Altec 421A impedance question

[GM]

I then ran a impdedance curve (WT2) and discovered they were roughly 5 ohms and rose slowly as frequency increased. They were only 7.5 ohms at 1khz.

So I'm thinking of running the 421A's in series for 10 - 12 ohms.

I've various 421 measurements from way back along with some more recent ones done by others and they all have somewhat lower Fs, Qts and close enough Vas, Le with ~5.3-5.5 ohms Re, so wondering if yours are either aftermarket re-cones or have some later Altec (GPA?) generic kits.

Le is low enough that running them in series should be fine if matched pairs measure very close in efficiency, otherwise at high power, one will dominate, turning the other into an expensive fuse.

GM