What is interior acoustics?
Room acoustics describes airborne sound in a room, i.e. how it propagates and interacts with the room's surfaces and objects. But it is also about our perception of the room's acoustic properties.
At room temperature, sound travels at 344 m/s (1,250 km/h), resulting in many reflections off walls or objects in a normal-sized room before a sound wave is attenuated to a level below the threshold of hearing. Inside the room, we can only affect the sound wave by its reflections in walls or objects.
Three things can happen to the incoming sound energy:
REFLECTION
A hard surface, such as concrete, glass or wood, acts as a mirror for the sound wave and thus reflects it.
ABSORPTION
A sound wave can propagate into a porous material where it is converted into heat by viscous friction.
DIFFUSION
The sound wave is reflected in a disorderly, almost random way. Like the ocean wave crashing into the rocky shore.
ALL THREE OF THESE PROCESSES ARE IMPORTANT FOR CREATING GOOD ROOM ACOUSTICS IN A ROOM.
Most practical items include all three, but to varying degrees. A completely flat glass surface has very little absorption and scattering, its acoustic properties are dominated by pure reflection. An upholstered sofa, on the other hand, is dominated by absorption and diffusion due to its softness and shape.
The acoustic properties of a room must be adapted to support the activity in the room. Good room acoustics are rarely noticeable. Because there are so many different activities that can take place in rooms, there is no such thing as universally good room acoustics. Each activity has its own challenges, and therefore its own acoustic solution. To assist acousticians in the design of room acoustics, a number of measures have been developed, the most common of which are mentioned below.
THE MOST COMMON MEASUREMENT IN ROOM ACOUSTICS IS REVERBRATION TIME.
Reverberation time can be said to be a measure of a room's echo because it is the time it takes for a sound to decrease by 60 dB from its original sound level. The reverberation time (T) can be easily calculated from the room's volume (V) and absorption area (A) through Sabine's formula, T = 0.16 V/A.
THE ABSORPTION AREA CAN BE UNDERSTOOD AS THE AMOUNT OF "PERFECT SOUND ABSORBING"
and is usually measured in m2S (square meter Sabine). However, a very important assumption for Sabine's formula is that all surfaces of the room must have equal sound absorption or that the room must have a diffuse sound field. A diffuse sound field can be understood as a completely disordered or random sound field. A practical consequence, then, is that a room must have a large amount of scattering properties, or a large amount of diffusion, to be suitable for use of Sabine's formula.
In addition, there are many other acoustic measures that can be used in the design of room acoustics, e.g. STI (Speech Transmission Index), C50 or C80 (Clarity) and G (Room strength).
An example of a "perfect sound absorber" is an open window, since none of the sound hitting the opening will be reflected back into the room.
