Do ported tower speakers match well with sealed subs?

[Ropeburn]

Why not?

The amount of time it takes for the air to do its first "phase rotation" is much less than the amount of time it takes to hit the walls of your room and bounce back.

Second, ported designs roll off sharper below the tuning frequency. Sealed is -12dB per octave, ported is -24dB. Nothing to do with "in order to blah blah". We use port because it gives us more bass at tuning frequency at the expense of steeper rolloff below tuning frequency. Excursion is higher, while power needed per SPL is reduced.
When it goes below 20Hz or below -10dB, it no longer matters anyway.

Subs are good for
1) When your ported towers have high distortion by playing lower frequencies loud, sub takes over hence increasing maximum output volume
2) Sub covers the final lowest octave

Ports can also be used to reduce excursion at and around driver resonant frequency, giving more mechanical power reserves and lower distortion. Works well!

 

[Flaesh]

my speakers (9) are sealed in addition to my 3 subs. I'm old school and have avoided ports on towers or subs.

Aren't 8 subwoofers and two speakers enough?
What exactly school and how old is it? It seems like speakers are often\usually sold with holes in them for decades.

 

[witwald]

But how do I know what the best crossover frequency is? That’s what I’m wondering. Like does higher/lower crossover affect headroom in a way maybe? Should I pick one that high passes the towers or do I let them dig as deep as they can?

In general terms, it will be beneficial to have a high-pass filter active on main speakers. This will reduce the cone excursion that they need to produce at any given sound pressure level. A 2nd-order high-pass filter is generally sufficient for this purpose, and it can be set to approximately 80 Hz for good results.

Which ones? Group delay?

Lower group delay is one advantage of a sealed subwoofer system. For the same −3 dB low-frequency cut-off point, a sealed subwoofer has about half the group delay at the −3 dB point. Below is an example comparing SPL and GD responses of a sealed subwoofer (solid black line) and a vented subwoofer (dashed magenta line). Here the −3 dB point was chosen to be 25 Hz for both systems, and a 4th-order 80 Hz Linkwitz–Riley low-pass filter has also been applied.

The sealed subwoofer also has the advantage that in many rooms the roll-off in its low-frequency response will be reduced by the boost action of the low-frequency room gain transfer function. How much will depend on the size of the room and its acoustical properties. Of course, if high SPLs are required, then a vented system will generally be able to achieve the desired levels with lower cone excursion, due to the added low-frequency output from the vent(s).

Below is a simulation of adding a sealed subwoofer to an exsiting main speaker system. The main speakers are vented, and roll off at 24 dB/octave below 45 Hz. A 2nd-order Butterworth high-pass filter has been applied to them, set at 80 Hz. The subwoofer is a sealed system, with a 25 Hz low-frequency cut-off point. A 60 Hz 4th-order Linkwitz–Riley low-pass filter has been applied to the subwoofer, and the subwoofer's gain has been adjusted to get a reasonably flat response through the crossover region. I hope this illustrates some of the parameters that are typically at play when trying to integrate a subwoofer with the smain speakers.