Phase IV rebuild complete

Over the weekend I finished the rebuild of the Phase-IV baffle. Actually the baffle was done a while ago but since my wife was unhappy having something so ugly in the house, I decided to try to improve how it looked by giving it a coat or ten of paint. There's a I need to learn about finishing.

The mid range and tweeter are now properly located in close proximity so the interference fringing around the crossover frequency should be fixed. By way of comparison, here's what the speaker looked like before. Not great, but a lot less like a building site.

The bass cab is now filled with a fair amount fiberglass insulation - I know there are better materials but this was cheap ($15 and I've used less than a quarter of the roll). Since this changes the bass response, I'll need to rebuild the crossover. So next weekend the measurement equipment comes out again.

Volume estimation

I am still going back and forth over the size of the cabinet; is 5000 cubic inches (about 80 liters) enough for the sealed bass enclosure? In building the Phase IV, I had used the volume information from the DM6 which has in internal volume of "between 51 and 60 liters" according the manual. I decided to look at the original B&W 801; based on the published overall dimensions and some pictures, I estimated the internal volume to be somewhere between 108 and 122 liters depending on the thickness of the cabinet walls (according to B&W's literature, the Nautilus 801 walls are 1.5 inches thick - I used 1 inch and 1.5 inches). Big difference!

The actual air volume is likely considerably smaller since there is a fair amount of internal bracing (the 'matrix' used in the Nautilus could take 10%-15% off this figure). However, since the dimensioning calculation I was doing ignores the internal bracing, I decided to compare only the raw internal volume.

The 801 bass cab volume (~115 liters ) was over double that of my Phase IV (54 liters) and suggested a complete redesign of the cabinet was needed. It probably also contributes to the poor performance below 100 Hz, though the small linear excursion of the Silver Flute drivers is clearly another factor. The Phase V needs a wider baffle to accommodate the 10" AC-250F1 driver, but this alone wasn't nearly enough; several iterations of changes led to a design that maintained the height at 40 inches, increased the depth from 21 to 24 inches (slightly deeper than the 801 which was 22 inches back to front) and kept about the same width (17"). The new bass enclosure will weigh in at 110 liters before bracing. (It will also be fairly heavy)