The influence of background noise level and signal duration on the judged annoyance of aircraft noise

THE INFLUENCE OF BACKGROUND NOISE LEVEL AND SIGNAL DURATION

ON THE JUDGED ANNOYANCE OF AIRCRAFT NOISE

by

G. W. Johnston and A. A. Haasz

L Q •• ~

THE INFLUENCE OF BACKGROUND NOISE LEVEL AND SIGNAL DURATION ON THE JUDGED ANNOYANCE OF AIRCRAFr NOISE

by

G. W. Johnston and A. A. Haasz

Submitted Mareh,

1978

t

Acknowledgements

We wish to thank W. G. Richarz for his help in the preparation of the nQise tapes. Also, we wish to express our appreciation to the jury members whose consciencious efforts have yielded the results presented in this paper. This research was supported by the Ministry of Transport, Canada.

r---- - - - -- - - --

---Summary

The effects of traffic background noise on the judged noisiness of aircraft flyover events has been further examined in the present study. A series of 72 flyover events were assessed by a jury of

35

observers, during 12 separate listening sessions conducted in a controlled test area designed to simulate typical indoor listening conditions . Each aircraft signal was superimposed on a controlled random traffic background signal having a dur a-tion exceeding that of the aircraft event.

The primary conclusions reached in this .investigation show that the presence of a steady mean traffic background noise can reduce the perceiVed noisiness of aircraft flyover events, provided that the judgment time aváilable is su:fficiently greater than the. event time (time in excess of background). For a given pea.k. event level, a reduction in associated background noise of 21 <IDA is shown to be equivalent subjectively to an increase of

5.5

<IDA in peak. event level, with fixed background conditions. Best linear data regressions were found using an index of the form Lo +

keLp -

Lo), where

Lp

and Lo are the peak. signal and mean background levels, respectively. Although the regressions obtained with the noise pollution index, LNP' for single event judgments generally showed a lower correlation than the Lo and

(Lp -

Lo) regression variables the score data did show a number of significant trends which are

also associated with the LNP index variations camputed for single noise events.

CONrENrS

Acknowledgements

i i

Sunn:na.ry

iii

1.

INTRODUCTION AND BACKGROUND

1

2 .

PROCEDURES

AND

MEn'HODS

3

2.1

Design and Preparation of Noise Tapes

3

2.2

Digitization of Tapes and Index Ca1culations

4

2.3

Preparation of Sound Reproduction System and Jury Listening

Roam

5

2.4

Jury Selection and Judgement Procedures

5

3.

RESULTS

ANI)

DISCUSSION

6

4.

5·

3.1

Single Regressions - Single Events

3.2

Double Regression - Single Events

3.3

Statistica1 Analyses

3.4

Session Results and Analyses

CONCLUSIONS

REFERENCES

TABLES

FIGURES

APPENDIX A - INSTRUCTIONS TO JURY MEMBERS

6

7

9

12

13

15

1 . INTRODUCTION MD BACKGROUND

The present methods of rating the communi ty response to aircraft

flyover events and airportnoise levels in gener.al ·do not explicitly include

the effeds of the community background noise that co-exists with the aircraft noise signals. The inherent as sumpti on , amply valid during the time frame prior to late 1960's, was that the aircraft noise events of most concern dominated the existing background levels by a minimum of 10 dB so that the total noise annoyance could be determined from the aircraft signals alone.

At sufficient distance from the airport site, this .condition was no longer

fulfilled; however, in these locations the noise problems were also less severe than nearer to the airport so that the complications introduced by the background were largely ignored. Beginning ih the middle and late 1960's aircraft noise suppression activity proceeded with a considerably accelerated pace. A much improved understanding of the main noise sources together wi th

some improved end products resulted. Continuing into ·the seventies this

acti vity has permitted a ,second generation of quieted aircraft to be presently

considered with rather remarkable noise red.uctions now feasible. Simultaneously,

new community noise sources have emerged principally due to high speed ground transportation modes.

The current problem of determining the contribution of aircraft noise signals to the total community noise response is therefore characterized by rather substantially differing conditions than those existing at the time when

the C.N.R., N.E.F., N.N.I., etc., indices (see Ref.

7)

were first introduced.

In particular the aircraft signal to background noise levels are expeded to be lower and potentially substantially lower than they were originallY. Thus

level differences as low as 10 ~ 15 dB are feasible at ground locations close

to and at the perimeter of the airport site. Under these condi tions the role

of the background noise must be included in any accurate assessment of' ·~he

community noise impact due to aircraft opera ti ons .

