I started this thread over in diyaudio.com but thought folks over here may have an interest in it too. It started off on a whim with me asking myself does the namesake speaker from B&W really sound nice because the spiral absorbs the back wave? Why not try it out on a smaller, cheaper scale and see? Normally, I model and simulate a speaker pretty thoroughly before committing to a build (even though it is in foam core - so no worries if it doesn't work out). I started by thinking of the max physical envelope I wanted this to occupy, hand drew a spiral that was 3 ft long (I did calculate this to makes sure that the 1/2-wave TL resonant freq was about 300 Hz). I basically have a driver that I use for almost all my speaker projects - the Vifa TC9FD - a wonderful sounding 3.5 inch paper cone full range high Qts driver that I have successfully used in a straight TL, MLTL, BLH (scoop, cornu, and BIB), and now a sealed TL. I first started with a single driver to see how it sounds. That was hugely successful so I went for 2 drivers to boost efficiency and max SPL. The back spiral effectively absorbs any backwave like an acoustic black hole. In single driver mode, the response was flat +/- 3dB from 150 Hz to 18 kHz and the imaging, soundstage, and clarity were just amazing. It needs to be paired with a woofer/subwoofer to round out the bottom end (that is the topic of the Nautaloss Sub - in the sealed subwoofer forum: http://www.hometheatershack.com/forums/sealed-subwoofer-build-projects/72373-nautaloss-sub.html
). But the vocals range, all the way to cymbals, high hats, bells are all sparkling clear. I don't want to repeat everything here so if you need more details please go to: http://www.diyaudio.com/forums/full-range/247598-nautaloss-ref-monitor.html
Here are photos of the finished dual driver speaker front and back. The overall dimensions are 13 in front (due to back tilt), 5-3/16 wide, 9 in deep:
Here is the SPL vs frequency.
Here is the Distortion, with THD typically below -50dB! This is measured at typical volume of about 87 dB at the listening position.
And here is the Impulse Response - very clean and tight - plucked strings, bongo drums, guitar, etc all sound very realistic and articulate.
When I started building these, they were meant as "Reference Monitors" as I needed a set of speakers to compare the sound to my other speaker builds and I wanted something that was clean and flat in response. I think I achieved it, but then I realized that the size, and low cost makes them perfect for HT installations where you want crisp, neutral, articulate sound without spending a lot. The fact that they are made of foam core has advantages of light weight for wall mounting or suspension from the ceiling.
If you are interested in how to make speakers out of foam core, check this out: http://www.diyaudio.com/forums/full-range/223313-foam-core-board-speaker-enclosures.html