Name: sound wave interference in speakers
Uploaded: 2023-04-30T11:11:36.000Z
Duration: 53 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Physical Science

Waves and Their Applications

PS.PSc.8.3

Sound Waves: Interference

L’interférence est un processus en vertu duquel deux ondes sonores ou plus interagissent simultanément les unes avec les autres et produisent une nouvelle onde résultante.
Si deux ondes sonores ayant la même phase et la même fréquence se superposent, leurs amplitudes sont renforcées, ce qui entraîne des interférences constructives.
D’autre part, si deux ondes sonores de même amplitude sont déphasées de 180° et se superposent, cela conduit à des interférences destructrices, entraînant une annulation complète.
De nos jours, le concept d’interférence destructrice est utilisé dans les casques à suppression active du bruit, où un deuxième son est introduit avec ses maxima et minima complètement inversés par rapport au bruit entrant.

ondes sonores: interférences

Les ondes sonores peuvent être modélisées soit comme des ondes longitudinales, où les molécules du milieu oscillent autour d'une position d'équilibre, soit comme des ondes de pression. Lorsque deux ondes identiques provenant de la même source se superposent, la combinaison de deux crêtes ou de deux creux entraîne un renforcement d'amplitude connu sous le nom d'interférence constructive. Si deux ondes identiques, initialement en phase, deviennent déphasées en raison de différentes longueurs de trajet, la combinaison de crêtes avec des creux entraîne une réduction d'amplitude connue sous le nom d'interférence destructive. Lorsque les ondes identiques sont déphasées de 180 degrés, l'interférence conduit à une annulation complète.

Par exemple, prenons le cas de deux haut-parleurs alimentés par un seul générateur de signal. Les ondes sonores produites par les haut-parleurs sont en phase et sont d'une seule fréquence, et elles interfèrent les unes avec les autres. Lorsque deux crêtes ou deux creux coïncident, il y a une interférence constructive. De même, lorsque qu'un creux et une crête coïncident, une interférence destructive se produit. La différence de phase est due aux longueurs de trajet parcourues par les ondes individuelles. Si la différence dans les longueurs de trajet est d'une longueur d'onde, cela conduit à une interférence constructive totale et une amplitude résultante égale à deux fois l'amplitude originale. Si la différence dans les longueurs de trajet est inférieure à une longueur d'onde mais supérieure à la moitié d'une longueur d'onde, cela entraîne une amplitude supérieure à zéro et inférieure à deux fois l'amplitude originale. Enfin, si la différence dans les longueurs de trajet est d'une demi-longueur d'onde, cela conduit à une interférence destructive totale et une amplitude résultante égale à zéro.

Une application astucieuse de l'interférence dans des situations quotidiennes peut être observée avec une paire d'écouteurs. Ces dernières années, les écouteurs ont été conçus pour annuler le bruit avec une interférence destructive en créant une onde sonore opposée au son entrant. Ces écouteurs peuvent être plus efficaces que l'atténuation passive simple utilisée dans la plupart des formes de protection auditive. Les pilotes à bord de l'avion Voyager, qui détient le record du vol sans escale autour du monde, utilisent de tels écouteurs pour protéger leurs oreilles contre le bruit des moteurs.

Ce texte est adapté de <a href="https://openstax.org/books/university-physics-volume-1/pages/17-4-normal-modes-of-a-standing-sound-wave">Openstax, University Physics Volume 1, Section 17.4: Normal Modes of a Standing Sound Wave. </a>

Ondes sonores: interférences

Les ondes sonores peuvent être modélisées soit comme des ondes longitudinales, dans lesquelles les molécules du milieu oscillent autour d’une position d’équilibre, soit comme une pression ...

Education

Enseignement

JoVE Core

Physics

Physique

Unit 1

Unité 1

Sound

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

sound wave interference in speakers

Sound wave interference can change the loudness of sound when two waves meet. Sound waves may be modeled as longitudinal waves, where molecules move around an equilibrium position, or as pressure waves. When two identical waves from the same source overlap, their crests or troughs can add together. This is called constructive interference, and it increases amplitude.

If identical waves start in phase but travel different path lengths, they can become out of phase. Then a crest can meet a trough, which causes destructive interference and lowers the amplitude. When the waves are 180° out of phase, the cancellation can be complete. The path length difference determines how strong the combined wave will be.

Two speakers driven by a single signal generator show this effect clearly. Their sound waves are in phase and have a single frequency, so they interfere with one another. When two crests or two troughs line up, the result is constructive interference. When a trough lines up with a crest, destructive interference occurs.

The size of the path length difference matters. A difference of one wavelength gives total constructive interference, with an amplitude twice the original. A difference of less than one wavelength but more than half a wavelength gives an amplitude greater than zero but less than twice the original. A difference of half a wavelength gives total destructive interference and an amplitude of zero.

Interference also has a real-world use in headphones. Some headphones use destructive interference to cancel noise by producing a wave opposite the incoming sound. These headphones can work better than the passive attenuation used in most ear protection. Pilots on the Voyager aircraft use this kind of headphone to protect their ears from engine noise.

