I have used this book back in my undergraduate level in Africa and PG here in UK, is still the most easiest to read and understand I have used so far, is very good for the beginner in vibration engineering up to Advance level, in particular there is an old edition (I think the 1988 ed) that do not contain much Matrix terminlogy go for that ed. if you have problems with Matrix eqns. the more recent versions are in Matrix form (which is the same only looks scary) in all I will rate this book 5 stars