Room acoustics play a decisive role in how we feel in our built environment; whether we experience it as pleasant and soothing or as stressful and burdensome.
This brochure answers relevant questions, defines essential key terms and shows examples of applications of the acoustically optimized USM Haller Modular Furniture and USM Privacy Panels in harmony with the architecture.

Room acoustics play a decisive role in how we feel in our built environment; whether we experience it as pleasant and soothing or as stressful and burdensome.
Noises, sounds, voices – these are all very strong sensory impressions that constantly affect us. Our hearing is extremely sensitive and always on reception, even when we are asleep. Our sense of hearing plays a correspondingly large role in how we perceive our environment. And we can’t simply switch it off, even if everything around us seems too loud and too stressful.
The topic of acoustics is complex and extremely important, especially in the workplace, where new forms of work and open room structures are becoming increasingly common. This brochure answers questions about relevance, defines essential key terms and shows examples of applications of the acoustically optimized USM Haller Modular Furniture and USM Privacy Panels in harmony with the architecture.

The development of modular absorption through acoustically effective USM elements is based on a long-standing partnership between the USM company and the renowned acoustician Dr. Christian Nocke, Akustikbüro Oldenburg.
Why are room acoustics important?
Eight basic questions about room acoustics
Why should I, as the user, architect or builder of a building, concern myself with this topic at all?

The most important question in room acoustics is: What surfaces can I use to create optimum listening conditions in the room? All surfaces – i.e. walls, floors and ceilings, including furnishings – are basic elements of architecture. They shape the space in which we live, in which we work, communicate and want to relax. The materiality of these surfaces, their texture and quality determine the essence of an architectural design.
Good room acoustics are not a luxury, not an „add-on“ – they are an integral part of good, forward-looking architecture. And for this reason, it concerns everyone involved. Today, it is assumed that around 70 percent of the working population work in offices. Surveys and studies have repeatedly shown that, alongside lighting conditions, acoustics are the most important factor for the well-being and therefore also the performance of employees in offices. This is all the more important as informal communication in open, flexible office structures is becoming increasingly widespread and noise is generally perceived by employees as the greatest source of disturbance in the workplace.

Where there is less noise, there is less stress, more concentration, lower staff turnover and fewer stress-related absences due to illness. In short: if a company takes active steps to optimize room acoustics, it will save a lot of money in the long term.
- If, as a user or tenant, I find rooms that initially seem ideal for my purposes, but then have high acoustic loads when in use, I am faced with unexpected costs.
- If I as an architect neglect the issue of acoustics in the planning process, I may have to live with the fact that visible surfaces and room structures in the building are subsequently changed.
- If I, as a building owner or investor, neglect room acoustics during the planning process, I may have to invest in additional structural measures later on to create more pleasant conditions.
What’s more, good room acoustics are not just a question of workplace quality in offices: Reduced noise pollution also has a positive effect in other sensitive areas – such as any large lobby, libraries, hotels or canteens. In addition, problems with room acoustics also occur in private living spaces – especially with high ceilings and hard surfaces made of glass, exposed concrete or screed. Anyone who values pleasant acoustic conditions in their private environment, for example those who appreciate real music enjoyment and particularly high-quality audio reproduction, will no longer want to do without the effect of acoustically optimized surfaces.
Why do room acoustics in buildings need to be improved so often?

