Modern Mechanix has an amusing 1922 ad from the Perfect Voice Institute

IS THAT the way you go after a job? You may have a fine set of brains but you must have a voice to prove it.

If you are not as successful as you might have been, start out right by confessing to yourself that something is wrong. There is something which prevents you from appealing to those who have an influence on your income.

Perhaps Your Voice is to Blame!

Have you ever considered that the trouble may lie with your voice? Your contact with the world depends upon your five senses—sight, smell, taste, touch and hearing. Certainly you try to dress well and to be pleasing in the sight of others. Probably you have developed a fine firm handshake. When you entertain friends at dinner you serve food that will please their taste.

But—do you do one single thing to make your voice pleasing to others? Remember that your voice is the one thing which puts you in audible touch with the world. Your voice is to you what the telephone is to your community. Your voice can make your future or it can spoil it.

You get but one chance at any big job. Are you sure that your voice won’t kill that chance?

You should see the illustrations and read the rest of the copy.