with the measurements for "near" and "far" in the Nest study... yeah cathedral ceilings will help but there may be some undamped reflections in this room. Measurements show great integration between the new Blanda Sub and the Blanda 108s, whether listening near @ the desktop or far across the room @ the fly tying desk. Near shows a bit of shout at 460Hz, probably induced by the desktop; it's rarely good to have a horizontal surface right below your speakers ~ I'm not worried about it given how great the Blanda 108s sound overall... especially now that they have bass support. I refined the Blanda Sub integration with the mains... I adjusted crossover to about 125Hz with gain on the amp about 60% ~ sounds good and measures right.

I am completely stoked at excellent sound from "far;" I did not expect that. This is a very solid DIY audio showroom made of salad bowls.