Use of Textile for noise absorption application is a cost effective method which does not required additional energy source and acts as passive medium.

1. By:
Virendra Kumar Saroj
2013TTE2764

2. Contents:
 Introduction
 Definition & measures
 Noise absorption by woven fabrics
 Sound absorbing curtains
 Noise absorption of tufted carpet
 Noise absorption behaviour of knitted spacer fabric
 Carbonized and activated nonwovens
 Pulp fibre-based sound absorbing materials (PSAMs)
 References

3. Introduction
 Sound is a sensation of acoustic waves
(disturbance/pressure fluctuations setup in a medium).
 Unpleasant, unwanted, disturbing sound is generally
treated as Noise and is a highly subjective feeling.
 Basically sound propagation is simply the molecular
transfer of motional energy.
 Workplace and environmental noise pollution pose a
significant threat to human comfort.
 A variety of ways are available to reduce noise and they
can be basically grouped by passive and active mediums

4.  Passive mediums reduce noise by disseminating energy
and turning it into heat, while active mediums need the
application of external energy in the noise reducing
process.
 In practical applications often textiles are employed as
sound absorbers, for example, textile interior parts of
automobiles or carpets in rooms that are used to absorb
sound energy.
 In these applications the absorbing material is mounted
directly onto an acoustical hard surface.
 The textile can then be regarded as a porous medium and
its sound absorption characteristic highly depends on its
thickness.

5. Definition & measures
 Noise reduction means to reduce the intensity of sound
either by converting the sound energy into heat energy
(Passive medium)or by application of an external energy
source (Active medium) which added exactly opposite
sound or vibration waves.
 Noise reduction ability of a medium is given by NAC
(Noise Absorbing Coefficient) or NRC (Noise Reduction
coefficient) or in terms of “Sound absorption efficiency”.
 The NAC or NRC is a scalar representation of the amount
of sound energy absorbed upon striking a particular
surface. NRC of 0 indicates perfect reflection and NRC of 1
indicates perfect absorption.

6.  ASTM C423 - 09a : Standard Test Method for Sound
Absorption and Sound Absorption Coefficients by the
Reverberation Room Method.
 In this method a band of random noise is used as a test
signal and turned on long enough (about the time for 20
dB decay in the test band with the smallest decay rate)
for the sound pressure level to reach a steady state.
When the signal is turned off, the sound pressure level
will decrease and the decay rate in each frequency band
may be determined by measuring the slope of a straight
line fitted to the sound pressure level of the average
decay curve.

7. The absorption of the room and its contents is calculated
from Sabine formula :
where:
A = sound absorption, m2
V = volume of reverberation room, m3 ,
c = speed of sound (calculated according to 11.13), m/s
d = decay rate, dB/s,

8. Noise absorption by woven fabrics
 For using woven fabrics as noise reduction application, it
is of prime importance to know the noise absorption
coefficients as a function of the intrinsic parameters
characterizing the fabric.
 The transmission loss of a sound wave of a given
frequency was predominantly dependent on the fabric
cover factor and less on its weight and thickness.
 The intrinsic parameters of the woven fabrics have a very
little effect on their noise absorption coefficients in the
low frequency domain (f< 500 Hz) but a significant impact
at the highest examined frequency (f= 4000 Hz).

9.  Since the shorter the wavelength of the impinging sound
wave, the higher the sensitivity to changes in the intrinsic
structure of the fabric.
 The air gap behind the fabric has a very significant effect
on the functional relations between NAC and the
frequency.
 If β defines the wavelength of the impinging sound wave,
then it is clearly observed that when the depth of this
gap, d, is approximately β/4 or 3β/4, there is maximum
sound absorption, whereas when d = β/2, it is a
minimum, as expected.

10.  Result shows that fabric density to be the major factor
determining sound absorption, even more than fabric
weight or thickness
 Sound absorption increased as fabric density increased to
a certain point, showing the highest value at about 0.14
g/cm3. After this point, sound absorption decreased.
 This is assumed to be because high-frequency sound was
absorbed more in dense fabric; in other words, in the
fibre itself, whereas low-frequency sound was absorbed
more in the air path or in the fabric’s pores.
 Thus it is recommended that fabrics be manufactured
with this density for high sound absorption.

