Reduction in noise level

Substantial reduction in noise level can be expected in the conditioned spaces by eliminating heat pumps at the zones. However central heat pump may require special attention to reduce the noise level. 

Improved tire designs have enabled reduction in noise levels. This has become an important environmental consideration. Optimum footprint... 

The simplest concept in the transmission of noise is the inverse square law. For example, if the distance from the source is doubled, the reduction in noise level would be ... 

The above approach is not a particularly sensitive technique for confirming the presence of a particular component in a mixture and MS/MS approaches give increased specificity of detection. By selecting a suitable precursor ion at the expected retention time a product ion spectrum is obtained. This can be compared with authentic materii to confirm the presence of the targeted analyte. Although this is less sensitive than a full spectrum the reduction in noise is so great that the overall limit of detection is improved due to the improved signal/ noise ratio. The most sensitive technique is to select the precursor ion in MSI and then monitor the product ion in MS2. This eliminates any chemical noise almost completely and often allows the limit of detection to be lowered to ppt (parts per 10 ) levels. 

Significant reductions in the level of fi noise can also be obtained in certain experiments where signal selection is achieved by pulsed field gradients, although homonuclear experiments such as COSY show little benefit in this respect, more notable gains being apparent... 

The overall reduction of noise levels involves developing a noise reduction plan. Here each of the sources needs to be checked and evaluated. Alternative techniques with lower noise levels may be applied and/or point sources may be enclosed. Examples for alternative techniques have been given in Section 4.2A.2 (oxybumer in RF) and 4.2.2.2 (foamy slag for EAF). Some examples of the enclosiue of sources have been given for furnaces (Section 4.5.3.1) and shakeout (4.5.9.3). 

The Control of Pollution Act provides general legislation for limiting community noise as well as other pollutants. No specific limits are set, but the Act empowers the Local Authority to require a reduction in noise emission and impose conditions for noisy operations, e.g. specify a level of noise emission for a particular operation which must not be exceeded at certain given times. In certain instances they may not only set the limits but specify how they are to be met or how equipment is to be operated, referring to the relevant British Standard . 

As with any detection system, an important consideration is the minimum detectable signal that can be recovered. The problem of differentiating analytical signal from noise becomes increasingly difhcult as the signal source becomes weaker (i.e., trace level concentrations). The ability of an instmment to discriminate between signal and noise is expressed in the signal-to-noise ratio (S/N) of the detection system. Any reduction in noise represents an increase in the S/N, and an enhancement of the detection system. 

FIGURE 2.11 Top The noise level in an infrared spectrum between 2200 and 2000 cm after 1 scan. Bottom The noise level in an infrared spectrum between 2200 and 2000 cm after 100 scans. The y-axis scales in the two spectra are identical. Note the reduction in noise for 100 scans versus 1 scan. 

I oise Transmission Reduction in HVACSystems. One common use of sound-absorbing treatment is to reduce noise transmission in heating, ventilating, and air-conditioning (HVAC) systems (6). The treatments ate used to reduce the transmission of fan noise and air turbulence noise through ducts into occupied spaces. Noise transmission reduction in duct systems is described in terms of insertion loss, the difference in sound power level or sound pressure level measured at a given location before and after installation of the treatment or sound attenuation, the reduction in sound power between two locations affected by a sound source. The units ate decibels. 

Because the sum exceeds 1.0, employees in this environment are immediately required to wear ear protection. On a longer-term basis, noise reduction control methods should be developed for the specific pieces of equipment with excessive noise levels. 

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