In this blog post I test the Altec 416-8B in a 100L sealed enclosure. Testing was done outdoors for the frequency response and then brought indoors for the distortion testing.
The woofers are new from Great Planes Audio. A customer has sent me the finished cabinets with drivers to integrate into a finished system using the Yuichi Aira A290 horn, so stay tuned for more on that. 
Measurements
I began by measuring the impedance sweep.
I then measured the frequency response at 1m outdoors.
Time Domain
Burst decay shows excellent results with nothing of concern.
The CSD plot shows the normal stored energy near the cabinet tuning (71Hz) however beyond that we see time domain performance normally reserved for much smaller drivers. Diaphragm breakup occurs at 1.8kHz.
I then brought the cabinet indoors and measured the distortion near field.
At 85dB (1m) we get H2 at 0.02% while H3 is a little higher at 0.12%.
Increasing to 95dB we see H3 increase to 0.40%.
I then tested intermodulation distortion at 85dB using tone ranging from 50Hz to 5kHz. We see IMD at -68dB for the bass region rising to -50dB at 600Hz.
Increasing the test signal to 95dB we see -60dB for the bass region rising to -42dB for the 600Hz region. (see below)
I then decided to test the driver with tones starting at 100Hz instead of 50Hz. This should improve the IMD performance. We see IMD improve in the 100Hz region to -73 rising to -68dB at 400Hz. The 600Hz region has improved to -56dB compared to -50dB that we saw with 50Hz modulating tones.
Increasing the test SPL to 95dB we see the 100Hz region still very low at -68dB. The 600Hz region has improved to -48dB compared to -42dB that we saw with the 50Hz modulating tones.
Conclusion
The Altec 416-8B maintains ultra low intermodulation distortion within the 50Hz-400Hz region. We see a very linear frequency response up to the mechanical breakup of the diaphragm starting at 1.8kHz. In an ideal use case scenario, the woofer should be low pass filtered at 500Hz, however I could envision this driver doing well up to 1.8kHz if a steep filter is implemented, assuming that the driver was used at moderate listening levels.