Frequently asked questions
Search for and find answers to some our most commonly asked questions.
Our new capability will allow us to manufacture new products that expand the creative options available to architects and designers, while meeting the practical considerations of contractors. Our factories will also operate more efficiently, reducing energy and water consumption, so that our products come with a smaller carbon footprint.
Since we evolved from Armstrong Ceiling Solutions in 2020, we’re taking advantage of the opportunity to improve our manufacturing capability. We are making significant multi-million investments in the future of our factories and committing to our UK manufacturing base.
Yes. We’re constantly looking for new ways to support contractors and help architects and designers meet their project requirements. Innovation is a core priority for our business.
Zentia trades in a number of European markets: Ireland, Spain, Portugal, Estonia, Latvia, and Lithuania. We have work with specialist distributors in those territories. Please visit our Find a Distributor page to learn more.
We manufacture the vast majority of our ceiling and grid solutions in our two UK factories, based in Team Valley, Gateshead. Our mineral tile plant has been operational since 1966, while our grid plant opened in 1997.
This is the time, in seconds, required for reflecting or reverberant sound in an enclosed space to decay to one-millionth (equivalent to a drop of 60 dB) of its original energy level after the cessation of the sound source.
It is the most common, and easily obtained, measurement or predictor of a room’s potential sound quality. The reverberation time (RT) for any enclosed space will be influenced by the room’s volume and how much sound absorption (which controls the reflection of sound) is present. Increasing the volume will increase the RT while increasing the amount of sound absorption will lower the RT. Because Zentia suspended ceilings can provide a substantial surface area and can provide more or less sound absorption depending upon the product chosen, they can significantly influence the RT of a space. However any room will have an optimum reverberation time (RT) requirement depending upon its use and size and whether the main activity is speech or music based. Providing too much sound absorption, and hence having a very low reverberation time (RT), can be just as acoustically damaging and undesirable as having insufficient sound absorption when an excessively long reverberation time (RT) will result.
Rooms with reasonable amounts of sound absorptive finishes appear quieter and less frenetic than those with little or no sound absorptive treatment. If the amount of effective sound absorption in a room is doubled (or halved), the noise level will be reduced (or increased) by 3dB (Decibels). However, it should be considered that a change of 3dB will only just be detected by the human ear, while a difference of 5dB is necessary to be really noticeable. In addition, sound absorptive treatments that are applied to the boundary elements (walls, ceilings, floors etc.) of a room, do not have any significant effect at enhancing the element’s sound reduction properties, ie when sound transmits through it from one adjacent room to another.
By using a mathematical model based upon the ‘Sabine’ formula which takes into account the significant surfaces of a room, their respective sound absorption coefficients and the room dimensions. Get in touch for a more detailed calculation which also considers specific user criteria.
A sabine (also known as the equivalent absorption area) is a measure of sound absorption afforded by a material which is defined as the product of its exposed surface area S (m2), multiplied by its random incident sound absorption coefficient alpha s. However the sabine is also specifically used to describe the total absorption provided by individual discrete objects, such as an acoustic canopy, where all of its surfaces may be influentially providing sound absorption and the use of as would not be sensible or realistic.
Once the total sound absorption present in a room (from both planar surfaces and objects) has been calculated, an estimate can be made of the room’s probable reverberation time. The installation of canopies in a reverberant space can significantly reduce the reverberation time and contribute to the reduction in background noise.
Some trends in modern building technology, such as the use of concrete thermal slabs as heat-sinks, requires that the slab be exposed to the occupied space. In these designs, a continuous (wall to wall) ceiling is not permissible because it could interfere with the airflow pattern around the room. But the downside of not having an acoustic ceiling will probably result in higher reverberation times and increased noise levels above those which would be acceptable to the users. Also in many existing spaces, even though a continuous ceiling is present and has to remain in place for various technical reasons, it may provide insufficient sound absorption than is suitable for the activities being carried out in the room. The installation of canopies in a reverberant space, in sufficient numbers and in a layout to satisfy both technical and aesthetic considerations, can significantly reduce the reverberation time and contribute to the reduction in background noise and improvement of aural comfort.
The speech frequency range is generally described as being between about 500Hz and 4000Hz. However it is not defined in any known national or international standard.
Sound absorption relates to the control of sound reflections within a room while sound attenuation is associated with the control of sound transmission between adjacent rooms via a continuous suspended ceiling.
