THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

14.8 Gears 373Figure 14.7. Gear noise spectrum.Harmonics—the noise and vibration at integer multiples of the tooth meshingfrequency—are usually present. The most significant contributions are usuallymade by the first two or three harmonics, f 2 = 2 f 1 , f 3 = 3 f 1 , and so on. A typicalgear noise spectrum is displayed in Figure 14.7.Tooth ErrorIf a single tooth is imperfectly cut, chipped, or damaged, then it will generate anoise impulse once every shaft revolution. The fundamental frequency of the noiseor vibration due to tooth error is given byf 1E = n 60(14.16)wheref 1E = fundamental frequency due to tooth error, Hzn = shaft speedHarmonics of tooth-error frequency may also occur. Moreover, if the shaft centerlineis not straight or if a gear or bearing is not concentric with the shaft centerline,noise and vibration at the tooth-error frequency may result. These can cause insideband frequencies f S that accompany the tooth meshing frequencies. Thesefrequencies are found as followsf S = f 1 ± f 1E (14.17)