Mouth trumpet is a vocal technique that imitates the sound of the trumpet.
The mouth trumpet sound is produced by using the vocal cords to produce the desired pitch and passing the sound through the lips that are held together with just enough tension so that they vibrate at the same frequency as the vocal cords, producing a trumpet-like sound.
In effect, mouth trumpet is like playing a trumpet backwards. To play a trumpet, the player vibrates the lips against the mouthpiece by blowing a stream of air through the lips. The desired pitch is produced by varying the length of the air column in the tubing of the trumpet by the use of three valves. The vocal cords are not normally used in playing the trumpet. To produce the mouth trumpet sound, the pitch is produced by the vocal cords before it reaches the lips and the lips then buzz to add the trumpet effect.
Lip trumpet is another trumpet imitation technique (also known as lip buzzing) in that air is blown through squeezed lips to make them squeak (like with the real trumpet) to produce a tone without vocal cords. The pitch is controlled by lip tension and position. The timbre can also be varied by tongue position. Particularly difficult is here to control the lip humidity which strongly changes the available pitch range. Both techniques can be combined to play 2 note polyphonic.
Similar play techniques were employed in jug bands to blow the jug, stove pipe and partly watering can.