It is interesting to note that the original C.N.R. index proposed .

in 1953 by Rosenblith and stevens (Ref. 2) for the U.S.A.F. included explicitly

a correction for the background noise. In the development anel evolution of

this index to its present N.E.F. form (on the North American continent) the explicit background corrections have been dropped (lost) and background con-siderations are only vaguely and implicitly built into the land use tables associated withthe N.E.F. index. The first controlled background testing

appears to have been carried out by Pearson (Ref. 3) in 1966. Pearson

con-cluded that the addition of background noise reduced the perceived noisiness of aircraft flyover by about 5 dB when the aircraft noise and the background noise were of equal intensity. However, the standard deviation of the results achieved were of the same order as the effect detected so that Pearson' s

results remained inconclusive. In a later study by Nagel, Parnel and Parry

(Ref.

4),

a much greater influence due to background noise was measured. The

data of Ref.

4

indicate a reduction of' about 30 dB for conditions where the

aircraf·t signal and the background noise level are equal and where both signals

have similar spectral distributions. Finally, the studies of Powell and Rice (Ref. 5) in 1975 confirmed the earlier quantitative results of Pearson for randomtraffic noise backgrounds, with individual aircraft flyover events. Powell and Rice also showed limi ted agreement wi th Robinson' s noise pollution

concepts and his LNP index (Refs. 6, 7, 8) for both the individual noise event

judgments and also a more extended noise exposure occupying approximately 1:2 minutes duration (9 successive events).

In addition to these experiment al s'tudies the ex'tensive activi'ties and proposals by D. W. Robinson with respect to the noise pollution index, LNP, must be noted (see Refs.

7, 8).

The LNP index is completely general in terms of the types of noise ~vents that may be quantita'tively assessed either

separately or concurrently. The role of the background noise may be there-fore explici tly defined in'terms of 'the index for any number and 'type of aircraft even'ts. The price of 'this information is the requirement for the provision of at least an approximation to the ac'tual sound level time his'tory for 'the noise event or events including the associa'ted background levels.

In view of this background,the sUbjec'tive testing set out in the present study had the fOllowing main objec'tives:

(i) To define the separate effects of the mean background level and the signal duration (and any interaction between the two) on the judged noisiness of single event flyover aircraft events presented in a traffic (highway) noise background.

(ii) To carry out a quantitative laboratory examination of Robinson' s Noise Pollution Index for a series of aircraft flyover events superimposed on a sui'table traffic (highway) noise background having a total 'time duration of approximately 10 minutes each and covering a practical range of indoor energy equivalent levels and level (time) deviations.

"The first of the above objec'tives .stems from 'the observation that if the

noise pollution concepts of Robinson are borne out then the signal duration

"time (or more properly ratio of the signal duration to 'the total judgement

time) will centribute to the LNP value and the associated judged noisiness of the event. Moreover the earlier studies of both Pearson and also Powell and Rice did not consider this separate variable. In both cases the value of this ratio (i.e., signal duration divided by to'tal judgement time) although" un-specified, appears to be fairly close to unity, while in cases of practical interest this ratio is expec"ted to be very much lower indeed.

The second of the above objec'tives was 'to be achieved by a series of indoor jury listening tests of the type used by both Pearson (originally) and by Powell and Rice, but wi'th 'the fOllowing changes:

(i)

The jury would be loca'ted in a controlled non-anechoic test area more closely simulating actual indoor aircraft noise exposure situations. (ii) The judged aircraft noise events would cover a broader range of indoor

energy equivalent (Le~) levels and deviations than those used by Powell and Rice, thus extending 'the range of variation of 'the LNP index more significantly.

(iii) Traffic noise backgrounds including a larger standard deviation in levels (typical of medium to intense 'traffic noise environments) would be utilized.

2 • PROCEDURES AND MErHODS

2.1 Design and Preparatiori of Noise Tapes

A series of 12 noise tapes were produced for the 1istening tests, each consisting of a constant mean level traffic ·background nOise, having a standard deviation of' levels of 4.0 dBA, with six separate1y recorded aircraf't f1yover events superimposed The duration of each tape or session (To) used was 660 seconds, and rthe period associated wi th each aircraft flyover event (to) was 110 seconds. The total f1yover event time is composed partia1ly of a period during which the aircraft noise level exceeds the mean background level (T) and partially of a period without aircraf't signa1 (to-T).

