Acoustics and Manufacture of Caribbean Steelpans Soren Eldred Maloney Wolfson College December 2010 This dissertation is submitted for the degree of Doctor of Philosophy To my Grandparents, Aunt Dovie and Valerie-Ann Preface This dissertation is the result of my own work and includes nothing which is the outcome of work done in collaboration except where specifically indicated herein. No part of this dissertation has been or is currently being submitted for any other qualification at this or any other university. The work herein was conducted solely at the Cambridge University Engineering Department from April 2006 to December 2010 and was funded by the University of Trinidad and Tobago. This dissertation is 64994 words in length and contains 105 figures and 37 tables, which is within the limits set by the Degree Committee for Engineering. Soren Eldred Maloney Cambridge, December 2010 i Abstract The Caribbean steelpan is a pitched percussion instrument that originated in Trinidad and Tobago during the Second World War. Despite several research initiatives to improve the making of this relatively new instrument, several areas remain unaddressed. This thesis presents new approaches to help improve the making of the instrument. These approaches are situated in the production, vibration and material aspect of the steelpan. A novel sheet forming technology termed Incremental Sheet Forming (ISF) is applied to the production of miniature steelpan dishes. The thickness distribution in the wall of the ISF dishes is compared to the wall thickness distribution in a traditionally formed steelpan dish and a wheeled dish. Unlike traditional forming and wheeling, ISF produces stretching in only a portion of the walls of the formed dishes. Multi-pass ISF is used to extend the stretched zone but this extension is minimal. A break even analysis is also applied to investigate the fiscal viability of ISF application to the production of miniature and full size steelpan dishes. The application of ISF to steelpan making is found to be commercially profitable but could be jeopardised by the tuning stage of the steelpan making process. A preliminary study on the effect of impact on tone stability is conducted on a pair of notes on a full size steelpan and detuning is found more likely to occur by repeated impact of the note at its centre. Mode confinement in test-pans is also investigated. ISF is used to produce miniature test-pans with test-notes that are geometrically identical to notes on full size pans. It is possible to confine modes by varying the curvature of the bowl surrounding the test-note. The number of localised modes in the test-note increases as the radius of curvature of the surrounding bowl increases. The natural frequency of the first confined mode in the test-notes is sensitive to material springback in ISF and the mechanism of confinement appears to be due to the change in geometry that occurs between the flat test-note region and the bowl wall. This control of mode confinement may find use in future efforts to completely or partially automate the steelpan making process. Material damping and mechanical properties in low-carbon steel used to produce steelpans are researched. Damping and mechanical properties are extracted from low-carbon steel that is subjected to identical stages to the steelpan production process. Material damping trends suggest that an annealing temperature between 300°C and 400°C would be appropriate for the heat treatment of steelpans. Air-cooled and water-quenched low-carbon specimens exhibit comparable damping trends. Hardness increases in cold formed low-carbon specimens is attributed to strain hardening and not strain ageing. Investigation of damping trends and mechanical properties in ultra- low bake-hardenable and interstitial-free steels reveals that a wider range of low-carbon steels may be suitable for steelpan making. ii Acknowledgements Firstly, I thank my supervisors, Dr Claire Y. Barlow and Professor Jim Woodhouse for their expert guidance, enduring patience and encouragement, and for their extraordinary manner of teaching. They taught me the importance of asking penetrating questions and refused to accept anything less than my best efforts. They also instilled in me the importance of developing an eye for detail. I endeavour to imitate their dedication and commitment to the advancement of knowledge and teaching. I would also like to thank the University of Trinidad and Tobago for providing me with the opportunity to conduct this very important research. A special thanks to technicians Len Howlett, David Miller, Gareth Ryder, Gary Bailey, Alan Heaver, Alistair Ross, Dr. Arul Britto and the many other technicians at the Cambridge University Engineering Department. My work would not have been possible without their expertise and patience. I also wish to extend thanks to master pan maker Aubrey G. Bryan for providing the pans used in this work and for the generous giving of his time and knowledge. A warm thanks to Roger Traynor of Polytec UK Ltd who willingly offered to conduct a 3D vibration analysis of a soprano pan. I am also greatly indebted to my fiancée Kudakwashe, family and close friends for their loving and unwavering encouragement and support. Their persistent prayers and encouraging words gave me the inspiration and determination to follow through to the end. My greatest indebtedness is owed to the creator of music. He has put it into our hearts, minds and souls to express ourselves musically. The steelpan invention is an exact manifestation of his existence. iii Table of Contents Preface .......................................................................................................... i Abstract ....................................................................................................... ii Acknowledgements....................................................................................iii List of Figures ............................................................................................. x List of Tables............................................................................................. xv Chapter 1 Introduction........................................................................... 1 1.1 The Steelpan: An Introduction..................................................................... 1 1.2 A concise history ............................................................................................ 1 1.3 The steelpan family and musical ranges...................................................... 1 1.4 Traditional steelpan crafting ........................................................................ 4 1.5 Note placement and standardization ........................................................... 6 1.6 Motivation ...................................................................................................... 7 1.6.1 Steelpan dish production .......................................................................... 8 1.6.2 Mode confinement..................................................................................... 9 1.6.3 Steelpan detuning...................................................................................... 9 1.6.4 The effect of manufacturing regime on vibration damping...................... 9 1.7 Dissertation Outline..................................................................................... 10 Chapter 2 Background.......................................................................... 11 2.1 Steelpan dish production............................................................................. 11 2.1.1 Traditional crafting ................................................................................ 11 2.1.2 Pneumatic and Robotic assisted dishing ................................................ 12 2.1.3 Conventional spinning............................................................................ 14 2.1.4 Problems associated with the use of vibrating hand tools ..................... 16 2.1.5 Hydroforming and deep-drawing ........................................................... 17 2.1.6 Incremental sheet forming ...................................................................... 19 iv 2.1.7 Stretch forming and Wheeling ................................................................ 23 2.1.8 Summary of steelpan dish production .................................................... 24 2.2 Materials and vibration damping in steelpans ......................................... 27 2.2.1 Vibration damping: material and non material damping ...................... 27 2.2.2 Material damping mechanisms............................................................... 28 2.2.3 Cold deformation and heat treatment effects on material damping....... 31 2.2.4 Carbon content on damping ................................................................... 33 2.2.5 Surface coating on damping ................................................................... 33 2.2.6 Pan material: low carbon steel vs. metal alloys..................................... 33 2.2.7 Mechanical properties and formability of low-carbon steels ................ 34 2.2.8 Cold deformation effects on formability in pans: low carbon steel vs. metal alloys............................................................................................. 40 2.2.9 Material influence on steelpan design.................................................... 43 2.2.10 Drawbacks in the use of metal alloys ....................................................