# Tagged Questions

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. Applications of acoustics are for instance the audio and noise control industries.

32 views

### What frequency is the scratching of finger nails on a blackboard?

This is the frequency/intensity that sets my teeth on edge. Does anybody know what frequency (roughly) it is? I am guessing it is near the top of normal human hearing, 20kHZ, but I'm not sure if ...
19 views

### Why the Doppler Ultrasound beam needs to be looking directly down at a pipe

So I was doing a question about "Doppler Ultrasound" It states that a Doppler ultrasound uses soundwaves at a frequency much higher than what humans can hear. They can me used to measure the speed of ...
9 views

### Speed of sound at phase transition — does percolation theory describe it?

I was discussing with a friend whether we expected liquid water or ice to have a higher speed of sound, near freezing; we figured it would be water since it was more dense. It turned out to be ice (by ...
16 views

### Frequency range possible from a mechanical music box [on hold]

Here is a small mechanical music box. The tines of a metal comb are tuned to emit a particular frequency when plucked. The material and structural characteristics of the comb, plucking cylinder, ...
3k views

### Why aren't the lengths of the bars on a toy glockenspiel proportional to the wavelengths?

As you might already know, frequency of musical notes is arranged in a such a way that if, for example, an A note has frequency of $x$, another A note which is placed one octave higher would produce ...
47 views

### Harmonic frequencies of a guitar string

I'm studying harmonic frequency at the moment but I'm just a bit confused about something. How are more than one different frequencies able to be produced from plucking a guitar string (fundamental ...
14 views

### Sound source localization in cylinder

I am training an animal (let's assume it's a rat) to do sound-source localization in a cylindrical plexiglass chamber that is approximately 30 cm in diameter (see figure). That is, the animal must ...
27 views

### Mathematical Relationship to find number of antinodes/nodes in a standing wave

So I have been learning about closed pipes (nodes at both ends), open pipes (antinodes at both ends) and open/closed pipes (node at one end and antinode on the other). I have also learnt that for a ...
29 views

### Do ten sounds sound twice as loud as loud or four times as loud as just one sound?

Oddly worded question, but here's the problem. So, basically, according to the HyperPhysics website, it takes 10 violins to sound approximate twice as loud as 1 violin. Assuming that they're all in ...
24 views

### How would I go about calculating the frequency and amplitude of a sound produced by a collision?

How would I go about calculating the sound pressure level, frequency and amplitude of a sound caused by a collision, given the velocities of the two objects colliding, their acceleration, densities, ...
13 views

### How to calculate static air temperature

Let's suppose I have an airplane flying at an unpecified altitude and the following data are given: Flight Mach number: $M=0.76M$ Ground speed: $v_{kts}=470kts$ My goal is to estimate the air ...
31 views

### Detect original sound waves

I have just presented a project of mine regarding sound recognition using neural networks. I told during the presentation that I decided to only recognize one sound (musical notes coming from a guitar)...
14 views

### Do Conch shell horns produce infrasound?

I was just reading an article about some guys at Stanford playing with ancient conch shell horns: http://news.stanford.edu/news/2011/february/conch-acoustic-musicians-020711.html They mention feeling ...
6k views

### Why are the harmonics of a piano tone not multiples of the base frequency?

I was trying to figure out which piano keys were being played in an audio recording using spectral analysis, and I noticed that the harmonics are not integer multiple of the base note. What is the ...
3k views

### The speed of sound is a single value yet the speed of atoms is distributed over many values. Does the sound wave front smear out?

Sound waves travel with constant speed, but air molecules that transfer action move with different speeds than the ones described by Maxwell distribution. Why does the sound wave not smear out and ...
19 views

### Ultrasound in hollow tube

Ultrasound in pulse-echo mode (reflection from air-water interface) is used to measure the level in a tank filled with water. Since the level is several meters, a hollow steel tube is used to ...
193 views

### Hearing background noise from earphone while there isn't any connection

Once my friend told me that he was listening some background noise while his earphones were not plugged in any device. I didn't believe him but 10 minutes ago I experimented the same. I can certainly ...
30 views

### Low Frequency Wind Chimes

I'm building a public sound sculpture made of tuned aluminum pipes -- think wind chimes that people can play. I want to include lower frequency chimes in the sculpture, but the fundamental frequency ...
70 views

### In which-pattern does the individual-particles move in a longitudinal wave?

Transverse waves, such as upper-surface of pond-water, or in shaking-rope; the Transverse-Wave can be easily understood and drawn (for different times such as at t second, t + 0.25 second, t+0.5 ...
27 views

### Can the intensity of a sound wave in a minimum be greater than intensity in a maximum?

Suppose to have two speakers $A$ and $B$ one in front of the other, producing coherent sound waves with the same frequency $f$ and power $P$. In different positions on the line connecting the speakers ...
34 views

### Sound wave dissipation near a solid body

In this answer to a Physics.SE question I found the following intriguing comment: Under typical conditions the sound absorption length is quite long, and not that much heat is produced. A more ...
98 views

### Doppler shift and change in intensity of a sound wave

How are the intensity of a sound wave and the Doppler shift of frequency related togheter? That is, if the source or the observer are in relative motion, how does the intensity change? For a sound ...
22 views

### Frequency shift in case of wind and no relative motion between observer and source

I've learned the following things about Doppler effect in the case of sound waves The Doppler effect formula is to be used in the air reference frame (where $v_{sound}=343 m/s$, at room temperature) ...
48 views

### Why pressure standing waves have different nodes location with respect to the corresponding displacement waves?

In acoustics the pressure wave has a $\pi/2$ phase difference with the displacement wave. But I do not understand how this leads to a different position of nodes of pressure inside a tube with ...
4k views

