Bearing acoustical noise is a function of both the bearing itself and the way in which it is used. Bearings can be specified as 100% noise-tested during manufacture. Bearing noise is not generally influenced by ABEC precision, but rather by manufacturers' internal quality standards, particularly raceway finish. There are no fixed reference standards among manufacturers for noise testing.
The standard instrument used for bearing noise testing is the Anderon Meter (sometimes called Anderometer) made by Sugawara Laboratories. This measures noise with an accelerometer contacting the outer race of the bearing while the inner race is rotated at 1800 RPM. Noise levels are separated into 3 bands, designated as follows:
High band 1,800 - 10,000 Hz
Medium band 300 - 1,800 Hz
Low band 50 - 300 Hz
According to the type of bearing (material and noise grade), a different attenuation is used for each band. Meters are calibrated in Anderons. Standard testing procedure requires that bearings are washed clean of any lubricant and 2 drops of fresh MIL-L-6085A oil lubricant added prior to testing.
Typical attenuation values for each band are given in the table below, according to bearing material and noise grade. A "pass" for any bearing grade is defined as < 40% of full scale on the Anderon meters for each band. In this case, this translates to pass levels of Low < 6.4, Med < 2.4, High < 3.2.
|Anderon Meter attenuation settings:|
|Material||Noise rating||Low band||Mid band||High band|
|ANDERON meter < 40% = Good bearing|
|DYNAROLL CODE||NOISE TESTING LEVEL|
|No Code||Standard bearing - not noise tested|
|E||Noise tested to meet electric motor quality quietness standards.|
|ER||Ultra low noise tested to spindle motor quietness standards.|