The reverberation standard, or what to pay attention to when designing interiors?
The Polish reverberation standard is a set of guidelines designed to make the process of creating a sound-friendly interior easier for designers and architects. It arouses a lot of emotion in our environment, mainly because it is a recommendation rather than a required law. So architects simply don't quite know what they should be guided by when arranging rooms in order to comply with the guidelines of the standard, and at the same time take care of the right design and freedom of choice of finishing materials.
Polish reverberation standard PN-B-02151-4
The PN-B-02151-4 standard, which has been in effect since 2015, deals with building acoustics and noise protection in buildings. In the few years since the regulations came into force, many myths have grown up around the standard. So it is worth taking a look at what is fact and what is myth in the standard itself and its interpretation.
First of all, the provisions of the reverberation standard are not rigid rules but only recommendations and guidelines. And contrary to what many designers think, the reverberation standard does not limit freedom and potential in interior design.
The acoustic standard does not give a ready-made prescription, but a diagnosis. Interior design and achieving the right acoustic paramenters are still in the hands of a wise architect. The possibilities for selecting materials to create designer rooms are still vast, notes architect Anna Baczkowska, technical advisor and acoustics specialist at Knauf Armstrong.
Step 1 - the starting point is the most important
According to the standard, shaping people-friendly acoustics depends on the type of room. This is because acoustic parameters should be calculated differently for large spaces such as sports halls, for example, and quite differently for lecture halls. Therefore, the provisions of the standard divide rooms into categories:
- category A inter iors - that is, those intended for verbal communication (classrooms and educational studios, auditoriums, lecture halls and conference rooms);
- CategoryB interiors - that is, interiors for which only the coefficient of maximum reverberation time is specified (doctors' and treatment rooms, enclosed office rooms, exhibition galleries, reading rooms, gymnasiums, and school common rooms);
- Category C - that is, rooms for which - in order to simplify design - only the requirements of minimum acoustic absorption have been adopted (tupu open space offices, call centers, kitchens, traffic routes - waiting rooms, corridors, stairwells).
The main acoustic parameters to pay attention to according to the acoustic standard:
- STI ( Speech Transmission Index) - speech transmission index
- T, Reverberation time - is determined in seconds, depending on the type of room it is recommended to be from 0.6 s to a maximum of 2.2 s
We count the coefficients - acoustical calculators are helpful
The acoustic environment of an interior depends on a number of factors, including the size of the room or what equipment elements are in the interior. In the case of equipment, it is important not only what it is, but, above all, what these elements are made of. This is because the sound absorption properties depend on this. Sound is absorbed differently by acoustic materials such as ceilings, carpets or furniture upholstery, and differently by hard surfaces such as partitions and wall coverings. The overall acoustic output will also be affected by the location of the sound source - i.e., for example, noisy printers, elevators, sounds from technical equipment, sounds generated by users, or, finally, those entering the room from outside.
Interactive calculators can make it easier to perform acoustic analyses.
At Knauf Armstrong, we created such a calculator together with acoustics and sound engineers from the Silesian University of Technology. It is available through our website*," reports Anna Baczkowska.
The standard limits the freedom of design - a myth
Many architects looking at the recommendations of the standard comment on the regulations as a lack of freedom in the choice of materials. Among other things, there is an abbreviated thinking that since the leveling of unwanted sounds must be high, materials with the highest absorption coefficient - that is, in class A, with an absorption coefficient of alpha at >0.90 - should be used. Meanwhile, this is a myth. As we explained above, the impact on the whole is influenced here by all the elements of the equipment counted together, including the size of the room.
How this works in practice can be seen, for example, on the example of just ceilings. This is the solution that has been used most often in interiors for years to shape friendly acoustics. By default, a suspended ceiling is associated with a white, modular grid. But in the choice of ceilings itself, the range of solutions is virtually unlimited, for example, Knauf Armstrong, in addition to classic mineral tiles, also has wooden or metal ceilings with perforations or acoustic inserts. So achieving a good acoustic environment even for the same room can be done using system solutions in many different ways.
And this is where creativity, the idea for the interior, its character and atmosphere, and not just the recommendations of the reverberation standard start to count," Anna Baczkowska hints.
And one more rule: more does not mean better. If we use too many design elements that strongly absorb sounds, we can overdo it, and instead of getting a friendly room, we will make the interior "deaf", which is very tiring for users.
How to develop an acoustic calculation and choose a suitable suspended ceiling that complies with the requirements of the reverberation standard?
Below we will consider acoustic modeling using one lecture hall as an example. The analysis shows how to creatively - and at the same time taking into account the reverberation standard - you can approach meeting the recommendations, but not give up an unusual design.
Let's analyze a Type A room - a lecture hall, with dimensions of 6.5×15.5 m and a height of up to 3.40 m. According to the reverberation standard, the sound absorption here should be less than or equal to 0.8 seconds (T<=0.8 s) and the speech transmission index greater than or equal to the value of 0.6 (STI>=0.6).
In the baseline condition, we have a room with hard cladding on the walls, hard floors like planks or tiles, wooden chairs and raw, unpainted concrete on the ceiling.
Assuming a sound source power of 60dB and a background sound level of 30dB, the average STI is 0.40 - that is, in the case of the above interior, we are dealing with too poor speech intelligibility. Similarly, the reverberation time - is too long.
So the use of additional acoustic materials is required.
How to improve the acoustics of the interior without losing its attractiveness?
Flat ceiling panels
We added to the interior 40 pieces of Knauf Armstrong Optima L Canopy decorative acoustic panels of 1200×1200 mm, at a distance of 400 mm from the ceiling, and min. 500 mm apart. How did the acoustic indicators change?
- Average reverberation time T=0.55s
- Average STI index 0.70 - good speech intelligibility
Parabolic panels and suspended ceiling with perforations
When we add not only hanging island ceilings to the interior (this used 10 Optima Curved Canopy panels), but also panels that sit smoothly on the ceiling ( Knauf Atmstrong Wood Vector modular suspended ceiling with perforations) the acoustic indicators are even friendlier.
- Average reverberation time T=0.57s
- STI 0.66 - good speech intelligibility.
Vertical acoustic panels
However, it may happen that the designer wants to keep the ceiling in just such a raw, concrete tone. Thus, vertical acoustic panels Baffles (300 mm high, with perforations) can be used in the interior. Mounted 30 cm apart, they raise the indicators to an ear-friendly level:
- Average reverberation time reduced to T=0.74s
- STI 0.63 - good speech intelligibility
Material combinations of metal, wood and mineral ceilings arranged in one smooth surface with island ceilings such as Canopy or Baffles allow for interesting and intriguing visual effects, which at the same time meet the requirements of the standard and are good for the user's ears, protecting them from stress and fatigue caused by nuisance noise.
The material is based on materials and research by Armstrong Building Products BV B.V. Sp. z o.o. Oddział w Polsce.