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Laboratory Evaluation of Annoyance of Low Frequency Noise

Annex A
1. Data from the Subjective Evaluations

1.1 Subjective Data from the Reference Group

The following tables show the evaluation of the various noises averaged over the eighteen test subjects in the reference group. Each test subject indicated his/her response by setting a mark on a scale consisting of a 10 cm long line.

An example of one of the annoyance scales is given here:

Average rating of loudness

Average rating of annoyance day/evening

Average rating of annoyance at night

Average of percentage of ‘yes’ responses

1.2 Statistical analysis of the subjective data from the reference group

All data (i.e. subjective evaluation, sound example number, nominal presentation level, measured A-weighted level (dB(A)), A-weighted level in the frequency range 10 Hz – 160 Hz (L_pA,LF ), repetition number, gender and age) were used as input to a statistical analysis program (Statgraphics 4.0). The analysis was made for each parameter separately.

The table below shows the significance levels for the different factors. If the number is less than 0.05, this factor has a significant effect on the evaluation on a 95% level or above (this means less than 5 % probability for drawing a wrong conclusion). If the number is above 0.05 it cannot be proved that this factor has a significant effect upon the relevant evaluation.

Table A-1.
The significance level of different factors that may influence the evaluation made by the reference group of listeners.

As expected, the noise example, the nominal level, the dB(A) level and the low-frequency level (L_pA,LF), all have a significant influence upon the evaluations from the test persons.

The repetition number (round 1 or round 2) is not significant and thus no training effect is seen in the data.

The gender of the test persons has influence on the evaluation of annoyance during the day and during the night but not on the evaluation of loudness and on the yes/no question about whether the noise is annoying or not.

The age of the test subjects is a significant effect. An inspection of the analysis shows that this is caused by one subject, age 21, with responses in the low end of the scale and another subject, age 24, with responses at the high end of the scale. The remaining subjects, age 19 to 25, gave responses in between.

1.3 Subjective Data from the Special Group

The same 10 cm long scale was used in the pilot experiment with the special group. Each of the four test subject indicated his/her response by setting a mark on a scale consisting of a 10 cm long line. The following tables show the evaluation of the various noises averaged over the four test subjects in the special group.

Average rating of loudness

Average rating of annoyance day/evening

Average rating of annoyance at night

Average of percentage of ‘yes’ responses

1.4 Statistical analysis of the subjective data from the special group

All data from the special group (i.e. subjective evaluation, sound example number, nominal presentation level, measured A-weighted level (dB(A)), A-weighted level in the frequency range 10 Hz – 160 Hz (L_pA,LF ), repetition number, gender and age) were used as input to a statistical analysis program (Statgraphics 4.0).

As the special group of listeners consists of only four persons, it is almost irrelevant to test for normal distribution of the data. Despite of this it was decided to perform an analysis of variance on the data from the special group. The analysis was made for each parameter separately.

The table below shows the significance levels for the different factors. If the number is less than 0.05, this factor has a significant effect on the evaluation on a 95% level or above (this means less than 5 % probability for drawing a wrong conclusion). If the number is above 0.05 it cannot be proved that this factor has a significant effect upon the relevant evaluation.

Table A-2.
The significance level of different factors that may influence the evaluation by the special group.

Noise examples: The annoyance evaluations are found to be close to the limit for being significantly different. The Annoyance day is just below the limit (i.e. the noises are evaluated as different) whereas Annoyance night is just above the limit. This may mean that all the noises are evaluated almost equally annoying by the special group. The evaluation of loudness is not significant. The result of the yes/no question is a significant effect, i.e. some noises are found to be annoying others are not. This is somewhat in contradiction to the findings from the annoyance scaling. The limited number of test subjects in the special group probably causes the contradiction.

The nominal level, the dB(A) level and the low-frequency level (L_pA,LF) are significant in all cases.

The repetition number (round 1 or round 2 with the same presentation) has no significant influence, which shows the absence of a training effect.

The gender of the test persons has no influence on the evaluations. The age is significant for loudness evaluation and for the response to the yes/no question but not for the annoyance evaluations.

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