spindle rotation at 12,000 rpm disappeared and a broadband noise
appeared. This behaviour is typical for aerodynamic noises [13].
Regarding the influence of the tool balance, Fig. 4 demonstrates
that the sound pressure level can be increased on average by 1–
2 dBA with an unbalanced tool. This small increase was due to the
higher radial force supported by spindle bearings.
To sum up, it was observed that the diameter of the tool is a key
parameter for noise emission at high rotational speed, whereas
tool balance is a secondary order parameter