SP395 SoundPro Audio Integrator Form7492 Operation Manual
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Noise Tools
The Noise Tools menu contains functions that measure speech intelligibility, room noise levels
and transmission loss. The Noise Tools menu includes:
ALCONS
RaSTI
STI-PA
Noise Curves
Transmission Loss
Audio Stethoscope
The Noise Tools menu.
The ALCONS, RaSTI, AND STI-PA are speech intelligibility tests that gauge how discernable
speech is at a particular position in a room in respect to the speaker. Noise Curves measure noise
in a room characterizing it to a single numeric value taking into account how the human ear
hears. Transmission Loss measures sound reduction (transmission loss) through a partition, wall,
door etc. The Audio Stethoscope combines the microphone input and sensitive audio
preamplifier with the audio monitoring headphones to form an audio stethoscope. Weighted
filters and octave or 1/3 octave band filters may be selected.
Speech Intelligibility - ALCONS
ALCONS is a speech intelligibility test. Percent Articulation Loss of Consonants (%ALCONS)
is a speech intelligibility measure that is intended to mimic the loss of consonants of speech,
which has been shown to be related to loss of intelligibility of speech. It is based on
reverberation time (RT60) and room sound level measurements.
Two different formulas are used, depending on whether the distance from speaker to listener is
less than or greater than the critical distance.
Critical distance is defined as:
Dc = 0.2 * SQRT(V/T).
At less than the critical distance, this formula is used:
ALCONS = (200 * D^2 * T^2) / (V + a)
Beyond the critical distance, this formula is used:
ALCONS = (9 * T) + a
Where,
T = RT60 time, in seconds
V = Volume of the room, in cubic meters
D = Speaker to Listener distance
a = Correction constant, typically 1.5%.
In operation, an amplifier and loudspeaker are positioned at the “speaker” position, and the
SP395 microphone is positioned at the “listener” position. The % ALCONS function measures
RT60 in a speech octave band, and computes the % ALCONS.
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