Vocal effort is a quantity varied by speakers when adjusting to an increase or decrease in the communication distance. The communication distance is the distance between the speaker and the listener. Vocal effort is a subjective physiological

Physiology

Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

 quantity, and is mainly dependent on subglottal pressure, vocal fold tension and jaw opening. Vocal effort is different from sound pressure

Sound pressure

Sound pressure or acoustic pressure is the local pressure deviation from the ambient atmospheric pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone in water...

. To measure vocal effort, listeners are asked to rate the distance between speaker and addressee.