Resonance in Sound Waves

9 Key excerpts on "Resonance in Sound Waves"

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  eBook - ePub

  The Speech Chain

  The Physics And Biology Of Spoken Language

  • Dr. Peter B. Denes, Dr. Elliot N. Pinson(Authors)
  • 2016(Publication Date)
  • Hauraki Publishing

    (Publisher)

  When a sound wave reaches a volume of air enclosed in a container, an increase in the sound pressure compresses the air in the container. The “springiness” of the air inside the container tends to push the compressed air out again. If the rarefaction of the sound wave reaches the container at the same time the compressed air is being pushed out, the pressure of the sound wave and the pressure of the compressed air will add together and the air particles will move with increased amplitude. If the rate of arrival of the sound wave’s compressions and rarefactions (the rate being equal to the sound wave’s frequency of vibration) corresponds to a natural frequency of the enclosed air, we get increased movement or resonance. When we fill a bottle with water, we can actually hear it filling up. Resonance explains this: the splashing water generates sounds of many different frequencies, but the resonance of the air column above the water level emphasizes only those frequencies in the sound that are near its own natural frequency. As the bottle fills up, the size of the air column decreases (this increases the column’s resonant frequency), and higher frequency components of the “splashing” are emphasized. We know from experience that, when the pitch of the sound from the bottle is high enough, little air is left in the bottle and it is time to turn off the tap. The simple spring-mass combination has only one resonant frequency; columns of air have many different resonant frequencies. We will consider only the resonances of tubes whose cross-sectional dimensions are small compared to the wavelengths of the sounds applied to them. The vocal tract is just this sort of tube for the frequencies of primary interest in speech. A tube with uniform cross-sectional area throughout its length has regularly spaced resonant frequencies. The values of these resonant frequencies depend on the length of the tube. Consider a tube closed at one end and open at the other

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  The Basics of Physics

  • Richard L. Myers(Author)
  • 2005(Publication Date)
  • Greenwood

    (Publisher)

  For example, when one person pushes another person on a swing, the frequency depends on the person doing the pushing. When the frequency of a forced vibration matches the natural vibration of an object, resonance occurs. Resonance leads to an increase in frequency. A simple example of resonance occurs when swinging. The swing has a natural period that depends on its length. In order to increase the amplitude, which in the case of a swing means a greater height, the person swinging should pump his legs at a frequency that matches the natural period of the swing. Resonance also explains the great tidal heights in places such as the Bay of Fundy. Natural water bodies have a natural period of vibration that depends on the shape of the basin. When the dimensions of the basin produce a natural period that matches the tidal forces of the Moon and Sun (roughly 12 hours and 24 hours, respectively), then the amplitude of the tide is amplified to a much greater height. The natural period of a water body is also evident when trying to carry a shallow pan of water. The water in the pan tends to resonate at a frequency that matches the frequency of walking, making it difficult to carry the water without it sloshing over the sides of the pan. Waves While vibrations consist of oscillations taking place over time at a specific location, waves can be thought of as a vibration that propagates through space. As the vibration travels through space, it creates a distur- bance that carries energy from one location to another. There is no net displacement of matter as a wave passes. This is observed when watching an object floating in water as waves pass. The object bobs up and down and remains in a relatively fixed location as the wave passes. Wind and other forces may cause the object to move laterally, but the wave itself causes a circular or elliptical motion with no net lateral displacement.

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  Introductory Physics for Biological Scientists

  • Christof M. Aegerter(Author)
  • 2018(Publication Date)
  • Cambridge University Press

    (Publisher)

