Questions and tasks
- Why do closed windows protect rooms on the upper floors of a building from road noise much more noticeably than on the lower ones?
- Wood is known to conduct sound better than air. Why is the conversation taking place in the next room muffled when the wooden door to this room is closed?
- Why is the sound louder if you knock not on the wall, but on the door?
- Where does the energy of sound vibrations go when the sound "freezes"?
- Why is the prompter booth upholstered with felt?
- When an orchestra performs in a large hall, the music sounds different depending on whether the hall is full of people or empty. How can this be explained?
- Our ancestors could hear the distant clatter of hooves, dropping their ear to the ground. Why was this sound not heard in the air?
- Why, in fog, beeps, for example, trains or motor ships, are heard at a greater distance than in clear weather?
- A tuning fork vibrating in the hand sounds soft, and if you put its leg on the table, the sound volume increases. Why?
- Will the “loud” tuning fork from the previous task last longer compared to the “quiet” one?
- How to explain the fact that at a great distance a voice can be heard, but the words cannot be made out?
- Members of the Antarctic expeditions, when they dug tunnels in the snow, had to shout to be heard even at a distance of five meters. However, the audibility increased markedly when the walls of the tunnel were tamped down. What is it connected with?
- Why is there no echo in a normal sized room?
- Why is the echo from a high-pitched sound, such as a scream, usually louder and more distinct than from a low one?
- Accidentally flying through the window, the bat sometimes sits on people's heads. Why?
- In the model of the "whisper gallery" shown in the figure, the sound waves from the whistle caused the flame of a candle placed against the opposite wall to flicker. But the flickering stopped if a narrow screen was placed near the wall to the side of the flame and the whistle. How did this screen block the sound?
- Why sometimes the sound "beam" of the locator, directed at a submarine from a short distance, nevertheless does not reach it?
Room acoustics.
Sound propagation in
closed and open spaces is subject to different laws.
Some of the energy is absorbed
some is reflected, some is scattered.
,
(5.1)
,
(5.2)
where aneg - reflection coefficient,
a is the absorption coefficient.
These coefficients are
frequency functions. If there is no diffraction, then
,(5.3)
,(5.4)
If there is diffraction, then
the reflected waves interfere with the incident ones, and, consequently, points are formed
nodes and antinodes, i.e. we get standing waves.
Room acoustics in the framework of statistical theory.
The processes of sound propagation in a room are considered as a decay
energy of multiply reflected waves. If there is no diffraction, then
,(5.5)
If a is small, then there is a lot of energy and
its distribution occurs without nodes and antinodes, i.e. energy density in
every point in the room is the same. Such a field is called diffuse. Only
for such a field, one can determine the average path length of the sound beam, which
typical for the size of the "golden section" room (length, width, height
should be related as: 2:1,41:1).
,
(5.6)
where is the average length
path of the sound beam,
V - the volume of the room,
S – surface area
premises.
(5.7)
,
(5.8)
where is the average
(statistical) travel time.
Consider
steady state, i.e. the amount of radiated energy is equal to the amount
absorbed energy for some time t.
,
(5.9)
where is the emitted
energy,
Ra–
sound source power,
t is the time interval. Some of the energy will be absorbed.
- energy in the room,
(5.10)
where em – density
sound energy, a is the absorption coefficient.
,
(5.11)
- steady state, then it will be
energy equality, as mentioned earlier.
,
(5.12)
is the steady state value of density
energy.
On the other hand, it is known
,
(5.13)
,
(5.14)
,
(5.15)
,
(5.16)
where is the effective
sound pressure in the room at steady state,
Ra – acoustic power .
These
the ratios are derived under the condition of a very small absorption coefficient,
limiting the surface, with an increase in a (halls, auditoriums, living quarters) emdecreases
nodes and antinodes appear. Those. the energy density is not distributed
uniformly. Formulas (5.10, 5.14) give an average value if
agreat.
,
(5.17)
- total absorption of the premises (fund
absorption). ,
.
1 Sabin (Sat) - it
absorption of 1 m2 of an open window without taking into account diffraction. Funds
absorption is a variable value and for different rooms these are different values.
