Sound

- Beats: two sound sources produce waves close in frequency. The waves will destructively and constructively add over time causing the sound to become louder and softer. A rhythmic beating sound is produced.

this is shown in the third virtual lab

-The Beat frequency is equal to the difference in frequency of the two sounds.

- The Pitch of the sound is the average of the two frequencies.

V. Pitch and Sound Intensity.

- Pitch is related to the frequency of the sound. The higher the frequency, the higher the pitch.

- Intensity is related to the square of the amplitude of the sound wave.

- Hearing Intensity Range: 10-12W/m2 to 1W/m2. A very large range.

- Unit of Sound Intensity: decibel. Rated in powers of 10. 0 decibels is the threshold of hearing (10-12W/m2). 10 decibels, is 10-11W/m2, 20 decibels 10-10W/m2. Increasing by 10 decibels increases the intensity by a power of 10. 60 decibels is a sound intensity that is a million times the threshold of hearing.

VI. Sound Quality

- Musical Sounds are made up of a combination of frequencies. These frequencies are multiples of the lowest frequency called the 1st harmonic.

- A tone that is twice the frequency of the first harmonic is called the second harmonic.

- A musical sound is made up of different amplitudes of various harmonics.

- Demo: Lissajous Patterns: Stable patterns occur at ratios of frequencies. Music majors will have to help me out with this demo! It so happens that certain ratios make a pleasing sound to our perception

- Breaking down a sound wave into its harmonic components is called Fourier Analysis. Demo: We will look at Fourier components of different sounds and different instruments.

- Fourier Synthesizer builds electronic sounds by adding harmonics of different strengths together.

- Fourier Synthesis Applet

-In Class Demo: Electronic Keyboard.

Waves and Sound Review:

The Review Questions located at the end of Chapters 18,19 and 20 in the book can serve as a guide to studying the topics on waves and sound.

Also look at the following Exercises:

Chapter 18: Exercises 2,9,12,16,18,22,26,33,30

Chapter 19: Exercises 7,9,12,16,20,31,39

Chapter 20: Exercises 2,10,11,13,14,19,