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    3 June 2016


    Effective oral communication in the field of education, and therefore in the learning process, is closely linked to the room used and the conditions it provides. Excessive reverberation and high levels of background noise reduce speech intelligibility. Certain studies have shown how students’ margins of error can vary by over 15% in a room where the reverberation time produces a sound above 60 dB. While below 55 dB this percentage falls dramatically to 4.3%. With this in mind, the acoustic design of a classroom aims to ensure that the person speaking is as comprehensible as possible. When working to correct the acoustics of a classroom, we must apply different types of materials so that the whole range of the frequencies concerned is absorbed.

    Silente is a single-sided sound-absorbing panel upholstered in fabric, which can be installed on the wall or on the ceiling with special tracks. Also available in a hanging version, Silente minimises acoustic disturbances from speech. The option of choosing from various colours and sizes makes the panels perfectly adaptable to any space and to any type of furnishings already in the room. Efficient LED lighting systems can be included upon request.



    The RT is the first factor to be examined to improve speech intelligibility, but on its own it is not enough to ensure the best results. Different factors which affect perfect speech intelligibility must be taken into account, such as the STI (Speech Transmission Index) and the %ALCONS.

    STI measures intelligibility on a scale between 0 (completely incomprehensible) and 1 (perfect intelligibility)

    ALCONS expresses the loss of articulation of consonants, with lower values being associated with greater intelligibility. For learning environments the value must be at least 5% or lower.

    C50 expresses the clarity of speech (used in particular in Germany) and indicates the sound energy relationship over the first and subsequent 50 ms.

    By comparing the data from before and after the acoustic improvements in an empty room, we can see a considerable improvement in the reverberation time. While in an occupied room the average RT will change from 500-1000 Hz at 0.59 s to a value of 0.51 s.

    Consequently, we also achieve a considerable improvement in the parameters that define speech intelligibility, such as the STI and the ALCONS.

    The STI changes from a value of 0.53-0.55, which represents normal conditions, to a value of 0.74-0.77, which can be considered excellent.

    We can also see an improvement when we look at the other parameter, the %ALCONS, *with nearly excellent values at 3-4 %.

    Loss of Consonants

    Al Cons aula occupata senza pannelliALCONS classroom occupied with people, values without sound-absorbing panels
    Al Cons aula occupata con pannelliALCONS classroom occupied with people, values with sound-absorbing panels


    C50 Speech intelligibility

    C50 aula occupata senza pannelliC50 classroom occupied with people, values without sound-absorbing panels
    C50 aula occupata con pannelliC50 classroom occupied with people, values with sound-absorbing panels


    Speech transmission index difference between direct and indirect sound

    STI aula occupata senza pannelliSTI classroom occupied with people, values without sound-absorbing panels
    STI aula occupata con pannelliSTI classroom occupied with people, values with sound-absorbing panels

    The square area of the graphs represents the listening area and to the right we find the respective key, while the examined frequency is 1000 Hz and the sound source used is a man’s voice without amplification.

    The panels are fitted onto the ceiling in a U-shaped arrangement with the base facing the back wall. Other panels are fixed to the back wall.

    This arrangement is particularly effective and ensures values close to excellent without any amplification.


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    LAMM S.r.l. a socio unico | C.F. / P.IVA 02655090344
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