CDIS 4313 1st EditionExam # 1 Study Guide Chapter 1- THE NATURE OF SOUNDI. OVERVIEW OF SOUND- Brownian motiono Air is made of lots of molecules that are all composed of different chemicals. These molecules move randomly and very quickly.o Because the molecules move randomly, they collide with each other. Each collision produces pressure.- Airflowo Air always moves from higher pressure to lower pressure. Think of two rooms. It is extremely crowded in one, but the other room is empty. The crowded room represents a high pressure area, and the empty room represents a low pressure area. Every person represents a molecule. You are standing in the crowded room. It is very uncomfortable since it is so crowded, so naturally you go into the empty room because it is more comfortable. This is what happens with airflow.o Volume Velocity is the rate (or speed) of flow.o Driving Pressure is when the difference in pressures of an area causes air to flow from the higher pressure area to the lower pressure area, like in the example above.o Laminar Flow is unobstructed.o Turbulent Flow in obstructed.- Air Pressure, Volume and Densityo Air Pressure and Volume have an inverse relationship. When the volume of an enclosed space increases, the air pressureof that space decreases. When the volume of an enclosed space decreases, the air pressure of that space increases. The previous two bullets are Boyle’s law, given a constant air temperature.  Air pressure and density are directly related.- If air pressure increases, the density will increase, and vice versa.- Changes in Air Pressureo Ambient pressure (Pam) is a relatively constant pressure at a given time or place.  Pam must be disturbed for sound to be generated.- Elasticity, Inertia and Frictiono Elasticity is where an object can spring back to its original size, shape, form, and location when stretched or bent in some way.o Inertia is the tendency of an object to: Continue to stay at rest when it is already at rest. Continue to move in the same direction with the same velocity (speed).o Elasticity and Inertia interact to keep molecules moving back and forth once they have been disturbed. - Wave Motion of Soundo Longitudinalo Wave motion in water is transverseo The individual air molecules of the wave move parallel to the direction that the wave is travelling.- Simple Harmonic Motiono Simple Harmonic Motion is a cycle of acceleration through the equilibrium and deceleration at the end points. It repeats like a cycle. An example of this would be a swing or a pendulum. On each sidewhen the pendulum is at its highest, it slows down (decelerates) until it stops then changes direction and begins speeding up (accelerating) until it returns to its starting point.- Frequency, Period, Wavelength, Velocity and Amplitudeo Frequency A back and forth movement of a molecule makes up a cycle of vibration. The frequency is measured in cycles per second or Hertz (Hz) F=velocity/wavelengtho Period (T) is the amount of time it takes each cycle to occur. T=1/F Periodic- each cycle has the same amplitude and takes the same amount of time to occur.- Ex: musical note Aperiodic- not every cycle takes the same amount of time to occur- Ex: noiseo Amplitude is the amount of pressure change in dB SPL (sound pressure level)o Wavelength is the distance between a point on the wave to the same point on the next cycle.o Velocity is how fast the wave moved.II. . PURE TONES†On a linear scale the units on the x (horizontal) and y (vertical) axis increase at the same rate, or in a 1 to 1 ratio. On a logarithmic scale does not increase by the same amount as you continue through the scale.LogarithmicLinear- Pure tones produce one sound wave that has one frequency.III. COMPLEX SOUNDS- Line Spectra are a graph with frequency along the horizontal axis and amplitude along the vertical axis. It displays the frequency content of periodic sounds. They are usually used for harmonics.o Line spectra display one moment in time.o Line spectra are not used to display complex periodic waves. Envelopes are used to display complex periodic waves. An envelope is a line connecting all of the frequencies at once.IV. SOUND ABSORPTION, REFLECTION, REFRACTION AND DIFFRACTION- Sound Absorptiono Travelling sound that runs into a boundary is called an incident wave. Incident waves can be transmitted, absorbed, or reflected.o Thick walls (especially concrete ones) transmit less sound than thin ones.o Absorption is the dampening of a wave. A wave is dampened because friction causes the air pressure to diminish. Each material absorbs a different amount of energy. Soft porous surfaces absorb a lot of energy, but hard flat surfaces do not.- A wave is reflected when a portion of the sound that is not transmitted or absorbed bounces back in the opposite direction of the incident wave.o Hard, smooth surfaces will reflect more than soft or rough surfaces.- Refraction is where a wave changes direction because of a local difference of temperature in the air.o A temperature difference will cause the wave to bend (refract) towards the cooler air. o An example of this would be a straw in a glass of water. If you look at the side of a clear glass of water with a straw in it, it looks as if the straw is bending as it enters the water. This is because the light wave hitting the water bends toward the cooler air.- When a wave changes direction as it passes through an opening or around an obstacle it is called diffraction. - The longer a sound’s wavelength is (or the lower the frequency is because sounds with longer wavelengths have lower frequencies), the more the wave will diffract.V. CONSTRUCTIVE AND DESTRUCTIVE INTERFERENCE- When two or more waves combine with each other it is called interference.o Constructive wave interference occurs when the compressions and rarefactions of two waves combine at exactly the same time and place. In this case, the amplitude of the wave would double.†On a linear scale the units on the x (horizontal) and y (vertical) axis increase at the same rate, or in a 1 to 1 ratio. On a logarithmic scale does not increase by the same amount as you continue through the scale.LogarithmicLinearo Destructive wave interference occurs when the compressions of one wave and the rarefactions of another combine at the same time and place. The amplitude of the resulting wave decreases, or in this case cancels out.- Waves of