Acoustics and Vibration Animations
Daniel A. Russell, Ph.D.Graduate Program in Acoustics The Pennsylvania State University All text and images on this page are ©2004-2011 by Daniel A. Russell and may not used in other web pages or reports without permission. |

## Measured Room ResponseThe room is 9.25 m long, 7.65 m wide, and 3.15 m high. The walls are painted cement blocks, and the floor was unpainted concrete (later covered with carpet). The ceiling is not flat, but has a number of cement "cross beams" which may increase the reverberation time by providing lots of reflective surfaces for sound to bounce around. Using a Tascam DA-P1 portable DAT recorder and an Audio Technica AT4041 microphone I made recordings of the room response to a hand clap and to human speech.- Hand Clap (room empty) (0.359 MB wav file)
- Hand Clap (with carpet) (0.455 MB wav file)
- Speech (room empty) (0.467 MB wav file)
- Speech (with carpet) (0.560 MB wav file)
## Estimated Reverberation TimeThe Sabine equation for estimating the reverberation time,T_{60} is
V is the volume of the room, c=343 m/s is the speed of sound in air, S is the total surface area of the room. is the average absorption coefficient for the room, calculated from
_{1} are the individual absorption coefficients for each surface S_{1} and S is the total surface area of the whole room.
The absorption coefficients for cement block walls and floor are:
Using these tables and equations, I calculate the reverberation time for the 1000 Hz band to be approximately 2.6 seconds for the empty room and about 0.93 seconds for the room with carpet. |
Composite photographs of the empty room
Composite photographs of the room with carpet |

Using the slopes of the 1000 Hz plot, I get a measured reverberation time of 3.3 seconds for the empty room and 1.6 seconds for the room with carpet. Notice that these are about 0.7 seconds longer than the estimate calculations from above. This is most likely due to the fact that the Sabine equation does not account for the cavities in the ceiling which can trap sound and allow it to bounce around before returning it to the rest of the room. One must also remember that the Sabine equation assumes a relatively uniform distribution of absorption (which is not true for our carpeted room). There are other equations available which might provide better estimates of the reverberation time for this room.