What is Acoustics in Building science?

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

• 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.