Probably not. Materials that provide high levels of sound absorption are generally lightweight and porous which is the direct opposite of the qualities required for sound reduction ie massive and impervious.
In terms of sound absorption there may be a small loss, depending upon the tile face pattern (fissures, perforations, scrim, etc), the paint type used and the thickness of the paint coating. It is unlikely that the ceiling’s sound reduction or attenuation performance will be adversely affected but if the spaces where the ceiling has to be repainted are acoustically critical, then laboratory testing to assess any possible differences in acoustic performance should be conducted on repainted samples.
It should be noted that the repainting of ceiling tiles could also adversely affect their other technical performance factors such as fire reaction, sag, light reflectance, among others, and the implication of such possible changes needs to be considered. Finally, it should be appreciated that the repainting of any tiles supplied by Zentia will invalidate any warranty that was provided when the tiles were new.
Zentia suspended ceilings are one of few building products with sound reduction performance that can be measured in two entirely different ways. These are sound reduction index (R or SRI = vertical or single pass), which is measured in accordance with EN ISO 140 Part 3, and Normalised Level Difference for Ceilings (Dnc = horizontal or double pass) which is measured in accordance with EN ISO 140 Part 9.
No. Although there are some empirically derived relationships between the two different values for the same product, there are no theoretically based methods for deriving one value from the other.
The decibel is a unit used in acoustics to describe the magnitude of sound levels. These levels can either describe how loud something is (eg 85 dB due to a passing bus), or they can describe the ability of a product or system to reduce sound. For example, a 35 dB suspended ceiling will reduce a sound level of 75 dB in one room down to 40 dB in an adjacent room. The bigger the number, the greater is the sound energy level or sound difference involved.
The terms ‘reduction’ and ‘attenuation’ both mean a decrease or lessening of something. These expressions describe the same process and are usually interchangeable. In relation to the acoustics of suspended ceilings, ‘sound reduction’ is generally used to describe the ‘single or vertical pass’ decrease (typically from a ceiling cavity to a room below) while ‘sound attenuation’ is reserved for the ‘double or horizontal pass’ lessening in transmitted sound energy where the ceiling is continuous above two adjacent rooms.
The Rw of the total construction is unlikely to be more than about 40 dB – an increase of up to only 5 dB on the floor construction. This is because the two separate elements are very close to each other and are rigidly connected together and therefore the sum of their two individual reductions cannot practicably be achieved.
This is not a problem that can be easily or simply solved by installing a further suspended ceiling below. It all depends upon the level of disturbance that is occurring and the type and construction of the existing floor and surrounding walls. Further advice should be sought from an acoustic consultant or specialist supplier of noise insulation materials.
Echoes are discrete sound reflections from a distant surface which, if they are of sufficient intensity and time delay, can be heard distinctly from the direct sound, ie you hear the same sound twice in quick succession. The expression ‘echoey’ is often used to describe the sound heard in an enclosed space which is particularly reverberant or ‘lively’. This is actually the wrong use of the term as, perhaps surprisingly, echoes are a rare phenomenon in most normal sized and occupied enclosed spaces. However excessive reverberation and noise can be controlled by the introduction of sound absorptive treatments, such as suspended acoustic ceilings.
Sound absorptive materials make a space seem less ‘echoey’ or ‘lively’ by reducing the amount of sound reflected back into a room. The room becomes less reverberant. In a commercial environment, the ceiling is often the most substantial and unobstructed area where sound absorptive materials (like ceiling tiles) can be introduced.
Whatever kind of project you’re working on, Zentia can provide a ceiling solution to match. Zentia ceilings can provide acoustic control with absorption values from 0.10 to 1.00 Alpha w, and attenuation values of up to Dnfw 44dB. So whether sound absorption or sound attenuation is your main priority, we can help. Get in touch with our experts if you aren’t sure which option is the right ceiling solution for your project.
Zentia’s recommended ceiling solutions for commercial kitchens meet the requirements as detailed in Regulation (EC) No 852/2004 Annex II Chapter II Paragraph 1(c):
‘Ceilings (or, where there are no ceilings, the interior surface of the roof) and overhead fixtures are to be constructed and finished so as to prevent the accumulation of dirt and to reduce condensation, the growth of undesirable mould and the shedding of particles.’
