84 Lecture 4 
4.6. ACKNOWLEDGMENTS 
‘The author is indebted to Dr. J.C. Snowdon and to the Director of The Uni- 
versity of Michigan Institute of Science and Technology for permission to repro- 
duce Fig, 4.13. 
REFERENCES 
1, J.C. Snowdon, "The Choice of Resilient Materials for Antivibration Mountings,” Brit. J. Appl. Phys., 
Vol. 9, 461-469 (1958). 
2, J.N. Macduff and J.R. Curreri, Vibration Control (McGraw-Hill Book Co., Inc., New York, 1958). 
3. C. E. Crede, Vibration and Shock Isolation (J. Wiley and Sons, New York, 1951). 
4, J.P. den Hartog, Mechanical Vibrations, 3rd ed.-(McGraw-Hill Book Co., Inc., New York, 1947). 
5. R.E.D. Bishop and D.C. Johnson, The Mechanics of Vibration (Cambridge Univ. Press, Cambridge, 
1960). 
6, J.C. Snowdon, "The Reduction of Structure-Borne Noise," Akust. Beih., Vol. 6, 118-125 (1956). 
7. J. Heyboer, P. Dekking, and A, J. Staverman, "The Secondary Maximum in the Mechanical Damping of 
Polymethyl Methacrylate: Influence of Temperature and Chemical Modification,” Proc. Second Inter. 
Cong. on Rheology, Oxford, Vol. 26 to 31, 123-133 (1953). 
8. J.C. Snowdon, “Reduction of the Response to Vibration of Structures Possessing Finite Mechanical 
Impedance, Part I,” Rep. 2892-4-T, Fluid and Solid Mech. Lab., Willow Run Lab., Univ. of Michigan 
(November, 1959). 
9. J.C. Snowdon, "Reduction of the Response to Vibration of Structures Possessing Finite Mechanical 
Impedance, Part II," Rep. No. 2892-T, Fluid and Solid Mech. Lab., Willow Run Lab., Univ. of Michigan 
(January, 1960), 
10. J.C. Snowdon, "Reduction of the Response to Vibration of Structures Possessing Finite Mechanical 
Impedance,” J. Acoust. Soc. Am., Vol. 33, 1466-75 (1961). 
11. R.N. Hamme, Handbook of Noise Control, C.M. Harris (ed.), Chapter 14 (McGraw-Hill Book Co., Inc., 
New York, 1957). 
12, J.C. Snowdon, "Steady-State Behavior of the Dynamic Absorber," J. Acoust. Soc. Am., Vol. 31, 1096- 
1103 (1959); and, "The Steady-State and Transient Behavior of the Dynamic Absorber," Rep. 1941-3-F, 
Willow Run Lab., Univ. of Michigan (November, 1958), 
DISCUSSION 
PROFESSOR T.S. KORN drew attention to the usefulness of the concept of 
mechanical impedance or of electroacoustical analogies generally in the study 
of mechanical vibrations. He emphasized the importance of the behavior of 
elastic mountings when the input impedance of the base is reactive and not in- 
finite. He discussed the concept of the transmissibility factor as the ratio of 
forces and the possibility of using the velocity ratio or the concept of apparent 
power transmitted to the base. 
DR. PARFITT: I, personally, find the use of mechanical circuit elements 
of considerable help in visualizing and sometimes in idealizing the behavior of 
a complex mechanical system, but their application does not, of course, alter 
the problem or otherwise assist in its solution. The same is true of represen- 
tation in terms of equivalent electric circuit elements, though there is, here, 
at least the possibility of actually building the electrical equivalent network and 
making with it electrical measurements which are often simpler than the analo- 
gous mechanical ones. : 
I certainly agree that calculations such as are given in the paper do not 
tell the whole story of sound emission from a ship. What has been presented is 
an attempt to isolate one aspect of the whole complex problem of noise trans - 
mission from engine to sea and to see what factors in it are the significant ones, 
at least in idealized cases. The beam foundation considered in the paper would 
in practice be attached at its ends to further members of finite impedance 