  4 Resonances and Waves 4.1 How Resonances and Waves Determine How We Interact with the Environment Our senses rely heavily on the interaction with waves from the outside world. Whether it is our ears that hear sound waves or our eyes that see light waves, most of the interactions that we have with the outside world takes place via waves that are transmitted from the objects we are interested in to our senses. Therefore, in order to properly understand our senses, we have to know how waves are created and transmitted and also how they can be sensed. When a wave hits our senses, vibrations are excited in parts of our senses. In our ears, sound waves excite vibrations in the basilar membrane, which changes the conformation of hair cells that lead to the firing of neurons. This is done in a frequency-specific way and only those parts of the basilar membrane in the cochlea that are fit for this frequency are resonantly excited. Similarly, in our eyes, electrons in the receptor molecules in our retina are excited to vibrate, which again results in the firing of nerves. All of these processes of excitation of our senses by different kinds of waves are due to the parts being resonant with certain frequencies of the waves. Thus in order to get a grasp of how this works, we will have to see how vibrating systems act when forced externally as well as when and how resonance occurs. This will be done in Section 4.2. But also in the field of instrumental methods, there are vibrations and waves that determine how a great variety of these methods work. In the case of nuclear resonance, it is again electromagnetic (radio) waves that stimulate an oscillation of nuclear spins; in seismology, sound waves are used in the earth in order to learn something about the structure of rocks (and where to find oil).

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  Physics

  • Fatih Gozuacik, Denise Pattison, Catherine Tabor(Authors)
  • 2020(Publication Date)
  • Openstax

    (Publisher)

  • A sonic boom is constructive interference of sound created by an object moving faster than sound. 14.4 Sound Interference and Resonance • A system’s natural frequency is the frequency at which the system will oscillate if not affected by driving or damping forces. • A periodic force driving a harmonic oscillator at its natural frequency produces resonance. The system is said to resonate. • Beats occur when waves of slightly different frequencies are superimposed. • In air columns, the lowest-frequency resonance is called the fundamental, whereas all higher resonant frequencies are called overtones. Collectively, they are Chapter 14 • Key Terms 443 called harmonics. • The resonant frequencies of a tube closed at one end are , where f 1 is the fundamental and L is the length of the tube. • The resonant frequencies of a tube open at both ends are KEY EQUATIONS 14.1 Speed of Sound, Frequency, and Wavelength speed of sound 14.2 Sound Intensity and Sound Level intensity sound intensity sound intensity level 14.3 Doppler Effect and Sonic Booms Doppler effect observed frequency (moving source) Doppler effect observed frequency (moving observer) 14.4 Sound Interference and Resonance beat frequency resonant frequencies of a closed-pipe resonator resonant frequencies of an open-pipe resonator CHAPTER REVIEW Concept Items 14.1 Speed of Sound, Frequency, and Wavelength 1. What is the amplitude of a sound wave perceived by the human ear? a. loudness b. pitch c. intensity d. timbre 2. The compressibility of air and hydrogen is almost the same. Which factor is the reason that sound travels faster in hydrogen than in air? a. Hydrogen is more dense than air. b. Hydrogen is less dense than air. c. Hydrogen atoms are heavier than air molecules. d. Hydrogen atoms are lighter than air molecules. 14.2 Sound Intensity and Sound Level 3. What is the mathematical relationship between intensity, power, and area? a.

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  The Working Voice

  Vocal Health and Effective Communication

  • Stephanie Martin, Olivia Darnley(Authors)
  • 2024(Publication Date)
  • Routledge

    (Publisher)

  6 Resonance

  DOI: 10.4324/9781003361114-7

  Introduction

  Resonance plays a crucial role for professional voice users, enabling effortless message delivery and amplification while minimising vocal strain and fatigue. Vocal resonance is essentially the sound of the note, or ‘laryngeal buzz’, augmented and modified by the shape and size of your distinctive resonating cavities, the throat, mouth and nasal passages. These cavities determine the specific qualities and nuances of your tone, timbre and the richness of your voice.

  Very simply put, the intensity, or quality, of the sound you hear when you speak or sing is caused by the reverberation of sound waves from your vibrating vocal folds, which are enhanced by the air-filled resonators through which it passes. There are six main resonating areas in the body – the larynx, the pharynx, the oral cavity, the nasal cavity, the upper skull cavity and the chest – which modify and enhance the sound.

  In this chapter, we will look in detail at how to find more resonance and utilise the natural resonator available to you: your body and, specifically, your vocal tract.

  What Is It, Exactly?

  The resonatory system modifies and amplifies the fundamental note and consists of:

  • – The chest.
  • – The pharyngeal, oral and nasal cavities.

