What is Sound: Definition and 1000 Discussions

In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz, the audio frequency range, elicit an auditory percept in humans. In air at atmospheric pressure, these represent sound waves with wavelengths of 17 meters (56 ft) to 1.7 centimetres (0.67 in). Sound waves above 20 kHz are known as ultrasound and are not audible to humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.

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  1. 5

    Intensity of sound behind a sphere

    If I have a sphere with radius r, a distance d away from a sound source of intensity I0. What will the intensity I of the sound wave be on the point of the sphere directly opposite the source? Preferably I would like to find the intensity of the wave at any point on the sphere.
  2. N

    Understanding the Speed of Sound in Fluids: An Explanation from Thermodynamics

    Hi The speed of sound in a fluid is defined as c_s^2 = \frac{\partial P}{\partial \rho} where P is the pressure and ρ the density. In my thermodynamics-course this was how we defined the speed of sound in an ideal gas, I have never read the explanation anywhere for, why this relation is also...
  3. Crazymechanic

    Why Do Identical Cast Iron Crankshafts Emit Different Pitch Sounds?

    Hi there , I have two cast iron crankshafts for an engine I'm building , now even though they are similar in every way , made ofr the same engine etc etc, there is one thing I noticed different and it got my attention , I took a stainless steel screwdriver and hit each one of the cranks at...
  4. A

    How Does Distance and Quantity Affect Sound Intensity?

    Homework Statement An alarm clock makes a sound that has intensity 60 dB at a distance of 1 m. What is the sound intensity of 100 such clocks which are all 100m away? (A) 0.6 dB (B) 40 dB (C) 50 dB (D) 60 dB Homework Equations I1/I2 = R2^2/R1^2 The Attempt at a Solution If...
  5. A

    "Sound Intensity Decreases with Distance

    Homework Statement At 1 m away from the source of a sound, the intensity of the sound is 90 dB. At 10 m away the intensity is…? The answer is 70 dB but I don't know how... Homework Equations I = Power/Area The Attempt at a Solution My thought was to set up the equations...
  6. H

    Waves and Sound: Find Moving Train Speed

    Homework Statement Two train whistles have frequencies of 180 Hz in air (v = 344 m/s). When one train is at rest sounding its whistle, a beat frequency of 2 Hz is heard from the moving train which is sounding its whistle as well. What is the moving train's speed if it is approaching the...
  7. H

    Waves and Sound - Air Column (Clarinet)

    Homework Statement A clarinet behaves as an air column that is open at one end. For a particular fingering, the length of this air column is 24.6 cm. At 20°C, this fingering sounds the pitch "F" which is 349.2 Hz. During a concert, the breath of the musician raises the bore temperature to...
  8. T

    How Does Observer Velocity Affect Sound Wavefront Frequency?

    Homework Statement A source of sound emits waves at a frequency f 450 Hz. An observer is located at a distance d 150 m from the source. If the observer is moving away from the source at a velocity vobs 40 m/s, how does the number of wavefronts change with time? dN/dt ? (in Hz)...
  9. H

    Waves and Sound - Bat Chirp/Echo?

    Homework Statement When near an object, a bat decreases the duration of its chirps and the time interval between chirps. If the chirps last 3 x 10-4 s, what is the minimum distance for an object at which the first part of the echo overlaps the ending of the chirp? Note: the speed of sound...
  10. T

    How do speakers produce sound?

    http://imageshack.com/a/img841/50/qgx3.png The above diagram shows the analyzer of waveform taken from a song. I wanted to know in terms of acoustics how is it that the different frequencies are produced at the same time by the same source. I know about interference but don't know how it...
  11. jerry0696

    Is sound wave a transverse wave?

    i had always belived that sound wave was a longitudinal wave till i come across something saying that its a transverse wave in solid.can anyone explain is it so??
  12. W

    Sound Intensity Peak: Find Time Between Peaks

    Homework Statement One wheel goes at 850 rpm and the other at 780 rpm, and obviously they make a noise. Standing in an enclosed room, you hear the sound intensity increase and then decrease periodically due to wave interference. How long does it take between successive times for the sound...
  13. S

    Sound Wave Attenuation: Why Does Water Attenuate More?

    Why does water attenuate sound waves more than air? Is it because of it's bulk modulus? This is what I understand. Speed through a medium is determined by the elastic component over the inertial component. Since water has a much greater bulk modulus (elastic component) than air, it makes the...
  14. W

    Sound (harmonic) waves questions

    Hello, I have two question regrading sound waves. The first one: The pressure P(x;t) at a point x at time t in a medium through which a harmonic wave is travelling can be described by: P(x,t) = Asin(wt -kx) If the equation describes a pressure wave traveling in air, with amplitude 2 Pa and...
  15. patrickmoloney

    What Distance from Speaker A Will a Microphone Detect Minimum Sound Intensity?

