### Strutt Help

RC-II Rating

Strutt|Criteria|Ratings|RC-II inserts the Room Criterion Mark II (RC-II) value calculated from the active row of the worksheet into Column D of the active row. The RC-II value is the arithmetic average of the octave band sound levels in the 500 Hz, 1 kHz and 2 kHz octave bands

The RC-II rating uses a Quality Assessment Index (QAI), which is used to assess the amount of deviation of the spectrum from the RC reference curve. The QAI is determined from three spectral deviation factors LF, MF and HF, which are calculated using the following formulae:

LF = 10log_10((10^(0.1 Delta_16) + 10^(0.1 Delta_31.5) + 10^(0.1 Delta_63))/3)

MF = 10log_10((10^(0.1 Delta_125) + 10^(0.1 Delta_250) + 10^(0.1 Delta_500))/3)

HF = 10log_10((10^(0.1 Delta_1000) + 10^(0.1 Delta_2000) + 10^(0.1 Delta_4000))/3)

where DL is the difference between the spectra value and the RC reference curve in each octave band. The QAI is the range from the highest to the lowest of HF, MF and LF, and is used to qualitatively describe the sound according to the magnitude of QAI. If QAI<5, the spectrum is assigned the Neutral (N) descriptor; if QAI>5, then the spectrum is assigned the descriptor of the spectral deviation factor having the highest positive value. The spectrum descriptors used with the RC-II rating are as follows:

• Neutral - RC##(N): Noise spectrum has no particular frequency quality
• Low Frequency Rumble - RC##(LF): Noise spectrum has an excess of low-frequency sound energy and has a 'rumbly' quality.
• Mid Frequency Road - RC##(MF): Noise spectrum has an excess of mid-frequency sound energy and has a 'roaring' quality
• High Frequency Hiss - RC##(HF): Noise spectrum has an excess of high-frequency sound energy and has a 'hissy' quality.
• Noticeable Degree of Sound Induced Vibration - RC##(LF)(A)
• Moderate, perceptible degree of Sound Induced Vibraion - RC##(LF)(B)

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