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Vinkelberoende ljudabsorption
KTH, School of Engineering Sciences (SCI).
KTH, School of Engineering Sciences (SCI).
2019 (Swedish)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesisAlternative title
Angle dependent sound absorption (English)
Abstract [sv]

När absorbenter ska väljas för att dämpa ljud med höga frekvenser i ljudtorra stora rum som t.ex. kontorslokaler, är absorbentens vinkelberoende absorptionsegenskaper av stort intresse. I dagsläget finns flera modeller för hur ljud absorberas i ett material beroende på bland annat ljudets infallsvinkel mot material-ytan. Få praktiska undersökningar har gjorts för att verifiera dessa modeller, i synnerhet för flackare ljudinfall. Detta kandidatexamensarbete i ljud och vibrationer är ett försök att mäta vinkelberoende ljudabsorption i en mätuppställning bestående av en lång kanal. Kanalens hålrum delades i två delar med en skärm placerad i mitten av kanalen, över vilken ett absorptionsprov lades. En högtalare med olika avstånd från skärmen emitterade vitt brus. Ljudtrycksnivån mättes på båda sidorna av skärmen. Två mätuppställningar med olika bredd användes. Med båda mätuppställningarna utfördes mätningar på två absorbenter - en fiberabsorbent och en skumabsorbent av melamin. Resulterande mätvärden utvärderades och användes för att uppskatta absorptionsfaktorer för ljud med olika infallsvinklar mot de båda materialen. Dessa värden jämfördes teoretiska värden för ett lokalreagerande material. Mätmetoden gav tydliga och reproducerbara resultat. Resultaten visade på att mätmetoden som den tillämpades i detta arbete var något otillräcklig för att uppskatta matrialprovernas absorptionskoefficienter. Metoden bedömdes vara mest tillförlitlig med den smala kanalen för tersbanden med mittfrekvens 793 Hz, 1000 Hz och 1259 Hz och för vinklar mellan 16 och 26.6 grader. De uträknade absorptionskoefficienterna från samtliga mätningar var stora jämfört med teoretiska värden.

 

Abstract [en]

When choosing a sound absorbing panel or roof to dampen high frequency noise in large rooms, for example in open space offices, the angle dependent properties of the material are of great interest. At the present day there are several theoretical models for how sound is absorbed in a material depending on, among other things, the angle of incidence of the soundwave against the material surface. Few practical tests have been carried out to verify these models, especially for grazing angles of incidence. This bachelor’s thesis in sound and vibration is an attempt to measure the angle dependency of sound absorption in a measurement setup consisting of a long channel. The channel is divided by a screen placed in the middle of the channel, above which a material specimen was placed. A loudspeaker, placed at different distances from the screen, emitted white noise down the channel. The sound pressure level was then measured on both sides of the screen. Two measurement setups with different width were used. Two different material specimen were used in both measurement setups – a sound absorbent fiber material and a melamine foam material pad. The resulting measured values were evaluated and used to estimate the absorption coefficients of sound with different angles of incidence for the two materials. These values were compared against theoretical values for a local reactive material.

The measurement method gave clear and reproducible results. The results showed that the measurement method, as it was applied in this project, was somewhat insufficient in estimating the absorption coefficients of the material samples. The method was considered to be most reliable with using the narrow channel for third ocatave bands with center frequency 793Hz, 1000 Hz and 1259 Hz, and for angles between 16 degrees och 26.6 degrees. The calculated absorption coefficients from all measurements were large compared to theoretical values.

Place, publisher, year, edition, pages
2019.
Series
TRITA-SCI-GRU ; 2019:186
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-254821OAI: oai:DiVA.org:kth-254821DiVA, id: diva2:1335482
Supervisors
Examiners
Available from: 2019-07-05 Created: 2019-07-05 Last updated: 2019-07-05Bibliographically approved

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