SOUND INSULATION
Sound insulation is a paramount aspect in the construction of residential units, particularly to reduce disturbance caused by external noises or sounds transmitted between flats. The development of effective vertical and horizontal partitions, which minimise the passage of unwanted noise through the air, is crucial for the building industry, particularly in ensuring tranquillity and privacy within each home. Understanding the experimental data on acoustic sound insulation or, more precisely, the soundproofing power of these partitions is essential from the design stage.
This is done check their suitability both with respect to the type of living space to be built (dwelling, hotel, hospital, school, office, shop, etc.), and with respect to the acoustic characteristics of the urban destination of the area in which the building is to be constructed (urban residential, industrial, etc.).
ISO Standards for Sound Insulation
Meeting The Challenges of Sound Insulation Testing
In building acoustics, particularly in sound insulation and footfall noise insulation measurements, there are several methodological issues and measurement uncertainties in the results obtained. For soundproofing power measurement, reproducibility is an important issue. This is the comparability, with relative uncertainty, of the results of measurements carried out on the same sample, according to the procedure indicated by the ISO 10140-3 standard, in different laboratories. A comparison carried out a few years ago, among 24 European laboratories, including three Italian ones, turned out to be rather worrying in this respect due to the too low reproducibility found, which was well below the standard’s requirements.
Many hypotheses are made as to the causes of these differences, which are not found in the repeatability, since the results of measurements on the same panel, carried out in the same laboratory, with the same measuring chain, by the same operator and at a short distance from each other, were found to be affected by a standard deviation that is fully compatible with the indications of the standard.
One of the most investigated factors was the perimeter frame of the test opening between the two reverberation chambers, i.e. the type of finish of the opinion to which the test panels are anchored.
The ISO EN UNI 10140-3 standard does not specify the frame characteristics, leading to variability in the frame materials used between laboratories. However, our analysis of the results of the mentioned interlaboratory comparison shows that reproducibility values improve significantly when the comparison is limited to laboratories, the majority of which are equipped with cement frames.
In addition, ensuring proper assembly of the samples is crucial to avoid direct sound passages and maintain the measured soundproofing power, especially at higher frequencies.
At XEFRA Laboratory, we specialise in sound insulation measurements according to ISO EN UNI 10140-3 standards. Our facility consists of two adjacent semi-reverberation chambers with a common wall containing the test opening. This setup is designed to minimise lateral sound transmission and ensure that sound energy passes primarily through the test opening.
The heavy wall structures in the chambers provide substantial insulation against external noise, resulting in a low background noise environment, particularly in the receiving environment. The volume and dimensions of the test opening, which, for example, may not be less than 10 m2 , must comply with the requirements laid down in the general standard ISO EN UNI 10140-1. As far as measurement accuracy is concerned, the reference standard is ISO EN UNI 10140-2, where the guidelines for determining the repeatability and reproducibility values obtainable with this procedure are given.
The measurement principle for soundproofing power is simple in concept but complex in practice. Once the sample partition under test has been installed in the appropriate opening, a sound signal with a constant sound pressure level in the frequency range between 63 Hz and 5 kHz is produced in the chamber known as the transmitting chamber by means of an omnidirectional source fed with white noise. This signal is picked up in both chambers by two microphone stations, each consisting of a microphone placed on a rotating rod. The two microphones are connected to a two-channel real-time digital spectrum analyser, by means of which the spectral distribution of the signals existing in the two rooms is determined, in addition to the sound pressure levels.
The measurement process involves recording the average sound pressure levels in both chambers across 1/3 octave frequency bands from 100 Hz to 4 kHz. This is repeated for three different sound source positions in the transmitting chamber, selected based on a specific acoustic qualification procedure outlined by the standard.
Acoustic Measurement and Insulation Testing in XEFRA’s Reverberation Chambers
In our acoustic reverberation chamber, a meticulous approach is taken to determine the existence of any sound leaks due to faulty assembly of the sample. This includes a phonometric check of the edges of the structure and any joints before each measurement. By overcoming these challenges, we ensure the integrity and accuracy of our sound insulation measurements, in accordance with the strict standards set by ISO.