Why Acoustics Matter

Strategic Analysis

Building generations with strong personnel and competitive communication skills, is starting from education and affected by the surround environment. The surround environment has a direct influence on human health, social behavior and productivity, accordingly the quality of life will be affected.

Classrooms or Lecture rooms are typical surround environment for receiving education, in which its acoustics , and speech intelligibility are major, often neglected, aspects in the learning process. Typical classroom acoustical design, worldwide, according to study that has been done in Florida (By Mr. Siebein, 1998) , concluded that speech intelligibility in those classroom is 50%, i.e. The students receive half of the information delivered by the teacher, especially if they are sited at the rear rows.

Thus; students does not only receive half of their education, but they have to work hard, joining down the missing information. Identifying the obstacles for poor classroom acoustic design, has been recognized for proposing adaptive plan and solution.

Reverberation and Echo

Each room has acoustic (sound-) reflecting areas, so that reflected sound waves are added to the direct sound waves. Depending on the character of reflections they can be divided into reverberation and echo.

The reverberation is composed of many room reflections. The first reflections have to reach the ear within 50 milliseconds (ms) to be a reverberation. If the reflection(s) will be received later, then the ear can distinguish between direct sound and reflection, feeling another sound source.

Increasing the speech intelligibility in a room requires decreasing the reverberation time. The reverberation time is defined as, the reduction of sound pressure level by 60 dB after the acoustic event. The reverberation time can be reduced, by using a loudspeaker with a wide and uniform sound distribution pattern.

Speech Intelligibility


The Speech Transmission Index (STI) provides the sound transmission with an objective value, focusing the physical phenomenon of sound mixing. In short, the easiness or difficulty of speech listening can be assessed by the resemblance of the original sound wave and transmitted sound wave to ears.

The STI values range from 0 to 1. If the transmitted sound to ears includes much more reflected sound than the original, in other words, the transmitted sound badly differs the original, the STI value decreases toward 0. (poor intelligibility) Contrarily the transmitted sound resembles the original sound, containing less reflected sound, the STI value increases up to 1. (good intelligibility) The STI value is generally required more than 0.6 for human speech to be intelligible.

Click here to hear and feel the difference in STI level corresponding to speech intelligibility