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. N

    Is it possible to identify something with sound?

    Is it to identify something (not necessarily very accurately but at all) with sound? Also, i know its possible with light but i don't exactly understand how, can someone explain?
  2. D

    How to Calculate Wave Velocity in a Tuned Violin String

    Homework Statement A tuned violin, with strings of 31.6 cm each, is placed in front of a speaker. When varying the speakers frequency between 500 and 1500 Hz, it was discovered that a certain string only vibrated at 880 Hz and 1320 Hz. Determine the velocity of the wave in this string...
  3. D

    Maximum sound and wave problem

    Homework Statement Speakers L_1 and L_2 are placed at a 2 m distance from each other. The speakers send out soundwaves that are in the same phase and the loudness (?) is examined in the point P (see figure). The velocity of the sound is 343 m/s and the distance L_2P is 6 m. L_1 L_2...
  4. I

    Principle Determining the Loudness (Intensity) of Sound

    A test question I was asked earlier in the year has been hanging around in the back of my mind: "If a radio is moved 3x further away from you, how is its loudness affected?" To answer this question one needs to know what determines the loudness of sound. What determines the loudness of...
  5. K

    Sound waves (node and antinodes)

    Homework Statement for part a , since we know that the sand particles will vibrate will max amplitude at antinode and the displacement of partcles is 0 at node. then , the sand should heap at antinode . why the solution gives the sand heap at nodes? Homework Equations The Attempt...
  6. K

    Equation of variation of displacement and pressure of sound wave

    Homework Statement i have attached the notes from 2 books below, i know that the graph of pressure of sound waves lag behind the displacement grpah by 90 degree. so it should be p=p max sin (wt-kx-(pi/2)) am i right? why the another book gives p=p max sin (wt-kx+(pi/2)) ? which is correct...
  7. E

    Effect of rain on velocity of sound

    I was suddenly asked this question by a friend... How a 'cats & dogs' rain would affect the velocity of sound through air?(as we know velocity of sound through water is five times than in air) I just couldn't be sure how to answer it... The raindrops are really small but there's a lot of...
  8. D

    Have headphone's sound any impact on human's brain?

    Hello! If a person hear song continuously for 15 hours every day for one year by head-phone then will there be any effect on his/her brain?
  9. K

    How far can your voice carry at 40 dB?

    You are in a park when you spot your friend 100 m away. At what lowest decibel should you shout your greetings so that your friend can just hear you? Assume that your friend has normal hearing. My prof never gave an example of how to do this and I can't figure it out. The correct answer is...
  10. B

    A tractor beam reels in objects with sound

    “A tractor beam reels in objects with sound” “A newly constructed device generates a beam of concentrated sound that, for the first time, exerts a continuous, perceptible tug on objects large enough to see.” https://www.sciencenews.org/article/tractor-beam-reels-objects-sound
  11. C

    Sound diffraction around obstacles; low and high frequencies

    Hi, I am posting here as I can't get a satisfactory answer from google. Could anyone explain to me why low frequency sounds diffract better than high frequnecy sounds around a corner (eg the wall of a building). I understand the idea of 'wave diffracts more when opening is around the same...
  12. M

    What is the frequency of a vibrating steel cable in its third harmonic?

    Homework Statement A steel cable is vibrating in its third harmonic. The Frequency is 150Hz 1. What is the length of the cable? 2. What is the wavelength?Homework Equations The Attempt at a Solution I am really stuck
  13. paulmdrdo1

    MHB Speed of sound - Uniform motion- linear equation application

    I need help with these problems. 1. Speed of Sound in Air. Two seconds after firing a rifle at a target, the shooter hears the impact of the bullet. Sound travels at 1100 feet per second and the bullet at 1865 feet per second. Determine the distance to the target (to the nearest foot). 2...
  14. Y

    Conversion of Light energy to Sound energy

    Is there a way to convert light energy to a sound energy? I read an article and the URL is http://www.photonics.com/Article.aspx?AID=52646 It is described that nano material lenses are used. Is there a much simpler way that I convert light to sound?
  15. Z

    Intensity of isotropic sound waves

    Homework Statement A loudspeaker emits sound isotropically with a power of 100db. Find the intensity in w/m at a distance of 20 from the source Homework Equations Intensity=power/area, For sound wave... power=ro*a*2pi^2*f^2*v*A^2, and I=2pi^2*ro*f^2*v*A^2. db=10log_10_(I/I_0_)...
  16. J

    How does an umbrella create a similar effect to a radio with sound?

