What is Reverberation Time?
Sound produced in a room will repeatedly bounce off reflective surfaces such as the floor, walls, ceiling, windows or tables while gradually losing energy. When these reflections mix with each other, the phenomena known as reverberation is created. Reverberation is thus a collection of many reflections of sound.
Reverberation time is a measure of the time required for reflecting sound to “fade away” in an enclosed area after the source of the sound has stopped. It is important in defining how a room will respond to acoustic sound.
Get a feeling for reverberation times in various rooms, just by clapping your hands!
How is Reverberation Time defined?
The reverberation time is the time the sound pressure level takes to decrease by 60 dB, after a sound source is abruptly switched off. Commonly-used abbreviation for Reverberation Time is RT.
Reverberation Time values vary in different positions within a room. Therefore, an average reading is most often taken across the space being measured.
Rooms with a reverberation time of < 0.3 seconds are called acoustically “dead”. Typically, the reverberation time increases with the room volume. Smaller rooms with a reverberation time of > 2 seconds are commonly considered to be “echoic”.
Why is reverberation important?
Too much reverberation has a negative impact on the intelligibility of speech. This can, for example, make it hard to hear what a class teacher is saying.
Reverberation is also particularly noticeable in a place of worship where the sound may be heard for several seconds while it fades away. The main reason religious leaders pronounce their words clearly and talk slowly, leaving small gaps between sentences, is to overcome this reverberation and make their speech clear (such a manner of speaking also has a beneficial side-effect of sounding reverent).
Conference rooms are an especially challenging acoustic environment. Collaborative white boards, stylish glass walls and the obligatory large table are all highly-reflective surfaces for sound. This tends to increase the reverberation time of the room which impacts speech intelligibility.
Typically, reverberation times can be reduced by damping using absorbing materials such as thick carpets, curtains, upholstered furniture or dedicated sound-absorbing panels. Furthermore, the presence of people in a room reduces the reverberation, and therefore produces a lower reverberation time value compared to the unoccupied room.
On the other hand, too little reverberation will reduce the rich, warm acoustic sound from an orchestra in a concert hall.
Get the right product for your measurements
The XL2 Acoustic Analyzer measures the reverberation time automatically, thus minimizes the time and effort spent measuring. It stores all data onto the SD card for direct transfer to the computer for detailed data analysis and reporting.
The DS3 Dodecahedron Speaker Kit offers a powerful omnidirectional sound source suitable for most applications, from small to relatively large rooms.
- lightweight for the 120.5 dB it delivers
- wireless remote control for mute/unmute
- the equalized pink noise covers the acoustic frequency spectrum from 100 Hz to 8 kHz
- low power compression ensures stable sound level over long time period
- re-useable at no expense
- meets all standards as it is not an impulsive sound source
An active portable speaker may be used for basic reverberation time testing. The MR-PRO Signal Generator provides the required randomly generated pink noise signal into the portable speaker.
The δ-Clapper is an acoustic impulse sound source for measuring reverberation time. The special design delivers a wide frequency range, and produces a bounce-free and easily reproducible impulsive sound.