Sound decibels

Reverberation Control. Reverberation time (T q) is defined as the length of time in seconds for the sound of an instantaneously stopped source in a room to decay by 60 decibels (dB). Reverberation time is one important factor in determining the acoustical character of a space and its suitabiHty for specific activities. For lectures and other speech activities a relatively short reverberation time is desirable so that syllables do not persist and overlap one another, causing difficulty with inteUigibiHty conversely, for music activities, a relatively long reverberation time is desirable to allow blending of the sound and a sense of being surrounded by the music. Without reverberation music usually sounds dull and lifeless. 

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. 

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 ... 

Sound power is the total energy emitted from a fan that is a function of the fan s speed and point of operation and is independent of the fan s installation and surrounding environment Sound power level is the acoustical power expressed in decibels (dB) radiating from a source. Sound power can be converted into predictable pressure levels (dBA) after the acoustical environment surrounding the fan is defined. Sound pressure for a specific fan varies with... 

I.D. of duct, ft decibels sound level polytropic efficiency, = m/m ... 

For convenience, the usual measurement of sound is expressed in decibels (dB), and ratings go from threshold of hearing to threshold of pain (135 dB). Figure 34.11 illustrates the common noise criteria, which can be expressed in sound-pressure levels (SPL). The human ear can detect 1 dB but 6 dB represents a doubling of the SPL, although it would need a 10 dB increase to make it sound twice as loud. 

The power of a source (measured in watts) can be similarly expressed in terms of decibels (in this case, called the sound power level) ... 

In practice, measurements are made with the use of an accelerometer. This device is connected to a sound level meter and may make measurements of acceleration in terms of decibels (or by changing scales or use of a device similar to a slide mle, in direct terms). An integrator can be connected between the accelerometer and the meter to express the results in terms of velocity or displacement. 

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

I really don t think it s wise to take it any further, she says, her voice dropping so suddenly, by an octave and several decibels, that I can tell she s forcing herself to sound reasonable. Fergus isn t in a position to make the right judgment, after all. He hardly knows the place. It s not as if he s ever lived there. ... 

Noise levels are measured in decibels. A decibel (dB) is a relative logarithmic scale used to compare the intensities of two sounds. If one sound is at intensity I and another sound is at intensity /0, then the difference in intensity levels in decibels is given by... 

An absolute sound scale (in dBA for absolute decibels) is defined by establishing an intensity reference. For convenience, the hearing threshold is set at 0 dBA. Table 3-7 contains dBA levels for a variety of common activities. 

Logarithms are especially useful for expressing values that span a range of powers of 10. The Richter scale for earthquakes, the decibel scale for sound, and the pH scale for acids and bases all use logarithmic scales. 

The sound emitted from methanol boiling on a copper tube at 1 atm. has been measured (W2). No forced convection was used. Figure 10 shows how the sound, in total decibels for the frequency range of 25 to 7500 cycles/sec., varies with the temperature difference. Nucleate boiling... 

These models were tested by firing cal, 45 Ml911 ammo. The sound was measured at 10m to the right of the muzzle. The measured intensities are shown below to be compared with the 141 decibels having no suppressor attached ... 

Sound strength is therefore location-dependent and is often quantified as a sound pressure level Lp in decibels based on the root mean square (rms) sound pressure value ps, where... 

Absorption is a material property, usually symbolised by a, which is a measure of the energy removed from the sound wave by conversion to heat as the wave propagates through a given thickness l of material. It is expressed in units of decibel/cm (dB/cm). 

Decibel The unit nsed for the measurement of the intensity of sound on a logarithmic scale based on measurements of sound intensity in watts per square meter and related to a reference. For instance, 10 W/m is the intensity of the quietest sound perceptible to the hnman ear Decomposition The breakdown of chemical snbstances into other substances or parts of componnds nsnally associated with heat or chemical reactions Delayed health effect A disease or an injnry that happens as a resnlt of exposure to chemical substances that might have occnrred in the past Delney clause An amendment enacted in 1958 to the Pnre Food Act that prohibits the addition to food of all detectable amonnts of a carcinogen Dementia (senile dementia) An acqnired progressive impairment of intellectual function... 

Both the total sound level, and the attenuation of sound, are often expressed in a dimensionless unit, the decibel, where the sound level (SL) in decibels is,... 

From Eqs.5 and 14 it follows that the attenuation of a sound wave propagating through a medium can be expressed either in terms of the coefficient a (nepers per meter), or as a reduction in sound level in decibels per meter. The relation between these units of attenuation is obtained by inserting x = 1 meter in Eg.5, and substituting the result in Eg.14,... 

These temperatures are accomplished by blasting a sustained 160-decibel tone—a sound 10,000 times louder than the loudest rock concert—into a mixture of inert gases. But because the device is so well insulated, you need a stethoscope to tell whether it is running. 

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