Voice high frequencies are more readily transmitted to the chest wall in abnormal lungs as compared to normal lungs.
Ask the patient to whisper '1-2-3' several times while auscultating across the chest walls. The lung area is abnormal if the '1-2-3' sound is understood. This is the abnormal '1-2-3'.
Compare this sound to the recording found in the Whispered Pectoriloquy - Normal lesson.