The acoustic characteristics of a room should be suitable for the its usage purpose. In classrooms, for example, a good speech intelligibility is hardly possible if the reverberation time is too long, whereas for a piano sonata in a concert hall, a longer reverberation time may be more effective for a pleasant acoustic sound. These common examples show how essential it is to adjust the reverberation time of a room to suit the planned application.
The reverberation time of a room is one of the most important parameters in room acoustics. The intended use of the room determines the reverberation time requirements. In a classroom, for example, depending on the size of the room, reverberation time should be between 0.5 and 1.0 seconds in order to achieve good speech intelligibility. This is often not the case, particularly in old school buildings, due to a lack of absorbing materials. In a concert hall, a reverberation time of between two and three seconds is desired to create a warm and rich listening experience.
For standard-compliant reverberation time measurements, a sound source with omnidirectional characteristics is needed. The sound energy must be radiated uniformly in all directions. The current building acoustics standards also require a flat frequency spectrum in the relevant frequency range. The DS3 Dodecahedron Loudspeaker fulfills these requirements while delivering high sound power and thus provides a perfect excitation signal for reverberation time measurements.
The XL2 Sound Level Meter provides reverberation time measurements in octave bands from 63 Hz to 8000 Hz. Since many manufacturers of acoustic absorbing materials specify the material properties in octave resolution, the manufacturer data sheets and values measured by the XL2 fit well together. If a reverberation time measurement is required in 1/3rd octave resolution, the "Extended Acoustic Pack" Option can be installed onto the XL2 at any time. The XL2 automatically triggers on an impulse sound source or a gated pink noise. When recording the reverberation times, it is possible to switch between T20 and T30; these two types of analysis differ in the level reduction required to trigger a measurement.
The Room Acoustics Reporter is a PC software for creating reverberation time measurement reports. The RT60 test result can also be compared immediately with a tolerance band; which is specified according to the volume of the reverberant space and purpose of the room; e.g. in accordance with DIN 18041. If the measured reverberation time exceeds the tolerance, the software allows for simulation with additional absorbers. The corrected reverberation time is calculated immediately using the Sabine reverberation formula and shown in the graph. This makes it easy to verify what quantity and type of absorbers have to be brought into the room in order to meet the room specifications.
For the simulation calculation described, the sound absorption coefficients of absorbers from various manufacturers are available for download and import into the Room Acoustics Reporter. The list of absorbers is constantly updated as soon as new absorber data is made available by the respective manufacturers. Also, users can define their own materials for a simulation calculation.
The "Room Acoustics Reporter" software can be installed on any number of computers. A “Room Acoustics Option” must be installed on the XL2 as a permanent license – alternatively the cost-effective annual subscription service "Room Acoustics Reporter 365" may be enabled. The software, including sample measurement data, is available for download for registered XL2 users.
The Room Acoustics Reporter requires firmware V4.20 or higher on the XL2. Users with a calibrated XL2-TA with older firmware should contact NTi Audio. Detecting reverberation times in 1/3rd octave resolution requires the Extended Acoustic Pack Option on the XL2.
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