This chart shows the frequency spectrum of the noise emissions at the exit of the L-1 Vertical Wind Tunnel located at Appalachian Amusement Center. The meter was located two feet above and two feet away on the building side from the exit (where the wind comes out of the machine) with the transducer pointing toward the center of the exit. At the time these measurements were made, there was some intermittent wind and background noises such as passing vehicles. While great care was taken to make the measurement between occurrences, some of these measurements may be slightly higher. There was wind induced by atmospheric mixing that may have elevated the readings at 500, 600 and 650 RPM at 20 and 25 Hz.. These measurements compared to similar measurements taken on 2-4-04 with the fan blades removed show that the mechanical noise is well below the noise created by air movement. It also shows the primary frequencies of the sound generated by the fan and drive are between 100 and 1000 Hz. There was no lower net during this test. We didn't want net noise to contribute to the readings. The upper net was allowed to float so it would be further from the sound meter and contribute as little as possible to the readings. It was at least 10 feet above the meter. I chose 500, 550, 600 and 650 RPM because 500 RPM is the slowest that will fly a small adult, while 650 is the fastest we have turned the fan thus far

Image shows sound meter located 2 feet out and two feet above the exit during the 2-4-04 test. The same position was used for this test.