Modern energy concepts such as thermal component activation are indispensable in architecture today. They ensure the responsible use of resources as well as a high level of comfort and a pleasant indoor climate for the building’s users.
The same applies to modern office concepts in new or existing buildings: Openness, transparency and working environments that promote communication are becoming increasingly important. The move from rigid hierarchies and office structures to teamwork in flexible structures has been completed in many places.
It has now been proven that creativity is much more likely to arise through encounters and exchanges than through concentrated individual work in the ivory tower environment of a cubicle office. Open space structures allow a high degree of space efficiency and a flexible response to changing team compositions. They can be used more densely or more airily, and new arrangements or groupings are easy to create.
Both developments have advanced architecture and opened up new possibilities and future prospects. However, they do not necessarily have a positive effect on room acoustics. Thermo-active concrete surfaces can only be clad with great effort, which means that the proportion of sound-absorbing surfaces in the room is constantly decreasing. Many employees generally find the noise level in open office environments disturbing, they feel distracted and stressed. Conversations or telephone calls from colleagues are not particularly distracting because of their volume, but because of the information they contain, which we cannot escape. Speech always has priority in our perception: we can close our eyes, but not our ears.
How can this problem be solved?
Various measures can help: Specially equipped furniture, flexible zoning modules, a special plaster, certain textiles such as carpets or curtains, sound-absorbing partition walls, acoustic sails or other additional absorbers. Put simply, these sound-absorbing elements help to convert sound energy into another form of energy and thus remove it from the room. This makes the room audibly quieter for us and speech easier to understand.
By combining the acoustically optimized USM Haller Modular Furniture with USM Privacy Panels, USM solutions bring sound absorption and sound shielding into the room – the two essential measures for pleasant room acoustics. The use of the systems contributes to effective conditioning of the room without the need for structural changes. In addition to its sound-absorbing surfaces, USM Haller offers the storage space that is needed anyway, while the USM Privacy Panels can be used for a wide range of zoning options in the room.

There are many, sometimes rather imprecise, ideas among non-experts about how sound is absorbed. For example, it is easy to think that sound is only „absorbed“ by the holes in a perforated surface. However, the decisive factor is rather what happens directly behind the holes, through which the sound penetrates unhindered. The acoustically effective USM Haller furniture with perforated door elements and shelves have a special acoustic fleece on the back that absorbs and dampens sound.
Even more important is the volume of the sound-absorbing element, in this case the storage space enclosed by the perforated door elements, side or rear panels of a piece of furniture. In the case of an acoustically optimized USM Haller filing cabinet or sideboard, it is the volume of the room that increases the absorption of the fleece. As in a musical instrument, the enclosed air volume acts as a resonating body, which in this case has an absorbent effect, even when the piece of furniture is full.
The perforated surface material is of secondary importance in this USM Haller furniture design due to the high degree of perforation – the acoustically optimized USM elements are also effective when they are made of powder-coated steel. As sound absorbers, they reduce the reverberation time and thus increase the often important speech intelligibility – and their effectiveness can easily compete with wall or ceiling panels made of wood, for example.
How do USM Privacy Panels complement the USM Modular Furniture Haller?

USM Privacy Panels are vertical elements in the room that, like the USM Modular Furniture Haller, are also modular and can therefore be used in a wide variety of configurations – for example as a top panel on tables or free-standing for screening and zoning room areas. They are based on the basic principle of a leaf structure and use a tubular structure similar to USM Haller. The USM Privacy Panels can be installed linearly or around corners, flexibly extended and combined with USM Haller furniture. Thanks to their textile and therefore acoustically effective surface and the slight overlapping of the individual panels, they have a soft appearance. Unlike the perforated fleece absorber, USM Privacy Panels are designed as classic, porous sound absorbers. The sound-permeable surface absorbs the sound. The closed surface supports the shielding effect.
The shallow construction depth provides absorption in the medium and high frequency range and thus complements the absorption of the USM Haller Modular Furniture in acoustic design, which has the highest absorption in low and medium frequencies. Here, too, the acoustic interaction of the USM Privacy Panels with the USM Haller demonstrates the modularity of the application The advantages of the modular USM Modular Furniture Haller are obvious – but what does modular absorption mean?
One of the outstanding strengths of USM products is their modularity. Within the USM modular system, it enables tailor-made solutions for every requirement and a flexible response to changing conditions. These strengths can be transferred one-to-one to sound absorption and sound shielding. Based on the respective elements and their dimensions, acoustic calculations and precise measurements can be used to determine the ideal location of a piece of furniture or the USM Privacy Panels and how much acoustically optimized surface is required in a room.
For the furniture, this means that depending on requirements and positioning – free-standing or against a wall, for example – only the rear sides, the side panels or a combination with door fronts can be used as perforated elements. This means that USM Privacy Panels can be used: It is possible to respond to the respective requirement with the corresponding necessary surface area and thus also different spatial configurations. This means that every room – including acoustically – has its own customized modular solution with USM products.
That sounds good, but it costs money. Is such an investment worthwhile?

