So, I found this person's experiment very, very, VERY interesting, since it might affect the outcome of my woofer/bass driver testing for my upcoming battle of the 10" bass drivers.https://www.diyaudio.com/forums/subwoofers/284636-xtra-neo-magnet-qts-0-39-0-34-a.html
Long story short, cylindrical Nd magnets (whose circular end faces are the poles) can be used to add B to a standard ferrite type motor, thus bringing Qes down, and ultimately changing T/S parameters, namely Qts, but also efficiency increases (a tiny bit) at the cost of changing the shape of the low-corner "knee" because the final Qts is now different. I particularly love this modification, because I prefer a low-ish Qts by way of a low Qes which is usually results in a better frequency response (not too lumpy). I'm definitely going to try this with my Ultimax 10s and my CSS SDX10, and try to get the Qts down in the 0.30 range. I can see a potential issue being that the final B must be consistent around the gap, thus the placement of the Nd magnets (assuming they are identical) is critical so you don't have more force on one side of the voice coil than on the other "side".