While all of Zentia’s mineral ceiling tiles emit very low levels of Volatile Organic Compounds, some of our products are more suitable than others for installation in commercial kitchens. Get in touch and speak to one of our technical experts for assistance.
Cradle to Cradle
Zentia’s Ultima+, Perla and Dune eVo ceiling tiles are all Cradle to Cradle Certified Bronze. As part of achieving certification, they received a Gold rating for Material Health. Our ceiling suspension systems are Cradle to Cradle Certified Silver. You can download Zentia’s Cradle to Cradle product certifications here.
Cradle to Cradle Certified is the world’s most advanced science-based, multi-attribute certification program for designing, making and verifying materials and products that are safe, circular and responsibly made. Cradle to Cradle Certified products are awarded certification based upon their performance across five critical areas of sustainability: Material Health, Product Circularity, Clean Air & Climate Protection, Water & Soil Stewardship, and Social Fairness.
Cradle to Cradle Certified® is a registered trademark of the Cradle to Cradle Products Innovation Institute.
Documentation & Certifications
The vast majority of our products come with at least a 10-year warranty. In fact, most of our products come with a 30-year system guarantee. You can find out the details on the individual product pages.
Beyond light, acoustics, and aesthetics, it’s also important to consider things like fire safety and durability. You may also wish to consider ease of installation and maintenance, so that the initial project can be completed on time and on budget, and so that the ceiling tiles, grids and the infrastructure they conceal can be maintained in the future.
A bright environment makes everything clearer. In a school, the main objectives is to make the best possible use of daylight to avoid having to use electricity. The ceiling can play a crucial part in optimising light reflectance which can allow energy savings, in case of indirect lighting. Combining high-reflectance mineral ceiling tiles with larger windows or floor-to-ceiling glazing provides an easy way to make this happen.
Research has also shown a conclusive link between the provision of natural light and academic success, with one study showing that students working in classrooms with higher levels of daylight achieve 7% to 18% higher test scores. Another – Clever Classrooms – suggests that the design of a classroom has a c.25% impact, positive or negative, on the academic progress of students over the course of a year.
On the flip side, too much natural light can cause eye strain or create glare that distracts students and staff alike. Reflectance must be balanced with diffusion – transforming the harshness of direct light into a more scattered, ambient glow, bathing classrooms in pleasantly bright light without it becoming an issue.
When it comes to classrooms, sound absorption is less important than you think. Ceilings that absorb too much sound deaden classroom environments and make it more difficult for teachers to communicate with students. To put it simply, teachers have to work harder to project their voices across the room, which results in vocal strain. Ceiling tiles with high sound absorption qualities do not make a good classroom environment for teachers and students.
Instead, we recommend ceiling tiles that offer a good balance between sound absorption and sound attenuation. These tiles take the edge off noisy classroom chatter, but reflect some soundwaves back into the room, so teachers don’t have to work quite as hard to be heard by their pupils while they’re teaching lessons. A balanced, practical ceiling solution that provides the best learning environment for all.
Finding the right product
Our specification team can help you identify the right Zentia products for your project. We have over 100 years of experience and knowledge in our business. So whether you’re designing classrooms or hospital wards, open plan offices or transport hubs, our team of experts can help you find the products that will achieve the right acoustical balance, visual effect and technical spec for your project.
You can narrow down your search using the Solution Finder right here on our website. If you’re still not sure, you can get in touch with Zentia here. We aim to respond within 48 hours.
Our ceiling tiles can be cleaned in a variety of different ways. For instance, Bioguard Acoustic can be cleaned with disinfectants without compromising its technical performance which, along with its antimicrobial performance, makes it an ideal ceiling solution for healthcare environments. Similarly, Clean Room FL can also be cleaned with disinfectants with no impact on performance.
You can find detailed cleaning recommendations on all of our individual product pages.
Yes. Zentia ceiling solutions are regularly used in NHS facilities in both clinical and non-clinical settings, as well as in the wider public sector.
Hospitality & Leisure
We recommend tiles with high relative humidity (RH) resistance. With 95% humidity resistance and class-A sound absorption, Hygiene is a great choice for commercial kitchens, while Hydroboard can resist permanent RH up to 95% and temporary conditions of up to 100% RH, making it a fantastic option for bathrooms and other areas with fluctuating temperatures.