Absolutely – because every investment in good room acoustics is an investment in employee satisfaction, health, concentration and therefore efficiency. Optimum room acoustics in the workplace reduce stress and increase well-being. It is possible to quantify how expensive every day of absence or every interruption to a concentrated work process is – there are numerous studies on this. An investment in proactively planned or subsequently optimized room acoustics quickly pays for itself and has a long-lasting effect.
In every area of life, questions of room acoustics affect our well-being in a fundamental way. In the office, they have a decisive influence on employee satisfaction, productivity and health management.
The modularity of the USM Haller Modular Furniture System, in combination with the newly developed USM Privacy Panels, allows for customized solutions to improve room acoustics – not as a retrofit solution, but as an integral part of a room concept.
Can I simply retrofit my existing USM furniture?

Yes, because the surface elements are simply replaced, which alone makes the enclosed volume acoustically effective. An advantage over other systems: Nothing is plugged on or curtained, the furniture does not become larger, nor is storage space or other functionality lost. If more shielding is required in the room, we recommend adding USM Privacy Panels to the furniture.
Terms and parameters for a better understanding of room acoustics
Building acoustics versus room acoustics

As an introduction to the topic, it is important to take a look at the subtle but crucial difference between the terms building acoustics and room acoustics, which are often used synonymously in the field of construction. The central question of building acoustics is: What proportion of the sound reaches the other side of a component under consideration? Or: How is the sound transmitted from one room to another? The decisive factor is the sound insulation properties of the separating component between two rooms. It is about the ability of components such as walls, ceilings, doors, windows, etc. to minimize the respective sound transmission.
In room acoustics, on the other hand, the question is: What surfaces can I use to create optimum listening and speaking conditions in the room?
The decisive property in this case is the sound attenuation or sound absorption of the materials in the room. Sound absorption describes the ability of materials to attenuate sound or convert the sound energy into another form of energy.
Audibility

DIN 18041 uses the euphonious term „audibility“ to describe the „suitability of a room for certain sound performances, in particular for appropriate verbal communication and musical performance“.
Many factors influence the audibility of a room, i.e. the speaking and listening conditions prevailing in it, such as the properties of the room’s boundary surfaces and furnishings, but also the people present. Put simply, a room has adequate audibility if we feel comfortable in it, can communicate easily in the room and do not find it too loud or too quiet.
Sound

In very general terms, sound can be described as an oscillation in an elastic medium. For room acoustics, the propagation of vibrations in the air is of importance, which is why we speak of airborne sound.
Sound events such as human speech, music or noises from technical equipment trigger a local and temporally variable fluctuation of air pressure in the air, which spreads from the place of origin into the surroundings. How each of us subjectively perceives an objective sound event – whether as disturbing noise or as a pleasant melodious sound – is initially independent of the physically measurable values of the sound.
Psychoacoustics distinguishes between two types of sound: the desired „useful sound“, which includes music at a concert or the voice in a conversation. On the other hand, there is the unwanted „background noise“. This can include distracting background noises, unwanted speech, but also music that is not particularly loud but is still perceived as „annoying“ and comes from an unpopular neighbor.
Not only speech can be both useful sound and background noise, an aspect that is becoming increasingly important, especially in multi-person offices.
Sound level

The sound pressure level L (or sound level for short) is a physical quantity that is usually expressed in decibels (dB). Human perception starts at around 0 dB and goes up to around 140 dB. Continuous noise above 80 dB or very short sound events such as a loud bang can cause permanent damage to our hearing. But even below these values, a sound level that is permanently too high can be unhealthy.
In Germany, many things are regulated by building law – surprisingly, room acoustics requirements for buildings are not. In the area of occupational health and safety, protection targets are defined that relate to the sound level at the workplace. These requirements indirectly relate to equipping rooms with sound-absorbing or sound-shielding elements. The values of the Workplace Ordinance and corresponding occupational health and safety regulations aim to prevent direct damage to hearing and health. However, correspondingly high sound levels are not usually achieved in the office environment. Although we demonstrably experience stress here, there is still no legal regulation on how to avoid this. The level is not the only decisive factor here; speech intelligibility also plays an important role. Experience has shown that intelligible speech is more distracting than speech that is not intelligible.
Frequency

