The XL2 is a precise and reliable RT60 measurement instrument. In addition to the T20 calculation, the XL2 Sound Level Meter now measures reverberation time using the T30 method. This enhancement is in line with the current ISO3382 standard and is free for all XL2 customers.
A reverberation time RT60 measurement represents the time taken for the sound level in a room to drop by 60 dB, after the sound source is suddenly removed. The XL2 employs a Schroeder reverse integration method to measure the RT60 reverberation spectrum in octave bands from 63 Hz to 8 kHz. The optional 'Extended Acoustic Pack' increases the measurement resolution to 1/3rd octave bands in the range from 50 Hz to 10 kHz.
Why do we measure RT60 reverberation time?
The determination of reverberation time in a room is important for several reasons. Firstly, it positively or negatively affects the intelligibility of speech, as well as the timbre of music. RT60 values most appropriate to the function of the room are desirable. Further, reverberation time values are required for the calculation of various parameters, such as the sound insulation of walls or the sound power of noise-generating products.
XL2 measures reverberation time in accordance with ISO3382 Standard
According to the ISO3382 standard, reverberation time can be determined using various measurement methods. The XL2 now offers two such methods; the new T30 method and the current T20 method. The procedure to measure reverberation with both methods is simple. With the T30 measuring method, the XL2 Acoustic Analyzer measures the time for a sound level to drop by 30 dB, while the T20 method measures a drop of 20 dB. These measured values are then extrapolated to 60 dB.
Increased accuracy with RT60 (T30)
The T20 method is used in circumstances where a smaller dynamic range and a lower signal level is appropriate. The T30 method achieves more precise reverberation times and increases accuracy in linear sound decay.
Impulse and gated noise source
Either an impulse or a gated noise can be used as the sound source. A starter pistol, a clapper board or a bursting balloon are typical impulse sound sources. The XL2 Acoustic Analyzer triggers on the impulse and automatically measures the RT60 reverberation time. For precise measurements using gated noise, such as pink noise, loudspeakers with an omnidirectional radiation pattern are recommended.
Omnidirectional Speakers Dodec Set DS2
NTi Audio offers the Dodec Set DS2 as an ideal, cost-effective solution for accurate reverberation measurements. The DS2 fills the room uniformly with acoustic energy. The XL2 automatically performs a series of measurements cycles, calculating the RT60 average in each frequency band. In each measurement cycle, the XL2 provides additional information on the linearity of the decaying sound level, and, after three measurement cycles, the measurement uncertainty is displayed as a percentage. These calculations and additional information are all in accordance with the ISO3382 standard.
Any XL2 can be extended for the reverb measurement in 1/3rd octave resolution with the optional 'Extended Acoustic Pack'. Advanced reverberation time measurement is available with the XL2 firmware Version 3.03 and is free for all XL2 customers.
More at http://www.nti-audio.com/en/products/xl2-sound-level-meter.aspx