Acoustics Definition and 51 Discussions

Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.
Hearing is one of the most crucial means of survival in the animal world and speech is one of the most distinctive characteristics of human development and culture. Accordingly, the science of acoustics spreads across many facets of human society—music, medicine, architecture, industrial production, warfare and more. Likewise, animal species such as songbirds and frogs use sound and hearing as a key element of mating rituals or marking territories. Art, craft, science and technology have provoked one another to advance the whole, as in many other fields of knowledge. Robert Bruce Lindsay's "Wheel of Acoustics" is a well accepted overview of the various fields in acoustics.

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  1. Aethermimicus

    I What is the function of the air cavity inside drums?

    I'm trying to understand the function of the air cavity inside drums. I've read that 'The air cavity inside the drum will have a set of resonance frequencies determined by its shape and size. This will emphasize some frequencies at the expense of others.' Then what are the resonance...
  2. mohamed_a

    I Acoustic wave properties and momentum

    I have read about doppler effect in acoustics so i searched for the relation ship between wavelength of wave produced by linear movement of body and its momentum along with other dependent variables such as density of fluid (leaving acoustics for a second) and temperature but souldn't find a...
  3. A

    B Simple Acoustics Question -- Which neighbor hears the other better?

    There are two blocks of apartments separated by a narrow alleyway. Person 1 is in the middle of the room in Apartment 1 (first floor if you are in the UK and second floor if you are in the USA!) and Person 2 is on the ground outdoors in the alleyway. If both people speak at the same volume...
  4. Tech_Rizzle

    I Amount of Noise extinction in Acrylic glass per thickness in mm

    Hey guys, I need your help with the following topic on which I couldn't find sufficient information on the internet to solve. In the need to further insulate my velux roof swing window against against airborne motor and tire sound from the nearby street, I came across the idea to install an...
  5. F

    How does a Western free reed work? (musical instruments)

    In this post, I will describe, as best I have been able to determine, how a Western free reed works. As it is unlikely I will run into a physicist here who specializes in reeds, I will just ask people to speculate on the behavior of a reed given what you know about fluid dynamics or the...
  6. jeremiahrose99

    I Solution to the 1D wave equation for a finite length plane wave tube

    Hi there! This is my first post here - glad to be involved with what seems like a great community! I'm trying to understand the acoustics of a finite plane-wave tube terminated by arbitrary impedances at both ends. So far all of the treatments I've managed seem only to address a different...
  7. N

    I Cavity resonances between two long parallel plates

    Consider two rigid and infinitely long parallel plates (say they are of infinite length in X direction, so running from -inf to +inf in X axis) separated by a distance d (say measured in Y-direction). Let the space between the plates be filled up with a fluid that supports acoustic waves. If we...
  8. K

    Engineering Best Resources to start with for waves and acoustics

    Hi All, i have been mostly into the structural analysis domain want to explore the world of sound waves/Acoustics. What should be the best way to start with? Regards Kapil
  9. Cathr

    Accoustic waves notions (propagation in a tube)

    Please help me with this problem I am facing, I am lacking notions of acoustics and I would be very grateful if someone could clarify them: A tube has a revolution symmetry arounf the ##x## axis and has a section dependent of the value of the abscissa (x), so the profile ##S(x)## is known. The...
  10. The Bill

    I Microphones at longer wavelengths than their size?

    Why are microphones pretty good at picking up sound that is much longer in wavelength than the size of the microphone? 1khz sound has a wavelength of around a third of a meter, varying a bit depending on atmospheric conditions. Yet a 1cm diameter electret microphone can pick it up reasonably...
  11. E

    Phase relation between strain and particle velocity

    I'm trying to understand the following derivation. Starting with the one-dimensional equation for a traveling wave ##u = u_0 \exp{[j(\omega t - \beta z)]}## the goal is to derive the phase relation between strain and velocity. The author first derives the relationship between strain and particle...
  12. I

    Angular frequency of a non-sinusoidal pulse

    Hey all, so I’ve been learning nonlinear acoustics and have encountered a conceptual hurdle in my studies. When using a model, such as a form of the classical Burgers equation, to propagate sound waves, you generally have a “characteristic angular frequency” in the equation (often represented by...
  13. Sophrosyne

    B How does the ear distinguish multiple different pitches?

    A chord played on a piano is multiple different pitches, each at a different frequency, played simultaneously. The ear hears this as separate sounds. The cochlea of the ear is organized by tone (tonographic organization), from highest to lowest frequency. So a triad chord will stimulate three...
  14. E

    I Helmholtz resonator with multiple necks--formula?

    Does anybody happen to know the formula for resonant frequency of a Helmholtz resonator having N necks? Physics is not my field and I'm a bit over my head. I need the formula for a computer program related to musical instruments--this is the only thing holding me up. It seems like it would...
  15. F

    Acoustics (Environmental Noise): LAFmax vs Shot Noise Level?