    So today I was holding up an umbrella near someone playing music, and it sounded like the music was coming from the top of my umbrella. Is this a similar effect to a radio? Can it be seen as sound being a disturbance of the air that causes the metal to vibrate which amplifies it to make it...
  17. C

    Intensity of a sound wave problem

    Homework Statement Two loudspeakers are placed beside each other and produce sound of the same intensity at the position of a listener. One speaker produces a low note of 40 Hz and the other produces a high note of 2560 Hz. What is the ratio of the maximum displacements of the speakers...
  18. A

    The amplitude of sound waves from two nearby speakers

    Homework Statement In the figure below, two speakers S1 and S2 emit sound waves of wavelength 2m, in phase with each other. Let Ap be the amplitude of the resulting wave at point P, and Aq be he amplitude of the resultant wave at point Q. How does Ap compare to Aq? a. Ap<Aq b. Ap=Aq c...
  19. Manraj singh

    Units of loudness of sound, being a subjective quantity

    I am learning sound. My teachers and textbook say loudness of sound is a subjective quantity, it is different for every person, while intensity is the objective quantity. The first section says intensity is a measurable quantity, WHILE LOUDNESS IS JUST A SENSATION. On the very next page they...
  20. barryj

    Doppler Effect: Airplane, Sound, & Frequency

    This is not homework but rather a concept question. If there was a siren on the front of an airplane that is traveling greater than the speed of sound, would there still be a sound emitted? If the airplane was traveling toward me what would be the frequency? Would I heart it? Where...
  21. Adithyan

    Speed of sound on a moving train

    Homework Statement Two trains A and B are moving with speed 20m/s and 30m/s respectively in the same direction on the same straight track with B ahead of A. The engines are at the front ends. The engine of trains A blows a long whistle. Assume that the speed of sound of whistle is...
  22. J

    Interference of Sound Waves in a Circular Tube

    1. A sound wave with frequency f = 2300Hz is sent into a circular tube of radius R=160cm through an opening at some point A. A receiver lies at point B, separated from A by an angle α=130°. The speed of sound in air is v=330 m/s. Sound propagates from A to B in both directions along the...
  23. P

    Sound & Light Wave Speed & Transfer: Explained

    So, sound is a longitudinal wave, while light is a transverse wave. The speed of sound varies going from one medium to another directly proportional to the bulk modulus and inversely proportional to the density of the new medium (i.e. from air to a steel pipe). Let's say a sound wave (consisting...
  24. A

    Light and Sound Waves: Theoretical Analogies and Differences

    Anybody has reference paper on light and sound wave's theoretical analogies? I want to read about the analogies and difference between this interactions in terms of waves. Thank you in advance. AGZ
  25. A

    Focusing Sound Waves: Acoustic Lens & Loss of Energy

    Is there any way to focus a sound wave BEHIND an acoustic lens i.e. the source and receiver are on different sides of the lens? Will it result in a significant loss of sound energy?
  26. B

    Reflection of sound. Changes to its properties.

    Hi guys and girls, Just had a question I have been thinking about for a while. Suppose you have a sound maker than makes a pure tone at a particular frequency. You play this tone for an instant directed directly at a flat wall (not absorbent at all). If you could measure the reflected tone...
  27. Manraj singh

    Speed of sound waves in various media.

    My tenth grade physics textbook says that sound travels faster in solids than air. But it also says sound will travel faster in air if its density decreases. I didn't really get the logic, as solids are denser than air, and that is why sound travels faster. Then they say as temperature of air...
  28. L

    Calculating Sound Pressure Level As Distance Changes

    Homework Statement The sound pressure level is 80db at a distance of 30 meters. What is the dBSPL at 60 meters? Homework Equations My book has provided me the following formula: dBSPL = dBr-20log(di/dr) - but it has not explained what "di" and "dr" are.The Attempt at a Solution I've been...
  29. L

    Question about Sound Waves: Faster Than Speed of Sound?

    Okay, so I was listening to someone via tinychat explaining how our current understanding of sound was wrong in some sense. He claimed that the source of the propagation of sound waves HAD to be moving faster than the speed of sound (in air). One particular analogy he used in order to...
  30. P

    Why is sound louder in a room with many people?

    Why is sound louder in a room with many people? Thanks
  31. T

    What is measurement unit of digital clear sound for devices

    like for example digital unit measurement for clear images in devices is ...pixel
  32. A

    Focus Sound Waves: Can We Refract Like Light?

