A. Cocchi, M. Garai, P. Guidorzi, "Active noise control in heating, ventilation and air conditioning systems", Proceedings of 7th International Congress on Sound and Vibration, 4-7 July 2000, Garmisch-Partenkirchen, Germany ABSTRACT Noise emitted by heating, ventilation and air conditioning (HVAC) systems is one of the main causes of disturbance inside buildings. High frequency noise can be reduced using passive devices, but noise components at frequencies below 400-500 Hz are hardly reduced in such way. Active noise control (ANC) has its maximum efficiency at low frequency and then it is the ideal complement to passive techniques for achieving acoustic comfort over the whole audible spectrum. In this paper the maximum performance of an experimental active noise control system is investigated. A real scale model of an air conditioning system was built and the ANC system was applied to it. The performance of the ANC system has been tested in a realistic case (HVAC system terminating into a room) and by placing an anechoic termination at the end of the duct.
G. Semprini, P. Guidorzi, M. Garai, "Experimental Evaluation of Noise Propagation through Rectangular Ducts in HVAC Systems", Proc. of Euro-Noise 2003, Napoli, 19-21 Maggio 2003 ABSTRACT Noise propagation through a rectangular duct of an HVAC system has been investigated in an experimental set-up, in order to evaluate the sound attenuation of rectangular straight and bend ducts excited by a pink noise source and a fan noise at different flow velocities. The noise attenuation and the self-noise generated by airflows of an horizontal straight duct and of bend ducts with different flow velocities are compared with theoretical formulations. Frequency transfer function measurements are also analyzed and compared with standard attenuation measurements, giving a good correlation.
P. Guidorzi, L. Barbaresi, M. Garai "La misura dell'assorbimento acustico con diverse metodologie: camera riverberante, metodi impulsivi e tubo a onde stazionarie" Atti del XXXIV Convegno AIA, Firenze, 13-15 Giugno 2007 ABSTRACT Nel presente lavoro vengono presentati i risultati di una serie di misure comparative del coefficiente di assorbimento acustico a in camera riverberante (con i metodi del rumore stazionario interrotto e dell'integrazione inversa di Schroeder di risposte impulsive misurate con segnali MLS e Swept-Tone), con metodo a riflessione (utilizzando segnali MLS e Swept-Tone) e nel tubo a onde stazionarie. Saranno evidenziate le difficoltà, i vantaggi, gli svantaggi e le differenze tra le misure ottenute mediante le differenti tecniche. Per una trattazione approfondita dei metodi di misura qui trattati si rimanda alle rispettive normative di riferimento e ai lavori citati in bibliografia. Saranno qui esaminati alcuni aspetti specifici dei metodi in esame che li caratterizzano e differenziano tra loro.
P. Guidorzi, A. Cocchi, "Costruzione e Analisi Sonora dell'Organo ad Acqua di Leonardo", Atti del XXXI Convegno Nazionale A.I.A. pp. 151- 157, 5-7 Maggio 2004, Venezia ABSTRACT L'acqua come elemento energetico per il funzionamento di macchine sonore è presente fin dall'antichità, in progetti di Vitruvio, Hero da Alessandria e altri. Ma queste macchine, nella maggioranza dei casi, utilizzano l'energia dell'acqua per ottenere aria compressa che metta in movimento aria all'interno di canne vibranti. Leonardo da Vinci, invece, progettò un organo le cui melodie sono ottenute direttamente dal suono dell'acqua in caduta libera. Nel presente lavoro si studiano le caratteristiche sonore di un organo ad acqua progettato seguendo strettamente le indicazioni di Leonardo, e costruito in occasione della mostra dal titolo "Leonardo, Machiavelli e Borgia: arte, storia e scienza in Romagna", al Castel Sismondo di Rimini nel 2003.
M.Garai, P.Guidorzi, “Using CEN/TS 1793-4 to develop an acoustically effective added device for road traffic noise barriers”, (invited paper), Proc. 19th I.C.A 2007, Madrid, Spain, ISBN 84-87985-12-2, Special issue of Revista de Acústica, 38(3-4), Paper ENV-06-004-IP (2007) ABSTRACT Part of the market of road traffic noise reducing devices is constituted of products to be added on the top of noise reducing devices and intended to contribute to sound attenuation acting primarily on the diffracted sound field (“added devices”), but as a matter of fact few of these devices are distributed on the European market with a certified performance. The intrinsic characteristics of sound diffraction of added devices can be assessed according to the European technical specification CEN/TS 1793-4, which became available at the end of 2003.The paper reports the application of this European test method to select and optimize a new industrial product, now protected by a patent. A test site was set up to carry out the research.Then full scale measurements were done on prototypal added devices with different shapes, with and without a sound absorbing treatment. The experimental results, here summarised, permitted the selection of the best shape/absorption combination, which was further refined to get the final product, which is not only acoustically effective but also cost effective.