Is it a problem to add ported subwoofers to a system with sealed loudspeakers? For example, adding Wilson Audio Master Subsonics or Submerges to Magico M6s or to YG Sonjas?
Ported speakers (including subs) have compromised transient performance compared to a sealed enclosure, but there's no particular problem running a ported sub with sealed mains. The sub will sound as it always does.
The problem occurs at the crossover point. A ported speaker running full range has a natural 12dB Butterworth roll-off at the bottom end. If you add a sub with a fourth order filter, which most are, it will be acoustically behind the mains at the crossover point and will sound slow. There are three solutions:
1. Use a second-order low pass crossover on the subwoofer, at or near the main speakers' -3dB point
2. Roll off the main speakers at 12dB per octave at or near their -3dB point, and roll the subs in at the same frequency with a fourth order low pass crossover.
3. Move the sub closer to the listening chair to account for the delayed sound.
Is it a problem to add sealed subwoofers to a system with ported loudspeakers? For example, adding REL subwoofers or Gobel Sovereign subwoofers or Magico Titan subwoofers to Rockport Lyras or to Wilson Audio Alexx Vs?
This can get messy if the main speakers and subs are reproducing the same frequencies, because the sound from the ports in the main speakers is in opposite phase to the sub output, causing lumpy bass response. If you want to use ported mains, with any sub, ported or sealed, bring the sub in at the -6dB point of the mains, and use a fourth-order high pass on the sub.
What are the pros and cons of mixing loudspeaker and subwoofer designs in terms of sealed and ported versus matching loudspeaker and subwoofer designs?
It's all about the crossover. The transition from a woofer to a subwoofer should be treated the same way as the transition from a tweeter to a midrange. The target is a perfect Butterworth or Linkwitz-Riley cross. If the mains are rolling off at 12db, 18dB or 24dB, roll the subs in with the same slope.
If you are rolling off sealed speakers with external crossover or DSP filters, you can use a second-order high pass on the mains at their -3dB point, creating a 4th-order Linkwitz Riley slope, which you would need to match in the sub's low pass filter.
If you are using an external crossover or DSP filters with ported mains, use a fourth order filter on both the mains and subs, but stay at least 1.5 octaves above the port frequency.