Since indoors
absorption coefficients are all different, we introduce the concept of the average coefficient
takeovers:
,
(5.18)
where SK- areas of the surfaces of the room, aKare their absorption coefficients.
indoor objects, people
etc. (their absorbing surface is difficult to take into account), therefore, equivalent
absorption coefficients an.
To account for all items
value, as the total absorption of the room:
,
(5.19)
where anNn
is the product of the equivalent absorption coefficient of objects and their number.
Consider the process
attenuation of sound in the room after turning off the sound source.
—
start time
—
after 1 reflection
—
after 2 reflections
—
after n reflections (5.20)
where t – elementary
moment of time.
,
(5.21)
,
(5.22)
,
(5.23)
where e is the energy density in
general view.
Let's move on to
exponential function:
(5.24)
Let's introduce a replacement:
(5.25)
Because no diffraction, then aabsorb (aWed) and aneg
linked through the unit.
, (5.26)
,
(5.27)
Let us describe the growth processes
and attenuation of sound in the room.
,
(5.28)
- this is how the decay process is described
sound in the room.
other songs from sound
-
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01:42sound
circular saw -
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00:17Sound
Sirens -
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00:06Sound
Guess who's calling -
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07:48Sound
Rain -
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00:55Sound
motorcycle engine -
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00:24Sound
sport bike engine -
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15:16►Sound
Thunderstorm and rain -
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00:06Sound
Shooting from a machine gun (from a distance) -
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00:41Sound
Bunch -
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00:41sound
heartbeat.. -
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03:28sound
car -
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00:11Sound
fire siren -
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00:11sound
tap water -
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00:23Sound
Boiling water -
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00:09Sound
Water in the shower -
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00:05Sound
Water in the sink -
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02:35Sound
The New Year is coming to us -
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01:17Sound
keyboards -
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00:05Sound
Running-sounds of footsteps -
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00:22Sound
Sex (operation Y) -
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00:21Sound
machine gun -
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00:06sound
phone ring -
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00:32sound
by SMS -
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00:25Sound
Prolonged female cry -
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00:08Sound
glass breaking 2 -
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00:06sound
my throat) -
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00:50sound
alert -
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00:07Sound
Opening a door on a space station -
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00:05Sound
door closing -
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00:24Sound
Motorcycle engine Yamaha R1=) -
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00:24Sound
Yamaha R1 motorcycle engine -
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00:18Sound
Dialing (old phone) -
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00:08Sound
time machines -
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00:42Sound
Trains -
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00:05Sound
alarm clock -
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01:24Sound
broken glass -
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00:15sound
broken glass -
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05:14Sound
Spirits of the Forest -
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00:07Sound
Drumroll -
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00:24Sound
Nexus Falcon scooter engine. -
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03:26Sound
Moto (music) -
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00:10Sound
This mother-in-law! resistance is useless ... -
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00:26Sound
Crowds of zombies (various sounds) -
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00:18Sound
tank movement -
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00:01sound
door creak -
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00:06Sound
Bullet whistle 2 -
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00:07Sound
Whistle of bullets -
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00:04Sound
football bugle -
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00:09Sound
Roar of the Bear -
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00:19sound
Water drops
Fundamentals of acoustics Basic principles of sound propagation
Basic Principles of Sound PropagationBasics of PsychoacousticsSoundproofingIndustrial AcousticsArchitectural Acoustics
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THE APPEARANCE OF SOUNDSound is a mechanical vibration that propagates in an elastic medium (usually air) and affects the hearing organs. If you make a sharp displacement of the particles of the elastic medium in one place, for example, using a piston, then pressure will increase in this place. Thanks to elastic bonds, pressure is transferred to neighboring particles, and the area of increased pressure, as it were, moves in an elastic medium. The area of high pressure is followed by the area of low pressure, and thus a series of alternating areas of compression and rarefaction is formed, propagating in the medium in the form of a wave. Each particle of the elastic medium in this case will oscillate.
SOUND PRESSURE AND FREQUENCY As a rule, the quantitative value of sound is determined by sound pressure or the force of action of air particles per unit area. The number of vibrations of sound pressure per second is called the frequency of sound and is measured in Hertz (Hz) or cycles per second. The figure shows two examples of sound vibrations with the same pressure level and different frequency.
