Sound Insulation can be defined in two ways. The first is the ability of an element to reduce the amount of sound passing through it (from one room to another room) and the second is the ability of a material to absorb sound energy (reflection of sound in the room).

These two 'insulations' are very different and have vastly different methods of both design and calculation and in assessing, as in testing on completion.

The first relies heavily on both mass and material stiffness and also air spaces (as in the cavity in a wall) and how these materials are supported. For example a rigid connection between two leaves of a wall will provide less insulation between two rooms that no connection. This insulation refers to a separating element’ ability to mitigate the transfer of airborne or impact sound through it. This includes vertical (walls) and horizontal (floors) adjacency's. When measured in a laboratory environment, a loudspeaker is measured inside one room (source room) and the same levels are measured on the other side of the separating element (receiver room). The surface area of the separating element, as well as the average absorption area in the receiver room are taken into consideration to calculate the Sound Reduction Index (R) value at multiple frequency bands. These values are then compared to a reference curve to obtain the single number value - Weighted Sound Reduction Index (Rw). When measured in the field, the same is done except the reverberation time inside the receiver room in considered and standardized to a reference reverberation time producing the Standardized Level Difference (DnT) in multiple frequency bands. This is also compared to a reference curve to obtain the single number value – Weighted Standardized Level Difference (DnTw).

Multiple different factors can generate sound; most elements can be characterized under airborne, structure borne or a combination of both.  A sound receiver can be defined as anything ranging from a microphone in a recording studio to a person with average hearing ability in an apartment. In the light of the statements as mentioned above, the term 'sound insulation' can be redefined as the restriction to the transmission of sound passing from a source to a receiver with the use of various engineered mitigation strategies

The second relies heavily on the material thickness and type. For example a soft thick material is likely to reduce more sound reflection in a room than a hard thin material. Of course the more material that is in the room the more the refection can be reduced.

In building acoustics, sound insulation may be further sub classified into external airborne sound insulation, horizontal/Vertical airborne insulation, horizontal/Vertical impact sound insulation, structure borne sound insulation, services sound attenuation etc etc.

Architectural acoustics will include but is not limited the acoustic design for a building’s envelope, internal structure and partitions (including walls and floors), treatment materials for sound absorption or sound insulation of building services.

Architectural acoustics is a branch of design science which, through the application of mathematics and physics, and the adherence to codes and regulations, realizes architectural form into a practical and functioning space in relation to sound.

The cooperation and coordination of the various building design disciplines are combined to produce both a visually and aurally pleasing and a successful working structure that is both usable, enjoyable and comfortable to be in. A strong acoustic example is in concert hall design in which specific acoustic requirements for the space are set out in the design in order to have the room provide the audience (listeners) with the best acoustic sound experience. Achieving these criteria involves architectural considerations, for example volume, location and angle of lateral walls and ceilings impacting and controlling parts of the reverberation time, and early reflections etc. Mechanical considerations such as acoustic design to ensure the HVAC systems are controlled so that the noise from them doesn’t interfere with the performance. Structural isolation is also considered to ensure that, for example a train or metro system linked under a concert hall doesn’t vibrate the building such that, it too, interferes with the performance aspects of the space.

Acoustic design criteria and application are just as important in all other building types, for example a residential apartment having weak walls so that noises from neighbors are easily heard to HVAC systems that vibrate and make so much noise that a person trying to sleep cannot due to the high noise levels, to a nearby train vibrating into a building and the sounds of aircraft or cars penetrating through the walls and windows of a school such that students can’t hear the lesson as well as impact isolation from floor noises above a hospital ward that disturbs patients recovery.

Architectural acoustics is often referred to as ‘the unseen calm of a space’. Sound is one of the five primary senses. Acoustic design value is often underestimated. 

The calculated control of sound in an enclosed space can be considered as a broad definition of room acoustics. The room can be considered as a system, and the design of the system would be room acoustics. The acoustic ‘sound’ of the 'system' will depend on the design of the system inputs and this would depend on the purpose of the space – is it a concert hall, a meeting room, an apartment?

Based on the required acoustic sound an Acoustic consultant will use various engineering methods to design the system. There are several elements that need to be carefully considered in a room’ design. Some of these include identifying room modes and controlling them by adjusting the basic shape and the resulting volume, identifying various sound reflection patterns inside the confined space and ensuring these are mitigated to remove negative sounds like flutter echoes and other tonal anomalies (modal responses) or reflections, calculating the reverberation time and adjusting this by adding or removing absorbing materials or including diffusion elements. Reverberation also causes additional noise and other factors that make communication and hearing all the words in some spaces difficult. Harder surfaces such as glass and brick have lower absorption properties and reflect sound. Softer surfaces such as fabrics and carpet etc. have higher absorption properties and absorb sound. Further studies in specialist areas, such as schools and performance spaces would also include evaluating the Clarity and Speech Transmission Index (among many other criteria) and controlling those by the use of carefully placed reflection and/or absorption which could also be aided in the electrical field by “Electro-Acoustic” design of audio systems.

Room acoustics is often analysed and evaluated using predictive computer-generated acoustic models and measurement systems. The 'Auralization' aspect of design software may be used to help acousticians and their clients understand the acoustic performance of the space prior to construction by listening to a room model through high quality headphones. Anechoic acoustic rooms fitted with speaker arrays are also used for this task.

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Environmental acoustics is an area of acoustics which predominately deals with all sorts of outdoor-related noise. This would involve the analysis and elevation of outdoor sound generation, radiation and propagation and provide noise mitigation strategies.

Noise sources would include transportation such as trucks, cars, trains, planes etc. as well as industrial noises such as wind farms and construction noise.

The measurement and assessment of noise is typically based on based on their duration, impulsivity, tonal spectrum etc. and compared to the background noise level and required human noise exposure criteria to then determine the significant of adverse impact of the noise at another specific location.

Environmental Acoustical consultants use various tools on a project by project basis to analyze, evaluate and provide noise mitigation strategies. Some of these revolve around on-site acoustic measurements and sound analysis software. The Sound analysis software help acoustic consultants to develop and predict future levels of noise in a region, produce noise contour maps based on the current and future noise generation to being able to create alternate noise reduction scenarios for comparison and evaluation