For an airborne partition where both the source and receiving rooms are smaller than 25 m3, the low-frequency procedure requires 20 additional level measurement positions. Combined with the requirements to treat each band separately, and to individually correct receiving room levels for background noise, the low-frequency procedure adds substantial bookkeeping to a project. Thankfully, Building Acoustics Partner handles all this bookkeeping for the user. The procedure is automatically triggered when needed, and intelligently integrated into the standard workflow. HBK 2255’s rigid microphone extension rod also makes it easy and safe to measure in room corners.
When the receiving room is smaller than 25 m3, there is also a low-frequency procedure for reverberation time measurements. The low-frequency reverberation time procedure requires that the 63 Hz 1/1-octave band is measured instead of the 50 Hz, 63 Hz and 80 Hz 1/3-octave bands. This single 1/1-octave band reverberation time is used instead of the 1/3-octave band values in the calculation of DnT and/or R'. The requirements for source and microphone positions are the same as for the standard reverberation time measurements.
HBK 2255 and Building Acoustics Partner implements the low-frequency procedure for reverberation time without any extra effort from the user. Instead of measuring all reverberation time positions separately for 1/1- and 1/3-octave bandwidths, HBK 2255 can measure reverberation time for both bandwidths simultaneously, halving the number of reverberation time measurements needed. The app automatically replaces the 50 Hz, 63 Hz and 80 Hz 1/3-octave reverberation time values with the 63 Hz 1/1-octave reverberation time when required.
The low-frequency procedure in ISO 16283 undoubtedly improves the reliability of low-frequency sound insulation measurements in small rooms but adds substantial complexity to the measurement procedure, bookkeeping and calculations. HBK 2255 and Building Acoustics Partner allow users to gain the benefits of this method in the simplest and most efficient way possible.