Tyco 579-769 Influences on Intelligibility, Frequency of Speech Contribution to Intelligibility

Influences on Intelligibility

Introduction The figure below lists the relative contributions of each frequency band:

Octave Band Contribution to Intelligibility

Relative Contribution to intelligibility

35%
30%
25%
20%
15%
10%
5%
0%
125	250	500	1000	2000	4000	8000

Frequency component of speech

Figure 3-1. Frequency of Speech Contribution to Intelligibility

Audibility is relatively straight-forward and deficiencies are relatively easy to correct. Intelligibility is a more complex characteristic of an installed audio system, involving room acoustics, speaker placement, and psycho-acoustic effects. There are many factors that affect the intelligibility of messages presented over public address systems in public and private spaces. Some major intelligibility factors include:

•Background noise.

•The configuration of the space being addressed.

•The acoustical properties of the materials on the walls, floors, and ceilings.

•The distortion and bandwidth of the sound equipment.

•The characteristics of the person speaking (male/female, accent, microphone technique, etc.)

Some of these factors are under the control of the system designer however many are not. The challenge of good audio system design is to compensate for the factors which cannot be controlled. This ensures that the system installed can provide intelligible messages in emergency situations.

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