Canopies and Baffles can be specified alone or in tandem to create stunning visual effects in entrance lobbies. Canopies can be used to create arresting ceiling clouds, while Baffles can be used to create different patterns across the ceiling soffit. Both ceiling products will reflect and direct natural and artificial light around the interior, as well as providing good sound absorption.
Canopies can also be attached to the wall and used as wall absorbers, providing additional sound absorption in high traffic areas.
DecoMesh adds contemporary class and brings an edgier aesthetics to restaurant interiors. Made from galvanised steel and available in eight different colours, DecoMesh makes a very strong design statement.
The course costs £495 per person plus VAT, payable in full on booking by Bacs transfer only. We do not accept credit cards.
Our remaining 2022 training dates are:
- 27-28 September (places available)
- 18-19 October (fully booked)
- 6-7 December (places available)
Please complete the form below to book a place.
On day one, the course covers:
- Health & Safety
- Mineral & suspension systems product overview
- Straight, flat square and white side down
- Tools, fixings, levelling & layout
- Wire straightening – demonstration
- Exposed grid installation – demonstration and then your turn
- Tegular and Vector tile perimeter cutting – demonstration
- Ultima+ Finesse concealed system demonstration
On day two, we cover:
- Manufacturing process including (mineral & grid) plant tours
- Semi concealed grid / SL2 plank
- Axiom product overview
- Axiom Canopy with SL2 Plank Installation
- Questions & Certificates
The course is taught by Ian Young, who has over 40 years of experience in the suspended ceilings industry.
The course takes two days to complete and is held at Zentia Limited, Kingsway South, Team Valley Trading Estate, Gateshead, NE11 0SP. It begins at 8am each day, so we recommend booking two nights of accommodation in the Gateshead and Newcastle area if you are travelling from more than an hour away.
The course covers the theory and practical installation of mineral fibre suspended ceiling systems. It provides an ideal foundation for both office and site based personnel.
The course is designed for individuals who wish to learn more about Zentia’s products and how to install them quickly and safely.
New Product Names
Product warranties are not affected by this change. The content of the warranties itself will be updated to reflect the new product name, but Zentia will honour warranties under the old product names at our discretion.
Our products will feature both product names for 12 months after the new product name is launched. The product codes will change however this will be limited to the last digit in the suffix. For example, if a product code previously ended with the letter A, it may now end with a B.
Back in 2020, Zentia evolved from Armstrong Ceiling Solutions. As part of this process, we’re simplifying and streamlining our product names to make our portfolio less confusing for architects and contractors just like you.
Ordering from Zentia
We offer a wide range of delivery options for our distributor partners. We are the UK’s only manufacturer of ceiling solutions, so we offer strong availability and shorter lead times. Get in touch with our team to find out how quickly your chosen product can reach you.
Zentia products can be ordered from our network of distributors in the UK, Ireland, Iberia, and the Baltics. Visit our ‘Find a Distributor’ page to find your nearest Zentia stockist and learn more.
Pinnacle by Zentia
Ceiling contractors can apply to join Pinnacle by Zentia here. [Link] To maintain the quality of our partnership programme, we perform an assessment of your business before admitting you to the programme.
If you’re a contractor, you can benefit from exclusive training on Zentia products (at our factory in Team Valley, Gateshead and in your business), certification from Zentia, and promotion on our marketing channels. There are other concrete benefits, too; for instance, you have exclusive access to Zentia’s off-cut recycling service, so you can provide cleaner, more environmentally friendly installation services.
If you’re an architect or designer, we can work with you to find the right Pinnacle Approved Partner for your project, so you know your design won’t be compromised at installation stage. All of our Pinnacle Approved Partners undergo training on Zentia products before being certified a Pinnacle Approved installer, so you know the project will be completed safely and swiftly.
In large open plan department stores, it’s important to improve intelligibility at payment counters. Installing a suspended ceiling like Canopies or Axiom Canopies above customer service points, or even Wall Absorbers, will absorb sound from the surrounding space and make it easier for people to understand each other.
Architects and specifiers use Axiom Canopies to create different ceiling effects in open spaces. As a floating ceiling system, Axiom Canopies can be suspended at different heights, adding visual excitement to the ceiling plane. As well as being visually appealing, they also absorb sound from above and below, helping to reduce sound reverberation – basically, they make a space less ‘echoey’.