12. Sound absorbing curtains
 A monolayer curtain of thin 100% porous cotton is found to be
of low sound absorption efficiency (%).
 However, on doubling these curtains leaving an air space
between the two layers, the absorption characteristics are
appreciably improved in spite of showing minima at certain
high frequencies.
 Results shows that a specific air space has to be determined to
give optimum effectiveness.
 The replacement of one of these two thin porous cotton layers
by a thin layer of non-porous cotton/polyester 35:65 is found
to be of reduced effect. This arrangement, beside being sound
absorbing, has the advantage of light insulation.

14. Noise absorption of tufted carpet
 Comparing the result between two fibre types, acrylic and
wool, acrylic fibres generally imparts better sound
absorption than wool.
 The difference (up to 10%) is more significant in the
higher frequency range (f >1000Hz) and in the closed loop
carpets with the thickest piles and highest densities.
 The average value of NRC (Noise Reduction Coefficient)
does not any trend with pile height; it may increase or
decrease or can have no apparent effect with increasing
pile height.

15.  For a given yarn count and pile height, increasing pile
density results in an increase in NRC regardless of fibre
type and construction.
 In all the samples when there is an air gap, NRC increases
several hundred percent in low and medium frequency
ranges (250 < f < 100).
 When the frequency of the sound wave increases, the
vibrating air molecules move more rapidly and energy
loss due to their friction with the piles is consequently
increases.

16. Noise absorption behaviour of knitted
spacer fabric
 The weft-knitted spacer fabric exhibits the typical sound
absorption behaviour of porous absorber .
 The warp-knitted spacer fabric exhibits the typical sound
absorption behaviour of micro perforated panel (MPP)
absorber.
 The noise absorption coefficient (NAC) increases with
increase of the frequency for both kinds of fabrics.
 The sound absorbability can be improved by laminating
different layers of fabrics.

17.  For the weft-knitted spacer fabric, the NACs significantly
increase from one layer to four layers and thereafter
more layers are no longer effective.
 However, for the warp knitted spacer fabric, the NACs can
continuously be improved with increase of the fabric
layers, but with a shift of the resonance region towards
the lower frequency side.
 The combinations of weft-knitted and warp-knitted
spacer fabrics can significantly improve their sound
absorbability, but their arrangement sequence has an
obvious effect.

18.  At higher frequencies, the NACs of the warp-knitted
spacer fabrics backed with weft knitted fabrics are much
higher than those of the weft-knitted spacer fabrics
backed with warp-knitted fabrics.
 However, at lower frequencies, the NACs of the warp-
knitted spacer fabrics backed with weft knitted fabrics are
much lower than those of the warp-knitted spacer fabrics
backed with weft-knitted fabrics.
 The air-back cavity can be replaced by multilayered warp-
knitted spacer fabrics to achieve high NACs at low and
middle frequencies.

19. Yarn path notation weft knitted spacer fabric

20. Fig: NACs of single layer spacer fabrics without air back cavity, A=weft knitted
B=warp knitted

21. Fig: NACs of weft knitted spacer fabrics laminated with different layers

22. Fig: NACs of warp knitted fabrics laminated with different layers

23. Carbonized and activated nonwovens
 Carbonization and activation is a thermochemical
approach for producing active carbon products.
 Activated carbon materials feature exceptional adsorptive
capacity and kinetics, because of their very high specific
surface area up to 2500 m2/g and a high micropore
volume up to 1.6 ml/g.
 Activated carbon materials are ideal for use as high-
performance absorbents.
 Textile materials in the form of fibres, yarns, and fabrics
can be converted into active carbon products by the
process of pyrolysis and activation.

24.  The use of fibres and fabrics as raw materials for making
activated carbon products has tremendous advantages.
 First, activated carbon fiber has significantly different
microporous structure that allows much more rapid
dynamic adsorption and desorption with less material.
 Second, a wide range of fiber polymers can be used for
producing activated carbon products, including celluloses,
thermosets, and thermoplastics.
 Acoustic nonwoven structure consists of a base layer and
a surface layer.

