Two very good resources available: Acousticslab and Auditory theory from Santa Fe University. Both include detailed explanations with illustrations and audio demos.
You may want to start by looking at the fundamentals of acoustics: 02 Acoustics from acousticslab; Intro to Sound; Physclips is also a very good source. Chapters 4 & 6 particularly useful for this.
An explanation and illustration of the phenomena of beating & roughness.
How the ear works: 3a Hearing & 4 Loudness from acousticslab; Introduction to Hearing;
Audio demos illustrating aspects of hearing (we will also examine some of these in class next week).
Further reading:
Brian C. J. Moore, 2012. An Introduction to the Psychology of Hearing. Emerald Group Publishing Limited.
William A. Yost, 2006. Fundamentals of Hearing, Fifth Edition: An Introduction. 5 Edition. Emerald Group Publishing Limited.
For next week - construct your own equal loudness curve using this website from our friends at UNSW.