EXAMPLES OF DIFFERENT SOUND SIGNALS The figure shows three types of different sound signals and their corresponding frequency characteristics: - a periodic sound signal (pure tone); - a single signal (rectangular pulse); - noise (uneven signal).
WAVE LENGTH AND SOUND SPEED Wavelength is defined as the distance between two adjacent points of a sound wave that are in the same vibrational position (have the same phase). The relationship between wavelength and frequency is given by the following formula
where c is the speed of sound propagation in the medium
TOTAL SOUND PRESSURE LEVEL According to the diagram, the total combined sound pressure of two independent sound sources is determined as follows1.The difference between the levels of both sources is calculated and a corresponding mark is made on the OX2 axis. The corresponding value on the OY3 axis is determined. The total sound pressure is found as the sum of the value found and the value of the louder noise source.
FREQUENCY BANDS OF VOICE AND MUSICAL INSTRUMENTS
SOUND DISTRIBUTION IN FREE SPACE If the sound source is omnidirectional, in other words, sound energy propagates uniformly in all directions (such as the sound from an aircraft in airspace), then the sound pressure distribution depends only on distance and decreases by 6 dB with each doubling of distance from the source sound.
If the sound source is directional, such as a loudspeaker, then the sound pressure level depends both on the distance and on the angle relative to the axis of sound emission.
Answers
- The greater the angle of incidence of sound waves, the less of them penetrate the glass.
- Wood conducts sound faster than air, so there is a limiting angle of incidence of sound rays, above which sound will not penetrate wood at all,
- With the same impact force, the door deforms more than the wall, so the amplitude of its vibrations is greater, and the sound is louder.
- The energy of sound vibrations is converted into the energy of thermal motion of air molecules and surrounding objects.
- Felt, which absorbs sound well, prevents it from spreading into the auditorium.
- Clothing and the human body absorb sound waves to a greater extent than loose chairs and the floor. In addition, the audience in the hall creates a kind of "uneven" surface that scatters sound in all directions. All this together affects the perception of music in a filled and empty auditorium.
- The answer is not that sound travels faster in the ground, but that it is scattered and absorbed to a lesser extent in the ground than in air.
- In foggy weather, the air is more homogeneous - there is no scattering of sound on the so-called acoustic clouds created by convection currents.
- The tuning fork leg excites forced vibrations in the table top, sound waves are emitted from a larger area, which leads to an increase in volume.
- No. Since the power of the sound emitted by the tuning fork increases, it will quickly use up its energy) and die down.
- Speech intelligibility is associated with the presence of high frequencies in the sound. However, the absorption coefficients of sound in air for these frequencies are greater than for low ones, so high-frequency vibrations are attenuated to a greater extent than low-frequency vibrations.
- Loose snow, replete with air cavities, is an excellent sound-absorbing material. As the snow compacts, the absorption of sounds in it weakens, and the reflection increases.
- In order for the echo to be distinct, the reflected sound must arrive with a certain time delay, which is difficult to achieve in small rooms.
- High-frequency sounds bounce off obstacles better and are more intense when returning.
- The hair absorbs the ultrasound emitted by the bat, and it, not perceiving the reflected waves, does not feel an obstacle and stumbles upon a person's head.
- Continuously reflected from the wall, sound waves propagate along it in a narrow belt, as in a waveguide. In this case, the sound intensity, as it turned out, decreases with distance much more slowly than in open space.
- The sound wave is deflected downward due to a decrease in water temperature with depth, which is associated with a decrease in the speed of sound and, accordingly, an increase in its refractive index.
Microexperience
The sound coming to us from a gnawing neighbor in the air scatters much more strongly than the sound propagating to your ear directly through the cranial bones.
The material was prepared by A. Leonovich
sound propagation
Sound
waves can travel through the air
gases, liquids and solids. V
airless space waves are not
arise.This is easy to verify in
simple experience. If the electric bell
put under airtight
cap from which the air is evacuated, we
we won't hear any sound. But as soon as
the cap is filled with air, there is
sound.
Speed
propagation of oscillatory movements
from particle to particle depends on the medium.
