# Tag Info

3

I've received an answer/explanation from Jim Wild at Lancaster University. I'll add it here in case anyone's interested. Full credit to him :) Jim Wild: But basically, no it's not just a single one-time bang. The pressure wave (which we perceive as a boom) is generated continuously as long as the aircraft is moving supersonically. This is why ...

3

Every twelve notes (semitones) span an octave i.e. the frequency doubles. In equal temprement tuning the ratio of the frquencies of each pair of semitones, call this $r$, is constant so: $$r^{12} = 2$$ and therefore $r \approx$ 1.0595. If by one note to the next you mean a full tone, i.e. two semitones, then the ratio of the frequencies is $r^2$ or ...

3

The energy produced by the Hiroshima detonation is estimated to be $63\text{ TJ}$ ( $63 \times 10^{12}\text{ Joules}$). Later detonations were much much larger. If an individual is going to excite the resonances of the wind instrument with that much energy, conservation of energy requires that the same amount of energy must be put into the instrument by ...

2

The reference pressure $p_0=20$ micropascals is equal to $2\times 10^{-5}$ pascals which is equal to $2\times 10^{-10}$ bar which is equal to $0.0002$ microbar which is also equal to $2\times 10^{-5}$ newtons per squared meter (the same unit, pascal, as watt per cubic meter) or $2\times 10^{-9}$ newtons per squared centimeter or $2\times 10^{-4}=0.0002$ dyne ...

1

The physiology of human ear (and perhaps brain) makes sounds with frequency ~3000 Hz sound louder than higher and lower frequencies, for same sound wave pressure perturbation; see https://en.wikipedia.org/wiki/Equal-loudness_contour

1

Bass consists of lower frequency ranges and longer wavelengths, meaning that produces those vibrations essentially over a longer distance, or at least with more "strength" so that the vibrations of the sound can travel through the plastic material. However since treble is of a higher frequency range, it travels shorter distances. This also means it cannot ...

2

There is a detailed review of this phenomenon here The phenomenon is known as sonoluminescence. One of the leading theories is that it is caused by "adiabatic heating of the bubble at collapse, leading to partial ionization of the gas inside the bubble and to thermal emission such as bremsstrahlung."

1

The speed of sound in the non-relativistic regime is much smaller then the speed of sound and agrees with your final formula. To see that you should remember that the particle density $n(\rho)$ is not a constant, but it is a function of the energy density. In fact, for the non-relativistic fluid $$\rho(n)=nm c^2+\kappa n^{5/3}.$$ Now you can check that ...

0

The amplitude at a resonance depends on damping friction and other energy dissipation mechanisms. Absent of those the amplitude is infinite. You need to provide a better description of the system in order to derive the amplitude frequency relationships.

1

Here's a similar question which will be helpful to resolve your apparent perception of Doppler effect. Because, Doppler effect is real. So would it be right to say that when the wave is reflected from B, we can think of it as a source kept on the car B? No. Because the frequency has already been altered (probably increased) by the moving car and the ...

2

The reason you can hear sound around the door is only in part due to diffraction. As you said, the walls are not completely rigid. In fact, the sound is passing through the door as well. Consider a speaker on the other side of a wooden door that is producing a sound. The door is completely shut. The reason you can hear it is because the sound is passing ...

1

Wavefield Synthesis can do this but not with a small number of emitters, uses a massive array of speakers create a field effect, and phase alteration can reposition sounds within that field. http://en.wikipedia.org/wiki/Wave_field_synthesis Downside is it's not perfect, it takes a big array of speakers placed very accurately, works best on higher ...

1

I suppose you could use destructive interference and set up speakers in just the right positions for it to work, but I also assume the calculations needed to achieve it would be complicated (luckily, you're not asking for that). It should be possible in theory

1

Let´s assume you could get speakers which are 100% directional, thus ensuring that nodes would be perfectly located around the room. You would still have to rule out difusion ocurred when the standing waves are formed. Then, let´s assume all the walls are totally smooth and reflective and provide no difusion at all, but their absortion coefficient is ...

4

You could use audio spotlights to make the sounds audible only along certain beams. This should be close enough to let people walk around in the room and only hear certain notes at certain places. These audio spotlights use intense ultrasound that makes the air along its path a nonlinear acoustic medium, so modulation in the audioble frequency range can be ...

1

Lower frequencies tend to dissipate in all directions, while higher frequencies tend to be "directed". (For example, you can place your subwoofer anywhere in the room, as the sound waves will propagate in all directions, while your other speakers are more "directed" because they reproduce higher frequencies). See this Wikipedia article on sound ...

0

Here is a TED talk on a sound laser type device. It probably could be fashioned to do what you are suggesting. http://www.ted.com/talks/woody_norris_invents_amazing_things.html

0

While I'm not sure the exact the answer to this, but there is a room in Grand Central where 2 points are connected acoustically so that you can hear each other clearly (despite being far) if you stand in the corners. http://www.sonicwonders.org/?p=426

0

You're right that sound waves can interfere constructively or destructively leading to dead spots or live spots (which is an effective phenomenon to be considered when constructing large auditoriums) which can be harmful sometimes. Your example of local noises in buildings fail for one reason you mention ... So is it possible that a large number of ...

0

The difference between solids and gases appears in the momentum conservation equation: $\rho\frac{d\vec v}{dt}=\vec S$ where $\vec S$ is a source term that expresses the rate at which momentum is exchanged between neighboring volumes, a "restoring force". In gases, $\vec S=-\vec \nabla p$, where the pressure $p$ relates to density and temperature through ...

-1

Think of it this way. Elasticity is a property of material that allows it to store energy and release it without dissipating. Solids have high elasticity, therefore, they can store and release energy quite efficiently. Liquids and gases have low elasticity. They are also viscous and dissipate energy instead of transmitting it. Please note that I am not ...

0

The speed of sound depends on temperature but not on pressure. A human voice or a wind instrument will have the same pitch at higher altitude (assuming constant temperature), but a higher pitch at higher temperature. A guitar's pitch won't change measurably, because its pitch is determined by the length, tension, and mass per unit length of the strings, none ...

3

I assume "faster in solids" means faster than in gases. The speed of a mechanical wave is in general proportional to $\sqrt{k/m}$, where $k$ is some measure of the restoring force (e.g., the tension in a string, or a Young's modulus), and $m$ is some measure of inertia (e.g., the mass per unit length of a string, or the density of the medium). Compared to ...

2

Sort of. I'm not sure about sound waves in air, but sound waves in a lattice can be described by quasi-particles called phonons. However I'm not sure whether the wavelength of the vibration would then correspond to the de Broglie wavelength of the phonon. The Wikipedia article states the momentum of the phonon (subject to some matters of interpretation!) is ...

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