Four mean levels of traffic background noise were selected and combined with six aircraf't event signals of constant duration and appropriate level to yie1d a constant Leq va1ue over the entire session, 660 seconds. Three constant va1ues of Leq (session) and associated aircraft signal duration were generated in this fashion at levels of 66, 70 and 76 dBA to complete the definition of the 12 tape set. The selection of the appropriate aircraft event levels at a given background level (Lo) to yield a constant session Leq was aided by a simp1e computer program based on a triangular level variation in time f'or each aircraft noise event.

An

idea1izêd tape design is sketched be10w with all random level f1uctuations suppressed for simplicity.

Level Lo I I I I t- '[ ---+f 1

I

' - ' [ - 1 3 I

I--

t ol

-I-

to ₂

.. t-

to ₃

t-Ti/toi

=

constant

=

0.20; 0.40; 0.80; I '[

I

r- 4Î I I

-I·

t₀₄

-r-T 0 t _oi

=

110 sec; t ₀

5

I , î ' [ - ,

, 6 ,

time

...

To

=

6t 0

=

660 sec.

The nominal peak aircraf't signal levels usedto develop the 12 session noise tapes covering four levels of mean background noise (Lo) and

3

levels of signal duration above background (T) are gi ven in the fol10wing tab1e.

' - ' .'. '

Session Leq and Leq -

66

L -

70

Leq -

76

Signal Duration T

=

22 sec T ~q44 sec T

=

88

sec Mean Background Noise Level L

=

44

66

71

76

66

71

76

91 71 76

0

81 86 86

81 86 91

81 86 91

L ₀

=

51

66

_{81 86 81}

71

76

66 71 76

_{81 86 86}

86 71 76

_{81 86}

₉₁

.

L ₀

=

58

66

_{81 86}

71

76

₇₁

66 71 76

_{81 86 81}

81 71 76

_{81 86}

₉₁

L

=

65

66 71 76

66 71 76

76 71 76

0

81 86 66

81

86

76

81 86 91

The final jury session tapes were prepared by electrically combining and re-recording preselected field recordings.of suitable aircraft overflight and traffic background noise events. The final tape recordings were then made by passing the signal through a

3

dBjoctave attenuating filter to simulate

the expected building transmission loss in the important subjective frequency range, for typical indoor listening conditions. The field recorded aircraft overflight signals were obtained at several locations adj acent to the Toronto International Airport. A number of commercial transport aircraft types were field recorded including a variety of take-off, approach, holding and en route flight conditions. Appropriate selections were then made for inclusion in the final jury ·tapes. The traffic background noise tapes were also derived from a series of field measurements taken adjacent to multi-lane, limited access intercity highway routes. A variety of trucks, buses and al tomobile

signals were thus included in the final traffic signals. 2.2 Digitization of Tapes and Index Calculations

Analogue copies of the final jury tapes were obtained to permit digital calculation of the necessary signal characteristics implicit to the appropriate noise indices. The digitization of the frequency weight test '

signal was accomplished by passing the output from the tape recorder (NAGRA) through a preamplifier unit (XlO gain), through a log voltmeterjconverter

(Hewlett Packard) and then to the AD converter; see bloek diagram below. NAGRA

The analogue signal was sampled by the digitizer at a rate of 1000 samples per second, corresponding to 500 samples pêr second in real time frame .

• Thus each complete noise session having a duratiön of 660 seconds was

sampled 330,000 times during digitization.

in

qrder to correctly simulate

the response characteristics of the ear, in the digitization, the frequency response of the log voltmeter converter was adjusted. The 50 Hz frequency range setting of the logging unit used (see Fig. 10) was found to be suitable.

The input voltage range of the digitizer used was +1.0/-1.0 volts which corresponds to a digitized output in the range 0-4,095. Since the output of the logging unit is constrained to the range 0 to +1.0 volts a resolution of 0.5 mV, corresponding to 0.05 dB, was obtained in the final digi tized signal. This data was again tape-recorded for input to sui table

computer routines to develop the necessary sign,al calcuiations. The main

digital calculations involved the evalua'_{tion of energy equivalent level (Leq)}

and standard deviation in levels

(0'-)

for the indi vidual aircraft flyover

events (duration 110 seconds) and for the complete session (six events, 660 seconds).

2.3 Preparation of Sound Reproduction System and Jury Listening Room

A lounge area at the Institute was prepared for the jury evaluations. Four high quality speaker units capahle of good audio performance in the range 100 Hz-lO,OOO Hz were carefully located at fixed locations in this area. The

speaker locations were chosen so as to provide as uniform a sound pressure

level at the listening positions. as possible. Two of the room walls were

covered by drapes and the floor was carpeted, the remaining room surfaces were relatively (acoustically) hard. The resulting room reverberation was therefore low and careful measurements with the listening tapes played through the final speaker configuration confirmed that variations in the A weighted

signal at all juror posi tions did not exceed

1.5

dB. Jurors were instructed

to utilize the same seat location during all test sessions. The noise isolation in the listening area was adjusted so that the inherent maximum background level,

without speaker input, was 32 dBA. This level is more than 10 dB below the

mean level of any artificial (traffic) background noise used with the jury tapes.

