Advanced

Absorption Characteristics of Periodically Perforated Suspended Ceilings

Holmberg, Dag LU (2003)
Abstract (Swedish)
Popular Abstract in Swedish

I innemiljöer är ofta innertaken nedsänkta för att ge plats åt elinstallationer, ventilationsdon och dylikt. Om innertaken från början består av plattor som reflekterar ljud, så kan dessa perforeras och förses med porösa skikt, och därmed även användas som ljudabsorbenter. Mekanismerna för denna ljudabsorption är i princip välkänd, men det tillkommer bland annat en del fenomen på grund av växelverkan mellan de respektive absorbenterna och rummet. I avhandlingen analyserades effekter som beror av den inbördes placeringen av absorberande repektive reflekterande partier i taket. Det vill säga, om man placerar absorberande ytor i olika mönster så kommer detta att ge olika absorptionsegenskaper.... (More)
Popular Abstract in Swedish

I innemiljöer är ofta innertaken nedsänkta för att ge plats åt elinstallationer, ventilationsdon och dylikt. Om innertaken från början består av plattor som reflekterar ljud, så kan dessa perforeras och förses med porösa skikt, och därmed även användas som ljudabsorbenter. Mekanismerna för denna ljudabsorption är i princip välkänd, men det tillkommer bland annat en del fenomen på grund av växelverkan mellan de respektive absorbenterna och rummet. I avhandlingen analyserades effekter som beror av den inbördes placeringen av absorberande repektive reflekterande partier i taket. Det vill säga, om man placerar absorberande ytor i olika mönster så kommer detta att ge olika absorptionsegenskaper. Vidare studerades hur absorptionen påverkas om perforeringarna är periodiska. Slutligen gjordes en modell av samspelet mellan ljudfälten ute i rummet och inne i innertaket.



Eftersom de analyserade modellerna har en hög komplexitetsgrad, så utvärderades, som en jämförelse, överensstämmelsen mellan en förenklad modell och mätningar. Denna överensstämmelse är i de flesta fall tillräcklig för utvärdering av vanliga tillämpningar. Styrkan hos de mer komplexa modellerna är istället att man ofta får en bättre förståelse av de mekanismer som styr absorptionsegenskaperna, och därmed bättre möjligheter att anpassa och utveckla absorbenter.



Vid modellering av absorptionsegenskaper behöver man förutom de fysiska dimensionerna dessutom känna till strömningsmotståndet hos de porösa skikten. En mätapparat konstruerades för att mäta strömningsmotståndet som bulkegenskap hos perforerade standardplattor med porösa skikt. (Less)
Abstract
The sound absorption characteristics of resonant absorbers, implemented as perforated suspended inner ceilings attached with thin porous layers, are investigated. Several existing theories model the principal absorption mechanisms, but the interaction with the outer sound field influences the absorption in ways that can be modelled with new approaches.



The effect of arranging the absorbing surfaces in various patterns is modelled with a variational model. Periodic effects, depending on correspondence of projected wavelength and the dimensions of the periodic cells for certain incidence angles and frequencies, is modelled with an approach that formerly has been used on periodically reinforced floors. The model presupposes... (More)
The sound absorption characteristics of resonant absorbers, implemented as perforated suspended inner ceilings attached with thin porous layers, are investigated. Several existing theories model the principal absorption mechanisms, but the interaction with the outer sound field influences the absorption in ways that can be modelled with new approaches.



The effect of arranging the absorbing surfaces in various patterns is modelled with a variational model. Periodic effects, depending on correspondence of projected wavelength and the dimensions of the periodic cells for certain incidence angles and frequencies, is modelled with an approach that formerly has been used on periodically reinforced floors. The model presupposes reflection from absorbing points and is therefore intended for small perforations. In this way an efficient mathematical treatment is gained at the expense of generality. This model is then extended to incorporate the backing field, which makes it possible to handle lateral waves within the absorber and therefore non-locally reacting absorbers.



In order to evaluate the presented theories, the static flow resistance, <i>R</i>, of the compound absorber (thin porous layer and rigid facing) has to be known. Since <i>R</i> of a compound absorber in many cases is hard to estimate from a <i>R</i>-value measured on separate samples of the porous layer, a new device for measurements of <i>R</i>. on compound absorbers was implemented. The device, which has a simple and robust construction, is intended for measurements on standard tiles of perforated plaster boards attached with a thin porous layer, but, by changing measurement interface, measurements can also be performed on the sole thin porous layer. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Rindel, Jens Holger, Reader, Ørsted•DTU, Copenhagen, Denmark
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Building construction, Byggnadsteknik, measurement device., flow resistance, suspended ceilings, periodically perforated facing, resonant absorbers, Room acoustics, building acoustics
pages
96 pages
publisher
Engineering Acoustics, LTH, Lund University
defense location
Knut Wicksell’s room, Beta 3, Ideon, Lund
defense date
2003-06-12 13:15
external identifiers
  • other:ISRN:LUTVDG/(TVBA-1010) / 1-96 / (2003)
ISSN
0281-8477
ISBN
91-628-5717-7
language
English
LU publication?
yes
id
bf2d4b6e-a68c-49d2-bde0-a201a56bae5d (old id 465979)
date added to LUP
2007-09-10 09:16:48
date last changed
2018-05-29 10:39:59
@phdthesis{bf2d4b6e-a68c-49d2-bde0-a201a56bae5d,
  abstract     = {The sound absorption characteristics of resonant absorbers, implemented as perforated suspended inner ceilings attached with thin porous layers, are investigated. Several existing theories model the principal absorption mechanisms, but the interaction with the outer sound field influences the absorption in ways that can be modelled with new approaches.<br/><br>
<br/><br>
The effect of arranging the absorbing surfaces in various patterns is modelled with a variational model. Periodic effects, depending on correspondence of projected wavelength and the dimensions of the periodic cells for certain incidence angles and frequencies, is modelled with an approach that formerly has been used on periodically reinforced floors. The model presupposes reflection from absorbing points and is therefore intended for small perforations. In this way an efficient mathematical treatment is gained at the expense of generality. This model is then extended to incorporate the backing field, which makes it possible to handle lateral waves within the absorber and therefore non-locally reacting absorbers.<br/><br>
<br/><br>
In order to evaluate the presented theories, the static flow resistance, &lt;i&gt;R&lt;/i&gt;, of the compound absorber (thin porous layer and rigid facing) has to be known. Since &lt;i&gt;R&lt;/i&gt; of a compound absorber in many cases is hard to estimate from a &lt;i&gt;R&lt;/i&gt;-value measured on separate samples of the porous layer, a new device for measurements of &lt;i&gt;R&lt;/i&gt;. on compound absorbers was implemented. The device, which has a simple and robust construction, is intended for measurements on standard tiles of perforated plaster boards attached with a thin porous layer, but, by changing measurement interface, measurements can also be performed on the sole thin porous layer.},
  author       = {Holmberg, Dag},
  isbn         = {91-628-5717-7},
  issn         = {0281-8477},
  keyword      = {Building construction,Byggnadsteknik,measurement device.,flow resistance,suspended ceilings,periodically perforated facing,resonant absorbers,Room acoustics,building acoustics},
  language     = {eng},
  pages        = {96},
  publisher    = {Engineering Acoustics, LTH, Lund University},
  school       = {Lund University},
  title        = {Absorption Characteristics of Periodically Perforated Suspended Ceilings},
  year         = {2003},
}