IME/IMO:
FWIWFM - Don
- Excessive bass tends to "overwhelm" the midrange, making the tonal balance "off" when the sound is undesirably bass-heavy;
- Distortion from the bass reaches well into the midrange (at 80 Hz, the second harmonic is at 160 Hz, third at 240 Hz, and so forth);
- Excessive bass can overload an amplifier used full-range and thus distort the entire frequency spectrum;
- A crossover does not fall instantly to 0 on either side; there can be significant energy an octave above and below, so too much bass can affect the mains as well; and,
- Integration may be the culprit, with interaction among sub(s) and mains as well as the room causing frequency peaks and dips well above crossover (see (4) above).
FWIWFM - Don