In ancient times, warriors applied
ear to the ground and thus discovered
enemy cavalry much earlier,
than she came into view. A
renowned scientist Leonardo da Vinci
15th century wrote: “If you, being at sea,
lower the hole of the pipe into the water, and the other
put the end of it to your ear, you will hear
the noise of ships very distant from you.”
Speed
propagation of sound in air for the first time
was measured in the 17th century by the Milan Academy
Sciences. On one of the hills
cannon, and on the other is located
observation post. time was recorded and
at the moment of the shot (by flash) and at the moment
sound reception. By distance between
observation post and cannon and
time of origin signal speed
sound propagation calculate already
was not difficult. She turned out
equal to 330 meters per second.
V
water speed of sound
was first measured in 1827 on
Lake Geneva. Two boats were
one from the other at a distance of 13847 meters.
On the first, a bell was hung under the bottom,
and from the second they lowered the simplest
hydrophone (horn). On the first boat
set on fire at the same time as the bell was struck
gunpowder, to the second observer at the moment
flashes started the stopwatch and became,
wait for the sound signal from
bells. It turned out that the sound in the water
spread more than 4 times
faster than in the air, i.e. with speed
1450 meters per second.
Echo
echo —
reflected sound.
Echoes are usually noticed if they also hear
direct sound from the source when in one
point in space can be several times
hear sound from one source,
coming along a straight path and reflected
(maybe several times) from others
items. Since the reflection of the sound
wave loses energy, then the sound wave
from a stronger sound source
bounce off surfaces (eg.
houses facing each other or
walls) many times, passing through one
point, which will cause multiple echoes
(such an echo can be observed from thunder).
Echo
due to the fact that sound
waves can
reflected by hard surfaces
associated with the dynamic picture
rarefaction and air seals near
reflective surface. If
the source of the sound is nearby
from such a surface turned towards him
under direct
corner (or
at an angle close to a straight line), sound,
reflected from such a surface,
like circles
reflected on the water
from the shore, returns to the source.
Thanks to the echo, the speaker can together
with other sounds to hear your own
speech, as if delayed for some
time. If the sound source is
at a sufficient distance from the reflective
surfaces other than the sound source
there are no extras nearby
sound sources, the echo becomes
the most distinct. echo becomes
audible if the interval between
direct and reflected sound wave
is 50-60 ms, which corresponds to
15-20 meters which sound wave
travels from the source and back
normal conditions.
It's curious that
... the methods of diagnostics, long known in medicine - percussion and listening - have found application in acoustic flaw detection, which makes it possible to determine the presence of inhomogeneities in the medium by scattering and absorption of a sound signal sent into the medium under study.
... the solution to the "whisper gallery" effect described in problem 16 was found in 1904 by the famous Lord Rayleigh during his observations and experiments in St. Paul's Cathedral in London. Almost a hundred years later, this type of wave became the subject of research and application in optics, for example, for frequency stabilization of lasers or frequency conversion of a light beam.
... infrasonic waves are very weakly attenuated in the atmosphere, the ocean and the earth's crust. Thus, a powerful low-frequency disturbance caused by the eruption in 1883 of the Indonesian volcano Krakatoa circled the globe twice.
... with distance from the epicenter of a nuclear explosion, the shock wave turns into an acoustic one, and short waves decay faster than long ones, and only low-frequency oscillations remain at large distances. The detection of such - infrasonic - waves was proposed in the mid-1950s by Academician I.K.
... Bell's invention of the telephone was preceded by a thorough study of acoustics and many years of work in the Boston school for the deaf and dumb, who also intended the sound amplifiers and devices designed by him for teaching speech understanding.
... the peculiarity of freshly fallen snow to absorb mainly high frequencies was noticed by the English physicist Tyndall, who combined acoustic and optical research. And Rayleigh, who was looking for something common in all oscillatory processes, was able to explain the increase in the tone of the echo in a pine forest by better scattering and reflection of short sound waves by thin needles than long ones, as in the scattering of light in the atmosphere.
...in one of the premises of the Conservatory in the Australian city of Adelaide it was impossible to listen to the piano playing - the hall resonated so piercingly and sharply. They found a way out of this situation by hanging from the ceiling several half-meter-wide strips of twill - cotton fabric with a special surface finish that allows good sound absorption.
