\nA2:<\/b> “Basics of Acoustics” (available May 2000)
\nA3:<\/b> “Product Characteristics—Acoustic Insulation, Absorption, Attenuation” (available April 2002; revised edition <\/p>\n
available September 2002)
\nA4:<\/b> “Acoustics in Buildings” (available October 2006)
\nA5:<\/b>“Acoustics in Rooms” (available May 2006)
\nA6:<\/b>“Industrial Acoustics” (available May 2004)
\n<\/Blockquote> <\/p>\n
Documents A2, A3 and A6 had been completed before the convention and were outlined in the presentation. Currently, <\/p>\n
document A5 is nearly complete, and a first draft of A4 (in French) has been written. The three completed documents are <\/p>\n
available from NIA, and it is anticipated that the remaining papers will be presented at NIA’s 2007 convention.<\/p>\n
\nThis series provides practical advice from a starting point of “principal considerations” (e.g., What sort of noise <\/p>\n
protection can be expected from a wall composed of the following elements?). These principles—”fundamental truths as <\/p>\n
bases for reasoning”—are found in document A2. Document A6 details the principles of sound propagation in industrial <\/p>\n
environments and places.<\/p>\n
\nBasics of Acoustics<\/b><\/p>\n
\nThis article is not intended solely for the insulation practitioner. Readers need not understand or be able to draw <\/p>\n
conclusions from the subsequent documents. Rather, this is for those who want to learn the physical reasons underlying the <\/p>\n
practical advice given in the manuals. <\/p>\n
\nThe document on principles (“Basics of Acoustics,” A2, quoted above) first gives a rationale for undertaking this endeavor <\/p>\n
and then briefly explains the physical laws that govern sound production and propagation:<\/p>\n
\nSince the mid-1900s, the steadily increasing population, rushing motorization, and the advancing mechanization of workplaces, <\/p>\n
in households and in leisure activities have led to a continuous increase of exposure to general noise. The consequences are <\/p>\n
concentration and sleep disturbances; damage to the autonomic nervous system, which can result in stomach, heart and <\/p>\n
circulatory debilities; and noise deafness, which has been recognized as the number-one occupational disease.<\/p>\n
\nAcoustics has been defined as the science of sound and its influence on human beings. For sound to travel from its source to <\/p>\n
the human ear, it must be able to pass through air or other media. In the absence of any medium (vacuum), sound propagation <\/p>\n
is impossible. <\/p>\n
\nAs sound pressure and frequency levels increase, so does the need to protect the human ear, where hearing ranges from “just <\/p>\n
audible” to “painful.” Figure 2 lists the practical sources of noise that are commonly associated with these sound pressure <\/p>\n
levels, from the peaceful rustle of leaves (just audible) to the painfully loud launch of a rocket (painful).<\/p>\n
\nHowever, the sound pressure level has no direct linear relation to the irritation that the sound causes for human beings. <\/p>\n
Here, the “physiological-psychological” effect must also be considered, as illustrated in Figure 3.<\/p>\n
\nFrom these very fundamental considerations, the document goes on to detail the influence of the source geometry on sound <\/p>\n
pressure change and sound propagation (Figure 4), and then to give the equations for sound propagation from different <\/p>\n
sources, respectively, in reverberation rooms. (Figure 5). All in all, document A2 contains 38 of these equations.<\/p>\n
\nAcoustic Insulation, Absorption and Attenuation<\/b><\/p>\n
\nDocument A3, “Product Characteristics—Acoustic Insulation, Absorption, Attenuation,” is a tool much more closely geared <\/p>\n
toward the day-to-day needs of the practitioner. The focus is on the phenomena (e.g., distance) and material barriers (e.g., <\/p>\n
walls, screens, etc.) that diminish the sound pressure level of the noise propagating from a source, and how they make this <\/p>\n
happen.<\/p>\n
\nFor instance, this document details the sound-absorbing qualities of “different types of walls” and what can be done to <\/p>\n
reduce “structure-borne” and “airborne” sound. It also outlines the influence of material obstacles on the propagation of <\/p>\n
sound. Figure 6 illustrates this, showing acoustic energy striking an obstacle and being reflected, absorbed and <\/p>\n
transmitted.<\/p>\n
\nThis leads to a discussion of the sound-attenuation qualities of single- and double-layer walls, detailing the <\/p>\n
sound-attenuation qualities of pipe insulations against the flow noise of media. The document explains the “law of mass” <\/p>\n
equation, which predicts that each time the frequency of measurement or the mass per unit area of a single layer wall is <\/p>\n
doubled, the transmission loss increases by about 6 dB.<\/p>\n
