The work presented by this thesis deals with the problem of the sound absorption coe fficient estimation, by means of in-situ measurements. These measurements are directly taken in the environment in which the surface under consideration is placed. Thus, there is not the need to remove material samples for a posteriori laboratory study. Consequently the method can be classified as non-destructive. The possible applications of this technique regard the estimation of the acoustical properties of unclassified, or simply unknown materials. The proposed solution is based on the direct measurement of the energy related to the signal incident to the surface under test, and to the reflected one. The separation between these two signals, temporally superimposed, is achieved by means of a highly directive microphone array. Moreover, the use of this kind of array allows the system to be robust against reverberation phenomena. The results for the sound absorption coefficient estimation are provided as a function of the frequency. On the contrary, no information about the angle of incidence is considered, due to implementation constraints. In fact, it is required that the incident signal wavefront is always normal respect to the surface under analysis. The proposed method has been validated by means of simulations and experiments.
Il lavoro presentato in questa tesi tratta il problema della stima dei coefficienti di assorbimento acustico di una superficie, attraverso misurazioni in-situ. Tali misurazioni sono effettuate direttamente nell'ambiente in cui si trova la superficie da analizzare, senza la necessità di asportare campioni di materiale, per uno studio in laboratorio a posteriori. Il metodo si configura quindi come non distruttivo. Le possibili applicazioni di questa tecnica riguardano la stima delle caratteristiche acustiche di materiali non classificati, o semplicemente sconosciuti. La soluzione proposta si basa sulla misurazione diretta del segnale incidente e di quello riflesso dalla parete. La separazione tra questi due segnali, temporalmente sovrapposti, è realizzata per mezzo di un array di microfoni altamente direzionale. L'utilizzo di questo tipo di array consente inoltre al sistema di essere robusto rispetto a fenomeni di riverbero. I risultati della stima dei coefficienti di assorbimento acustico sono presentati in funzione della frequenza. Non è invece considerata alcuna dipendenza rispetto all'angolo di incidenza, a causa di vincoli di implementazione. E' infatti richiesto che il fronte d'onda del segnale incidente sia sempre normale rispetto alla superficie sotto analisi. Il metodo proposto è stato validato attraverso simulazioni ed esperimenti.
A method for the estimation of the sound absorption coefficients of planar surfaces
RIVA, ANDREA
2010/2011
Abstract
The work presented by this thesis deals with the problem of the sound absorption coe fficient estimation, by means of in-situ measurements. These measurements are directly taken in the environment in which the surface under consideration is placed. Thus, there is not the need to remove material samples for a posteriori laboratory study. Consequently the method can be classified as non-destructive. The possible applications of this technique regard the estimation of the acoustical properties of unclassified, or simply unknown materials. The proposed solution is based on the direct measurement of the energy related to the signal incident to the surface under test, and to the reflected one. The separation between these two signals, temporally superimposed, is achieved by means of a highly directive microphone array. Moreover, the use of this kind of array allows the system to be robust against reverberation phenomena. The results for the sound absorption coefficient estimation are provided as a function of the frequency. On the contrary, no information about the angle of incidence is considered, due to implementation constraints. In fact, it is required that the incident signal wavefront is always normal respect to the surface under analysis. The proposed method has been validated by means of simulations and experiments.File | Dimensione | Formato | |
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Descrizione: A method for the estimation of the sound absorption coefficients of planar surfaces
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https://hdl.handle.net/10589/20545