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Building Acoustics

The science and engineering of achieving a good sound environment within a building space.

Building acoustics design is achieved by following an “intelligent layout” where noise producing areas are separated from noise sensitive areas. Acoustics design should also ensure sound insulation between rooms and sound absorption of excess sound to improve communication and reduce noise related distraction.

What is Acoustics in Building science?

Sound Insulation Building Acoustics Model

Sound Insulation

Reducing sound transmission between adjacent rooms

Sound Insulation is the reduction of sound (decibel level) as it passes through a partition. A partition can be a wall, ceiling or floor. The passage of sound into one room of a building from a sound source located in another room or outside the building is termed ''sound transmission".

For good sound insulation, the partition must be capable of blocking airborne sound and the construction must ensure no gaps and leaks using which sound can travel around the partition.

STC or Sound Transmission Class is a single number rating given to partitions which indicate the degree of sound transmission loss offered. A higher STC corresponds to a greater degree of sound insulation.

Sound Absorption Building Acoustics Model

Sound Absorption

Reducing noise within a room through absorbing

When sound meets a surface, a part of it is absorbed. The percentage of sound that is absorbed by a material is defined as the ‘Absorption Coefficient’ which is expressed on a scale 0-1. Sound absorption is important because it reduces sound levels inside a room.

Noise Reduction Coefficient (NRC):
Sound absorption of a material varies with the frequency of sound. Noise Reduction Coefficient is the mathematical average of absorption coefficient of a material at four frequency bands - 250, 500, 1000, 2000 Hz

Acoustics In Open Plan Offices

The open plan office model has been widely adopted by companies in India and across the world. Although this new model creates an open work environment, it continues to face criticism regarding its acoustic qualities. Some advantages and disadvantages are:


  • Encourages team work and transparency
  • Encourages a horizontal hierarchy
  • Cost effective and easier to refurbish


  • High levels of distraction due to people speaking, phones ringing, etc.
  • Poor environment for higher cognitive tasks such as problem solving and trouble shooting
  • Poor levels of privacy

The three key steps to good office acoustics are:

Sound Absorption: Reducing excess noise within an office by using sound absorptive materials for internal surfaces and furniture. Reduced noise improves communication between employees and also reduces noise related distraction.

Sound Insulation: Reducing sound transmission through walls, ceilings, doors and windows is essential for privacy.

Zoning: Intelligent layout of an office space keeping acoustics in mind. Often, materials are not the solution but an intelligent layout is.


Drywall partition systems are highly suitable for indoor spaces. Some of the advantages of using drywall systems for internal walls are:

  • Ease of installation: Installation time and resources used is significantly lesser than brick and concrete.
  • Lightweight: For large spaces, the weight of internal walls is a critical design factor. Drywall systems are lightweight and can be installed anywhere, not just on top of the supporting beam.
  • Refurbishment: If a new layout is implemented, drywall systems can be easily dismantled and set up according to the new configuration

Even though concrete is better at blocking sound than Plasterboard, a drywall system is more effective than a solid concrete wall. How?

The drywall partition works on the mass-spring-mass system. As sound transmits through the partition, the change in medium (from Gypsum to air/Glass Wool to Gypsum) causes high transmission loss. Therefore, the sound transmitted onto the other side is much weaker.

The open plan office model is the most widely adopted office layout format. Most companies around the world are switching to the open plan model and around 73% of employees work in the open plan office environment (Sykes, 2004).

Surveys have shown that poor acoustics is the most frequent complaint by employees citing office noise as a major distraction to their work.

Several research studies have proven that office noise severely reduces an employee’s ability to complete cognitively demanding tasks.

Along with ventilation and lighting, acoustics is critical to the sense of office comfort.

