1.3 THE HUMAN EFFECTS OF SOUND

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The human ear does not hear all sounds as equal.

One simple measure is the `phon', it is based on experimental data. (Note that Lp = phon at 1KHz). [Source Irwin and Graf]

Another measure that is adjusted for loudness is the `sone'. This compensates for what we would consider a perceptual loudness level.

As we saw before, sound is made up of a variety of frequencies, so we must determine how all of the components are combined into a single value.

The loudness index contours are given below. [Irwin and Graf]

Try problems S13, S14, S15

We can use a similar method for the perceived noise level using the `noys' graph below, and use this in place of the graph in the previous method. [source Irwin and Graf]

1.3.1 Background Noise

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The previous measurement methods are suited to measuring for specific noise sources, but there is also ambient background noise.

Noise Criteria Curves, use the given curves for Noise Criteria (NC) or Preferred Noise Criteria (PNC) [Source Irwin and Graf]

To use the curves, plot on values, and the highest NC curve that is touched is the NC level

There are some basic suggested levels for background noise indoors,

try problems S16, S17, S40

1.3.2 Weighting Sound Values to Compensate for the Human Ear

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Previous methods use graphical techniques to adjust sound response.

We can also use an adjusted weighting [source Irwin and Graf]

Try problem S18

1.3.3 Speech Interference

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A simple measure to estimate interference with human speech is the Speech Interference Level (SIL) and more recently the Preferred Speech Interference Level (PSIL)

The values can be correlated to speech levels and distances that they may be heard at, [Source Irwin and Graf]

Try problem S19