2.4

Jury Selection and Judgement Procedures

Five separate groups of seven observers each were separately selected and used to evaluate all of the 12 prepared noi se tapes. Three of the groups were composed of graduate students at the Institute, one group was selected from the staff at the Institute and the final group comprised under-graduate senior engineering students from the University of Toronto, st. George

Campus. Each juror selected was given an audiometric check prior to the

listening sessions; all jurors were shown to have audiologically normal hearing. Since the majority of the observers had no previous experience in judging noise signals of this type, a preliminary learning test sequence was utilized for allobservers. During the learning sessions the observers were exposed to typical flyover noise signals as weIl as the extreme noise

conditions inherent in the prepared tapes. The learning sessions also acquainted the observers with the types of judgements required, the general character of the noise events and the degree of concentration required. Each group of observers a'ttended three separate meetings each having a duration of

about 90 minutes. The first meeting was devoted to the learning test sequence; the last two meetings comprised the "live" evaluations and these eaCh included the evaluation of six noise sessions, with ten minute breaks scheduled aft er' the second and fourth sessions.

The task of the jurors was to rate, ,on a numerical scale fram 1 to 9 inclusive, their subjective assessment of thei:r "annoyance" reaction

(more precisely their subjective impression of the "perceived noisiness", as defined by Kryter, Ref.

9)

to the aircraft noise signals presented. Jury ratings were carried out with three different evaluations, as follows:

Part A

Part B

Part C

Each individual aircraft flyover event was judged as it appeared in the traffic background noise, on a numerical scale from 1 to

9·

Each group of six aircraft events (one session) was judged as they appeared in the traffic background noise also on a numerical scale fram 1 to

9.

Each group of six aircraft events (one session) and the associated background noise, as a single extended duration event, was judged on a scale fram 1 to

9.

Appendix A is a copy af the "Instructions to Jury Members" prepared for these evaluations. This outlines additional testing details and includes as well the suggested judg~ent criteria to be used ,in the assessments of the noise signals based on the work of Kryter, Ref.

9.

3 •

RESULTS AND DISCUSSION

3.1 Single Regressions - Single Events

For each of the three signal durations

(T)

used, four conditions of background intensity level (Lo ) were tested. Slight variations were encountered in the test background intensity conditions, at the differing signal durations; however, by averaging the subjective response of all observers at all values of Lo, for a given signal duration, the actual test scores were corrected to the following standard mean background conditions for all signal durations.

Lo

=

47.5

dBA

Lo

=

54.5

dBA

Lo

=

61.5

dBA

Lo

=

68.5

dBA

The corrected stibjective scores for each session, averaged over all

35

observers for the standardized background levels, are plotted in Figs. l(a), l(b), l(c) for the signal durations T

=

22,

44

and

88

respectively. All aircraft flyover event signals were presented with a preceding and succeeding background signal at mean level Lo such that the total judgement time available

was 110 seconds. , Thus the ratios of signal duration time to total judgement time are 0.20, 0.40 and 0.80 for the three aircraft signal durations used.

In

addition,a single regression of the mean subjective score on the peak value of the aircraft signal level has been obtained for each signal duration and each standardized background level. The regression lines obtained are included in these same figures together with the values of the associated correlation coefficients. It is noted that the correlation coefficients obtained for these single regressions are generally high, but with a consis-tent trend of a'reducing correlation with an increasing signal duration. Thus the ave rage correlation coefficient at T = 22 is 0.98 dropping to 0.95

at T = 44 and 0.93 at T = 88. This general tendency towards a greater

scatter in observer response data with increasing T values was gene rally and

repeatedly encountered in the statistical analysis óf test data.

