Audible noise

By tire coiTect choice of the metal oxide/carbon ratio in the ingoing burden for the furnace, the alloy which is produced can have a controlled content of carbon, which does not lead to the separation of solid carbides during the reduction reaction. The combination of the carbon electrode, tire gaseous oxides and the foamed slag probably causes tire formation of a plasma region between the electrode aird the slag, and this is responsible for the reduction of elecU ical and audible noise which is found in this operation, in comparison with tire arc melting of scrap iron which is extremely noisy, and which injects unwanted electrical noise into the local electrical distribution network. 

Of primary importance in any converter design is not what happens to the output when we perturb the reference (which is what the closed loop transfer function really is), but what happens at the output when there is a line disturbance. This is often referred to as audio susceptibility (probably because early converters switching at around 20 kHz would emit audible noise under this condition). 

One of the most recent areas to be attacked is the turbulent regime. Turbulent flames are of dominant importance, and are typically emitters of audible noise. Since Reynolds criterion for turbulence... 

Punching sheet metal, especially thicker and tougher materials such as stainless-steel alloys, is inherently noisy. As noted in Section I.E and as shown in Fig. 8, noise is drastically reduced through the use of shear face punches. In addition, the fully controllable hydraulic ram offers yet another method to reduce audible noise slowing the speed of the punch as it strikes the workpiece. Although productivity in terms of strokes per minute is reduced, this trade-off may be necessary in some applications and in some fabricating environments where loud noise is at issue. 

In an old reinforced concrete building, AE measurement was carried out in advance of rebuilding the house. A plan view of the two-story building is given in Fig. 13.1. Since the structure was old and not in service, the audible noises were readily observed due to the traffic load. At five locations circled in the figure, continuous monitoring was conducted for a week. To analyze AE data, two waveform parameters of the RA value and the averaged frequency stated in Chapter 4 were applied. 

In addition to performance and durabilify, fhe fuel cell system needs to be tested for other characteristics such as audible noise level, electronic noise level, overloading capacity, startup time (especially at the lowest designated temperature), and various warning and protective functions. 

Mechanical problems in NIR instrumentation can be a real problem, especially for online instiument-ation where environmental noise may defect our ability to hear audible noise that would normally be detected in a quiet laboratory. Mechanical noise, causing the lamp filament to vibrate, can be transferred to the spectrum. Information in the Fourier spectrum is a good indicator of this type of noise. Because the power spectrum is easily computed from the following ... 

In order to protect occupation health, especially with respect to protection against audible noise-causing reductions in staffs productivity, the limit and action values of noise exposure are defined, for example, by EU Directive No. 2003/10/EC, on the minimum health and safety requirements with regard to workers exposure to risks caused by physical agents (noise), as follows ... 

In [30], Siewiorek et al. presented SenSay, a context-aware mobile phone that sensed physical and environmental changes in order to determine current user interruptability. SenSay determined if a user was in a busy (uninterruptable) state based upon their electronic schedule, their movement, and any audible noise in the environment. However, the device was limited due to its reliance on external measures in the user s surroundings, which are not always related to interruptability. 

The sliding nature of the contact in lead screw drives puts great importance on the role of friction on their performance. In addition to efficiency concerns, driving torque requirements, or wear, friction can be the cause of dynamic instabilities, resulting in self-excited vibrations which deteriorates the performance of the system and may cause unacceptable levels of audible noise. 

In a case study (Chap. 9), an actual product is studied where friction-induced vibration in the lead screw drives resulted in unacceptable levels of audible noise. An important part of this study is the development of a novel approach to identify system parameters including the velocity-dependent coefficient of friction between lead screw and nut. 

The first step toward finding the cause of the excessive audible noise in an operating mechanical system may be to analyze the noise signal and the external conditions under which such a noise is generated. In this section, some of the preliminary observations made on the powered seat adjuster are presented. First, a series of tests were performed on the complete seat adjuster. Figure 9.1 shows the test setup and the instrumentation used. A wall-mounted pneumatic cylinder was used to apply various levels of axial force to the seat adjuster s firame. 

Audible noise (sound wave) recording A general purpose PC microphone... 

Sample measurement results are presented in Fig. 9.5. In this test, a horizontal force of about 200 N (Fig. 9.5c) was needed to induce the noise at a traveling velocity of approximately 20 mm/s (Fig. 9.5d). The audible noise continued for about 4 s with a dominant frequency of about 150 Hz (Fig. 9.5a) accompanied by an almost 20 dB increase in the noise level (Fig. 9.5b). The frequency spectrum of the recorded noise at f = 3 s is plotted in Fig. 9.6. This plot clearly shows the dominant signal frequency of 150 Hz. 

Consistency in the frequency of the generated audible noise between complete seat tests and single slider tests, points toward the lead screw vibrations as the source of the noise. In addition, a rough estimate of the natural frequency of... 

Fig. 9.3 Audible noise frequency content at 8 s for the test results shown in Fig. 9.2a. Peak amplitude at 162 Hz...

Each point in Fig. 9.20 represents the averaged experimental values of the amplitude of vibrations over a 2-ms interval, where a limit cycle was detected. These results show that the amplitude of vibration increases with gearbox output angular velocity. This finding also agrees with the perceived intensity of the audible noise generated by the system. 

A practical case study is presented in Chap. 9 where friction-induced vibration in a lead screw drive is the cause of excessive audible noise. Using a complete dynamical model of this drive, a two-stage system parameter identification and fine-tuning method is developed to estimate the parameters of the velocity-dependent coefficient of friction model. The verified mathematical model is then used to study the role of various system parameters on the stability of the system and on the amplitude of vibrations. These smdies lead to possible design modifications that can solve the system s excessive noise problem. 

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