Why our voice echos in an empty room but doesn't echo in a room filled with lots of furniture and other things ?
Why our voice echos in an empty room but doesn't echo in a room filled with lots of furniture and other things ?
The speed of sound is roughly vs=340 m/svs=340 m/s (1100 feet per second), and hearing an echo requires at least
- a perceptible time between the end of your shouting and the onset of the returning wave (not sure how long, but lets say tc=0.1 stc=0.1 s as a guess (a lot of human perception works on time scales not to far from that))
- that the returning wave be sufficiently loud to be distinguished above the background noise
- that the returning wave be sufficiently distinct from the returning waves from other surfaces
- a surface that gives a good reflection
So lets think about how a indoor situation might fail:
-
The room is too small. If the longest dimension is much less than vs∗tc≈34 mvs∗tc≈34 m then the maximum delay between the end of a loud shout and the onset of the echo may be too short for you to distinguish the echo
-
The multiple returns from the several walls are overlapping and preventing you from picking out one echo.
-
The ventilation system and other ambient noises are comparable in volume to the echo.
-
The walls may be non-flat or made of materials that absorb much of the sound energy (this is often a design goal for large spaces)
The speed of sound is roughly vs=340 m/svs=340 m/s (1100 feet per second), and hearing an echo requires at least
- a perceptible time between the end of your shouting and the onset of the returning wave (not sure how long, but lets say tc=0.1 stc=0.1 s as a guess (a lot of human perception works on time scales not to far from that))
- that the returning wave be sufficiently loud to be distinguished above the background noise
- that the returning wave be sufficiently distinct from the returning waves from other surfaces
- a surface that gives a good reflection
So lets think about how a indoor situation might fail:
-
The room is too small. If the longest dimension is much less than vs∗tc≈34 mvs∗tc≈34 m then the maximum delay between the end of a loud shout and the onset of the echo may be too short for you to distinguish the echo
-
The multiple returns from the several walls are overlapping and preventing you from picking out one echo.
-
The ventilation system and other ambient noises are comparable in volume to the echo.
-
The walls may be non-flat or made of materials that absorb much of the sound energy (this is often a design goal for large spaces)