    Can we focus parallel sound waves using convex and concave lenses since they essentially follow the same laws of refraction as light? If not, is there any way to focus parallel beams of sound to converge at a point?
  33. S

    Deriving sound from simulated interactions

    Hi all, First, I hope this is in the right place, apologies if it isn't. I'm looking into the possibility of deriving sound from the simulated actions of simple bodies in a 3D space. As a toy example of my aim, I hope to be able to compute the sound that would be generated by a metal...
  34. J

    Distance from Source to Reach 180/170 dB Intensity Level

    Not a homework... simple curiosity by trying to know this a bit better in order to learn and understand possible effects of sound to marine mammals auditory systems. In sea water, at distance of 1m from a localized sound source, you measure the intensity level as 237 dB. How far away from the...
  35. Saitama

    Solve Sound Wave Problem: Frequency of Sound in Air (336 m/s)

    Homework Statement A source of sound S and a detector D are placed at some distance from one another. A big cradboard is placed near the detector and perpendicular to line SD as shown in figure. It is gradually moved away and it is found that the intensity changes from a maximum to a minimum as...
  36. J

    Understanding Interference of Sound Experiment

    Can someone please help explain an experiment which I am struggling to understand. You have a speaker without any of the outer casing (just the small disk part) and secure it onto a clamp stand. You then have two microphones; one above the speaker and one below it which are both the same...
  37. GreatScot

    Sound in space and the end of the universe

    Hello I am trying to get into physics and astronomy as a hobby so please excuse the crudity of my posts, I regrettably have no physics education past high school level but nevertheless I aim to slowly but surely learn either self-taught or through some further eduction whether at college or...
  38. P

    The police car moves faster than the speed of sound? Sonic boom.

    Hi, Suppose the police car moves faster than sound's speed and runs away from the person on the street. Will the person hear the siren? Regards,
  39. P

    The police car moves faster than the speed of sound?

    Hi, Suppose the police car moves faster than sound's speed and runs away from the person on the street. Will the person hear the siren? Regards,
  40. jaumzaum

    Sound Interference Experiment: Explaining Intensity Increase

    I cannot understand the following: Imagine you have 2 sound sources and build up an interference experiment, where far away from the sources you have a receptor. Imagine you put the receptor at the same distance from the sources. If you turn off one source the receptor will receive a sound...
  41. T

    Question for dangerous sound waves for health effect?

    Which one has the more dangerous health effect...ultrasound or infrasound.? and why...
  42. T

    Question for sound waves effect. .?

    Which one has more dangerous effect for health ...ultrasound or infrasound.? and why...
  43. Q

    About sound levels and feedback

    FYI, I'm not very knowledgeable in this topic however I have noticed something intriguing whenever dealing with sound levels and feedback. My question is.. Why is it that if I were to say turn my headphones to 100% volume and my PC volume is 50% the sound will sound a little "distorted or fuzzy"...
  44. N

    Calculating Frequencies and Lengths of Hinged Wires in a Harmonic System

    Homework Statement The rod of length l and mass m_0 is hinged on two same wires (Fig. 3 on second page - example ,,4. Zvučící dráty" - http://fyzikalniolympiada.cz/archiv/55/fo55a1_z.pdf). With this load, each of the wires gives basic tone height c in natural tuning, f_c = 264 Hz. A) Move the...
  45. D

    Can a Photon be Vibrationally Tuned with Sound?

    I have a question. I was wondering if it was possible to put a vibrational sound frequency to a photon? Another way of putting it, is it possible to pump sound into a laser beam and give the photon a vibrational frequency consistent with the sound added? Thanks.
  46. H

    Is sound affected by gravity at all?

    I'm doing some MCAT practice, and one question asks: A submarine sends a sonar signal in a direction directly downward. It takes 2.3 seconds for the sound wave to travel from the submarine to the ocean bottom and back to the submarine. How high up from the ocean floor is the submarine? (The...
  47. A

    Rijke tube: Why Sound is maximum when heated 1/4th length from bottom

    Why is it that the maximum sound coming from a Rijke tube happens only when heated wire gauze is placed at 1/4th the length of the tube from the bottom. According to Rayleighs criterion(copy pasted) "If heat be periodically communicated to, and abstracted from, a mass of air vibrating in a...
  48. 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.
  49. 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...
  50. 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...
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