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Reverberation Time






What is - Reverberation Time?

bulletReverberation is the length of time that a sound continues 
after the sound has been produced.
bulletReverberation is a phenomenon in which the sound attenuates by repeating multiple reflections in the acoustic space surrounding the sound source and the listeners and provides the impression of reverberated sound even after the sound source being cut off.
bulletReverberation time (sound echoed off smooth surfaces such as walls or ceilings) increases in rooms with high ceilings, bare floors and walls and reduces a child's ability to hear clearly.

Reverberation Time - Defined

bulletReverberation Time is defined as the time that it takes for a signal to decrease in intensity by 60 dB.

Suitable - Reverberation Times

bulletAccording to the American Speech-Language-Hearing Association the "Reverberation Times should not exceed 0.4 seconds."
bulletHowever the Acoustical Society of America "Classroom Acoustics"
Document has published the following limits:

Reverberation Time & Speech Clarity & Intelligibility

bulletThe Reverberation Time along with the Signal-to-Noise Ratio  
  affect the Speech Clarity & Intelligibility (see the chart below).
bulletThe data below is from the Acoustical Society of America 
"Classroom Acoustics" Document.

RT (sec)

S/N (dB)

Speech Intelligibility (%)


+ 10

90 %



55 %


+ 10

75 %



30 %

Note: Please be aware that Speaker Characteristics also do affect the
            Speech Clarity & Intelligibility.

Reverberation Time & Speaker Volume 

bulletIf you turn up your Classroom Amplification System excessively 
the amplified sound may be more perceptible to having echo 
because it takes longer for these amplified sounds to die out.

How to Calculate the Reverberation Time?

bulletPlease refer to the Appendix of this "Classroom Acoustics" Document

How to Measure the Reverberation Time?

bulletPlease View the Norsonic Website to find out how it is possible
to Measure the Reverberation Time..

How to reduce the Reverberation Time?

bullet"There are two ways to reduce the Reverberation Time of a Room:
either the volume must be decreased or the sound absorption must be increased." (This quote is from the above "Classroom Acoustics" Document.)
bulletReverberation Times can be reduced with Sound-Absorbent Materials in the Classroom such as: floor carpets and sound absorbing wall panels. The student's bodies also absorb some of the sound.


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Last modified: September 02, 2002