Building Blanda Salad Bowl Speakers ~ Nothing Is Parallel In The Googly Eyes 21Dec23-26Dec23

I've enjoyed designing and building custom speakers for the NestMT and have some additional "needs" I will fill with a new pair of DRC DIY speakers. They'll most likely adorn my study desk at the Nest so need to be small and great for close field listening. I've read about building spherical cabinets (few standing wave issues and significantly reduced diffraction interference) and have heard commercial (B&O) designs employing them as well. In fact, some DIY forums suggested that a build based on Ikea Blanda Matt bamboo bowls are effective and inexpensive! I bought four 8" bowls and gave it a try. In just 4 hrs I was enjoying HiFi sound with surprisingly good bass thumps.

I was impressed prior with the sound and performance of Tang Band full range 6.5" drivers I'd tried in the NestMT BLHs when I was settling on drivers for them. I dove hard on their line of 4" full range drivers for the Blandas and settled on a brand new and fairly wild design, the W4-2356. The design uses a patented offset voice coil and custom polymer cone which supposedly avoids concentric cone modalities and considerably reduces diffraction issues in any cabinet (though that will already be a small effect in a sphere with no flat front baffle). The driver is not cheap as it is new and uses a neodymium magnet; it is less efficient (85 dB/w) than I'm used to using, but early lab tests were very good, so I gave it a try.

Design choices beyond driver selection were very constrained given the cabinet is basically set from the get go... it's whatever two 8" salad bowls glued together will yield. That's 3.6 liters before adding the driver to a flat cut opening and 2.7 liters after removing that section. I sketched stuff and used modelers to help me choose bass reflex port dimensions given Theil/small parameters and the cabinet. The sealed cabinet variant performance would not have been good from initial modeling, so I went right to the ported style. I saw some Onken-like port mid-sections from other DIY builders but decided simpler & faster is warranted here.

Once supply chains caught up with my ideas, my first fabrication step was the most challenging part of the project. That was to cut a hole for the driver in the "front" bowl... the cuts needed to be perfectly sized and reveal a flat lip to secure the driver well while looking smooth to the sphere. The pro alternative was to use CO Lumber's power planer to repeatedly and carefully plane down sections to the right size from the sphere. Nah... I went full hand woodworker. Drawing the cut lines was done using a compass and I used a hacksaw to start the cut, then a simple fine toothed Japanese pull saw (flexible and thin) and took my time freehand to make the driver hole. The driver dry fit looked fine though the first bowl cut was a little large and I adjusted on the 2nd... gaskets will seal around the drivers to the bowls.

I then used a hole saw to cut a hole in the "back" for my ~ 1" x 4" flared port. I also drilled for the banana plugs. The port was a good friction fit but I glued it in place anyway. It's not a great location for the port directly behind the driver but the off-axis nature of this particular driver added confidence it'd be fine. I like it there aesthetically to remove the bowls' original manufacturing indentations & markings. Once the holes were completed I sanded the lips of the bowls to allow better acceptance of the glue. We don't want the spheres to roll around so I added 2 ball feet (drawer pulls) to each cabinet while the 3rd point of rest on the surface is the cabinet itself, which was dotted with a silicon foot. I then glued and clamped the bowls together into cabinets.

Once dried, I stuffed 6 oz of poly fiber fill into the interior and wired up the drivers. I laid a sealing gasket around the drivers and secured them to the "fronts" carefully with black wood screws.  All the hardware is silver/nickel to match the drivers' accents. Matt called them Googly Eyes.

I don't expect much great from a measurement standpoint ~ these aren't the best cabinets ever conceived, and they are tiny. However I was shocked and pleased at the listening results. The drivers are smoother at the mid-high end than other 4" sounding close-fields I've heard. The bass is just decent of course, but present at the rear tuned port as hoped ~ they could still use subwoofer support as you can imagine. I listened for a couple hours or so in the COS family room and lower level setups using just the Blandas and they are very nice... hell yeah, I can listen close or fill an entire room.

I measured the Googly Eyes on-axis close (green), off-axis close (brown), behind to check bass port (blue), and "far @ ~3m (purple). On axis close performance is great and confirms my sense about upper-mids. Off axis attenuates this some as expected. The bass is there as measured on the rear tuned port (blue) ~ and is fine in front when positioned close to a rear wall. Basically the Googly Eyes are fit for purpose in close field use and work surprisingly well in normal listening, and they measure out this way. Maybe I should damp the cabinets a bit more for even smoother performance.

I decommissioned the NOnkens and so tried the Fostex FE108NS drivers in the Blanda Bowls; the sizes and hole patterns were equivalent. I made no other changes other than the drivers. I listened and measured. Just as I noticed in the NOnkens, the New Sols are very nice near field drivers. And in fact, they sound great in the Blandas, with even nicer near and far sounds than with the wild Tang Bands, and they are more efficient. The measurements below were conducted exactly as prior with the Googly Eyes with one graph showing nearfield sweeps and the other showing sweeps captured from 10 ft. The Googly Eyes are better at some bass but the Blanda 108s are better at mids & highs... listening to tunes sounds like this too. I'm leaving the FE108NS drivers in the bowl cabinets for now but I will definitely need a subwoofer. I am hoping I can get a viable sub design from an 11" diameter Blanda bowl.

I even took the Blanda 108s for a spin in the NestMT CC spot ~ awesome. I still believe they'll be most unique in a Blanda 2.1 configuration. Loaded with the FE108NSs, the Blandas don't look as cool as the Googly Eyes with silver accents (given hardware I chose) but ultimately I think I'll make a different cabinet for the Tang Bands, but it's close.

And finally the Blanda 108s sit atop my desk, for which they were built. The bamboo looks cool on my bamboo desktop. Sometime ya just don't wanna wear headphones.

Update 27Jan24... I was concerned I might strike the drivers with something and hurt them, so wanted to protect them somehow. I bought some cheap Chinese (metal) grill covers and took them out of their frames and then just used neodymium magnets to secure the grills only to the drivers. Worked great.