Frequency refers to the number of sound pressure changes per second. Sound events with a high frequency are perceived by the human ear as high-pitched sounds, while sound events with a low frequency are perceived as low-pitched sounds. Sounds such as the sound of a waterfall or traffic noise generally contain a large number of frequencies.
The unit of measurement for frequency is the hertz. It indicates the number of vibrations per second, abbreviated to 1 Hz = 1/s. The human hearing range is between 20 Hz and 20,000 Hz, whereby hearing ability decreases with age, especially at high frequencies.
Human speech covers a frequency range of around 200 Hz to 1000 Hz in adults and up to 2000 Hz in children. Our hearing is particularly sensitive in this range. On the one hand, this makes interpersonal communication easier, but on the other hand it also makes us particularly susceptible to interference.
Sound propagation
Sound propagates in all three directions in a room. Even if the sound radiation of many sound sources depends on their exact orientation, it is helpful to assume that sound is radiated approximately evenly in all directions. Such sound sources are referred to as spherical sound sources.
At high frequencies, sound propagation can be compared to a beam of light, which is why the term „sound beams“ is also used in this context. The idea of the sound beam leads to an idea of how sound propagates in space. As in optics, the same applies here: Angle of incidence equals angle of reflection. The geometric view is sufficient for many applications in room acoustics.
The important difference between direct sound and reflected sound must be recognized. It becomes clear that in addition to the shape of the room, the room boundaries and furnishings also have an influence on the acoustics. Basically, the speed of sound propagation (or speed of sound for short) depends on the material or medium.
In the air, the spatial propagation of a sound wave takes place at a speed of approx. 343 m/s or 1200 km/h. It should be noted that all frequencies of sound propagate at the same speed in air. In small rooms, the sound therefore reaches everywhere after a short time. The larger the room, the more important the positioning of sound absorbers and sound screens in the room becomes. The targeted interplay of absorption, reflection, sound shielding and sound transmission leads to good acoustics. While sound propagation in a lecture room should be controlled with the aim of achieving good speech intelligibility, sound propagation in multi-person offices often needs to be reduced through shielding and absorption.
Reverberation time
The reverberation time is the oldest room acoustic parameter. It can be used to compare different rooms with each other and evaluate their room acoustic quality. The reverberation time indicates – again in very simplified terms – the length of time it takes for a sound event to cease before it is no longer audible in a room. It was originally defined by the acoustician Wallace Clement Sabine and determined using a stopwatch and subjective auditory impressions in various rooms. Today, of course, the measurement is much more precise. Technically
the reverberation time T is defined as the period of time during which the sound pressure level in a room drops by 60 dB after the source is switched off. The relationship derived by Sabine between reverberation time, room volume and absorption in the room is still valid.
The reverberation time has a direct influence on speech intelligibility in a room. What can be impressive for organ music in a church – a long reverberation – is of little benefit in the workplace or in a conference room. Reverberation time and speech intelligibility in a room are interdependent, even if they are each separate room acoustic parameters. As a general rule, the average speech intelligibility in a room decreases as the reverberation time increases.
Level reduction
The volume at which a sound source is perceived from a greater distance depends, among other things, on the room geometry and the reverberation time, and in offices particularly on sound screens positioned between the source and the receiver.
The effect of such sound screens on room acoustics can be described by various room acoustic parameters, in particular by the average decrease in sound level when the distance is doubled and by the sound level of an average speaker at a distance of four meters.
Shielding
The term „sound shield“ generally refers to an obstacle that interrupts or reduces the direct propagation of sound from a source to a receiver. This function can be performed by an attachment on a desk, a partition, a cabinet or any other piece of furniture. The closer a sound screen is to the sound source, the more effective it is. If a sound screen can also form an angle and partially „flow around“ the sound source, it is more effective than a screen that is only arranged linearly. The greater the detour for the sound that the sound screen triggers, the more effectively the sound propagation is reduced.
If sound screens are equipped with an absorbent surface, sound propagation is further reduced both throughout the room and directly in front of and behind the screen. In this case, a sound screen can also contribute to absorption in the room.
Speech intelligibility
Speech intelligibility cannot simply be measured or determined for an entire room, as it depends on the position of the listener in relation to the sound source. A classic but very time-consuming method of measuring speech intelligibility in rooms is to systematically interview a sufficiently large number of people with standardized lists of syllables and sentences. The Speech Transmission Index (STI) is a physical measurement that was developed on the basis of such subjective studies to describe speech intelligibility. Put simply, the more the transmission is disturbed by the influence of the room, for example by reverberation, echoes or other sound sources, the poorer the speech intelligibility and the lower the STI value.
