Façade sound insulation

The DPCM 5.12.97 prescribes that façade sound insulation performances should be measured on site in conformity with norm UNI 107008-2 by measuring the standardized façade sound insulation D_2m,nT defined by:

(1)

The measurements of levels L_i must be carried out "n" times for each 1/3 octave band; n is the number immediately higher to the environment's volume tenth. In any case its limit value is 5.

T = receiving environment reverberation time.

Fig.5

Another façade sound insulation index used is R¢ defined by the relation

(2)

L₁" is the front sound pressure level of the tested wall without its reflecting effects (measured in open field away from the building or provided by the speaker manufacturer)

L₂ is the receiving environment average sound pressure level, assessed from the levels measured in the environment itself using the formula (2)

A = receiving room equivalent absorption area

S = façade surface

¢ = speaker angle

Comparison with other European Countries shows that the parameters used are different. For example, Germany and Austria use the resultant soundproofing power R’_res to specify the limit value of the façade sound performance obtained from the soundproofing power weighted average of the various façade components. R’_res can be compared with D_2m,nT except for correction terms that consider external environment dimensions, façade form and lateral sound transmission. Denmark and Sweden only enforce limit values for the internal sound level. France uses a parameter similar to the Italian one. Italian regulations do not set territory acoustic ranges. For example, the same values must be observed by a school inside a park or near a train station.

To obtain the façade insulation evaluation index D_2m,nT,w the different façade elements soundproofing power need to be known; the calculation procedures to obtain the sound insulation of the different structures are contained in norm UNI 8270 special project.

Table C

Limit values for residential buildings defined according to different European Countries regulation documents with reference to the quantities in column 2.

Requirements to perform the measurement according to ISO 140-5

To perform the measurements in conformity with norm ISO 140-5 a series of conditions are necessary, such as: sound source type, microphones type and position, room dimensions.

The most important are listed here:

• The source spectrum must be flat with a maximum difference of 6dB between bands.

• The signal power must ensure that each spectrum band signal is at least 10dB greater than background noise in the receiving room.

  If the signal and background noise difference is between 3dB and 9dB, a correction given by the following table needs to be inserted

The measurement cannot be performed for differences below 3dB

• The procedure prescribes a series of measurements of the background noise spectrum and of the spectrum with the source on, in a certain number of positions (minimum 5), in relation to source and receiving room dimension and form.

• The minimum microphone position distances must be observed:

  0.7 m between the various microphone positions.

  0.7 m between each microphone and room surfaces.

  1 m between each microphone and tested element.

• The measurement must be carried out using 1/3 octave band filters with central frequency

100 - 125 - 160 - 200 - 250 - 315 - 400 - 500 - 630 - 800 - 1000 - 1250 - 1600 - 2000 - 2500 - 3150 (Hz)

or with octave band filters with central frequency from 125Hz to 2000Hz.

• For the spectrum measurements, set an integration time on the instrument that generally should not be less than 6s.

• From these measurements a signal and background noise average spectrum is obtained for the receiving room from which L₂ can be obtained and used in (1) and (2).

• For the receiving room reverberation time T2 calculation to be used in (2), a series of measurements (minimum 6) in various positions need to be taken in order to obtain the average reverberation time later used in the formula.

For a complete knowledge of the measurement requirements and procedure, please see the norm ISO 140-5.

Classification of dwelling unit environments

The Framework Act 447 prescribes the issue of several decrees and assigns the compilation of the necessary technical regulations to the UNI. The UNI got these norms from CEN who got them from ISO: consequently, the rules are mainly the same in all Countries applying them.

Particularly interesting are norms UNI EN 20140, UNI EN ISO 140 and DPCM 5.12.97 that identify the different types of buildings and establish, for each type, the passive acoustic requirements. There are some remarks concerning the decree: the levels for each category are set independently of the area in which the building is located. Consequently, the same specification can be too strict in some cases but insufficient in other ones. Furthermore, the prescribed insulation levels for some buildings are much less severe than those prescribed for plants. Finally, the application scope was not clarified and therefore could also be extended to already existing buildings.

Table A - Classification of dwelling unit environments

Table B - Passive acoustic requirements for buildings, their components and technological plants

(*) Values of R_w referred to separation elements between two distinct houses.