Can you increase the efficiency of vintage speakers?

NO

You can sometimes improve the efficiency of a multi way speaker system but only if you use multi amplifiers and remove any padding.  For instance, tweeters are often padded down about 3 dB or more to match mids.  To do this they use resistors which generate heat from the lost signal.

Remove the resistors, use a line level volume control, and voila, no more wasted heat.

The other way to improve output is to use boundary reinforcement.  That is, push the speakers as close to as many walls as you can.

erik_squires
Thanks for your input... BTW: Miller carbon pointed out to me that the speakers are much more efficient than I was led to believe.
Presently: they are only about 12" away from the walls and sound amazing!

millercarbon
...enjoying these speakers immensely: presently using solid core 14g copper wire twisted together (homemade) as speaker cables - would changing this to 16g "modify"/change the sound?

"Oh sure someone will come along and prove me wrong. It’s a sport. You could win a prize."
+1 MC

middle mass

Sorry - but I am confused by your comment... Are you word-waring with millercarbon for reason?

And please explain your "+1 MC" note - it's meaning is obtuse to me within the context of this forum and my question...