Noise: acoustics, 4—5, 7 control

For Tu < 0.10 %, the transition location is insensitive to Tu. Such low levels of disturbances are typical of acoustic noise that controls... 

Acoustical control can also be achieved by proper space planning. For instance, workstations that are positioned too closely do not provide suitable speech privacy and can be a source of disturbing conversational noise. As a generi rule, a minimum of 8-10 ft between employees, separated by acoustical panels or partitions, wUl provide normal speech privacy. 

There are a variety of control techniques, documented in the literature, to reduce overall worker exposure to noise. Such controls reduce the amount of sound energy released by the noise source, divert the flow of sound energy away from the receiver, or protect the receiver from the sound energy reaching him or her. For example, types of noise controls include proper maintenance of equipment, revised operating procedures, equipment replacements, acoustic shields and barriers, equipment redesign, enclosures, administrative controls, and personal protective equipment. 

Acoustic control identification of sources of noise enclosure of noise muffling re-design of noise producing parts. 

Most automotive R D projects within adaptronics are concerned with active vibration control (AVC) and active structural acoustic control (ASAC) for optimization of NVH (noise, vibration and harshness) characteristics and even soimd design. Furthermore, active measmes to increase the passive safety of vehicles are being developed. Shape and position control as well as structmal health monitoring (SHM) are stiU of secondary importance. 

Active structural acoustic control (ASAC) Reduced structure-borne noise and sound emission/imission, increased passengers comfort, weight reduction, interior sound design... 

The form of acoustic control will vary with the configuration of the work station, but it is important to use the design stage to ensure that design of equipment or tooUng within a workplace, which makes up part of a work station, is always the primary method of attacking noise problems. This assumes that the process and the equipment... 

Acoustic control materials are used to reduce noise problems where the design of a machine or tool hasn t solved the problem, or to add to the reduction in noise resulting from good design. As noted earlier, acoustic control materials take two basic forms -porous material which reduces reflection of sound, known as reveiberation, or material of a relatively high density which can reduce the vibration of sound-emitting surfaces or reduce the transmission of sound through a barrier, such as a wall or floor. Certain composites achieve the same effect with less density. 

Again, it is useful to remember that machine design can reduce the noise level before acoustic control materials are employed. It should also be remembered that partial sound barriers are more effective against high frequency noise (a loud squeak) than low frequency noise (a rumble). 

In a suitable workplace of yorrr choice, identify equipment arrd tools used which have been designed with the use of acoustic control material, or with engineering controls on noise. 

The objective of this paper has been to characterize the acoustical performance of a novel viscoelastic microcellular material and to examine its potentials for passive noise reduction (control) in auto vehicles. 

C. M. Harris, ed.. Handbook of Acoustical Measurement and Noise Control, 3rd ed., McGraw-HiU Book Co., Inc., New York, 1991. 

There are two approaches to fluid-generated noise control—source or path treatment. Path treatment means absorbing or blocking the transmission of noise after it has been created. The pipe itself is a barrier. The sound pressure level inside a standard schedule pipe is roughly 40-60 dB higher than on the outside. Thicker walled pipe reduces levels some at more, and adding acoustical insulation on the outside of the pipe reduces ambient levels up to 10 dB per inch of thickness. Since noise propagates relatively unimpeded inside the... 

Most louver systems have a pitch between 30 mm and 100 mm. Where noise control is required, louvers can be supplied either in the form of acoustic louver with a pitch of 300 mm and acoustic material in the louver blade or as standard louver with an attenuator section behind it. A bird or insect guard (as applicable) is normally mounted behind the louver. 

That the authorities have refused unreasonably to accept compliance with alternative requirements or that the requirements of the notice are otherwise unreasonable in character or extent, or are unnecessary. This defense is self-explanatory. The local authorities are only permitted to ask for works that will abate the noise nuisance. Other works (perhaps to comply with legislation) should not be specified in the notice. They may, however, be contained in a letter separate from the notice. An example of this would be where the fitting of acoustic enclosures to food-manufacturing machines breached food hygiene requirements. Readily cleanable enclosures may be a requirement of the Food Hygiene Regulations, but it should not be contained in a Section 58 Control of Pollution Act notice. 

SHARLAND, L, Woods Practical Guide to Noise Control, Woods Acoustics, Colchester, 1973... 

Industrial Noise Control and Acoustics, Randall F. Barron... 

Number two on this list, Acoustic Psycho-Correction is the self same Mind Control technology that has the ability to control minds and alter behaviour of civilians and soldiers and which also involves the transmission of specific commands via static or white noise bands into the human subconscious without upsetting other intellectual functions, that is aimed at altering the behaviour on willing and unwilling subjects, reported in the Defence News article discussed earlier on page 3. 

Acoustic emissions are the stress waves resulting from sudden movements in the stressed sample material. The most obvious example is the tin cry due to stress in a wooden structure due to the load. It is very important that the measured acoustic emission signal be corrected for the background noise signal. Acoustic emission energy is due to the elastic stress field in the sample material. Acoustic emission is monitored by applying a controlled variable load. The principle of the method is illustrated below (Figure 2.14). 

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