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.