Abstract: A vibrator is held in contact with a structure undergoing testing, such as n airplane wing. Vibrations are distributed through the structure and structural defects such as fissures will respond by emitting an acoustic signal. The acoustic signal may occur over a wide frequency range. A pick-up having a crystal transducer also makes contact with the surface of the structure to detect acoustic emissions. The crystal has a wide band response capable of detecting structural defect acoustic emissions. The pick-up has electrical leads connected thereto so that the acoustic emissions are converted to electrical signals which may be recorded or viewed on an oscilloscope. Movement of the pick-up across the surface of the structure will help determine the location of the structural defect.