Helmholtz absorbers are a common solution for controlling the low-frequency modes found in small rooms. These devices only perform in a narrow spectrum range with the tuning depending on each room’s geometrical configurations. Consequently, their development still operates on a case-by-case basis. A possible alternative to optimize the production of these acoustic solutions is the development of a tunable Helmholtz absorber capable of changing its geometrical configurations according to each room’s acoustic needs. The present work shares the results of tests performed on varied samples of different configurations of absorbers. The samples were chosen aiming the control of the three first modes of each direction in rooms with volume ranging from 20 to 60 m3. The research revealed that the use of a single tunable absorber has the potential to produce sound absorption coefficients higher than 0.8 in almost the entirety of the frequency spectrum considered.
TakahashiD.A new method for predicting the sound absorption of perforated absorber systems. Appl Acoust1996; 51(1): 71–84.
5.
CoxTJD’AntonioP.Acoustic absorbers and diffusers. New York: Spon Press, 2006.
6.
PanteghiniAGennaFPianaE.Analysis of a perforated panel for the correction of low frequency resonances in medium size rooms. Appl Acoust2006; 68: 1086–1103.
7.
SanadaATanakaN.Extension of the frequency range of resonant sound absorbers using two-degree-of-freedom Helmholtz-based resonators with a flexible panel. Appl Acoust2013; 74: 509–516.
8.
NakanishiS. A pilot study of sound absorption by a perforated panel with bending tube extension built in the panel. In: INTER-NOISE and NOISE-CON congress and conference proceedings, InterNoise15, San Francisco, CA, 9–12 August 2015.
9.
IwaseTSugieSAbeMet al. Modeling and verification of perforated plate structure for high sound absorption at low frequency with extending parts behind holes into shallow air space. In: INTER-NOISE and NOISE-CON congress and conference proceedings, InterNoise15, San Francisco, CA, 9–12 August 2015.
10.
KimKHYoonGH.Absorption performance optimization of perforated plate using multiple-sized holes and a porous separating partition. Appl Acoust2017; 120: 21–33.
FazendaBWanklingMHargreavesJet al. Subjective preference of modal control methods in listening rooms. J Audio Eng Soc2012; 60(5): 338–349.
19.
KonishiSYodaMSugiyamaSet al. Tunable acoustic absorber using a micro acoustic hole array. Electr Commun Jpn2000; 83(1): 95–100.
20.
WuXFuCLiXet al. Low-frequency tunable acoustic absorber based on split tube resonators. Appl Phys Lett2016; 109: 043501.
21.
SouzaANPatraquimR. Analise preliminar da viabilidade de ressoadores de helmholtz adaptaveis para optimizacao da resposta acustica de salas pequenas. In: Anais do VIII Congresso Ibero-americano de Acustica, Évora, 1–3 October 2012.
22.
ISO 354:2003. Acoustics—measurement of sound absorption in a reverberation room.
23.
TakahashiYOtsuruTTomikuR.In situ measurements of absorption characteristics using two microphones and environmental “anonymous” noise. Acoust Sci Tech2003; 24(6): 382–385.
24.
PratoACasassaFSchiaviA.Reverberation time measurements in non-diffuse acoustic field by the modal reverberation time. Appl Acoust2016; 110: 160–169.
25.
ISO 10534-1:2001. Acoustics—determination of sound absorption coefficient and impedance in impedance tubes: method using standing wave ratio.
26.
ISO 10534-2:2001. Acoustics—determination of sound absorption coefficient and impedance in impedance tubes: transfer-function method.
27.
ParreiraRJPG. Paineis acusticos perfurados em madeira: estudo e avaliacao experimental de solucoes. Master’s Thesis, Instituto Superior Tecnico, Universidade de Lisboa, Lisboa, 2008.
28.
EverestFAPohlmannKC.Master handbook of acoustics. New York: The McGraw-Hill Companies, 2009.
29.
KuttruffH.Room acoustics. New York: Spon Press, 2009.
30.
BodenHAbomM.Influence of errors on the two-microphone method for measuring acoustic properties in ducts. J Acoust Soc Am1986; 79(2): 541–549.
31.
HanJHerrinDWSeybertAF. Accurate measurement of small absorption coefficients. SAE technical paper 2007-01-2224, 2007.
32.
PompoliFBonfiglioPHoroshenkovKVet al. How reproducible is the acoustical characterization of porous media?J Acoust Soc Am2017; 141(2): 945–955.
33.
OldfieldRBechwatiF.Accurate low frequency impedance tube measurements. Proc In Ac2008; 30(4): 1–11.
34.
EconomouPEconomouC. Reverberation time (RT) calculation based on room modal decay and using wave based geometrical acoustics (wbga) and modal parameter estimation. In: Proceedings of Euronoise conference, Heraklion, 27–31 May 2018, pp. 2099–2106.
