Sound reduction index table
Table shows sound reduction indexes (SRI) for common materials.

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# External walls#

 Material Area related weight [kg/m2] SRI [dB] RA2 [dB] full ceramic brick (25 cm) 450 53 48 ceramic block Mega-Max P+W (24 cm) 190 45 42 ceramic block Mega-Max P+W (24 cm) + mineral wool (10 cm) + air gap (3 cm) + clinker brick (12 cm) 190 71 64 ceramic block Mega-Max P+W (24 cm) + polystyrene (15 cm) + thin-layer plaster 190 43 40 ceramic block MAX (19 cm) 180 46 43 ceramic block MAX (19 cm) + mineral wool (15 cm) + thin-layer plaster 180 44 40 ceramic block AKU (25 cm) 466 60 53 cellular concrete, variety 700 (24 cm) 160 46 43 expanded clay concrete block (24 cm) 244 48 45 silicate block (25 cm) 467 60 55

# Internal walls#

 Material Area related weight [kg/m2] RA1 [dB] brick full (12 cm) 215 47 perforated brick (6 cm) 90 38 ceramic block (11 cm) 120 42 silicate block (8 cm) 110 43 silicate block (12 cm) 170 45 full silicate block (18 cm) 300 55 aerated concrete, variety 600 (12 cm) 70 34 plasterboard wall single-layer sheathing (7 cm) 26 36 plasterboard wall, double-layer cover (10 cm) 50 43

# Glasing#

 Material SRI for glass [dB] SRI for window [dB] glazing 4-16-4 31 35 glazing 8-16-4 37 39 glazing 6-12-8 38 40 glazing 9-16-10 (special) 45 44 glazing 13-16-9 (special, glued) 48 46

# Sound insulation#

• When a sound wave moves through the air meets a barrier in the form of a wall, part of the acoustic energy is reflected, part is absorbed inside the wall (converted to heat), and the another part is transmited out (on the other side of the wall). We can write it mathematically as follows:
$\alpha + \beta + \tau = 1$
where:
• $\alpha$ - absorption coefficient (determines the part of the energy that was absorbed inside the wall),
• $\beta$ - reflection coefficient (defines the part of the energy remaining in the first room),
• $\tau$ - transmission coefficient (defines the part of the energy that was emitted to the second room).
• The transmission coefficient can be used as a measure of the acoustic insulation, because it determines the sound intensity ratio on both sides of the wall:
$\tau = \frac{I_t}{I_0}$
where:
• $I_t$ - intensity of the wave on the other side of the wall (sound intensity level audible in the second room),
• $I_0$ - incident wave intensity (sound intensity level audible in the first room).
• In practice, the transmission factor is most often given in the logarithmic scale. In this way, we obtain a decrease in sound intensity given in decibels, so-called transmission loss:
$\Delta TL = -10 ~ log (\tau) = 10 ~ log \left(\frac{1}{\tau}\right)$

# Sound insulation ratings#

• Sound insulation depends, among other, on the frequency of the acoustic wave. This means that the complete information on the insulation properties of a given material should contain serie of numbers for different frequencies.
• The weighted sound reduction index determines the partition insulation in relation to the model curve. By applying a predefined formula to the curve measured, we can simplify it to the single number.
• Both Rw and STC describe the insulation against typical air noise.
• The method of measuring the Rw coefficient is defined by the ISO 10140-1: 2016 standard.
• The method of measuring the sound transmission class (STC) is defined by the ASTM E413-87 standard.
• Ther Rw is more common in Europe, when STC is more common in USA.
• To reflect the fact that insulation is different at different frequencies the ISO standard defines two additional coefficients with different frequency curve:
• RA1 - more sensitive in the range of medium and high frequencies, better reflects the insulation in the case of noise sources such as:
• conversation, music, radio, TV,
• children's fun,
• rail traffic with medium and high speed,
• traffic on a fast road> 80 km/h,
• jets at close range,
• industrial plants emitting mainly medium and high frequency noise,
• etc.
• RA2 - more sensitive in the range of low and high frequencies, better reflects the insulation in case of noise sources such as:
• city traffic,
• rail traffic at low speeds,
• helicopters,
• long-range jets,
• disco music,
• industrial plants emitting mainly low and / or high frequency noise,
• etc.

If you're interested in calculators related to acoustics, check out our other calculators:
• Sound intensity level (dB) - if you want to learn what is decibel and how the sound intensity level is measured,
• Sound velocity in materials - if you want to learn how the type of substance affects the speed of acoustic wave propagation,
• Acoustic impedance of substances - if you want to learn what is acoustic impedance and how it depends on the type of substance,
• Sound wave reflection - if you want to find out how an acoustic wave behaves when it encounters an obstacle in the form of media boundary,
• Mass law: single wall - if you're interested in building acoustics and would like to estimate the acoustic insulation of a single wall,
• Mass law: double wall - if you're interested in building acoustics and would like to estimate the acoustic insulation of a double wall with an air gap between the walls,
• Sound absorption coefficients - if you're interested in acoustic adaptation of room and you would like to learn how different materials absorb the acoustic wave,
• Noise propagation - if you want to learn how sound intensity level changes with distance from the source,
• Sound insulation countours - if you want to learn more about acoustic insulation assessment standards used over the world,
• Sound reduction index (SRI) - if you're searching for acoustic insulation of popular building materials expressed in the coefficient Rw,
• Sound transmission class (STC) - if you're searching for acoustic insulation of popular building materials expressed by the index STC.

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