The effect of surfaces
Three dimensions of the acoustic effect
The acoustic effect of surfaces in a room is essentially described by absorption, reflection and diffusion or scattering of sound waves on the surfaces. Absorption generally serves to reduce the sound level in the room or to attenuate reflections and thus reduce the reverberation time. Reflective surfaces in rooms are needed to direct sound to specific areas of the room. In order to avoid the localization of individual sound reflections, surfaces often have to be designed to diffuse sound. The diffusion aspect of sound is generally used for sound design in particularly high-quality rooms. In everyday rooms such as living and working spaces, it is generally sufficient to consider the absorption properties of surfaces.
Diffusion: Distribution of sound in the room Absorption: Reduction of sound in the room Reflection: Direction of sound in the room
Sound absorbers
From the perspective of room acoustics, the ability to absorb sound is the decisive ability of materials and surfaces. Sound absorbers are used to convert sound energy in a room into another form of energy and thus remove it from the room. Their use not only makes the room quieter, but also optimizes sound propagation in the room by changing the reflections.
The effect of sound absorbers is generally frequency-dependent. It can be said that high frequencies can generally be attenuated by sound absorbers with a low installation height, while sound absorbers with a greater installation height or large dimensions are required to attenuate low frequencies.
The sound absorption of flat arrangements such as ceiling, wall or floor coverings, but also sound screens, is described by the sound absorption coefficient. For elements such as tables, chairs and cupboards, where it is ambiguous or impossible to determine the surface area, the so-called equivalent absorption area is specified directly. Sound absorption coefficient and equivalent absorption area can be compared directly if the surface area of the absorber is known.
Sound absorption coefficient
An essential basis for room acoustic planning is the specification of the sound absorption coefficient of the materials used. It describes the ability of a material to convert and thus absorb incident sound. An ideal sound absorber that „swallows“ 100 percent of the incident sound has a sound absorption coefficient of 1, whereas a completely reflective surface has a sound absorption coefficient of 0.
The so-called reverberation chamber method is used to determine the sound absorption coefficient α of a material. Here, a sample of the material to be tested is placed in a laboratory room whose reverberation time has been determined in advance. The change in reverberation time with the sample in the room can then be used to determine the sound absorption coefficient αS and describe exactly to what extent and at what frequencies the material absorbs the sound.
The sound absorption coefficient indicates the absorption effect of a material in relation to one square meter of the material. However, it is not only the sound absorption coefficient α of the material that is decisive for the sound-absorbing effect in the room, but also the size of the absorber surface in the room. The effective or equivalent absorption surface is the product of the absorption coefficient and the geometric absorption surface S, i.e. α × S. A small surface S with a high absorption coefficient α is therefore just as effective as a large surface S with a low absorption coefficient α. It should be noted that the equivalent absorption area, which is decisive for the effect in the room, also shows different values for different frequencies.
Equivalent sound absorption area
In the reverberation chamber, the equivalent absorption area of the respective element can be determined directly for non-surface elements by comparing the measurement with and without a sample in the room. This equivalent absorption area of an element or object is referred to as Aobj. For a cabinet, the acoustic effect is thus described by the corresponding equivalent absorption area, which is also frequency-dependent. If several cabinets are placed in a room, this effect adds up. Accordingly, two cabinets have twice the absorption of a single cabinet. USM has carried out extensive measurements for various configurations of the USM Haller Modular Furniture system.
If a fully furnished room with different surfaces is considered, each material (e.g. carpet, plaster, acoustic ceiling, curtains, windows, shelving, etc.) can be assigned a sound absorption coefficient and its equivalent absorption area Aeq can be calculated by multiplying it by the area of the material.
The number of objects multiplied by the equivalent absorption area of the respective object results in the equivalent absorption area of the objects in the room. The equivalent sound absorption areas for all materials and objects are then added to the total equivalent sound absorption area of the room. This equivalent sound absorption area of the room, A for short, then determines the reverberation time.
Sound propagation in space
The propagation of sound can be visualized using sound beams. After the direct sound, reflections via the ceiling and walls arrive at the listening point. Multiple reflections with longer paths also occur. The reflections define the reverberation time of a room and are therefore the main factor for the auditory impression in the room.
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