  • Higher privacy
  • Better communication
  • Lesser distraction
  • Sound insulation decreases with stiffness: The more rigid the material the worse its sound insulation. Therefore, brick and concrete are not preferred sound insulators.
  • Impractical for large construction projects: Though, heavier mass implies greater sound insulation, for every additional 6 dB of insulation, mass has to be doubled which is very impractical for large construction projects. Brick and concrete are weak absorbers: Brick and concrete are highly reflective. Although they may prevent sound from transmitting through the wall, they do not absorb the sound but simply reflect it back into the room.
  • This runs the high risk of creating a noisy internal environment
  • The roof of an indoor space provides the largest available cross sectional area for sound absorption material and reducing overall sound level.
  • False ceilings contain an air cavity behind which provides good sound insulation from the floors above.

Acoustics treatment, if predicted and dealt with properly in the Design Stage of a building construction, is straight forward and inexpensive. Some reasons to keep acoustics in mind are:

  • Acoustic environment has a direct relation to personal comfort
  • Acoustics design will decide the ease of communication and degree of privacy
  • Poor acoustics lead to a poor work environment and low levels of productivity
  • Acoustics treatment is simple in the design phase and expensive in refurbishment
  • Acoustic quality plays an important role in overall aesthetics

It is safe to assume the architectural space in question has an acoustics problem if at least one of the following is true.

  • I can hear people speaking from the adjacent room through the partition wall
  • I can hear noise being carried through the HVAC duct
  • I can hear foot falls and other impact sounds from the floor above
  • I find it difficult to understand speech because of reverberation
  • There is high level of noise due to electrical and mechanical noise.
  • I can hear traffic and other noises when I am indoors.
  • Noise induced hearing loss
  • Increased levels of stress
  • Lack of concentration and decreased productivity
  • Poor communication
  • Vibration can result in structural fatigue or failure in extreme situations
  • Vibration can interfere with sensitive laboratory equipment

When painting sound absorption panels, the painter should be very careful that he does not close up the surface perforations. It is through these openings in the surface that sound waves enter the body of the acoustical material and are absorbed. At minimum, repainting will result in a .05 reduction in NRC

Some acoustics problems can be diagnosed easily since we all hear. Hence we can all attempt to diagnose an acoustics problem. Often, however acoustics can be very unintuitive. For example, it may seem intuitive that brick and concrete will block sound better than drywall or wood but actually this is not always true. Sound transmission depends less on materials and more on transmission path which we shall discuss over the next few pages.

  • Measurement and analysis in the field of Architectural Acoustics is conducted by Acoustics Consultants.
  • International standards which are referred for measurement and analysis are ISO, ASTM, BS EN, DN

Some basic acoustic diagnosis can be done independently as well. Clap your hands in a room to judge the reverberation. Play sounds at increasing frequencies near a partition wall and listen on the other end to judge its insulation characteristics.

Acoustics in building science is broadly about Sound insulation and sound absorption. Both these parameters are equally important in building spaces. Different materials exhibit different degrees of performance for both these topics.

Sound insulation is the property of a partition wall to be able to block the transfer of sound from one side of the wall to the other. In a way, sound insulation is a concept applicable for room to room acoustics.

On the contrary, sound absorption is about the degree to which a material absorbs sound in order to reduce reflections within the room. Absorption is applicable for room acoustics where speech intelligibility is an important criterion.

There are various terminologies to measure sound insulation of walls. Most commonly used terms are STC (Sound Transmission Class) and Rw (Weighted Sound reduction index)

A 100mm Brick wall is tested to give an Rw = 35 dB, whereas a 200mm Brickwall is tested to give an Rw = 44 dB.

A 200mm AAC blockwork wall gives an Rw = 46 dB

Gypsum based drywalls give varied levels of sound insulation depending on the thickness, board used, metal framework, insulation material, air gap etc. Since overall thickness of Gypsum partitions vary from 75mm to 300mm and even above in some cases, the sound insulation provided range from Rw= 35 dB to Rw = 60 dB and even higher with increased thickness.

A 100mm Plain Gypsum board partition gives Rw= 48 dB.

Various factors influence the sound insulation of walls – Total system thickness, type of Gypsum board used, density of Gypsum boards, flexibility and bendability, additives inside the Gypsum board, insulation material used in cavity, air gap, metal framework, joints and finishes etc.