I usually use 8 ohm, wire series for 4 ohms, parallel for 16
for technical clarity, maybe this statment needs amending, otherwise take every speaker you have, mix n match til you find a pair that gives you that giddy feeling
Fine, I will clarify more. I build 2, 12 cabs from pine and Burch. They are similar to a baseman cab, but taller to allow for a baffle which can be closed or open. Either side, one open one not, both open or not. These are built 3/4 pine or birch and fingerprinted. There are 4 rolling casters, but only 2 swivel. All interior boards are covered with Robotex, which is the material used in luxury cars to keep out exterior noise.
The back panels are 3 pieces so open back is an option as well. Since I generally play wet/dry, I install a single jack plate with 4 inputs. The 2 that are 8 ohm, I can use individually. Another is wired series (and pardon me) 16 ohms and another parallel for 4 ohms.
There are always 4 handles. 2 on the top like a vox and 2 inset on the ends. This way if I need to I can lift it over another piece of gear. I forgot, the casters remove. I prefer my cab on the floor.
With this said, you can see each individual speaker must work by itself and sound good. If you want to know some experiments I have made with speakers, let me know. Again, I prefer an Alnico for clean, blues. Think weber 12A125 and Celestion greenback for a pair. The Weber sounds like a Jensen or similar and a greenback is the sound of classic rock, but not limited. Both of these speakers breakup at about the same volume, but the greenback crunches mids whereas the weber compresses and is dominate in upper mids and highs.
Also, since you can, plug in a Blackface deluxe to one 8ohm and a 18 watt marshall into the greenback. Use the 18 watt for hard hitting overdrive and use the Deluve for clean and modulation effects. Remove the top 2 pieces from the weber side and close the port. Your effects will be more ambient, but you will never lose your main tone, or have effects make it sound mushy. Leave the 18 watt closed, but open the port and it will make the bottom more solid which an 18 watt needs