Sound Wave Interference in Speakers

sound waves

How Sound Travels Through Matter

Sound travels through matter as pressure changes in a medium. These changes make the particles of the medium move back and forth around their mean position. Sound can also be modeled as particle displacement as the wave passes through air, water, or another material. In most fluids, sound waves are longitudinal waves. That means the particles vibrate in the same direction that the wave moves. Fluids do not support lateral pressure well, so sound in liquids and gases mainly moves this way. <br...

sound as pressure waves

Sound Pressure in Longitudinal Waves

Sound waves are longitudinal waves that create changing pressure in a medium. Their displacement amplitude can be modeled as a function of position and time. As one column of the medium moves, nearby columns also move. The difference between these successive displacements produces a pressure change compared with the surrounding pressure. This pressure change is called gauge pressure. It varies across the medium because the pressure fluctuation depends on how much one point is displaced...

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perception of sound waves

How Ear Sensitivity Shapes Sound

The human ear does not respond the same way to every sound frequency. Sounds with the same pressure can seem louder or softer when their frequencies change. Ear health also affects this perception, and hearing can decline with age. Regular exposure to loud noises may also damage the ears over time. Pitch depends on both frequency and pressure amplitude, which is the size of the sound wave’s pressure change. Two sounds with the same frequency and pressure amplitude have the same pitch. If the...

speed of sound in solids and liquids

Why Sound Moves Faster in Dense Materials

Sound moves faster in solids and liquids because their particles are close together and can pass along disturbances quickly. Most solids and liquids are incompressible, which means their densities stay nearly constant throughout. When an external force acts on them, the molecules try to return to their original positions. That restoring motion happens because the particles interact with one another. These interactions let sound waves carry information through the material. As a result, sound...

speed of sound in gases

What Changes Sound Speed in Gases?

Sound speed in gases depends on gas properties, pressure, volume, and temperature. Gas molecules move freely, so gases are highly compressible. Because of that compressibility, sound waves travel more slowly through gases than through many other media. The speed of sound in an ideal gas can be found using thermodynamics. Thermodynamics links pressure, volume, and temperature, which helps describe how sound moves through a gas. Newton's laws of motion and the continuity equation from fluid...

deriving the speed of sound in a liquid

Sound Speed in Fluids: Bulk Modulus

Sound speed in fluids depends on a fluid’s bulk modulus and density. These two properties describe how stiff the fluid is and how much inertia it has. For mechanical waves in a fluid, that relationship follows the same pattern used for Young’s modulus and density in solids. The speed of sound in a liquid can be derived by treating the wave as a longitudinal wave moving through the medium. The derivation uses the gauge pressure expression and the impulse-momentum theorem. This same result...

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sound intensity

Measuring How Loud Sound Is

Sound intensity helps describe how loud a sound source is. It depends on how energetically the source vibrates, because those vibrations make the molecules in the medium vibrate as well. Intensity is the energy emitted per unit time per unit area. The area must be perpendicular to the direction the sound wave travels. Using time and area makes the measure reflect the source’s own loudness, even when the source vibrates over a longer time or spreads energy over a larger area. A sound source...

sound intensity level

Measuring Sound with Decibels

Sound intensity level helps measure how loud sound is. The human ear sends sound waves to the brain, and the brain turns those waves into hearing. The loudness of the surrounding environment affects whether a person can tell different sound sources apart. The ear can detect a very wide range of sound intensity. Because of that range, scientists use a logarithmic scale to describe intensity level. Intensity level is a ratio of two intensities, so it has no unit. The standard reference is the...

intensity and pressure of sound waves

Sound Intensity from Displacement and Pressure

Sound intensity can be linked to displacement and pressure in a wave. The key idea is to use the wave expressions and the definition of intensity. To do that, the power carried by the particles is written as force times velocity, and the force per unit area is treated as pressure. The particle velocity can be found from the displacement of the medium. A sinusoidal term averages to zero over time because it is positive and negative for equal parts of each cycle. Its square does not average to...

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sound waves: interference

Sound wave interference can change the loudness of sound when two waves meet. Sound waves may be modeled as longitudinal waves, where molecules move around an equilibrium position, or as pressure waves. When two identical waves from the same source overlap, their crests or troughs can add together. This is called constructive interference, and it increases amplitude. If identical waves start in phase but travel different path lengths, they can become out of phase. Then a crest can meet a...

interference: path lengths

Interference from Different Path Lengths

Interference from different path lengths explains how two sound sources can create changing patterns in space. The sources may or may not start in phase, but they emit waves at the same frequency. When they are in phase, they are called coherent sources, and that is easy to arrange by feeding both speakers from the same source, such as a tuning fork. These synchronized sources start with the same frequency and the same phase. As the waves move outward, they travel different distances to reach...