    Homework Statement Two loudspeakers A and B of equal power are separated by a distance of 1.4 m. Both the speakers emit sound waves in phase and of frequency 450 Hz. If a microphone were to be moved from A in a direction perpendicular to AB, at what distances from A will it detect a minimum...
  16. A

    How Do Different Aperture Shapes in a Styrofoam Box Affect Wave Harmonics?

    I did an experiment for school, and I put a speaker in a styrofoam box with a rectangle cut out of the front. I had styrofoam bricks that fit perfectly in the hole, each with a hole cut out. The hole shape differed, with things like a funnel, a diagonal line, a circle, a square, etc. I was...
  17. W

    The factor by which the acoustic power is changed is 7943.28

    Sound "Factor of" Homework Statement The intensity level of a particular sound coming through a medium gets reduced from 80 dB to 41 dB. By what factor is the acoustic power that can pass through changed by? B1=80 B2=41 Homework Equations 10*log(\frac{I2}{I1}) = B1-B2 The...
  18. W

    Sound Wave, Microphone and Electromagnetic Induction

    Dear all, I have encountered an issue in understanding how microphone works and I hope you guys can assist. There are two scenarios involved. In the first scenario, there is tuning fork and a microphone. The microphone contains a small disc attached to a magnet and a fixed coil. (Please...
  19. S

    Determine depth of a well using the speed of sound

    Homework Statement If you drop a stone into a deep well and hear a splash 4.68s after dropping the stone, how far down is the water level? Neglect air resistance and assume that the speed of the sound in air is 3.40x10^2 m/s Homework Equations v=d/t d=v1t+1/2at^2 The Attempt at a Solution Here...
  20. G

    Speed of sound wave and particle velocity

    This may be fairly straightforward but it is a concept that I am really having problems understanding. A sound wave is a pressure disturbance that travels through a medium by means of particle to particle interaction, so why is the wave velocity so much faster than the velocity of the particles...
  21. ajayguhan

    Whistle - How does a a whistle produce sound?

    whistle -- How does a a whistle produce sound? How does a a whistle produce sound? And what makes galton or dog whistle to produce high frequencies ...?
  22. Borek

    Problems recording sound on the computer

    Not sure where to post it, but perhaps EE will be OK. I have problems recording sound on my computer, and I have these problems for as long as I remember - using several microphones and several computers in the last 20 years. I always thought reasonable quality mic and reasonable quality...
  23. M

    What is the largest wavelength for maximum sound intensity?

    Homework Statement Two sources, A and B, emit a sound of a certain wavelength. The sound emitted from both sources is detected at a point away from the sources. The sound from souce A is a distance d from the observation point, whereas the sound from source B has to travel a distance of...
  24. B

    Please help Speed of sound in air/temperature relation

    Homework Statement The density of a sample of air is 1.211 kg/m3, and the bulk modulus is 1.42 · 105 N/m2. a) Find the speed of sound in the air sample. b)Find the temperature of the air sample. Give answer in °C. Homework Equations The Attempt at a Solution I found...
  25. A

    Sound Travel from Water to Air - Visualizing the Possibilities

    can sound travel from a body of water to air? if so, what might it look like?
  26. W

    Is my expeirmental procedure sound?

    Homework Statement Using the apparatus that I've drawn, I have to deteremine the % composition H2O2 in an unknown solution. 2. Relevant information H2O2 (aq) -enzyme-> H2O(l) + O2(g) or 2H2O2 -Enzyme-> 2H2O(l) + O2(g) when balanced The test tube (1) contains H2O2 solution with an...
  27. K

    Supersonic airplane emits a sound when right over a listener

    Hello, I'm having a bit of a problem with the following problem: A supersonic airplane flying at the velocity v is flying horizontally to the ground with altitude h. At the exact moment when the plane is vertically above a listener on the ground, it emits a sound. It takes Δt seconds for the...
  28. N

    Wavelength of sound and windspeed

    Both source and observer are at rest. If the wind blows from source to observer will the wind affect the wavelength of sound??
  29. B

    Rock off cliff - calculate height by using speed of sound

    You are climbing in the High Sierra where you suddenly find yourself at the edge of a fog-shrouded cliff. To find the height of this cliff, you drop a rock from the top and 8.50s later hear the sound of it hitting the ground at the foot of the cliff. Ignoring air resistance, how high is the...
  30. P

    Doppler effect with 2 sound sources

    Homework Statement A fly is moving with a speed vl=3m/s and a bat is chasing it with vs=5m/s. The bat is emitting a sound with fs=50kHz. They are moving on the same line towards point C which is a source emitting a sound at f'=57Hz. Find the frequency of the total sound the fly is hearing. The...
  31. Z

    How are square sound waves possible? How does a speaker sustain peak?

    Hello everyone :smile:, after spending many hours watching youtube videos, reading wikipedia articles and other related material, I came to the conclusion that my best hope at understanding this is to have an explanation personally explained to me, and I trust this is the right place to ask for...
  32. P

    Electrical noise ( I mean sound waves )

    Hello physicsforums. What causes noise in electrical cables and/or transformers and/or electrical stations ? By noise I mean mechanical sound waves like bzzzzzzzz, not signal noise. And what is the proper way to search in google for this, I could not find a wikipedia article on this.
  33. rshreyas

    Best ways to learn about sound energy

    i am interested in learning about sound .so please can anybody provide a website for learning about it .
  34. J

    What does a sound wave amplitude physically consist of?

