Could I do one ported and one sealed to get better dynamic range? Or would I run into problems with sound waves cancelling each other out?
That isn't how dynamic range works. Dynamic range is the difference between the minimum and maximum output levels offered by the subwoofer.
How you design a subwoofer is take the T/S parameters of the woofer (measure them yourself, manufacturer tolerance makes their numbers unreliable), then model a cabinet with software like WinISD or VituixCAD. If you are a perfectionist, heat the voice coil by playing pink noise at 25% of the RMS power for a few minutes, then measure the T/S parameters again. This gives you data similar to when the subwoofer is actually in use, without having to measure the large signal parameters using Klippel gear.
For measuring T/S parameters, you can either use hardware like a DATS v3, or DIY it with a PC soundcard + pair of resistors (the DATS is basically a PC soundcard with software attached).
Dayton Audio DATS V3 Computer Based Speaker & Audio Component Test SystemDayton Audio DATS V3 Computer Based Speaker & Audio Component Test SystemThe Perfect Companion for Audio ProfessionalsWhen designing the DATS V3 measurement device, Dayton Audio took everything customers love about the DATS...
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Learn how to measure thiele small parameters, or just a speaker impedance measurement using your sound card. Software used: Room EQ Wizard.
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You should not mix ported and sealed subs in the same system, unless you are knowledgable about using DSP to smoothly blend the subs. Ideally, all subs in a system are identical.
When you spread subwoofers throughout the room, it results in a smoother frequency response, because of reduced room mode influence.
On the topic of using 2 drivers per subwoofer, this is possible, but isobaric is generally the wrong answer. Isobaric loading halves the air volume required, so you can build a smaller box, but you are paying the cost of 2 drivers, for the same SPL output (because efficiency is halved, and power handling doubles), which means you also need twice the amplifier power.
The better choice is placing the drivers on opposing faces, so that cabinet vibrations are minimized. This can reduce distortion, particularly if your cabinet is not structurally robust.