... sound vibrations with a frequency of 200-400 hertz at sufficiently high levels of their intensity can mask almost all overlying frequencies very strongly. For example, the melodies of the organ and double bass are clearly audible in the orchestra, although their relative loudness does not exceed such high-sounding instruments as the violin and cello.
… if you “sound” pipelines for transportation of bulk cargoes — flour, coal dust, crushed ore — with sirens, then their throughput increases. Such devices are used in ports to unload powdered materials from the holds of cargo ships. Their only drawback is their piercing howl.
…sound frequency oscillations can be used for drying various materials at relatively low temperatures, including due to their local heating during the absorption of acoustic waves.
…ultrasound is capable of “mixing” mercury or oil with water, pulverizing solids in the manufacture of medicines, punching a square hole in metal, cutting and drilling glass and quartz, joining “solderless” materials, and much more amazing, but here’s how to create an ultrasonic weapon , alas, it is impossible. Features of the propagation and absorption of ultrasound lead to such a strong attenuation that even at a distance of only a few tens of meters it transmits energy sufficient to operate only ... a light bulb from a flashlight.
Improving the sound without radical steps
Of course, the ideal hall for a Hi-Fi/High End system must be acoustically treated. Only here, in the concept of "acoustic processing" there are a lot of nuances. You can order a professional solution - for several million rubles, they will take measurements for you, and they will take the design, and they will do everything on a turnkey basis. Well, if you want to save money, there is no way to launch a full-fledged repair - read our article.Seven simple steps can dramatically improve the sound of your room without a hole in your wallet.
1. We buy a carpet
A large, thick carpet on the floor is the key to good bass quality, minimizing resonances and “thumping” of the low-frequency line. The ideal solution is a natural carpet with a thick, dense pile. If you are very afraid of dust, you can find lint-free carpets (there are such for relatively humane money, say, in IKEA). They give less dust, but they also affect the sound less radically.
2. We hang heavy curtains
The main source of resonances in an ordinary living room is windows. Even when using modern double-glazed windows, resonances from glass can sound quite painful to the ear. Get thicker, thicker curtains and use them to cover your windows while you're listening - you'll get a clearer midrange and better treble resolution.
3. Orienting the system along the long wall of the hall
Often households ask to install the complex along the short wall of the room - this saves space. But, and it affects the sound much worse - it's all about the length of the bass waves. With this setting, the bass wave has room to turn around and create a lot of unpleasant resonances. Install the system along the long wall of the hall - and get a much more accurate and textured bass.
4. Use bass traps
There is hardly a room that is devoid of bass modes without a full-fledged floating floor and a ten-centimeter sound absorber on the walls. The easiest way to get rid of them is to install vertical tubular bass traps in the corners of the hall - commercial models can cost over a thousand dollars, and to save money, you can use rolls of foamed synthetic rubber (at least a meter high). In order not to spoil the design, you can sew hall-style fabric covers for them.
5. A heavy sofa is the key to success
The sofa is not only the main ergonomic center of the listening room, but also can significantly improve the sound of your system. The heavier and more voluminous the model, the better, constructions filled with polyurethane foam (without springs) work great for improving sound quality. Actually, we published a separate article on sofas.
6
We pay attention to the rack for equipment and stands for speakers. Most Hi-Fi stands can be filled with sand or shot
Do not neglect this - this way you will significantly increase the mass of the system and reduce its resonances. Actually, approach the stands for shelf speakers in the same way, and you can put custom-made marble or granite slabs under the floor speakers. The connection will be even better.
Most Hi-Fi stands can be filled with sand or shot. Do not neglect this - this way you will significantly increase the mass of the system and reduce its resonances. Actually, approach the stands for shelf speakers in the same way, and you can put custom-made marble or granite slabs under the floor speakers. The connection will be even better.
7. Check and configure everything with Dirac Live software
To work with Dirac Live, you will need a PC and a miniDSP umik-1 USB microphone - but the game is worth the candle. You will be able to take measurements yourself at various points in the hall and identify possible problems with the frequency response. Then try to move the system, furniture - and improve performance. That's quite possible!
Denis Repin
October 14, 2019
