To compare sound insulation properties you need to take into account the area of the dividing partition/wall, as well as the volume and sound absorption properties of the receiving room. To do this, measurements are Normalized to a Reference Absorption value or Standardized Reverberation Time.

A single number to present the results and compare products would be useful, this is where the Weighted term comes in.

See also : Sound Insulation Test Equipment.

where :

D = level difference

S = area of the test specimen (m

A = equivalent sound absorption area of the receiving room

See also : Sound Reduction Index

**C and Ctr** Spectrum Adaption Terms

At a certain frequency and angle of incidence, the bending oscillation of the partition will be amplified and the acoustic energy will be transmitted through the partition almost without attenuation.

**D : Level Difference
Dn : Normalized Level Difference
DnT : Standardized Level Difference
DnT,w : Weighted Standardized Level Difference
DnT,w + Ctr : Weighted Standardized Level Difference with Spectrum Adaption Term Ctr
Dw** : Weighted Level Difference

L1 = average Sound Pressure Level in the source room

L2 = average Sound Pressure Level in the receiving room

**Ln** : Normalized Impact Sound Pressure Level laboratory measurement.

**L'n** : Normalized Impact Sound Pressure Level field measurement.

**LnT** : Standardized Impact Sound Pressure Level laboratory measurement.

**L'nT** : Standardized Impact Sound Pressure Level field measurement.

**Ln,w** : Weighted Normalized Impact Sound Pressure Level laboratory measurement.

**LnT,w** : Weighted Standardized Impact Sound Pressure Level based on laboratory measurement of LnT.

**L'nT,w** : Weighted Standardized Impact Sound Pressure Level based on field measurement of L'nT.

where :

A = measured equivalent sound absorption area in the receiving room

Ao = reference absorption area.

D = level difference in dB

A = Equivalent Sound Absorption area of the receiving room in square metres

Ao = Reference Absorption area in square metres (10 m²)

**R** : Sound Reduction Index laboratory measurement.

**R'** : Apparent Sound Reduction Index field measurement.

**Rw** : Weighted Sound Reduction Index laboratory measurement.

**R'w** : Weighted Apparent Sound Reduction Index field measurement.

L1 : average sound pressure level in the source room

L2 : average sound pressure level in the receiving room

S : area of the test specimen (m

A : equivalent sound absorption area of the receiving room

See also : Apparent Sound Reduction Index

See also the IEC Definition of Transmission Loss

Ctr : A-weighted urban traffic noise spectrum.

Ctr can also be added to DnT,w or Rw to take into account low frequency noise

where :

T = measured reverberation time in seconds

To for dwellings = 0.5 seconds.

D = level difference

T = reverberation time in the receiving room

To = reference Reverberation Time, 0.5 seconds for dwellings.

**Transmission Loss : TL** a generic term widely used when discussing sound insulation.

● Note : not be confused with the IEC definition of Transmission Loss

There is no flanking (indirect) transmission loss, so only the element under test needs to be considered.

Definitions Specific to Sound Insulation Measurements

Ao is the equivalent absorption area in square metres

V is the volume of the receiving room in cubic metres.

** 32 dB is often quoted as the unfavourable deviation. This is the total deviation across the 16 one-third octave bands ... 32/16 = 2.0 dB average deviation