Sound reduction index

At very low frequencies the movement of the panel will be controlled by the stiffness, as inertia is a dynamic force and cannot come into effect until the panel has measurable velocity. Stiffness controls the performance of the panel at low frequencies until resonance occurs. As the driving frequency increases, the resonance zone is passed and we enter the mass-controlled area. The increase in the sound-reduction index with frequency is approximately linear at this point, and can be represented by Figure 42.8. 

SRI sound reduction index RW weighted sound reduction STC sound transmission classification... 

The sound reduction, attenuation or insertion loss is defined as the difference in sound pressure level or sound power level before and after the enclosure (or any other form of noise control) is installed. The performance of the enclosure will be largely dependent on the sound reduction index (SRI) of the outer wall , assuming approximately 50% of the internal surface is covered with mineral wool or other absorption materials °. Typical values of sound reduction index for materials used for enclosures are shown in Table 20.3. Absorption coefficients are shown in Table 20.4. 

Sound reduction index (transmission loss) A logarithmic criterion for the sound insulation of a partition-... 

A mean sound reduction index is often indicated which (for sound incidence from all directions) is obtained as the arithmetical mean in the practical range of 100 to 3200 Hz adopted in architectural acoustics. As a rule, it corresponds to insulation at a frequency of 500 Hz. According to DIN 52210, Sheet 4, the adjusted value R should preferably by used as a single-figure rating to indicate the sound reduction. For "single-leaf" partitions, approximately Rw = Rm - 2. 

Walls which, for whatever reason, do not present a fully closed surface often have sound reduction indexes of less than 30dB (see VDI2571). 

Table 14 Average sound reduction indexes for wall and floor construction materials...

Table 15 Average sound reduction indexes for doors and windows...

Testing of panels. The traditional procediuie for measuring the transmission loss, or sound reduction index, of building components is described in the series of... 

FIG. A-13 Comparison of the pressure and intensity methods for measuring the sound reduction index of panels. (Source Altair Filters International Limited.)... 

Sound is generated in the left hand room and the sound pressure levels in the two rooms are measured. Assuming that the sotmd energy in the rig t hand room comes through the panel then the sound reduction index (SRI) of the panel is given by ... 

For these reasons one can dispense with the second reverberation room altogether. The sound reduction index is then given by ... 

If the panel contains a weak area, such as a window, the sound reduction index of the window can be assessed separately. But this will only work if the panel is a greater sound insulator than the window. 

FIG. A-16 Sound reduction Index for a typical flat, unlined panel. (Source Altair Hlters International Limited.)... 

When a sound wave is incident on a wall or partition, some of the sound energy is transmitted through the wall. The fraction of incident energy that is transmitted is called the transmission coefficient. The accepted index of sound transmission is the sound reduction index, which is sometimes called the transmission loss. This is related to the transmission coefficient by the equation ... 

Material Measured or Predicted Sound Reduction Index, dB ... 

FIG. A-24 Predicted and measured sound reduction index o1 panei 1. (Source Aitair Fiiters intemationai Limited.)... 

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