Report from the audio front lines…
1) The factory sub signal has a 50Hz low pass filter on it. Midbass information has to be recovered from the door speaker signals.
2) The amplifier has some kind of protection mode for the door speakers where it lowers the whole system volume upon the detection of sustained mid bass content.
3) The car is actually *too well sealed* to support the airflow requirements of an upsized subwoofer when the windows are up. The seals between the doors and the pillars, and other parts of the interior, are so good that the constant air pressure pushing back on the subwoofer is substantial. This may explain both the tuning of the factory sub, and the protection mode… pushing against high air pressure for sustained durations could cause amplifier overheat.
Stereo shop and system tuner (who have plenty of experience with other Honda/Acura systems including the ELS ones) were scratching their heads for a while until this picture all came together.
Contributor: Ben Englert