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 Acoustic Glossary of Terms

Acoustic. Glossary of Terms

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        <i class="icon-chevron-right"> Acoustic bridging
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         <p>Vibration thro​​​ugh solid &amp; inflexible connection points - including clamps, anchors and penetrations - can allow noise to bypass extensive acoustic insulation measures. This process is known as “acoustic bridging” and can be avoided by using flexible materials to decouple direct structural paths. </p>
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        <i class="icon-chevron-right"> Air-flow erosion
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        <p>Fibre erosion and migration is an important consideration when using dusty or fibrous insulation to acoustically line ductwork - especially ductwork with a high air-flow velocity. The process particles are torn away by the moving air and carried along the air-stream is known as air-flow erosion. </p>
   <p>Closed cell foams experience essentially no air-flow erosion and can be used inside ductwork without special erosion resistant coverings.  </p>
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        <i class="icon-chevron-right"> A-weighting
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        <p>Because of the way that human hearing works noise at some frequencies will always sound louder than at others - even when the sound pressure level is exactly the same. A-weighting is the name given to the technique of adding to or subtracting from the sound pressure level to better reflect how loud the noise appears to sound. </p>
   <p>Other weighting curves were once defined - including B-weighting, C-weighting and more - but these are now rarely encountered whilst A-weighting sound levels is standard practice throughout the industry. </p>
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        <i class="icon-chevron-right"> De-Coupling (Vibration Isolation)
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        <p>De-coupling is the process of introducing flexible materials between solid &amp; inflexible connection points that would otherwise form “acoustic bridges”. De-couplers, otherwise known as vibration isolators, prevent these components from coming into direct contact with each other. </p>
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      <a href="/know-how?sid=113">For more information: FAQ Sound De-coupling</a></p>
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        <i class="icon-chevron-right"> &#39;dB&#39;
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        <p>The decibel (dB), in the context of acoustics, is a unit that indicates how loud a noise is in relation to the reference sound level of 0 dB - a sound pressure level of 20 micropascals - which represents the average minimum threshold for human hearing. </p>
   <p>Decibels are actually a logarithmic unit and so an reduction of 3 dB represents a halving of the sound pressure level.  </p>
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        <i class="icon-chevron-right"> &#39;dB (A)&#39;
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        <p>The human ear is not equally sensitive to all sound frequencies and noises at the frequencies of maximum human sensitivity (somewhere between 2,000 Hz and 4,000 Hz) sound louder than noises outside this range. A-weighted decibel levels (&#39;dB(A)&#39;) are decibel levels that have been A-adjusted to better reflect how loud humans will perceive the noise to be.  </p>
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        <i class="icon-chevron-right"> ISO 140/717
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        <p>ISO 140/717 are internationally approved standards for classifying the performance of acoustic insulation for under flooring application. Only products that have been tested to ISO 140 and classified according to ISO 717 are advised to ensure effective control of impact noise in buildings.  </p>
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        <i class="icon-chevron-right"> ISO 15665
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        <p>ISO 15665 is an international standard that specifies a test for acoustic systems on industrial process pipework and classifies systems based on the results. The results from an ISO 15665 test are presented in the form of &#39;insertion loss&#39; values at each octave frequency band that show how many dB the system will reduce noise by at that frequency. </p>
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        <i class="icon-chevron-right"> NRC Rating
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        <p>The Noise Reduction Coefficient (NRC) is a single figure measurement that gives a measure of how effective a material is at absorbing sound. This is achieved by taking the mean average of sound absorption at 4 different octave frequency bands (250, 500, 1,000 and 2,000 Hz) and rounding to the nearest 5%. The lowest value possible is 0 (perfectly reflective) and the highest normally possible is 1 (perfectly absorptive).  </p>
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        <i class="icon-chevron-right"> Sound Absorption
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        <p>At the simplest level sound is the movement of air molecules and, as such, kinetic energy. Sound absorbing materials convert this into other forms of energy with the result that the sound wave becomes less powerful as it passes through the absorbing material. </p>
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      <a href="/know-how?sid=112">For more information: FAQ sound absorption </a> </p>
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        <i class="icon-chevron-right"> Sound Barrier
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        <p> Sound barriers are high density layers that reflect air borne noise backwards towards the source. In contrast with sound absorbers which reduce the sound power level, barriers reflect noise but do not reduce the energy carried by the sound wave.</p>
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      <a href="/know-how?sid=114">For more information: FAQ Transmission loss / Sound barrier </a></p>
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        <i class="icon-chevron-right"> Transmission Loss
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      <a href="/know-how?sid=114">For more information: FAQ Transmission loss / Sound barrier </a> </p>
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        <i class="icon-chevron-right"> Vibration Damping
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        <p> Vibrating surfaces push the air around them as they move up and create a partial vacuum that pulls the air back in as they move down. The effect of this is to create a pressure wave in the air, converting the structure borne vibration into air-borne noise.</p>
   <p> Minimising how much a surface is able to vibrate by applying a dampening material to absorb the vibrating motion is known as vibration dampening and is one of the key techniques for noise control. This approach is also sometimes referred to as &#39;Sound Deadening&#39;. </p>
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      <a href="/know-how?sid=115">For more information: FAQ Vibration Damping </a>​ </p>
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The basic language and terms of acoustics

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