  The resonators above the larynx can alter in size, shape and tension through the movement of the base of the tongue and the soft palate. In addition, further modification can occur through contraction of the pharyngeal and extrinsic laryngeal muscles.

  Although the larynx is obviously the primary contributor to the production of voice, without the acoustic influence of the resonators the voice would sound very thin indeed. Most of the quality and loudness characteristics associated with the voice are the result of the resonators. In the same way that the weak vibrations of the strings of a musical instrument are altered by the resonating body of the instrument, so the tone that is produced at the level of the larynx, the laryngeal buzz, is altered by the resonators. The airway above the larynx acts like an acoustic filter, which can suppress or maximise some sounds as they pass through. Alterations can also occur in the configuration of the vocal tract by varying tongue positions, raising or lowering the soft palate, and as an effect of the degree of relaxation or tension present.

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  Electronics and Instrumentation for Audiologists

  • Paul James Moser(Author)
  • 2013(Publication Date)
  • Psychology Press

    (Publisher)

  Figure 13.26 , has a resonance frequency, although the resonance frequency changes as the stiffness varies.

  Acoustical Vibration

  In the previous sections, you studied the vibrations and resonances of mechanical systems and the resonances of sound waves in pipes. There are also acoustical systems that vibrate much like mechanical systems but behave differently from pipes containing standing waves. A simple example of such a system is a Helmholtz resonator, a container with a neck at the opening.

  A jug is an example of a Helmholtz resonator. If you blow across the opening, you can make a very deep sound—much deeper (lower frequency and longer wavelength) than could be produced by a narrow pipe of a similar length. If you place your mouth tightly over the mouth of an empty (air-filled) jug and blow into it, you will find that, as air passes into the jug, your mouth and lungs must exert an ever-increasing pressure to push more air into the jug. This is like pushing against the force of a spring. Also, since there is air in the neck of the jug, it must move as air flows into and out of the jug.

  If the jug resonates, then air in the neck moves back and forth, like a mass on a spring. Also, the air within the volume of the jug responds like a spring by pushing back with increasing or decreasing pressure on

  the incoming air. Figure 13.29 shows that the resonator has a mass and stiffness, just like a mass on a spring. To complete the analogy between the two systems, Figure 13.30 shows that a fine wire screen can be used to resist the motion of the air in the neck, thus introducing a resistance.

  Figure 13.29 Helmholtz resonator.

  Figure 13.30 Helmholtz resonator with resistance.

  Acoustic Impedance

  Acoustic impedance ZA defines the relationship between sound pressure p and the volume velocity U measured at a particular surface. The volume velocity

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  Sound Studio

  Audio techniques for Radio, Television, Film and Recording

  • Alec Nisbett(Author)
  • 2003(Publication Date)
  • Routledge

    (Publisher)

  An important feature of any musical instrument is that its vibrating surfaces or columns of air do not radiate equally efficiently in all directions. Different frequencies, too, may radiate more or less powerfully in different directions, so that the mixture of tones changes with angle.

  There are many other essential qualities of musical instruments. These may be associated with the method of exciting the resonance (bowing, blowing, plucking or banging); or with qualities of the note itself, such as the way it starts (the attack , which creates an irregular transient) , is sustained and then released , changing in volume as the note progresses (to create its envelope ).

  [2.16 ] Vibration of a drumskin

  (a stretched circular membrane, clamped at the edges) The suffixes refer to the number of radial and circular nodes (there is always a circular node at the edge of the skin). The overtones are not harmonically related. If f 01 = 100 Hz, the other modes of vibration shown here are: f 02 = 230, f 03 = 360, f 11 = 159, f 12 = 292, f 21 = 214 Hz.

   

  [2.17 ] Wind instrumental formants

  1, Oboe. 2, Horn. 3, Trombone. 4, Trumpet. The formants, imposed by the structural dimensions of parts of the instruments, may be broad or narrow. They provide an essential and recognizable component of each instrument’s musical character.

  Air resonance

  Air may have dimensional resonances very much like those of a string of a violin, except that whereas the violin string has transverse waves , those in air, being composed of compressions and rarefactions, are longitudinal waves . Radiated sound moves through air in the form of progressive waves , but dimensional resonances stand still: they form stationary or standing waves .

