How can silence in a room be created?

About Acoustics

The average noise level of a conversation equals 60 dB (A). Where there are no acoustics, i.e. in the open, the sound pressure decreases by 6 dB when the distance is doubled.



In a reverberating room, sound is reflected and reverberations appear. As a result, the level of sound takes more time to decrease, and a minimum amount of sound remains in the room. In a concert hall, for instance, just thi is desired. When there are reverberations, the acoustics are good, the sound comforting and the room silent and balanced. As concert halls are usually big, sound reflections need a long time to return.

In small rooms, by contrast, sound reflections return to us within milliseconds: parallel walls that have even surfaces, such as wardrobes, shutters, blinds or plants, cause reflections to repeat themselves quickly, and so-called flutter-echoes to appear. As the reverberations mix quickly with the direct sound, the typical sound effect of an “empty bathroom“ is produced.

The walls of a balanced room, on the other hand, are uneven enough to distribute the sound (in acoustic terms this process is called diffusion). A sufficient amount of sound absorbing material on the walls, the ceiling and/or the floor helps to prevent undesired reflections or echoes and to shorten the reverberation time. But also the tone colour of a room plays an important role. Many rooms are reverberant, which means that medium and high frequencies linger on longer, or materials that are used in the house, the garden and the kitchen, such as curtains and floor covering, lead to the fact that mainly medium and high frequencies are absorbed. As a consequence, a room may “hum“ or sound “muddy” and poorly defined. 
When music is played in a room or good speech intelligibility is required, any room can be adapted to the specific needs by designing a suitable acoustic concept and using the right materials.

Flutter echoes during a measurement:


Hoekrijgje1

After the first impulse, the needle shows clearly that the walls in the room above reverberate too much. 
When the loudspeaker is directed at the wall, we can observe the following: