This was the same sub as this one, except that now we were using a 40 Hz low pass filter and ~6 dB low-Q boost at 18 Hz. This represents a more typical configuration during normal use. Naturally the shape of the frequency response changes due these electronic alterations. The highs get cut off while the lows are boosted. A 6 dB boost requires 4 times amp power, and unfortunately the 300 W NAD couldn’t quite handle it. Also the driver itself was reaching its maximum excursion at low frequencies. THD skyrockets below 30-35 Hz so that the higher harmonics went above the amplitude of the fundamental, hence the small undulation in 50-100 Hz range (90 dB and 95 dB sweeps). THD stays really low above 30-35 Hz because of the low pass filtering. Group delay shifts up above ~60 Hz due to low pass filtering, but it’s still reasonably low. There’s a little bit of added overhang in the spectral decay graph. Spectral contamination test shows quite a lot of distortion already at low test level, indicating that the driver nor the amp can not handle very high output levels with these settings. Something which we all should remember while applying a lot of boost at any frequency.
+ Good extension
+ Low group delay
- Extremely high deep bass distortion
- Low maximum output capability
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