Transmission of sound

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  

Where the sound power level is known the resulting sound pressure level at a distance is given by  

Where distances exceed 200-300 metres other absorption factors should be taken into accoimt. These include atmospheric attenuation and ground absorption effects. Atmospheric attenuation (molecular absorpHon) is proportional to distance, but groimd absorption is dependent on the intervening terrain between the somee and receiver. 

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The roof and walls of the fan room should be lined internally with absorbent materials in order to reduce the sound level in the fan room. The wall insulation should be sufficient to reduce the transmission of sound to adjoining silent premises. 

The attenuation coefficient a is not the only factor which determines the performance of an anechoic coating. Equally important is the initial transmission of sound from the surrounding medium (usually air or water) into the coating. The simplest case is when the boundary between the medium and the coating is a plane surface, as shown in Fig.2a, and the sound is incident normally. The... 

Figure 2a. Reflection and transmission of sound at the fluid-acoustic coating interface.

As the design matures, the direct measurement of the acoustic properties becomes necessary. These properties include the longitudinal wave speed, the coefficient of attenuation and the acoustic impedance, which can be obtained from measurements of the reflection and transmission of sound by the material. Two acoustic techniques are available for these measurements, the impedance tube and the panel test. 

IX. Submarine Signalling and Transmission of Sound through Water. By C. V. Drys-dale, D.Sc.(Lond.). 

The transmission of sound through the air actually consists of an alternate compression and raxifaction of the molecular structure of the air itself. When this wave-like movement... 

We can expect the same to be tme of medicine empowered by IT. One rapidly growing trend of medical IT is telemedicine, normally considered as the transmission of sound and pictures between patient and physician as opposed to both being physically in the same place. But some industry analysts have used the term to indicate any transmission of medical information... 

Transmission of sound and pictures is conducted at radio frequencies or radio wavelengths. We are immersed in radio waves from the day we are bom. A radio or television is our "detector" of these waves. Radio waves are believed to cause no physical harm because of their very low energy, although some concern for people who live very close to transmission towers has resulted from recent research. 

Isolation resistance to the transmission of sound by materials and structures. 

The principle underlying the application of sound is that the vibration created by the energy associated with the transmission of sound will disturb and dislodge deposits on surfaces, i.e. "to shake" the deposit free. Cavitation produced by the propagation of sonic waves in the continuous phase near the deposit surface, can also assist the removal process. 

Early hints of the wave nature of light included the seventeenth-century discovery of diffraction by Hooke and other manifestations of interference. It was obvious that dropping a rock into a pond created waves, and Boyle showed that air was necessary for the transmission of sound waves. Thus, it appeared that there had to be a medium for transmitting light waves and it was thought to be a kind... 

To facilitate the transmission of sound into the water, shipboard sonars are mounted in large plastic bilges near the bow, requiring the relocation of the ship s anchors to avoid hitting them. Because of the distinctive sound, the return echo used on an active sonar beam to find a submerged object was known as pinging the target. 

Various factors may interfere with the transmission of sound impulses. Normally, the pressure on either side of the ear-drum is equal but when a difference occurs, as with airline passengers who fly when suffering from a cold, temporary hearing impairment can be experienced. Infection of the... 

Figure 5.9 The variation of phase angle with distance along a polyethylene monofilament for transmission of sound waves at 3000 Hz. (Reproduced with permission Ifom Hillier and Kolsky, Proc. Phys. Soc. B, 62, 111 (1949))...

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. 

The following data apply mainly to acoustic ceiling treatments, but other surfaces may be similarly treated. These data do not apply to through-transmission of sound. Low sound transmission accompanies high density or weight of material. 

Sound insulation Prevention or reduction of the transmission of sound through a partition (wall, ceiling, etc.). Most of the sound is reflected from the partition. 

Install silencers or mufflers on gas exhausts. There are two types. A reactive muffler contains baffles and chambers that block the transmission of sound. These are used for low-frequency noise source, such as that generated by... 

The dynamics of atoms in solids is responsible for many phenomena which cannot be explained within the static lattice model. Examples are the specific heat of crystals, thermal expansion, thermal conductivity, displacive ferroelectric phase transitions, piezoelectricity, melting, transmission of sound, certain optical and dielectric properties and certain aspects of the interaction of radiation such as X-rays and neutrons with crystals. The theory of lattice vibrations, often called lattice dynamiosy and its implications for many of the above mentioned phenomena is the subject of this two-volume book. 

Conductive hearing loss is a form that usually involves an outer or middle ear obstruction that reduces transmission of sound vibrations through air space, bone, or tissue into the middle ear. The treatment for this problem is with medicine or surgery. Hearing aids may also be used. 

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