[Chas]

The resonances will change when or if the speaker is used in the plate circuit or the radio. The DC will bias the coils with a new magnetic force with superimposed audio.

In the 20's at least on radio magazine did a combination of resonance and sensitivities tests on several horn and cone speakers. generally, the larger the diaphragm, the lower the tones, the larger/longer the horn as well. Some speakers used a bi-polar driver with aluminum diaphragms others used mica diaphragms. No horn speaker sounded as good as the "worst" cone speaker. Somewhere in the middle of all these speakers came the Magnavox which used a voice coil driving the diaphragm

A high sensitivity 3 to 4" speaker taken from an old pair of modern headphones is often the solution for a rotted diaphragm driver. Silicone glued to the gutted driver housing and a small output transformer to make the match.
Some of the best sounding of the "vintage" speakers I have heard are the Air-Chromes. A linen diaphragm speaker with a bi-polar driver.

Strangely enough, it is possible to build one of these linen speakers with common materials and tools requiring only a drive from a ruined speaker. Will need hardwood lumber, felt, linen, colodion (canoe dope), some wood screws, table saw, hide glue, wood stain and a suitable grille cloth. Joann fabric and the lumber store will have it all. An outdoor supply will have the colodion. Some Air-Chrome speakers have rustic landscape scenes painted on the diaphragm, very attractive.

Yes, I know the hearing of the young... As a teenager I serviced TV's for pocket money. I could easily hear the horizontal sweep frequency or 15khz, I could tell if it was too low or had a distortion component to it.

GL Chas