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sound waves: resonance

Sound Waves in Tubes and Strings

Sound waves can form resonance patterns in strings and tubes when the boundary conditions match the wave frequency. On a string under tension, symmetrical boundary conditions create a node at each end. A node is a fixed point where the string does not move. Some frequencies then produce standing waves, while other frequencies interfere destructively. Resonance also appears in a hollow tube. In a tube closed at one end and open at the other, a vibrating tuning fork near the open end sends an...

beats

Sound Interference and Beats

Sound interference creates beats when two or more close frequencies combine. In music, this shows up as a changing loudness that rises and falls. The pattern comes from superposition, the adding together of waves. Constructive interference makes the sound stronger, while destructive interference makes it weaker. Music usually contains many changing frequencies from instruments and voices. A single sound at one frequency for a long time can feel dull or even irritating. It can sound like the...

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doppler effect - i

Doppler Shift in Sound and Light

The Doppler effect describes how the frequency of a wave changes when the source and the observer move relative to each other. It was named after the Austrian physicist and mathematician Christian Johann Doppler in 1842. He studied both moving sources and moving observers. A simple example is an ambulance passing a person standing on a street corner. As the ambulance approaches, the siren seems louder. As it moves away, the sound gets quieter. The pitch also changes. The high siren sound...

doppler effect - ii

Doppler Radar and Heart Blood Flow

Doppler effect applications appear in weather forecasting and medical imaging. In these uses, a change in frequency helps show motion. The reflected signal can reveal whether an object is moving toward or away from the source. Meteorologists use Doppler radar to study weather events. A transmitter sends radio waves at a set frequency toward the sky from a weather station. The waves bounce off clouds and precipitation and return to the station. If the reflected radio frequency decreases, the...

shock waves

Sonic Booms and Supersonic Motion

Sonic booms and supersonic motion happen when a sound source moves as fast as, or faster than, sound in the medium. In the Doppler formula for sound, it is usually assumed that sound travels faster than the source. When that assumption fails, a shock wave can form. As the source gets close to the speed of sound, successive wavefronts build up by constructive interference right behind it. Scientists once thought this pressure buildup would keep an airplane from breaking the sound barrier and...

echo

Echo Sound and Distance Detection

Echo is a reflected sound that returns after the original sound has been heard. The human ear cannot tell two sounds apart if they arrive within about 0.1 seconds of each other. When the reflected sound takes longer than that to return, the ear hears two separate sounds instead of one. This effect is easy to notice when the sound source is close to a surface that sends the sound back. If the sound and its reflection are separated by enough time, the result is an echo. A minimum distance of...

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key terms and concepts

Explore how sound waves add or cancel through constructive and destructive interference, with speaker examples and noise-canceling headphones.

Sound Wave Interference in Speakers | JoVE K12

physics

JoVE Core Physique présente plusieurs branches de la physique fondamentale grâce à des vidéos animées concises et faciles à comprendre ; cela inclut: la cinématique, la dynamique, la mécanique des fluides, la mécanique statique, les ondes et l'acoustique. En parallèle, les vidéos de scientifiques à l'action démontrent l'application de concepts associés à ces domaines dans des expériences de recherche classiques et originales réalisées dans des laboratoires modernes du monde entier.

Pennsylvania State Academic Standards

Waves and Electromagnetic Radiation

3.2.9-12.V

Louisiana Student Standards for Science

High School

waves-and-their-applications-in-technologies-for-information-transfer

Waves And Their Applications In Technologies For Information Transfer

HS-PS4-1

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Energy And Waves

Waves

Wave properties

Tennessee Academic Standards

Waves and Their Applications in Technologies for Information Transfer

PHYS.PS4.4

PHYS.PS4.6

PHYS.PS4.7

Virginia  Standards of Learning

HIgh School

PS.6

PS.6.c

PH.5

PH.5.b

Alabama Course of Study Science

9-12.PS.2.2.e

9-12.P.3.7.b

Next Generation Science Standards

HS-PS4-3

Texas Essential Knowledge and Skills

PHYS.8

PHYS.8.D

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Waves and Electromagnetic Radiation

HS-PS4-3.

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PS.PSc.8.1

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Electromagnetic Wave Equation

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Use models to compare the characteristics of mechanical and electromagnetic waves.

PS.PSc.8.2

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Reflection of Waves

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Propagation of Waves

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Sound waves can be modeled either as longitudinal waves, wherein the molecules of the medium oscillate around an equilibrium position, or as pressure ...

Interference: Path Lengths

Consider two sources of sound, that may or may not be in phase, emitting waves at a single frequency, and consider the frequencies to be the same.
Two ...

Use models to explain the wave interactions of reflection, refraction, diffraction, and interference.

Standing Waves

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Modes of Standing Waves - I

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Modes of Standing Waves: II

The starting point for expressing the modes of standing waves is understanding the boundary conditions that the waves must follow. The boundary conditions ...

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Obtain, evaluate, and communicate information to explain how instruments that transmit and detect waves are used in everyday life.

PS.PSc.8.4

Analyze the nature of waves and their applications.

Sound Wave Interference in Speakers

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