\nDouble-layer walls are discussed in some detail, as they constitute—in practical building applications—the solution of <\/p>\n
choice when it comes to “sound insulating” rooms against each other. (Figure 7)<\/p>\n
\nThese brief explanations of the physical principles underlying propagation (e.g., the construction of barriers to sound <\/p>\n
propagation) have practical implications, such as the sound reduction to be expected for different types of walls. There is a <\/p>\n
clear correlation between total surface mass and the sound-reduction results. The sound-reduction quality of a double-layer <\/p>\n
wall is increased considerably when a layer of mineral wool is inserted between the two walls. Although this does not <\/p>\n
increase the total surface mass to a measurable degree, it does increase the sound-reduction properties.<\/p>\n
\nThe principles governing the sound-reduction qualities of double-layer walls, with or without an intermediate layer of <\/p>\n
mineral wool, also govern the sound-reduction performance of insulated pipes: The pipe wall is the “first partition,” the <\/p>\n
cladding is the “second partition” and the intermediate layer is the mineral-wool insulation. (Figure 8)<\/p>\n
\nNormally, the two partitions are mounted on one frame, since the distancers connect them. Figure 8 shows how using a flexible <\/p>\n
substructure between the pipe wall and cladding can diminish this “one-frame effect.” It also demonstrates a method for <\/p>\n
increasing total surface mass by increasing the surface mass of the second partition-the cladding-with an added “de-booming <\/p>\n
layer” on the inside of the sheet metal. This de-booming layer not only increases the surface mass of the cladding but also <\/p>\n
lowers the propagation of the structure-borne sound into the cladding and the airborne sound outward of the cladding.<\/p>\n
\nAfter traveling through the solid structure, the structure-borne sound is transmitted to the surrounding air, where it <\/p>\n
excites a surface able to radiate like a loudspeaker membrane. In Figure 8, the “membrane” is the outer surface of the <\/p>\n
cladding. If this transmission to the air around the structure did not occur, the human ear could not hear structure-borne <\/p>\n
sound.<\/p>\n
\nIt is somewhat self-evident that the smaller the vibrating surface, the smaller the sound level. However, it is less obvious <\/p>\n
that an increase in the rigidity of the transmitting structure may also increase the radiation efficiency and thereby the <\/p>\n
sound level. This is the reason for the flexible substructure of pipe insulation claddings, where an attenuation of the flow <\/p>\n
noise through the pipe is also a consideration.<\/p>\n
\nOf course, as with all sound propagation and sound insulation phenomena, this depends very much on the frequency of the <\/p>\n
sound. Figure 9 illustrates the sound-reduction qualities of pipe insulation with claddings and rigid and elastic <\/p>\n
substructures, respectively, and the dependence on frequency.<\/p>\n
\nIndustrial Acoustics<\/b><\/p>\n
\nThe last of the three completed documents from the FESI acoustic documentation series is document A6, “Industrial Acoustics.” <\/p>\n
This paper focuses on applying the information from documents A2 and A3 to industrial working environments. The document <\/p>\n
begins with another short discussion of the principles of sound propagation indoors and out in the open and then concentrates <\/p>\n
on “noise control.”<\/p>\n
\nDistance from the noise source is a key consideration because the sound-pressure level decreases by 6 dB per doubling of the <\/p>\n
distance between the source of sound and the listener. One important consideration for this “decrease by distance” is the <\/p>\n
question of whether the propagation is spherical, hemispherical or quarter-spherical. In the equations shown in Figure 10, Lp <\/p>\n
is the sound-pressure level and r is the distance from the source. The increase in sound-pressure level decrease per distance <\/p>\n
is dependent on the pressure of sound-reflecting surfaces near the source.<\/p>\n
\nIn addition, the principles of industrial noise control are outlined in Figure 11, followed by practical advice on how to <\/p>\n
organize and execute noise-control measures in an industrial environment.<\/p>\n
\nThis short overview of the content of these three papers is not an attempt at a full report on practical acoustical problems <\/p>\n
and their solutions, as explained in the documents. Instead, the aim of this article is to indicate the ways in which <\/p>\n
problems can be addressed and to relay the practical advice given in the documents regarding solutions for these problems in <\/p>\n
insulators’ daily work. <\/p>\n
![](\"https:\/\/insulation.org\/wp-content\/uploads\/2017\/06\/IO051002_01.gif\")
<\/a>Figure 1<\/b><\/div>\n