What is Reverberation and Reverberation Time?

Acoustic Tile

What is Reverberation and Reverberation Time?

Reverberation time (in seconds) is the time it takes for a sound to decay by 60decibels or a millionth of its sound energy.

In modern architecture, reverberation issues can be a result of large hard flat surfaces. Current design trends typically use large areas of glass, vinyl floors and other sleek hard building materials. We don’t dispute that these spaces look fantastic. However, excessive reverberation (echo) can have several adverse effects on the room user, such as loss of speech intelligibility and irritating echo.

Speech intelligibility in layman terms is the scale of how easy it is to hear the spoken words of another person from across the room. Rooms that have high reverberation times reduce speech intelligibility making it difficult to understand others when communicating. High reverberation levels also lead to higher ambient noise, causing the sound to bounce around the room instead of being absorbed or dissipated

Reverberation time is measured in seconds. A higher reverberation time means a longer echo and a compromised acoustic environment. We can treat high reverberation times by installing additional absorption into the room. High-quality absorbers such as Alpha, Echo & Absorb can be strategically placed around a room to drastically reduce the reverberation time, creating an improved acoustic environment and user wellbeing.

Tech Materials products undergo thorough verification by the University Of Salford Acoustic Department to qualify their effectiveness. They are tested to latest standard BS EN ISO 354:2003. Below summarise the coefficients at 1/3 octaves typically used in room calculation, We hold coefficients for all frequencies from 80hz – 8khz for specialist treatment.

Coefficients explained – This section will hopefully explain coefficients in layman’s terms

Absorption Coefficients – This figure represents the absorption percentage of materials, 0.90 @250Hz means that 90 % of the 250hz soundwave that strikes our absorber will be absorbed. Within Echo acoustic panels, the tiny membranes of the foam vibrate converting the sound energy into movement and heat energy. Stopping the sound re-entering the room and helping to reduce the reverberation time in the room.

0 = Perfect reflection 1 = Perfect Absorption

αw, Alpha weighted: Is a weighted single number reference. It aims to allow consumers to compare products side by side. It attempts to express the effectiveness of an absorber using 125, 250, 500, 1000, 2000, 4000 Hz.

Class – A to D, A being the best it categorises αw coefficients into bands of effectiveness for the consumer to compare products.

NRC – Noise Reduction Coefficients. It is the arithmetic average of frequencies of 250, 500, 1000 and 2000 Hz. Again a way to allow for consumers to compare products side by side, the predecessor of αw. Still used typically in the ceiling grid industry. It may be used for products where including the 4000Hz in αw would show a lower rating.

BB93 Tmf Specifically for schools and education, mid-frequency reverberation time is the arithmetic average of the reverberation times in the 500 Hz, 1 kHz and 2 kHz octave bands, or the arithmetic average of the reverberation times in the one-third octave bands from 400 Hz to 2.5 kHz. (Although these are not mathematically equivalent, in practice the difference will be small, and in the interests of simplicity and ease of measurement, either is acceptable)

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