Abstract
The Acoustic Double Holography (A D H) proposed inthis paper is a simplified approach with higher resolution of the noise source locations than that of the conventional AH methods. The ADH methodbasically uses dual measuring planes and does not require near field measurement. The ADH measurementswere carried out on several types of diesel engines under the full load operation. The highly noise radiating areas on the engine surface were visualized efficiently. Through these experiments, it was reconfirmed that the visual observation techniques on sound field have been playing a very important role on engine noise refinement works.