25.  Based on six non-woven composites with two surface
layers (ACF and glass fiber) and three base layers (cotton,
ramie, and PP) it was evaluated that the non woven
composites with ACF as a surface layer had significantly
higher sound absorption coefficients than the glass-fiber-
surfaced composites in both the low-frequency range
(100–1600 Hz) and high-frequency range (1600–6400 Hz).

26. Fig: Absorption coefficient of PP-based composites

27. Fig: Absorption coefficient of cotton-based composites

28. Fig: Absorption coefficient of Ramie-based composites

29. Fig: Absorption coefficient of ACF surfaced composites

30. Fig: Absorption coefficient of Glass fibre surfaced composites

31. Pulp fibre-based sound absorbing materials
(PSAMs)
 It has been seen that decreases in important fibre
characteristics (e.g., fibre length, width) after the beating
process caused a significant increase in the sound-
absorbing properties of the PSAMs.
 Scanning electron microscopy indicated that after the
beating treatment, many new microfibrils detached from
the cell walls and were reconstructed into new
nanopores, which led to a decrease of the pore radius
and an increase of the pore volume.
 These new nanopores served as new channels for sound
wave movement and contributed to the increased
consumption of sound energy.

32. Fig: Effects of beating degrees on the average sound-absorption coefficients and the
thicknesses of the PSAMs. Note that pore structures consist of pore a (pores between
fibres), pore b (pores within fibres’), and pore c (pores between microfibrils).

33. Fig: Dependence of the raw pulp fiber-based PSAMs’ thickness on the basis
weight, and the corresponding average sound-absorption coefficients.

34. Fig: Different sound-absorption coefficient curves for various
samples’ thicknesses.

35. Fig: Comparison of the sound-adsorption coefficients of different sound-absorbing materials with
different ratios of pulp fibres (P)/alumina silicate fibres (A)/glass fibres (G): bottom panel: P/A/G
100:0:0; middle panel: P/A/G 50:50:0; and top panel: P/A/G 50:0:50.

36. References
 1. Sound Absorption Behavior of Knitted Spacer Fabrics ,Yanping Liu, Hong
Hu1 Institute of Textiles and Clothing, The Hong Kong Polytechnic
University, Hung Hom, Kowloon, Hong Kong,China TRJ
 2. Noise Absorption by Woven Fabrics, Y. Shoshani, G. Rosenhouse ,Applied
Acoustics 0003-682X/90/$03-50 O 1990 Elsevier Science Publishers Ltd,
England
 3. Sound Absorption Coefficients of Micro-fiber Fabrics by Reverberation
Room Method, Youngjoo Na1,Jeff Lancaster and John Casali,Gilsoo Cho ,TRJ
 4. Sound Absorbing Double Curtains from Local Textile Materials ,Y. I.
Hanna & M. M. Kandil* National Institute for Standards, Shama al-Tahrir,
Dokki, Cairo, Egypt
 5. Effect of Pile Parameters on the Noise Absorption Capacity of Tufted
Carpets, Y.Z. Shoshani and M.A. Wilding, Textile Research Journal 1991 61:
736
 6. The effect of physical parameters on sound absorption properties of
natural fiber mixed nonwoven composites,Merve Ku¨ c¸u¨k1 and Yasemin
Korkmaz2, TRJ

37.  7. Multi-fiber needle-punchednonwoven composites: Effects of heat
treatment on sound absorption performance,Nazire Deniz Yilmaz1, Nancy
B Powell2, Pamela Banks-Lee2 and Stephen Michielsen2, TRJ -2012
 8. Carbonized and Activated Non-wovens as High Performance Acoustic
Materials: Part I Noise Absorption ,Y. Chen1 and N. Jiang ,School of Human
Ecology, Louisiana State University Agricultural Center, Baton Rouge, LA
70803, U.S.A. TRJ
 9. Preparation and design of green sound-absorbing materials via pulp
fibrous models,Detao Liu, Kunfeng Xia, Wenxiong Chen, Rendang Yang
and,Bin Wang, Journal of Composite Materials 46(4) 399–407) 2011