A treading noise over a floor or stairs is often more audible in other rooms than in the room where the sound was produced because the vibrations produced on the building structures are solid-borne propagated to the whole building without any damping. The system to reduce treading noise consists of installing floating floors to avoid acoustic bridges or more simply by laying carpets. Treading noise level is measured in laboratory and on site. When it is necessary to determine the soundproofing properties of a ceiling, a standardized impact-noise machine is used: this machine is composed of five 0.5-Kg hammers in line dropping 40 mm with a rhythm of 10 hits per second. The average sound pressure level is measured in the floor below, filtered by 1/3 octave bands.
On site measurements: The norm UNI EN ISO 140-7 defines the standardized impact-sound pressure level L’n with lateral transmissions as
| (1) | |
A2 = receiving room equivalent absorption area
and defines also the standardized impact-sound pressure level L’nT as
(2) |
 |
T2 = receiving room reverberation time
To determine the evaluation index Ln,w, independently of the frequency, the norm UNI 8270 is applied.
The standardized curve of ISO 717-2, the frequencies of which range from 100Hz to 3150Hz in thirds of octave intervals, is used. The curve must be translated upward until the sum of positive differences between the experimental curve and the ISO curve is less than 2 (with third of octave frequencies).
Ln,w is given by the value of the reference curve at 500Hz.
Algebraically:
(3) |
 |
N = number of values,
n = number of points when the standardized curve is above the experimental.
To obtain the index, n must diminish unit by unit, that is to say, translate the standardized curve downward until the inequality is verified.
To perform a measurement in conformity with norm ISO 140-7 a series of conditions are necessary, such as: sound source type, microphones type and position, room dimensions.
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
Signal and background noise difference |
Correction factor (to be subtracted) |
3dB |
3dB |
between 4 and 5dB |
2 dB |
between 6 and 9dB |
1 dB |
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 receiving room dimension and form.
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.
From these measurements a signal and background noise average spectrum is obtained for source and receiving room from which L2 can be obtained and used in (1).
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 140-7.
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.
| Category A: residential occupancy or similar buildings; |
| Category B: office occupancy or similar buildings; |
| Category C: hotel, boarding house occupancy and similar buildings; |
| Category D: hospital, clinic, nursing home occupancy and similar buildings; |
| Category E: all schooling levels occupancy and similar buildings; |
| Category F: recreational or worship activities occupancy or similar buildings; |
| Category G: commercial occupancy or similar buildings; |
Table A - Classification of dwelling unit environments
| Categories of Tab. A |
Parameters |
||||
| Rw (*) |
D2m,nT,w |
Ln,w |
LASmax |
LAeq |
|
| 1. D |
55 |
45 |
58 |
35 |
25 |
| 2. A, C |
50 |
40 |
63 |
35 |
35 |
| 3. E |
50 |
48 |
58 |
35 |
25 |
| 4. B, F, G |
50 |
42 |
55 |
35 |
35 |
Table B - Passive acoustic requirements for buildings, their components and technological plants
(*) Values of Rw referred to separation elements between two distinct houses.