    Frequency is pitch. Or how fast it oscillates. So what does the amplitude translate to in physical space? I know its volume, or the amount of energy. But what does it actually do to the air when you increase the amplitude?
  35. B

    Sound vs Distance: Why Do We Hear It Better Closer?

    Hello Everyone, I have a somewhat simple question: Why do we hear a sound better when we're closer to the object making it?Or less when we're farther? (ie a car siren is disturbingly loud when standing next to the engine but not the same when standing like 10 feet away). Could it be because...
  36. adjacent

    Why Do Some Sound Waves Reflect While Others Are Absorbed?

    I think they(longitudinal waves)hits the air,but they are not reflected back because air is very light.In the same way,when they hit a wall,as the wall is not going to vibrate vigorously,Some of the waves are absorbed(i.e. they make the wall vibrate)and the others are reflected back. If I am...
  37. T

    Converting sound to electrical energy

    Is there any possibility to converting sound energy to electrical energy by using piezo electric material.
  38. G

    Similarity and difference between light and sound?

    They talk about light's unique dual nature, that it can be both a wave and a particle (photon). One illustration for that is the following experiment, a single photon can go through one hole, and leave a particle like mark, or it can go through two holes, and leave interference marks...
  39. B

    Does Density Affect Sound Velocity in Condensed Matter?

    does density affect sound velocity ? i know sound velocity is dependent on inertial and elastic properties but does it depend on density ? or just molecular mass ? if two objects having the same atomic mass , but one has higher density than the other due to the difference in bonding...
  40. S

    Sound Power Reduction When Halving Air Flow Velocity and Doubling Grill Area

    If the velocity of air flow through a grill is halved but the area of the grill is doubled, By what factor will the sound power be reduced? air flow through a grill represents a dipole sound source, so it depends on the 6th power of velocity, but how does it depend on the area? If I take sound...
  41. J

    Which Formula to Use for Sound Intensity Calculation?

    Here's a question I got on an exam: During a typical workday (eight hours), the average sound intensity arriving at Larry's ear is 1.8 x 10-5 W/m2. If the area of Larry's ear through which the sound passes is 2.1 10-3 m2, what is the total energy entering each of Larry's ears during the...
  42. A

    Is max sound intensity at the displacement node in a standing wave?

    Good afternoon all My question is, when we observe stationary waves, and we know that at a certain point, the sound is maximum, is this the displacement node or the displacement antinode? I have read a few different sources and currently i have encountered both. To me it makes more sense...
  43. F

    Equation to find relative sound intensity with angle from source

    What is the equation to find relative sound intensity from a source when given the angle?
  44. O

    What is the distance to the target?

    Hello. Homework Statement A person holds a rifle horizontally and fires at a target. The bullet has a muzzle speed of 20 m/s and the person hears the bullet strike the target 1.00s after firing it. The air temperature is 72 degrees F. What is the distance to the target? Homework...
  45. C

    Microphone that can detect wheezing sound from the chest

    Hi all! I am searching of types of microphone/disc that can detect wheezing sound from the chest area but I am totally clueless of what type of microphones to use. Also, there should be less noise when picking up the signal. Currently I am using a piezo disc, but that could not detect the...
  46. gauss44

    How can sound move faster in one pipe than another? If both in air?

    (A question from The Berkeley Review MCAT prep book. The book gives the answer in the form of the equation below. I'm still having trouble figuring out how an example of this would look in real life. If someone would provide a hypothetical narrative where the following could take place, that...
  47. F

    Is half of a soundwave, really a sound?

    Hi Guys! I am interested in physics as amateur and this is my first post so be nice please :) What I wonder is about soundwaves but I don't know if this is the right section to write... If not, you may move the thread to appropriate section. My question has two steps. 1. I have a soundwave in...
  48. B

    Need advice on capturing sound

    I am looking to find a way to monitor a mechanical objects noise frequency. The end result would be the ability to see when the sound changes. Here's my thought process: A mechanical object that is making repetitious movements, would generate a particular 'sound' or 'frequency' within a...
  49. M

    What Determines the Unique Characteristics of Human Voices?

    I've been trying to teach myself the physics of sound. Specifically I've been trying to find out the variables that make up the human voice- the entirety of what separates one voice from another. But after browsing through one too many overly technical wikipedia articles, and finding one two...
  50. S

    Sound amplification decreases when connecting a capacitor

    Hi, An electronics newbie here.. I'm trying to produce sound using a 555 timer. When I tried using the schematic(attached file), a definite sound came. But when I removed the capacitor C2 in the circuit, the sound (amplitude) actually increased! Why does this happen? Why then, do we use a...
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