    Hello, new poster, I am trying to do a fairly simple, but non-standard, environmental noise model run for a shooting range. The standard against which noise from the shooting range is to be compared is the Shot Noise Level (SNL). SNL is defined as the logarithmic average of the 25 highest...
  16. R

    Applied Acoustics - decouple a speaker and a wooden table

    If several sheets made of some kind of rubber are being used as acoustic insulators, which configuration would be more efficient to decouple a speaker and a wooden table, absorbing most vibrations? (Ps: Image not drawn to scale)
  17. Rorshach

    Tympani in a concert hall: calculating Sound Pressure Level (SPL) and delay

    Homework Statement Hello. I have a problem, which is as follows: A seat in a concert hall is 84 ft from the tympani. The tympanist strikesa single note. The sound pressure level of the direct sound of the note at the seat is measured to be 55 dB. The first reflection from the nearest sidewall...
  18. D

    A Helmholtz Resonator: attenuation vs. amplification

    Hello guys, I read the other threads about HR, resonances and so on, but I couldn't find a clear explanation of what the practical implications of using a HR are. From one side, HR is described as a "reactive element", used in several contexts to attenuate a specific noise by means of...
  19. M

    I Effects of Ultrasonic Transducer in contact with glass

    I'm looking for a way of using ultrasonic cleaning to clean the inside of a glass vessel filled with some sort of fluid by transmitting ultrasounds through the glass, rather than submerging the entire glass vessel. If an ultrasonic transducer, let's say something with a maximum frequency of 40...
  20. D

    Mean free path and acoustics

    Hello everyone, I have a question regarding the implication of mean free path and pressure acoustics. I have seen several publications on the internet and also calculated the minimum displacement of a wave in air using the formula dp=v * rho * *2*pi*freq. * dx The values of displacement can...
  21. J

    A Calculate Third Octave Band Response from Narrowband Data

    I have a signal that I am able to calculate through an acoustic model for airfoil noise. I am told that the model solves for a narrowband frequency response, however, my measurement data is provided in third-octave band representation. How do I convert my current dataset to the third octave...
  22. T

    B Why does end correction in pipes change with radius

    This being WRT resonating pipes. Apparently the acoustical length of the pipe is different to the physical length due to the vibration of the sound particles moving the particles at the opening so that the physical length is no longer the length of resonance. I've found many sources on the...
  23. Alfreds9

    Finding the acoustic point in a valley

    Hello, I have a practical problem, I'd like to find the "best" spot to hear sounds in a valley (forgive me if "acoustic point" isn't an appropriate term, I just couldn't come up with anything better and scrolling an acoustics text didn't help), or at least a non-blind spot (one which instead...
  24. T

    Acoustics Bessel Functions

    Homework Statement For the FM modulation, the amplitudes of the side bands can be predicted from v(t)=ΣAJn(I)sin(ωt) Where is a sideband frequency and Jn(I) is the Bessel function of the first kind and the nth order evaluated at the modulation index .Given the table of Bessel functions...
  25. D

    Amplitude and Energy: A Simple Explanation

    I tried to come up with a simple calculus-free explanation for why the energy in a sound wave is proportional to the square of the wave's amplitude for my musical acoustics class. I think this makes sense, and seems to just be an elaboration of what Donald Hall writes, but I haven't seen it...
  26. D

    Explaining the Sine Formula to Acoustics Students

    I'm (a music academic) teaching a musical acoustics course to a very mixed group (music students, science students, and neither). Today, I covered the basic concept of simple harmonic motion and how this produces a sine wave pattern of motion over time. In the extra time we had left over, I...
  27. T

    Optimizing sound energy transfer through plastic medium

    Hi everyone, I am looking to improve the transmission of sound from a small 1/2" electro-mechanical transducer through a plastic medium (about 1/4" thick). I understand plastic is not a great medium for this but I do not have the ability to change this. The defacto setup doesn't work too...
  28. andrewkirk

    Acoustic 'beats' from mismatched musical frequencies - Comments

    andrewkirk submitted a new PF Insights post Acoustic 'beats' from mismatched musical frequencies Continue reading the Original PF Insights Post.
  29. D

    Musical Acoustics: Beats

    I have a question about 'beats' between two sound waves of slightly different frequencies. Basically, I think I understand everything on this page (and have read a few textbooks on this): . And in practice, I work with this concept all the...
  30. NPB777

    Ultrasound Transducers and Simulator

    Presently I am working on Underwater Acoustic Wireless Transmission. I desire to measure water parameters at the bottom of the surface of the water and then pass it to the water surface using Ultrasound. There will be a buoy at the surface which is half submerged and half floating. The floating...
  31. NPB777

    Variation of Frequency of sound underwater

    Hello, I am very much interested to how frequency of sound varies in water. Also, how the frequency varies with temperature and depth? What are the different formulas related to this? Secondly, how can we determine the best frequency of operation? I would be very thankful if anyone could answer...
  32. E

    Group velocity definition

    In the propagation of non-monochromatic waves, the group velocity is defined as v_g = \displaystyle \frac{d \omega}{d k} It seems here that \omega is considered a function of k and not viceversa. But in the presence of a signal source, like an antenna in the case of electro-magnetic wave or a...
  33. P

    Acoustic horns and impedance matching

    I found a fast solenoid valve lying around (~1ms rise time) so I thought it would be fun to hook up to a compressed air line and use to generate some really loud bass. I hooked it up to a function generator and air supply only to find that it was disappointingly quiet (well not quiet, but...
  34. K

    Sound standing waves paradox....

