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The room requires intervention related to environmental acoustic correction because given its size it presents an acoustically uncomfortable environment and unsuitable for conversations for long periods, presentations, theatrical performances or conferences.
In an acoustically non-optimal environment, the presence of people will create an absorption coefficient, but at the same time the noise will be amplified leading to discomfort, often at an unconscious level, and to a consequent general negative judgment.
This is why there was a need to insert sound-absorbing material with hanging islands and ceiling paintings, partly with fabric covering, to optimize the acoustic impact and make the multipurpose hall a comfortable environment also from an acoustic point of view.
In any closed environment, the sound that is heard is the result of a combination of sound waves that reach the listener directly and sound waves that arrive reflected, or that propagate from the source until they affect the various rigid surfaces that delimit the environment from where they are reflected, often several times, before reaching the listener. The quantity that describes this acoustic characteristic of closed environments, often erroneously referred to as “echo”, is the reverberation time (TR), i.e. the time during which a certain amount of sound energy continues to persist inside a closed environment after the beep has stopped. The longer this time is, the greater the contribution of the reflected sound compared to the direct one. For example, if a sound source ceases to radiate in a room, the sound level decreases the more slowly the lower the sound absorption of the walls.
Reverberation has negative aspects, such as the risk of masking speech syllables or musical phrasing, and positive aspects, such as reinforcing the intensity of the source; however, the latter aspect can become a negative aspect in potentially noisy environments such as canteens, corridors, and gyms, as the internal reverberation contributes decisively to increasing the sound intensity, leading to excessively noisy environments. The elements present inside a closed environment (walls, furnishings, people, etc.) condition the acoustic propagation, since they absorb the sound energy that affects them to varying degrees. These phenomena can alter and deteriorate the quality of the sound perceived by the receiver, causing, for example, the degradation of verbal communication or listening to music.
To define the acoustic quality of a room, the quantity called “reverberation time” has been identified, which indicates the time, in seconds, necessary for the sound level to decrease by a certain amount in a point of a closed room compared to that which occurs when a sound source is interrupted. As a rule, the reverberation time T60 is used, i.e. the time interval in which the sound energy decreases by 60 dB after the source is switched off. In an environment having spatial dimensions fairly close to each other, the value of T60 can be calculated according to Sabine’s formula.
T=0.161V/A (s)
where V is the room volume in m3 and A is the total absorption equivalent area in m2. The value of A is obtained with the following relationship:
A = Σ αi Si (m2)
where αi is the i-th absorption coefficient and Si is the i-th surface area of the elements present in the environment. Acoustic absorption represents the ability of a material to convert the energy of an incident sound wave into a form of energy other than acoustic energy (usually into heat).
The determination of the reverberation time of an environment is therefore fundamental in order to be able to judge its acoustic characteristics and decide whether to intervene on the structures that delimit it, increasing its sound absorption capacity. It is necessary to intervene if the value of the reverberation time T60 is not at least close to the optimal value, obtained on the basis of table values in the literature or from sector standards.
By way of example, the diagram below shows the optimal values of the reverberation times as a function of the volume of the room and its intended use, taken from the literature on the subject.
However, the phenomenon of reverberation has both positive and negative aspects. In fact, if a certain value of the reverberation time helps to reinforce the direct sound and therefore to improve listening, on the other hand, an excessive value of the sound tail compromises its quality, making the sound muddy. Obtaining optimal reverberation time values represents the right compromise between achieving a sufficient sound level for effortless hearing, in all points of the room, and reducing the disturbance caused by an excess of reverberation. In general, for rooms intended for listening to speech, the ideal values of T60 are shorter than those for rooms intended for listening to music, as the diffusion of music requires a greater emphasis on the spatial effect. Furthermore, it is necessary to consider that an increase in the volume of the environment corresponds to an increase in the optimal reverberation time. In this case, it is necessary to slightly compromise listening in favor of a higher sound level value.
With regard to the passive acoustic requirements and the acoustic quality of the environments, it is useful at this point to underline that in July 2010 the UNI 1136700_2010 standard was published which establishes the new evaluation criteria of the acoustic requirements and the acoustic classification of the buildings, going to correct the gaps in the law in force (DPCM 5/12/97); this legislation has not yet been implemented by the legislator, therefore it is currently a voluntary acoustic quality standard.
It should be emphasized that this technical standard in Appendix C also takes into consideration the internal acoustic quality of the rooms on a general level, indicating some acoustic quality parameters including the reverberation time:
See below an extract from the aforementioned appendix C, which indicates a method for determining the optimal reverberation time for different types of environments, i.e. environments used for speech or used for sporting activities.
With the proposed acoustic correction intervention, a significant decrease in the reverberation level will be obtained with respect to the initial times, reaching values in line with the optimal times foreseen.
The proposed solution is completely decisive, with an excellent value for money and a great visual impact:
ROUND HANGING ISLANDS
We have provided 24 rock wool acoustic islands (40 mm) which will be hung with 24 special certified suspension kits (3 per island). The shape of the islands will be round 120x120x40. The face has a minimalistic, painted, straight A-edge and is coated with a super-white, super-matte, smooth-finish varnish veil that has antistatic properties that prolong its life cycle. The back of the island is covered with a white acoustic veil.
WALL PAINTINGS
We have planned to place panels on the wall that can be 120×120 or 60×120 in different colors equal to 80.64m2 for a total of 56 panels. Each panel will have its own structure around it for a total of 80.64m2 of structure. These panels have a resistant and long-lasting surface, the highest sound absorption index (Class A), the best fire reaction class (A1 and A2- s1,d0), a humidity resistance of up to 100% UR and total recyclability.
It will be possible to choose between different colors. Finally, we have provided a dozen panels covered in fabric of the same color and material as the chairs in the hall in order to give aesthetic continuity also through the panels.