ICC-ES recognizes Zentia Seismic Rx Suspension Systems as seismic code compliant solutions to meet ESR-1308. This evaluation and confirmation by ICC-ES provides evidence supporting the Zentia Seismic RX as a code-compliant alternative to IBC requirements. The performance of the Zentia Seismic Rx System is based on a specific combination of components and methods of installation.
Suspended ceilings and fire safety
Fire reaction refers to the surface burning of materials and the rate at which they contribute to the growth of a developing fire within a particular area.
Fire resistance is concerned (after the fire has developed) with preventing the fire from spreading through the building and attacking and destroying elements of structure.
This is the harmonised European classification for the fire reaction performance of building materials which may appear (in descending order of significance) as A1, A2, B, C, D, E or F.
Also, and depending upon national market legislation, additional information regarding smoke production and flaming droplets or particles may be required, for example A2-s1, d0.
In relation to suspended ceilings, fire resistance can only be achieved by a combined tile and grid system. There is no such thing as a fire resistant tile or a fire resistant grid.
Depending upon national market legislation, the type of structure to be protected i.e. wood, concrete or steel, and our product offer, our Zentia ceiling systems can typically provide 30 or 60 minutes of protection. Full details of the ceiling type and construction, protected structure and tested time are given in each fire report, copies of which are available on request.
The need for clips depends upon national market legislation, practice and product offer. Get in touch to discuss the issue with our experts. (link to contact page)
If your enquiry relates only to the fire reaction performance of Zentia ceilings, then hold-down clips are not necessary for this application.
To some extent this depends upon national market legislation and test performance, so our experts will be able to tell you which products are tested and the performance that they provide.
Within the EU, there is a system that describes three basic criteria for fire resistance as REI. These are defined as:
R = load bearing (capacity to provide structural stability)
E = integrity (capacity to remain intact)
I = insulation (capacity to maintain a defined temperature on the unexposed side of the building element).
Each member state is free to determine the criteria that shall apply within their own markets, so these letters may also appear as RE or EI and all three combinations will be followed by a number e.g. EI 30, indicating the minimum time in minutes that protection can or must be maintained.
This is dependent on national market legislation, the type of structure to be protected, and our product offer. Please get in touch with our experts, who will be able to advise you on the specific products that can be used.
The fire protection of buildings can be “active”, for example the use of detectors, automatic alarms (to people and emergency services), water sprinklers or gaseous systems. Or it can be “passive”, which is the provision of suitably tested lining materials and building constructions which inhibit the growth and spread of fire.
Have the light fittings been successfully tested or assessed by a recognised expert in conjunction with the proposed Zentia ceiling?
If they have not, you should speak to the relevant fire authority and obtain approval before commencing the Zentia ceiling installation. You should rely on unauthorised methods, such as overlaying or surrounding the lighting fittings with ‘fire blankets’, mineral wool pads or offcuts from the ceiling tiles, to assume that the ceiling’s fire resistance will not be compromised.
In the event of a detected fire, a GFP system will rapidly release an inert gas into the room that will suppress and extinguish the fire without damaging the room’s contents. The rapid introduction of the gas will result in a significant over-pressure within the room, albeit of a short duration. This could result in lay-in ceiling tiles being lifted from the grid if sufficient and suitable pressure relief devices have not been included as part of the GFPS installation.
You should consult with your client to see if hold-down clips (e.g. BP A7890) are required to minimise tile movement. The use of metal clip-in tiles is an ideal solution for these types of installation because the positive gas pressure cannot dislodge the tiles from their grid.
If you are just relying on the partition/grid fixings to locate the partition, this should not adversely affect the ceiling’s structural fire protection, provided you ensure that the partition is not fixed to a main runner either side of the grid’s expansion cut-out which would prevent it from activating in the event of a fire.
However, if you are also using the ceiling grid to provide lateral restraint to the partition then, in the event of a fire, this could contribute to the premature collapse of the ceiling system with the consequential loss of protection to the structure.
If it is this second reason why you want to provide the partition/grid fixings, you should speak to the relevant building control and/or fire authority and obtain approval before commencing the installation.
In general, any overlay that is added directly to the back of a Zentia suspended ceiling to try to increase its fire, thermal or acoustic performance, and which has not been successfully tested or assessed by a recognised expert in conjunction with the ceiling, could have an adverse effect on the structural fire protection and fire reaction properties of the ceiling system.
You should not undertake the installation of any overlay for this purpose without speaking to the relevant fire authority and obtaining approval.
