Tham khảo tài liệu 'gear noise and vibration episode 2 part 1', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 140 Chapter 9 and pinion. Frequency analysis is of little help since all frequencies or all multiples of a couple of very low frequencies are present. Which of these types of noise causes the irritation depends to a large extent on what the listener is expecting. One engineer will often expect a b and d and ignore them but will be highly irritated by c whereas another might reject due to b . One car driver might be irritated by a and ignore d while another would react the opposite way. Occasionally as with a car it is not the noise itself which irritates but the fact that the noise has changed from a familiar accepted normal noise. There is interaction in human response between the various sounds and sometimes it is possible to use the deliberate addition of pitch errors in a drive to break up the sound pattern. This technique is sometimes used in chain drives if the customer is irritated by a steady whine. Problem identification From what has been said in section the accurate specification of the problem is not always easy. Occasionally it is a simple pure tone that is heard and if a quick check with a sound meter straight into a frequency analyser or oscilloscope see section confirms that the frequency is once-per-tooth diagnosis is easy. Checking the character of the sound is a great help and if the sound is complex some form of artificially generated range of sounds can help identify the type of noise. This can be done using predominantly analog equipment but it needs quite a complicated setup so is more cheaply tackled by generating a series of repetitive time sequences with and without the various errors in a standard PC. The resulting time series for each revolution is then fed via an output card into an audio amplifier and loud speaker or can be played out on a sound card. The problem with standard soundcards is that varying the frequency is not easy. Reasonable resolution is obtained if each tooth interval is say 30 samples long and 25 teeth .