    If you seal a loudspeaker at the end of a tube and close the other end of the tube you will get standing waves; but what are the boundary conditions at the speaker for the sound pressure wave? Pressure =0 or Pressure = MAX? I find no mention of this in the literature. To find out I performed a...
  35. Y

    Classical Good acoustics book

    For college we have to write a 3000 word essay on a subject so an idea I had was to firstly explain the maths/physics behind music and then break up a piece of classical music into its sine waves. However, my acoustics knowledge is limited. Does anyone know of a good book/books that explain...
  36. spareine

    Wineglass singing vs. pinging

    I recorded the sound spectra of a singing wineglass (rubbed the rim with a wet finger) and a pinging wineglass (tapped anywhere at its wall) with a smartphone. Evidently the fundamental tones of both vibrations are identical, but the overtones are very different (harmonic vs. anharmonic). As the...
  37. E

    Odd (pretty) waveform for third harmonic of violin E-string

    I lightly placed my finger a quarter of the length down the E-string of a violin and drew the bow, forcing the third harmonic. I used an oscilloscope app to look at the waveform. I got this unusually regular pure pattern...
  38. Kyle Burris

    Mechanical noise - A/C and radon fan standing wave hum

    Hello, I am moving into a new house, remodeling, etc. & am installing a new A/C compressor and radon fan. Being that low frequency noise highly bothers me & affects my insomnia quite a bit, I am trying to look at all considerations regarding acoustics, mechanical sound propagation properties...
  39. M

    Absorptive type sound insulation

    Could you tell me the physical reason, why the absorptive type sound insulation (Windowpane with some thickness) is effective only at high frequencies of sound source?
  40. Vir27

    Low tech telecommunications (sound)

    I'm a historian. I've struck on a curiosity about telecommunication technology in pre-modern times. I've read about a number of methods, and I'd like to ask some physics questions that got beyond my ken. This information is for my curiosity and creativity, not for any rigorous study, so I may be...
  41. Saumya Kar

    Difference between acoustic pressure and fluid pressure

    While the sound waves travel in a medium, let's say a fluid, what is the difference between fluid pressure and acoustic pressure ? Are these entities same?
  42. A

    Physics investigation guidance: Vibration of circular plate

    Hi, I have previously made a post in order to gain some insight in my rather out of control project. Long story short I am investigating vibration of a circular plate and its standing waves. After consultation at this forum I have been guided in the direction of acoustics and bessel functions...
  43. H

    Planar wave expansion cancelling through interference

    Hello everyone! In a hypothetical 3D space, with no boundaries around, homogeneous normal conditions, what would happen to the advancement of a planar wave front produced at t=0 with 2cycles in length, λ=3.5m, moving with vector speed "c-arrow=1i-arrow" if an identical planar wave of 2cycles in...
  44. R

    Ultrasound absorption by particles in water

    Hi All, I am in need to calculate the ultrasound (20MHz) absorption of particles (polystyrene of size 15 microns) in water. I tried to search in the internet, but couldn't find any simple analytical expressions. Can someone please help me ! Thanks in advance! Regards, Radel...
  45. V

    Damped Driven Harmonic Oscillator.

    Homework Statement An oscillator with mass 0.5 kg, stiffness 100 N/m, and mechanical resistance 1.4 kg/s is driven by a sinusoidal force of amplitude 2 N. Plot the speed amplitude and the phase angle between the displacement and speed as a function of the driving frequency and find the...
  46. X

    FDTD of (ultrasound) wave propagation through muscle

    Im a mechanical engineering student currently, with a third year project of simulating ultrasound propagation through the abdomen. Currently i just want to simulate it going through muscle with no obstacles. I don't really understand where to start, I have formed some equations based on the wave...
  47. S

    Continuity of velocity at the interface

    Dear experts, While solving the wave transmission at an interface for an acoustic wave problem, a boundary condition states that the "velocity of a fluid particle at the surface must be continuous". Could you please let me know why is it required, and a physical insight of what would happen if...
  48. N

    Acoustics + Optics + Oceanography ?

    Hi Everyone, I am about to finish my PhD in underwater acoustics. I am thinking of postdoc positions and research areas which might cover: oceanography and optics with acoustics. I still have to learn a lot before generating any ideas on my individual research career. But was wondering if...
  49. D

    M.S. Mechanical Engineering in Mechanics vs Robotics/Controls

    Hello fellow PF members, I'm currently in my senior year in Mechanical Engineering at Oregon State University. I'm considering going on to get my Master's Degree to gain more knowledge (since I'm fascinating by them). I really like Math and have a Math Minor already. I am looking to go into a...
  50. SalfordPhysics

    Helmholtz Resonator using voltmeter

    Hi, I am trying to understand how precisely a voltmeter is used to measure the resonant frequency of a sound wave in a helmholtz resonator. Is it simply that the maximum voltage corresponds to the resonant frequency? A detailed description or external link would be great. Many thanks.