DNW’s Dynamic Data Acquisition (DDA) system was specifically designed for collecting huge amounts of data generated by its high-precision measurements. The system was developed in cooperation with the German manufacturer GBM, a company specialized in measurement technology. The DDA system consists of hardware and software for both data acquisition and data processing, and provides connectivity for a wide range of measuring equipment, including any type of microphone.
For instance, DNW uses phased microphone arrays equipped with 144 microphones. Because all microphones measure and collect data simultaneously while data is acquired continuously over a time interval of typically 30 seconds, the entire volume of data to be stored and processed amounts to approx. 1 GB raw time data per data point. Thanks to its state-of-the-art storage and processing systems, DNW is capable of meeting this demand, enabling it to perform accurate acoustic measurements. Moreover, DNW’s high-speed network and parallel processing facilities make the first source plots available within a matter of minutes.
Despite advances in test techniques in open jet situations, disturbances in measurements remain a limiting factor for high frequencies, mainly due to the shear layer and partly due to the long distance between the model and the microphone array. However, DNW developed several measures to obtain the optimum results from the usable frequency range up to 15 kHz.
Detailed research into the structure of microphone measurement systems resulted in special arrays with microphones in random positions and with software-based corrections for the structure of the microphone array. This enabled measurements of high frequencies of up to 50 kHz, not limited by the minimum distance between microphones, and resulting in high resolution source plots. The high standards in qualitative measurements allow DNW to determine the precise location of a noise source. Moreover, progress made in quantitative measurements has resulted in a significant reduction in the gap between acoustic results from the closed test section and results from far field measurements in the open jet test section.