Selected Papers
Signal Processing applied to Acoustics
P. Guidorzi, M. Garai, “Impulse responses measured with MLS or Swept-sine signals:
a comparison between the two methods applied to noise barriers measurements”,
Proc. AES Convention, Roma, Italy,
ISBN 978-0-937803-91-2, Paper ID 8914, 1-10 (2013)

A sound source and a microphone grid are used for measuring a set of impulse responses
with the purpose of estimating the in-situ acoustical characteristics of noise barriers (sound
reflection and airborne sound insulation) following the CEN/TS 1793-5 European standard
guidelines as improved by the European project QUIESST. The impulse responses are
measured using MLS (Maximum Length Sequence) and Swept-sine signals.
The acoustical characteristics of the noise barrier, obtained using the two signals, are
generally equivalent, but in some critical measurement conditions a discrepancy can be found.
Differences and advantages between measurements, obtained by means of MLS or Swept-
sine signals, are analyzed and discussed in this paper.
P.Guidorzi, M.Garai, "Signal analysis in the sound absorption measurement
procedure: the importance of time subtraction and reference surface corrections",
Proc. Acoustics ‘08, Paris, France, ISBN 978-2-9521105-4-9, 1755-1760 (2008)

The in situ measurement of the sound absorption coefficient (following the ISO 13472-1
standard) of highly absorbing materials, which are typically employed in room acoustics
correction, presents some inherent difficulties. These materials present high sound absorption
coefficient indeed, but usually low sound insulation index and are installed over highly reflective
surfaces. This leads to some measurement problems, partially solved by means of the
reference surface method. In this work some measurement examples on the same materials
but with different boundary conditions are analyzed and the improvements on the results, due
to reference surface normalization and time domain subtraction of free field response, are

P.Guidorzi, M.Garai, “Sound absorption measurement using MLS method. How much
is the final result affected by the non-linearities of the measurement chain?”,
Proc. 19th I.C.A 2007, Madrid, Spain, ISBN 84-87985-12-2,
Special issue of Revista de Acústica, 38(3-4), Paper RBA-11-009 (2007)

The measurement of the acoustic properties of a material using impulsive methods can be
performed through low-cost instruments, such as computers and good quality soundcards. In
the measurement chain an acoustic source and a microphone are also involved. Since they
cause most of the non-linearities, these items can be considered the weak link in the chain. In
this paper different ways of equalizing the measurement chain are shown and their influence
on the final result is discussed.

M. Garai, P. Guidorzi, “Reflection index measurement on noise barriers with the
Adrienne method: source directivity investigation and microphone grid
implementation” (invited paper),
Proc. Inter-Noise 2011, Osaka, Japan, Paper 427100, 1-6 (2011)

In this work the sound source directivity influence on the Reflection Index measurement has
been investigated. Two different sound sources and two different noise barrier surfaces
(absorptive and reflective) were used. The measurements have been performed following the
CEN/TS 1793-5 European standard (“Adrienne” method) using a 3 x 3 microphone grid
instead of the single microphone required by the standard. The loudspeaker has been rotated
on the horizontal axis for both the free field and on barrier measurements, covering an angle of
180 degrees in steps of 10 degrees. The results clearly show that the source directivity has
limited influence on the final measurement results and that the average of the measurement
values on the grid is more accurate and reliable than the single microphone measurement. It is
also shown that the signal subtraction can reliably be done without a rigid connection source-
P. Guidorzi , L. Barbaresi, M. Garai, F. Testoni, "Confronto tra misure di isolamento
acustico secondo la normativa ISO-140 e tramite misure impulsive" Atti XXXVIII Conv.
A.I.A., Rimini, Italy,
ISBN 978-88-88942-34-6, Paper S4-A6, 1-8 (2011)

In questo lavoro si analizzano alcune misure di isolamento acustico, svolte in camera semi-
riverberante. Le misure sono state effettuate simultaneamente mediante due sistemi di
misura: un analizzatore Larson Davis modello 2900 e un sistema di acquisizione basato su
PC, scheda audio e software di misura e analisi. I risultati parziali e finali delle misure sono
confrontati e analizzati, valutando le differenze tra i due sistemi. Le misure sono state
effettuate nelle camere semi-riverberanti affiancate in dotazione al laboratorio di acustica del
DIENCA. Una parete in cartongesso è stata eretta a separazione delle due camere e varie
sessioni di misure di isolamento acustico sono state effettuate, seguendo le direttive della
normativa UNI EN ISO 140-1 e 3, ora sostituita dalla serie di norme UNI EN ISO 10140-1, 2 e
4, ma ancora in vigore al momento di questo studio. Per valutare diverse condizioni al
contorno si è creata artificialmente una perdita di isolamento sulla parete effettuando un taglio
orizzontale con due altezze diverse (Caso A e Caso B), richiudibile in parte o completamente
(Caso C). In tal modo si è potuto valutare il potere fonoisolante della parete in tre diverse
configurazioni A, B, e C.
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Selected papers
Signal processing