  These stationary waves can again be represented diagrammatically as transverse waves. The waveform chosen is usually that for displacement amplitude. This makes intuitive sense: at nodes (e.g. at solid parallel walls if the resonance is formed in a room) there is no air-particle movement; while at antinodes

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  College Physics, Volume 1

  • Raymond Serway, Chris Vuille(Authors)
  • 2017(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  . . [14.19] 14.11 Beats The phenomenon of beats is an interference effect that occurs when two waves with slightly different frequencies combine at a fixed point in space. For sound waves, the intensity of the resultant sound changes periodically with time. The beat frequency is y is y f b b 5 | f 2 2 2 f 1 1 | [14.20] where f 2 2 and f 1 1 are the two source frequencies. vibration of a stretched string of length L, fixed at both ends, are f n n 5 nf nf n 1 1 5 n 2L Å F m n 5 1, 2, 3, . . . [14.17] where F is the tension in the string and is the tension in the string and m is its mass per unit length. 14.9 Forced Vibrations and Resonance A system capable of oscillating is said to be in resonance with some driving force whenever the frequency of the driving force matches one of the natural frequencies of the system. When the system is resonating, it oscillates with maximum amplitude. 14.10 Standing Waves in Air Columns Standing waves can be produced in a tube of air. If the reflecting end of the tube is open, all harmonics are present and the natural frequencies of vibration are CONCEPTUAL QUESTIONS 1. (a) You are driving down the highway in your car when a police car sounding its siren overtakes you and passes you. If its frequency at rest is f 0 0 , is the frequency you hear while the car is catching up to you higher or lower than f 0 0 ? (b) What about the frequency you hear after the car has passed you? 2. When dealing with sound intensities and decibel levels, a con- venient approximation (accurate to 2 significant figures) is: For every doubling of the intensity, the decibel level increases by 3.0. Suppose the sound level at some location is 85 dB. Find the decibel levels if the sound intensity is increased by factors of (a) 2.0, (b) 4.0, (c) 8.0, and (d) 16. 3. Fill in the blanks with the correct values (to two significant fig- ures), assuming sound propagates as a spherical wave.

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  Architectural Acoustics

  • Marshall Long(Author)
  • 2014(Publication Date)
  • Academic Press

    (Publisher)

  6

  Wave Acoustics

  Abstract

  Chapter 6 includes a discussion of the factors that separate acoustical phenomena that can be modeled based on energy from those that must take into account the wave behavior of sound. It begins with an analysis of simple oscillators and their resonances (for example air spring oscillators) and moves on to Helmholtz resonators, deriving the wave equation in one and three dimensions, and characterizing simple point sources and various configurations of line source. It details coherent planar sources (examples include the piston in a baffle) and discusses the construction of loudspeakers (e.g., cone and horn) and their modeling.

  Keywords

  wave equation ;  resonance ;  Helmholtz resonator ;  monopole/dipole ;  doublet ;  noise cancellation ;  arrays ;  line sources ;  comb filter ;  loudspeaker ;  constant directivity horn

  Much of architectural acoustics can be addressed without consideration of the wave nature of sound. For example, environmental acoustics and the transmission of outdoor sound, for the most part, can be visualized and modeled as a flow of energy from point to point, although many effects, such as ground and barrier attenuation, are frequency dependent. Nevertheless, for many critical aspects of acoustics, knowledge of wave phenomena is essential. Wave acoustics takes into account fundamental properties that are wavelength and phase dependent, including the scaling of interactions to wavelength, the phenomenon of resonance, and the combination of amplitudes based not only on energy but also on phase.

  6.1 .

  Resonance

  Simple Oscillators

  Many mechanical systems have forces that restore a body to its equilibrium position after it has been displaced. Examples include a spring mass, a child’s swing, a plucked string, and the floor of a building. When such a system is pulled away from its rest position, it will move back toward equilibrium, transition through it, and go beyond, only to return again and repeat the process. All linear oscillators are constrained such that, once displaced, they return to their initial position. The movement repeats at regular intervals that have a characteristic duration and thus a characteristic frequency, called the natural frequency or resonant frequency of the system.

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