This method of voicing was used before the voice prosthesis was developed. Esophageal speech is the oldest method and can be one of the most difficult to learn. Only 1 in 3 people attempting this technique will be able to do it, and often their speech is limited to short sentences.
This technique uses the body’s natural tissues as the new voice source and requires you to swallow small amounts of air into your oesophagus before expelling it into the pharyngo-oesophagal segment (throat), which will vibrate to produce sound.
Air is trapped in the mouth and then swallowed using your tongue. The column of swallowed air is then pushed back into the upper esophagus causes the food pipe to vibrate, generating the sound.
The sound is further modified by the tongue and lips to create words.
The video below will give you an idea of what it sounds like when you speak using the esophageal method.