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Acoustic Response of a Room

Measuring the acoustic response will enable you to properly adjust the equalizer settings on your sound system for optimum performance.  A typical procedure is described below:

Key Settings: 
Mode:  Real-Time
Views:  Spectrum, Time Series
Amplitude axis:  Logarithmic
Frequency axis:  1/3 Octave
Standard Weighting:  Flat
Mic compensation:   Yes, if your mic is not sufficiently "flat"
Sampling rate:  44100Hz
FFT size:  8192 or 16384.
Decimation:  1
Averaging size:  infinite
Smoothing Window:  Uniform
Sampling Format:  16 bit, Mono

Procedure:
  • Set your sound system equalizer settings to zero or take it off line.
  • Connect a pink noise generator to the input of your sound system.
  • Place the measurement microphone in the center of the room.
  • Adjust the sound card input gain and/or sound system output gain to produce an "on-scale" reading on the time series view.
  • Run the analyzer and examine the spectrum view.  Stop the analyzer when the averaged spectrum response has settled sufficiently.

    Interpret the results:
    An acoustically "flat" room will produce a perfectly flat spectrum.  In this instance, we are not concerned so much with the absolute values of the spectrum as with their relative response.  Each 1/3 octave band corresponds to a slider on your 1/3 octave equalizer.  Simply adjust the sliders on your equalizer to compensate for the acoustic response of the room.  You may wish to run a second test to verify the results.  

    Narrowband frequency response (optional):
    One limitation of 1/3 octave analysis is that each band represents a rather wide span of frequencies.  If narrowband frequency components are present, 1/3 octave analysis lacks sufficient resolution to detect these components.  Set the frequency axis scaling to linear and substitute white noise instead of pink and repeat the measurement above (you may wish to use a smaller FFT size such as 1024)