### Why does sound absorption in oceans depend on the pH?

I was reading "The Sixth Extinction: An Unnatural History", by Elizabeth Kolbert, and there she comments that high level of $CO_{2}$ in the atmosphere lowers the pH of oceans (which makes sense) and, ...
35 views

### Beats: frequency of resulting wave vs. beat frequency

The beats frequency heard from the interference of two sound waves with frequencies $f_1$ and $f_2$ is $$\nu=|f_1-f_2|$$ Nevertheless the frequency of the resulting wave is not $\nu$ but the mean ...
30 views

### What enclosed geometry amplifies sound the most?

I am going to build a record player. It will read sound electronically but I also want it to be able to project sound mechanically, like a classic record player. So if sound enters a tube, can you ...
21 views

### How to Calculate Sound Pressure Levels using Microphone Sensitivity Rating

This is sort of a cross between a computer science and Physics question, but I would be grateful if anyone here could help me. My objective is to calculate the sound pressure level (in dB) of a ...
121 views

### Significance of wave number?

Till now all I know about the wave number is its formula i.e. ${\frac{2\pi}{\lambda}}$. I always wanted to know what it really means. So can anyone please, explain me its physical significance?
72 views

### Can sound travel in the form of transverse waves?

We all know that sound is a longitudinal wave but in some books, I have found that sound travels in the form of both longitudinal and transverse waves while passing through rocks. Can anybody explain ...
534 views

### Is there any effect on mechanical waves by electromagnetic waves (and vise versa)?

Do electromagnetic waves like light and gravitational waves (due to moon for instance) affect on mechanical waves like sound? Can sound change the path of light?
178 views

### Why do we hear better during the night? [duplicate]

At night, we hear weak and far sounds approximately clear, while during the day we cannot. My high school physics teacher was saying that “this is because of interference of sound waves. During the ...
2k views

### Why do you only hear the bass when someone nearby is wearing earphones?

When someone nearby is listening to music through earphones or headphones, usually you can only hear the bass (unless it's really loud where you can hear the singer's voice and the other instruments ...
45 views

### Speed of sound in solid — temperature dependence

Let $v$ denote the speed of sound in a fixed solid, at a fixed temperature $T$. This will depend on properties of the solid (such as the bulk modulus and density). Given an increase in $T$, does $v$ ...
28 views

### What's the effect called when vibrations move through a cable under tension?

I'm not sure how to describe it, but there is a certain sound of vibrations through a tensioned cable, you might hear it as sound effects in a movie where cables are snapping, some have described it ...
17 views

### What happens when sound source is radiating through a hole in a cavity?

What happens to the external sound field , when loudspeaker attached to one wall is radiating inside a box and other wall has a aperture size of a diaphragm? Do we experience Helmholtz effect?
35 views

### Water in glass tubes producing different pitches when tapped. Why exactly is this?

So I've been making a DIY instrument for my physics project at school. I decided to try this experiment where I put different volumes of water into a glass cup, and I tap it with a spoon to create ...
52 views

### What is the difference between real value and abs value? [closed]

I am confused here, though I have been reading about it for years. What is the difference between a real value and an absolute value? For example, when do we take the absolute value of pressure or the ...
63 views

### Why do we hear a different timbre when someone speaks with helium (or other gases) in their lungs?

Let me make one thing clear: I am fully aware that the change in timbre comes from the change in acoustic wave speed when going through a different medium (just like light). However, would I not ...
64 views

### Percent variation of a physical quantity: how to choose who is in the denominator?

I came up with a very basic doubt on percent variation of a physical quantity,say $f$, defined as $$\delta f_{\%}=|{\frac{\Delta f}{f}}|\cdot 100$$ The problem is with the denominator. I'll make a ...
17 views

### Impulse response of air

Has someone captured impulse response of air with as few reflections as possible? It is said that high frequencies are diminished as sound travels, but I haven't seen any actual results of how say, ...
32 views

### Why do certain materials of nature ring when struck?

There are a wide range of elements and natural materials that will give off a ringing sound based on the material and the profile of the object is correct, most first think of metals ring best because ...
63 views

### Why do we add intensities for coherent sound sources?

When there are N coherent sound sources playing the same note at equal loudness, their sound waves add up to make a sine wave of the same frequency but most likely different amplitude (can be anything ...
25 views

### how sound quantity in a period of time is measured by? [closed]

Let's suppose that I'm singing for 10 minutes and I obviusly produce some sounds, and let's imagine that I hold an instrument for measuring the amount of sounds produced within that period of time. I'...
153 views

### 'Slapping' sound when trains pass each other

I have noticed that when riding in a train travelling at over 100 kmh$^{-1}$, a loud 'slap' can be heard when another train travelling at a similar speed passes in the opposite direction, followed by '...
113 views

### Why does a rolling thunder always starts with a high pitch and ends with a deep, low sound? [duplicate]

Rolling thunders always come cracking in with a high frequency, and the sound grows more deep as the rolling advances, ending with the deep sound of a roaring lion. Why? This is not the same question ...
57 views

### How to counteract Doppler's effect? [closed]

I am working on a robot in which I am detecting obstacles on sides using Ultrasonic transducers. Now the problem is, the target speed for the robot is 8.5 m/s and at this speed, the doppler's effect ...
68 views

### Sonic boom breaking glass

It's a well known fact that a sonic boom from something such as concord can shatter glass. I'm interested to know why a human is seemingly fine in the presence of the shockwave and yet the glass is ...