A very easy way to test a 1920's horn or cone speaker is to use a battery (weak 9 volt or a  D cell) touch the terminals of the battery with the leads from the speaker, if you hear a click the driver and cord of the speaker are good. Sometimes if you don't hear a click from the speaker the cord from the speaker is bad, in that case you can use your Ohm meter and test the terminals on the speaker driver for continutity. Below are photos of a typical horn speaker and a cone speaker