INDUSTRIAL NOISE
Objective: То measure the parameters of noise, to evaluate the effectiveness of
measures for its reduction.
ТЬе concept of а sound generally associated with auditory sensations of а person
with normal hearing. Hearing sensations are caused Ьу the vibrations of an elastic
medium, which are mechanical vibrations that propagate in а gaseous, liquid or
solid medium, and the action оп the human hearing. In this case, f1uctuations in the
environment are perceived as sound only in certain frequency range (16 Hz-20
kНz) and sound pressures above the threshold of human hearing. Purity of the
medium f1uctuations, which lie above and below the range of hearing, called the
inftasonic and ultrasonic. ТЬеу have по relationship to auditory sensations are
perceived as human and physical impact of the medium.
Parameters of the sound wave.
Acoustic oscillations of particles of an elastic medium are complex and сапЬе
represented as а function of time. ТЬе simplest process is described Ьуазпшзок]:
А= агпэпкот,
Where ат - агпрйшое, т; О) = 21[/ - angular frequency, rad I s; /-ftequency, Hz.
Harmonic oscillations with an amplitude and frequency of F ат called а tone.
Depending оп the method used to excite vibrations аге distinguished:
plane sound waves created Ьуа plane vibrating surface;
cylindrical sound wave created Ьуа radially oscillating lateral surface of the
суйпоег;
spherical sound waves created Ьуа point source of oscillations of а pulsating
sphere.
ТЬе main parameters that characterize the sound wave are:
Parameter Symbol Unit
Sound pressure SPL РА
Sound intensity 1 W 1т2
Sound wavelength L m
Wave velocity u m I s
Oscillation frequency f Hz
р
SPL = 20 19 20 П
J.1' аdB
From а physical point of view of the spread of the oscillations is the momentum
transfer of motion from one molecule to another. Momentum transfer requires а
certain amount of time, resulting in the movement of molecules in the observation
point is а delay with respect to the movement of molecules in the excitation of
oscillations. Thus, the fluctuations are distributed at а certain speed. Velocity of
propagation of sound waves - it is а physical property of the medium.
Sound vibrations in the air leads to its compression and expansion. In areas of
compression the air pressure increases and decreases in the areas of rarefaction.
The difference between the pressure existing in the disturbed environment at the
moment, and the atmospheric pressure, called sound pressure.
Table. 1. The specific acoustic impedance of various media
Substance / t ос / Specific resistance, kg / Density,, / I (М2С) / kgjm3
Hydrogen / О / 114 / 0,09
Air / 20 / 414 / 1,2
Oxygen / О / 455 / 1,43
Rubber / 20 / 600 / 950
ТиЬе / 20 / 1 ,2х1 05 / 250
Alcohol / 12,5 / 1 ,Ох1 06 / 810
Water / 13 / 1,4х106 / 1000
El / 20 / 2,4х106 / 510
Oak / 20 / 2,9х106 / 720
Aluminum / 20 / 1,4х10/ / 2700
Copper / 20 / 3,1х107 / 8900
А sound wave is асагпетof energy in the direction of its motion. The amount of
energy carried Ьу sound waves per second through а cross-section area 1 т2,
perpendicular to the direction of motion, called the intensity of sound. The
intensity of sound is determined Ьу the ratio of sound motion to the acoustic
impedance environment, W 1т2.
ТЬе ongoing work
1. Measurement of noise level in the absence of sound-insulating walls.
Laboratory stand connected to the mains. With the switch tums the light inside the
booth as well.
Ifnecessary, removed from the layout tools soundproofing. Microphone that сате
with the measurement of noise and vibration are mounted опа stand in the right
chamber layout.
Then connects the generator to the stand of low- frequency signals. Оп the
generator set tone frequency 63 нz with ап amplitude of О - 0.5, and installing
other values of the frequency of the signal amplitude must Ье constant.
Next, measure the sound pressure level Ьу measuring the noise.
Then the measurement is repeated at а frequency ofsignal 0.125, 0.25, 0.5,1,2,4
and 8 kНz. Results are entered in the third line of ТаЬ. 2. Then filled the second
row - the normalized values of sound pressure levels. Comparing the measured
values with the normative, the conclusion оп the admissibility of the sound
pressure level in the layout design bureau.
ТаЫе. 2. Summary table ofmeasurements
63 / 125 / 250 / 500 / 1 / 2 / 4 / 8Bulkhead type / Hz / Hz / Hz / Hz / kHz / kHz / kHz / kHz
Normalized values, / 95 / 87 / 82 / 78 / 75 / 73 / 71 / 69
dB
None / 85 / 84 / 77 / 76 / 38 / 38 / 22 / 21
Fibreboard / 84 / 84 / 57 / 54 / 47 / 34 / 21 / 20
Particleboard / 84 / 83 / 54 / 53 / 52 / 23 / 21 / 20
After the job generator and measuring noise and vibration аге disabled. Toggle
light cameras tumed off, then stand off from the mains.
2.Measurement of noise when using soundproof partitions.
Similarly, the method described аооуе, measure the sound pressure levels using
sound-insulating walls made of different materials (the number ofpartitions
specified in the teacher). The measurement results аге recorded in ТаЫе 2.
After the job generator and measuring noise and vibration off. Toggle light
cameras tumed off, then stand off from the mains.
3.Calculation performance soundproof partitions.
То calculate the effectiveness of insulation is used the formula
L-L
Э =' ',]
, L
,
where Е, - the sound pressure level measured for the i-th octave frequency bands to
use soundproofing L"'J - sound pressure level measured for the same frequency
band Ьу using sound-insulating walls.
The result of calculations (%) for аН the funds агс recorded in ТаЫе
soundproofing. 3.
Hz / Hz / Hz / kHz / kHz
Fibreboard / 1,176 / О / 26 / 29 / -236 / 10,5 / 4,5 / 4,76
,
Particleboard / 1,13 / 1,19 / 29,9 / 30,26 / -368 / 39,47 / 4,5 / 4,76
,
...--..--J
Conclusion: During laboratory work have Ьееп measured noise parameters in
various acoustic conditions. We found that the use of sound-absorbing barriers
MDF increases the efficiency of protection against noise in comparison with the
fencing of the CPD