sound waves

Reflection, Absorption and Transmission of sound…what is the difference?

Feeling stressed because of noise? Not sure why your environment is so noisy? Noise or sound pollution is an unpleasant and sometimes unexpected sound, that can have many adverse health effects like high blood pressure, heart disease, sleep disturbances and stress. Let us start with the explaining the general concept sound.


SOUND – what it is?

Sound is produced by an object vibrating, which changes the air pressure, and this causes the air to create waves. Like water, sound waves will find the easiest path to penetrate any gap (also known as flanking path). The behaviour of sound depends on materials, temperature, and air humidity. In an enclosed space sound waves can then either be reflected, absorbed, or transmitted.

sound waves illustration


What is sound reflection?

Sound reflection happens when waves hit rigid or hard surfaces and these waves bounce back. The best analogy would be imagining a hard ball, like a tennis ball, bouncing on a concrete floor.  The reflection of the sound waves off hard surfaces will create echoes and the intelligibility or understanding of words, will worsen.

reflective wave

What is sound absorption?

Sound absorption is the process by which a material, structure or object decreases the sound energy in the air. With this example, you can visualise what happens: Spill a glass of water and wipe up the liquid with a sponge. The sponge will absorb the liquid. This is what happens with sound. The ‘sponge’ will absorb the sound, hence sound absorption.

absorbed sound wave

Sound absorption is crucial especially in areas where a lot of concrete, glass, and steel is used as building material. These materials are hard and do not absorb any sound, resulting in echoes and reverberation.

Figuring out what absorption you need, depends on the application and space. An acoustic consultant will be the best to assist and advise. At home it is easy to ascertain if a space needs some fine-tuning by doing the clap-test.

The Clap-Test

Stand in the room and clap your hands. Listen to the sound. Warmer, softer sounds suggest the room already absorbs and scatters sounds in a good way. Harsher, metallic sounds are reasons to look for improvements. There is always something extra you can do to make a room sound even better, but the clap test is a good way to get a sense of what the space needs.

Credit: PSY Acoustics Clap Test (YouTube)

What is sound transmission?

The last term to be explained is sound transmission. As the word transmission implies, sound is transmitted from one space or point to another through or between materials. These materials include air, glass, bricks, concrete…. and sound waves can also move through any medium: gas, liquid, or solids.

Sound transmission and sound insulating go hand in hand when discussing acoustics. You can read more about acoustics in our blogs: “Acoustics Refreshed” and “Understanding acoustic ratings: STC vs RW vs DnTw.”

Back to explaining the concept of sound transmission. In classrooms, offices, and conference halls it is very important to decrease sound transmission from one space to another. This is where people speak of “Sound proofing” and it is quite literally to reduce the amount of sound that can get into or out of a room.

sound transmission

Looking at the physics and behaviour of sound, good acoustics in a room, office, theatre, conference area or concert hall requires knowledge and expertise. This will in turn help alleviate the effects of noise disturbance which can have negative effects on health, wellbeing, and general quality of life.

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