The shape of the frequency response becomes a bit better when plugging one of the ports, though there is still some excessive deep bass output. There is around 5 Hz more extension due to this operation. The maximum deep bass output will get higher at the expense of mid/upper bass output. The deep bass output is still clearly limited by the port area (2x4"). THD stays quite low close to the tuning frequency, though rising quite a lot in the upper bass range at the highest output levels; luckily it’s mainly 2nd order. Group delay stays low down to 30 Hz, but grows rapidly below. Spectral decay shows a lot of ringing around the tuning frequency. Spectral contamination test shows high output capability with lower than average overall distortion, though a little bit worse than with the 25 Hz tune.
+ Good extension
+ High overall maximum output capability
+ Low overall distortion
+ Overall price/performance ratio
- Shape of the frequency response
- High deep bass output compression
- High upper bass distortion at high output levels
- High deep bass group delay and ringing around the tuning frequency
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