1. Microphones and Sound Chapter 5

2. The Basics of Sound Sound itself is a vibration—a specific motion—of air molecules. A sound source creates changes in air pressure. When molecules are pushed together, they are said to be in compression. Areas of low pressure, where molecules are pulled apart from one another, are called rarefactions. See figure 5.1 on page 96.

3. The Elements of Sound A pure-tone sound is represented by a sine wave. A sound wave depicting sound is a graphic representation of the rarefactions and compressions of the air molecules. See figures 5.2, 5.3 and 5.4.

4. Cycle One complete movement of a sound or electrical wave through its naturally occurring pattern to its starting point. The time it takes for a wave to make a complete cycle is called an interval.

5. Frequency The measure of how often a cycle is repeated in any given period. Frequency is measured in hertz (cycles per second).

6. Amplitude Amplitude is the height of the sine wave and indicates the volume of the sound. The higher the amplitude, the louder the sound.

7. Waveforms Sounds consist of combinations of wave patterns or waveforms. Most are a combination of many waves of different shapes and frequencies and are called complex waveforms.

8. Frequencies and Your Ears The human ear can hear frequencies from about 35 to 20,000 Hz. This depends on the age and health of the person. Older people generally don’t hear high frequencies as well as younger people do. The low end of the scale is a deep bass rumbling; the high end is a thin whine that’s barely audible to people.

9. How Frequency Shapes Sound A sound is a combination of various waves, some higher and some lower. For example, the fundamental frequency of the male voice is 300 Hz but consonants such as t and d are much higher, perhaps in the 1000 Hz range.

10. Amplitude Amplitude of the sine wave represents the volume of the sound. Another way to measure sound volume is in decibels. The higher the decibel, the louder the sound. These measurements are expressed in db SPL (decibel sound pressure level). An increase of decrease of 1-2 db SPL is the smallest change in sound level the human ear can perceive. An increase of 6 db SPL is what the human ear perceives as a doubling of the sound’s volume.

11. Other Characteristics of Sound Pitch—the ear and mind’s subjective interpretation of frequency and loudness Duration—the amount of time sound exists Loudness—the way we perceive volume Quality or Timbre—the way we interpret the complex waveforms

12. The Ear Sound-pressure waves are collected into the aural canal by way of the outer ear’s pinna and are directed to the eardrum. The soundwaves are changed into mechanical vibrations which are transferred to the inner ear by way of three bones called the hammer, anvil and stirrup. These bones significantly increase the vibrations coming from the eardrum and reduce the level of loud, transient sounds. The vibrations are then applied to the inner ear (cochlea). Tiny hair receptors lining the cochlea respond to certain frequencies which results in neural stimulation that gives us the sensation of hearing.

14. Thresholds Threshold of hearing—an SPL that an average listener can hear a specific frequency only 50 percent of the time--usually denoted as 0 dB SPL. Threshold of Feeling—an SPL that causes discomfort in a listener 50 percent of the time— about 118 dB SPL between the frequencies of 200Hz and 10kHz. Threshold of Pain—the SPL that causes pain in the listener 50 percent of the time—about 140 dB SPL between the frequencies of 200Hz and 10kHz.

15. The Microphone The microphone is a transducer. It changes the energy of the motion of sound into electrical energy. Basically, it transforms sound into something usable by the record and playback units hooked up to the radio console.

16. Microphone Design Three transducer types are: Moving Coil or Dynamic Ribbon Condenser

17. Moving Coil or Dynamic Microphone In principle, the dynamic pickup system operates by using electromagnetic induction to generate an output signal. They use a magnet, a coil wrapped with wire and a diaphragm that sits over the top of both. Soundwaves hit the diaphragm and moves the coil across the magnet. This creates a voltage that travels out and along the mic cable.

18. Ribbon Microphone The ribbon mic also works on the principle of electromagnetic induction but instead of a coil and diaphragm, a thin metal corrugated ribbon is stretched across the magnetic field. Soundwaves hit the ribbon and move it across the magnet.

19. Condenser Microphone Condenser mics operate on an electrostatic principle rather than the electromagnetic principle. The head (or capsule) consists of two very thin plates, one movable and one fixed. These two plates form a sound sensitive capacitor (an electrical device that’s capable of storing an electrical charge). Phantom power charges a capacitor which holds a charge in the fixed plate. When the movable plate moves in response to a soundwave, a charge is developed in relation to how much movement it makes.

20. Microphone Pickup Patterns Omnidirectional Bidirectional Cardiod

21. Onmidirectional Picks up sounds from all sides

22. Bidirectional Picks up sound from the front and rear but rejects it from the sides

24. Cardioid “Heart-shaped” Often called unidirectional Picks up sound from one direction

26. Frequency Response The on-axis frequency response curve of a microphone is the measurement of it’s output over the audible frequency range when driven by a constant, on-axis input signal. This response curve (which is generally plotted in output level (dB) over the 20-20,000 Hz frequency range) often yields valuable information and can give clues as to how a mic will react at specific frequencies.

27. Components of Frequency Response Range—the amount of the frequency spectrum a mic can hear Shape—the level of response at various frequencies within the mic’s range

28. Physical Types of Microphones Hand-Held Studio Mounted Headset Lavalier Shotgun

29. Microphone Selection Type Pickup Pattern Element (see chart on page 115) Frequency Response Personality