A beautiful or not-so-beautiful voice can be made more beautiful by sticking Carpi’s voice rectifier in one’s mouth, perhaps. The well-more-than-century-old device is enshrined in a patent:
Be it known that I, VITTORIO CARPI, of Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Voice-Rectifiers; and I do hereby declare that the following is a full, clear, and exact description thereof, reference being had to the accompanying draw ings, and to the letters of reference marked thereon, which form a part of this specification. This invention relates to devices to be used by singers and others in vocal exercising for the purpose of correcting and perfecting stiff and defective voices and assisting such persons in the proper cultivation and development of the voice….
When the high notes sound too disagreeably thin or woody the practice should be conducted alternately with and without the plate A in the mouth until the person obtains control of the voice, cures the defects above pointed out and acquires a regular, even, extensive and round voice. To this end the voice rectifier will be found extremely convenient in curing throaty and nasal voices and uneven voices in the different registers.
Mis-placement of the device could make the voice less beautiful, perhaps.
BONUS (possibly related): The pebbles of Demosthenes