UK and Republic of Ireland Building Regulations require that building linings, such as suspended ceilings, meet the appropriate fire reaction performance depending on the area of application.
Fire reaction performance for suspended ceilings is shown using the Euroclass fire reaction classification. Products achieving B-s2,d3 (or better) are defined as Class 0 in the Building Regulations – a performance that is easily met by all Zentia ceiling products. This means that they can be used in all areas of a building.
Suspended ceilings in offices
According to research, employees’ cognitive function across a number of functions is improved by low VOC office environments, by up to 61% on average. Particularly large spikes in improvement are seen in crisis response, information usage, and strategy. Zentia’s low VOC-emitting ceiling tiles can contribute to a more productive workforce, as well as helping projects meet green building standards like BREEAM and WELL.
The right light reflective ceiling can make a big difference to employee wellbeing, particularly when paired with natural lighting. Employees who are exposed to natural light during working hours report a 51% drop in the incidence of eyestrain, a 63% drop in the incidence of headaches and a 56% reduction in drowsiness, enhancing productivity.
Bright working environments can also reduce the amount of electricity used on artificial lighting, so there are financial benefits to high light reflecting ceilings, too.
Zentia ceiling solutions can be used in office refurb or refit projects, just as they can on new office projects.
Zentia’s Ultima+, Perla, and Dune eVo ceiling tiles are all Cradle to Cradle Certified Bronze. As part of achieving certification, they received a Gold rating for Material Health. Our ceiling suspension systems are Cradle to Cradle Certified Silver. You can download Zentia’s Cradle to Cradle product certifications here.
Cradle to Cradle Certified is the world’s most advanced science-based, multi-attribute certification programme for designing, making, and verifying materials and products that are safe, circular and responsibly made. Cradle to Cradle Certified products are awarded certification based upon their performance across five critical areas of sustainability: Material Health, Product Circularity, Clean Air & Climate Protection, Water & Soil Stewardship, and Social Fairness.
Cradle to Cradle Certified® is a registered trademark of the Cradle to Cradle Products Innovation Institute.
A wide range of Zentia ceiling solutions provide BREEAM building requirements, as well as SKA, LEED, and WELL. You can find out more here.
Zentia is on a sustainability journey of its own and we are working hard to research our key improvement areas. Zentia has recently established a sustainability committee to assess our environmental impact in more depth, beyond the scope of our ISO 14001 certification. We intend to set rigorous and trackable goals that will have a positive, measurable impact on our manufacturing processes and reduce our carbon footprint.
For restrooms and cloakrooms that include shower facilities, we recommend suspended ceiling tiles with good humidity resistance such as Hydroboard, Ceramaguard, and Dune eVo Max. For restrooms that are less humid, mineral tiles such as Dune eVo and Perla OP dB can be good solutions depending on project requirements. Please get in touch to speak with one of our experts.
Canopies and Baffles are floating ceiling solutions that absorb sound from both sides of the board, unlike a suspended ceiling tile which is fixed to a metal grid and exposed to sound only on one side. The more Canopies and Baffles that are installed in an open space, the better the sound absorption, and the more background noise levels are reduced, making concourse areas feel more relaxed and open.
Understanding Product Information
Noise Reduction Coefficient is a method for providing a single number rating of sound absorption. It is defined in ASTM C423 as the arithmetical average of the measured sound absorption coefficients for the four one-third octave band frequencies centred at 250, 500, 1000 & 2000 Hz, rounded to the nearest 0.05. This US based system has been used extensively in Europe for many years but is now becoming less popular with the advent of the Weighted Sound Absorption Coefficient αw.
Alpha w (weighted sound absorption coefficient) is a method for converting a wide frequency based range of sound absorption coefficient values into a single number, but this is done using a curve fitting process. More complex to derive, Alpha w is considered to be more representative of how the human ear interprets sound. The method is fully described in EN ISO 11654 and has now become the preferred European unit for making a simple and rapid comparison of sound absorption performance.
No. Although they are both single number descriptors of sound absorption neither one can be deduced from the other as there is no direct relationship between them.
This is a system for the classification of Alpha w values which is defined in EN ISO 11654. Because it groups consecutive Alpha w values together into six broad-bands (each successively identified as A to E & ‘Not classified’), it is not so precise and therefore provides less useful detail than when individual Alpha w values are specified or selected.