New York Speakers Part 3: Satellite Design

Thanks to the extra volume I got from making the sub a bit bigger, I could make real 2-way satellite speakers. I splurged a bit and chose a tried-and-true complement of Audax drivers, a 4" Shielded Aerogel Midbass and a 1" Textile Dome Tweeter. Although I've never used these drivers before, I've seen them paired in several designs so I felt it was a safe bet. Playing around in WinISD, the woofer seemed to work with both sealed and vented alignments, so due to personal preference I chose a sealed cabinet. The cabinet has an internal volume of 3L but with padding is equivalent to about 4L, for a roll-off around 90Hz to mate with the subwoofer.


Honestly designing a sealed box for a 4" woofer is not rocket science, whereas crossover design is always a challenge. Since I don't have access to commercial crossover design software, I decided to write my own Matlab program to auto-calculate crossover values, based on real response curves and a chosen topology. Here is the tweeter response:

And here is the woofer response:
From a quick visual observation, it looks like the tweeter is solid in the lows, while the woofer suffers some chunk around 2kHz, and then gets really squirrely around 5kHz. (Neither "chunk" nor "squirrely" are real engineering terms.) Even though I'm pairing a 1" tweeter with a 4" woofer, between which there is significant overlap, I don't want to crossover too low. Otherwise I'll risk damaging the tweeter or I'd have to use a higher-order crossover. In the interest of simplicity, I'll use a first order crossover for both the highs and lows, with a tweeter resonant peak cancellation and woofer inductive rise cancellation, and tweeter output attenuation to make it match the less efficient woofer. The script, downloadable as a .m file at the bottom of this post, also takes into account the offset acoustic centers of the two drivers when calculating the on-axis response. Due to a phase lag in the tweeter at crossover, the smoothest response was obtained when the tweeter's phase is reversed, something unconventional with this crossover topology. The final response expected is thus:
Since I was going all out for these speakers, I decided to have PCBs (silkscreened, no less!) made for the crossovers. I know, it's like half a dozen holes and four traces, and no one will ever see them. Whatever. I used my favorite--meaning, most fully featured yet affordable--schematic capture and layout tool, Eagle, to make the crossovers. The files can also be downloaded below.
The satellite SketchUp file is here, with a cutlist here.
The crossover matlab scripts including the driver response files are zipped up here.
The PCB art for the crossovers is here. The folder contains everything you need to place an order with AP Circuits.