Properties of Sound Waves

C. Sound Interference1. Interference occurs when waves that overlap combine, forming a new wave.2. When a compression meets another compression, it is called constructive interference, and the wave formed has higher intensity and greater amplitude than the original waves.3. When a compression meets a rarefaction, it is called destructive interference, and the waves cancel each other out.4. When waves of slightly different pitch interfere, beats occur.a. Beats are repeating increases and decreases in amplitude.b. Differences in frequency determine how often a beat occurs.5. Objects vibrate with a fundamental and overtones 1.a. The lowest frequency at which a material naturally vibrates is its fundamental.b. Higher frequencies at which the material vibrates are called overtones 2. D. Music1. The mix of the fundamental and overtones of a musical instrument is the sound of the instrument.2. Resonance is an increase in amplitude that occurs when an object that is vibrating at its natural frequency absorbs energy from a nearby object that is vibrating at the same frequency.3. String instruments produce sound when a string vibrates, and wind instruments produce sound when your lips or a(n) reed vibrates.4. A(n) percussion instrument makes sound when you strike it.5. Vocal cords are the source of sound in your voice. Complete the chart by sorting each correct sentence in the space provided. Each sentence is used only once and each category has 3 correct statements. String Musical instruments include a guitar, a violin, a harp, and a piano. These instruments produce sound when a string vibrates. The pitch a string makes depends on its thickness Wind An air column vibrates by resonance. The length of the air column determines pitch. The vibrating medium is air. Percussion Sound is made by striking the instrument. Musical instruments include a drum, cymbals, and a bell. The pitch depends on the instrument’s size, its thickness, and the material from which it is made. Voice Other parts of the mouth and throat also affect the sounds this instrument makes. Muscles in the throat allow an increase in pitch by pulling the cords tighter. The source of sound is the vocal cords. Recognizing SoundHow do you recognize the sound of a friend’s voice? How do you know that someone is playing a piano in the next room rather than a guitar?Sound Quality Sounds are described by their pitch (frequency), loudness (amplitude), and quality. Sound quality, or timbre, includes the properties of sound that let the ear distinguish sounds with the same pitch and loudness.One important part of timbre is the harmonic content of a sound. When a piano plays a middle C, the string vibrates with a fundamental frequency of 256 Hz. Parts of the string vibrate at other frequencies that are small, whole number multiples of the fundamental. These are the overtones. Each overtone has a different pitch and amplitude. The sum of the fundamental and overtones compose the harmonic content of the sound.When a trumpet and piano play the same note, their overtones give them different harmonic contents. The difference between the harmonic content of the two instruments lets you hear the difference.Overtones in Voices Notice the position of your tongue, throat, teeth, and lips as you pronounce sounds such as k, s, m, and o. The mouth and throat form chambers that have different shapes for each letter. Because people’s mouths are shaped differently, sound vibrating in each chamber produces characteristic overtones for that person, so the person’s voice is unique.Attack and Decay Attack and decay involve the changes in amplitude of a sound. For example, when you hit a cymbal with a drumstick, the peak amplitude occurs right away. The amplitude then decays, or gets smaller, over a period of time until the sound is no longer heard. Some instruments have a longer period of decay than others. This contributes to the overall quality of the sound and helps the ear identify the sound source.Vibrato and Tremolo Periodic changes in pitch are called vibrato. Periodic changes in loudness or amplitude are called tremolo. In the human voice, both occur at the same time.The ear can tell the difference between a voice and an instrument playing the same pitch because of the absence of vibrato in the instrument. Players of some instruments can add vibrato. For example, a guitar player might rapidly rock a finger back and forth over a string to produce this effect.Applying Critical-Thinking Skills 1. Apply Which qualities would let you distinguish between the sound of a cymbal and a bass drum?2. Infer Some instruments such as a Stradivarius violin are rare and expensive. What might make one violin worth more than another in terms of sound? Directions: Answer each question in the space provided below.