Decibel, unit

While reflectivity and transmissibility are simple ratios, it is more common to present these parameters in decibel units. The corresponding parameters are then echo reduction (ER) and transmission loss (TL) ... 

The factor 17-36 arises from the use of decibel units and the magnetic permeability has been taken to be 1. Strictly /S is a summation over all ionic species. However the mass of the ion in the denominator means that only electrons contribute significantly unless o) is much less than ft)j, the collision frequency. 

Similar expressions represent the decibel units of sound intensity L/,... 

The use of decibels merely results in a rescaling of the Bode plot AR axis. The decibel unit is employed in electrical communication and acoustic theory and is seldom used today in the process control field. Note that the MATLAB bode routine uses decibels as the default option however, it can be modified to plot AR results, as done in Fig 14.2. In the rest of this chapter, we only derive frequency responses for simple transfer function elements (integrator, first-order, second-order, zeros, time delay). Software should be used for calculating frequency responses of combinations of these elements. 

In Fig. 2, however, a comparison has been made of the respective numerical values for physically inconunensurable quantities such as acceleration power density with velocity and displacement power density. Therefore, Eqs. 2 and 3 and the following two text lines do not imply that the decibel units on both sides of the equal sign mean the same. They only look the same because the incommensurable reference levels were omitted. For this reason, three decibel scales for acceleration power, velocity power, and displacement... 

For optical transmission, tire parameters of greatest importance are attenuation (i.e. loss) and material dispersion. In effect tliey define tire limits of tire optical communication system. Loss, due to absorjDtion and scattering, limits tire lengtlis between tire transmission nodes. In transmission quality fibre, tire loss is in units of decibels per kilometre. 

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. 

Units and Rating Procedures. The unit of sound pressure level is the decibel (dB), defined as follows where L is the sound pressure level, p is the measured sound pressure, andis the reference sound pressure of 20 p.Pa. TL and AiR also are expressed in decibels. 

This unit is also a decibel. Note that the decibel is a pure number. 

When two sound sources are added, it must be remembered that the decibel is a logarithmic unit. Therefore, they cannot be added arithmetically but must be combined as follows ... 

The unit of sound measurement is the decibel, defined by the expression ... 

In most electrical engineering or industrial control books, the magnitude is plotted in units of decibel (dB) as... 

The acoustic flux intensity is the power per unit area 1= (PjS) = 2ji2v2A2pc. Relative acoustic intensity is often expressed in a logarithmic scale (decibel or dB) ... 

The units of log modulus are decibels (dB), a term originally used in communications engineering to indicate the ratio of two values of power. Figure 12.13 is convenient to use to convert back and forth from magnitude to decibels. 

In the engineering literature, the decibel (db) unit is frequently used. The transfer function in terms of decibels is... 

Ratios of power in electronic circuits are measured in decibels. A hypothetical unit of a Bel would describe the logarithm to base 10 of the ratio of two power levels the decibel (dB) is a unit of a tenth of a Bel. Hence the ratio of two power levels Pi and P2 may be described as a = 10 x log10(P[/P2) dB. Conversely, Pi = P2 x 10 /10. The decibel is dimensionless and, since it is a logarithmic unit, amplifications and attenuations expressed in decibels can... 

Microbar A unit of pressure, commonly used in acoustics which equals 1 dyne per square centimeter or one newton. A reference point for tire decibel, is 0.0002 dyne per square centimeter, or 20 Newtons/M2. 

BEL (B). A dimensionless unit for expressing the ratio of tsvo values of power, being the logarithm to the base 10 of the power ratio. (The more commonly used unit, decibel (dB), is 10 times the logarithm to the base 10 of the power ratio. A bel is 10 decibel.)... 

NEPER (Np), A dimensionless unit for expressing the ratio of two voltages, two currents, or two power values in a logarithmic manner. The number of nepers is the natural (Napierian) logarithm of the square root of the ratio of the two values being compared. Thus, the neper uses the base of 2.71828 in contrast with the bel (or decibel) which uses the common-logarithm base of 10. One neper equals 8.686 decibels. 

PHON (phon). A unit of loudness level. The pressure level in decibels of a pure... 

Here A is the amplitude of the wave, and x is the distance traveled. The attenuation coefficient is determined by measuring the dependence of the amplitude of an ultrasonic wave on distance and fitting the measurements to the above equation. The attenuation is often given in units of decibels per meter (dB nr1) where 1 Np = 8.686 dB. 

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