It is noted that for the first two duration values used, T =22

and T ~ 44, the regression lines obtained are ordered progressively with

increasing Lo values such that at a given peak level the averaged subjective response is always reduced with increasing background levels. At the longest duration used, T = 88,however, this ordering of the regression lines is not observed, and in fa ct there is indication of a possible reversal such that for a given peak aircraft noise level the averaged score now tends to rise with increasing baCkground levels. The statistical significance of indicated trends with background level as shown in these figures is discussed below. 3.2 Double Regression - Single Events

It is of considerable interest to determine a suitable index which incorporates the effects of the background noise and duration effects directly, and which is itself highly correlated with the subjective response. The noise pollution index LNP proposed by Robinson (Ref. 7) is one possibly attractive choice. The LNP index combines the two parameters Leq and cr, for a time

dependent noise pulse, with t

and = 10 loglO o

J

10L(t)/10dt o t o LNP ~ L + 2.56 cr eq

(1)

(2) (4 )

with L(t) = arbitrary noise time history defined by level variation with time, including appropriate frequency weighting,

t

=

time interval during which the signal is evaluated (judged) • o

For a .simple sloping ramp noise puls~, as sketched below, the LNP index can be readily expressed in terms of the pulse characteristics. For the sketched pulse the LNP index is,

with Level { X + 2x ' _ (x. 2+ x' )' 2 Jl/2 + 25.6y - ~

2-

=

x«

1)·

t _o - ' T'

t

=

x'

(~x); o ~'('

_-...

t.L .1. I ~ '( _~ Lo ~ t 0 . -1 j & y = -10 Lp time

(5)

Values of (LNP - Lo) as functions of the time variable, x, for fixed values of y (ISL/10) are drawn in Fig. 2. for the fixed pulse shapes gi ven by T' / T

=

0 (triangular); 0.3; 0.6; and 1.0 (square). Values of (LNP - Lp) as functions of the pulse height variab1e, y, for fixed values of x for the same pulse shapes are plotted in Fig. 3.

It is seen that for cases where the pulses are not too sharp so that x' ~ x, and x is small but not too small, .x must be such that x

»

10-y

(x' 1'::$ x),. then we may write the approximations:

( 6)

(7)

so that

( 8)

for fixed x

=

T/to with kl

=

(1 + 2.56 xl/2) and k2

=

10 10glOX. Since for the cases of interest in this study the effects ofk2 would be expected to be smal1, relatively,

it

appears that a simple double regression of the stibjective scores (averaged over observers) using variables

&

=

(Lp - Lo) and Lo would throw light on the sui tabili ty of the proposed LNP index.

These regression lines are shown in Figs. 4a, 4b and 4c where the averaged .

subject scores, for fixed signal durations of T

=

22, 44 and 88 sec,are plotted against the approximate LNP index Lo + keLp - Lo). (Since all test signals have been presented for judg._{ement with equal total durations (t o), constant} T values

are taken to imply constant x values as well.) The correlations obtained were encouragingly high with R values of 0.983, 0.948 and 0.935 for T

=

22, 44 and 88

seconds respectively. The dependence on ~ given by the regression lines is, however, considerably reduced from that given by the approximate LNP, Eq. (8)

above, through the kl coefficient. In fact the kl coefficient obtained for the

T = 88 tests is slightly less than "Unity (0.92) and kl values less than unity do not appear to follow from any simple approximation for LNP, appropriate to the present test signals.

To further examine the applicability of the noise pollution level index in relation to the present score results, the single event data was also processed using regression variables Leq and cr. The 1eq and cr values were calculated from the digi tized data obtained from the test session noise tapes. The level fluctua-tions used to calculate 1eq and cr thus contain the variafluctua-tions associated with the (random) background traffic noise superimposed on the aircraft signal level variations. These regressions, shown in Figs. 5a, 5b, 5c, exhibit uniformly lower correlations than the regression using the simpler 10 and tiL variables, wi th the redudions being of the order of 10%.

Ignoring the slight dependence of the approximate 1NP relation, (Eq.

(8») on the signal duration variable x, a doUble regression of the subjective

scores for all durati ons, T

=

22, 44 and 88 seconds, was again obtained using

variables 10 and &.. This data is plotted in Fig. 6, and i t is seen that a high correlation is still achieved including all test duration data (R = 0.941).

Re-gression of the srume test data (covering all T values and all 10 values) against the 1NP variables Le and cr is shown in Fig. 7. Again a rather significant reduction in correla%ion is noted with these independent variables (1eq and 'cr) wi th respect to the simpler 10 and ~ variables .

3.3 Statistical Analyses

It is of interest to determine whether the trends of the data, with treatment effects due to background noise (10) and signal duration

(T)

can be considered statistically significant considering the sample size and the inherent variability due to individual juror effects. In the present experi~

ments each juror evaluated six aircraft flyover events, under four differing conditions of background levels and three differing signal durations. For each individual observer a single score (corresponding to a hypothetical aircraft event having a peak magnitude of 82 dBA) and a single slope were obtained. The single observer score, at 1p

=

82 dBA was obtained by a least square fit of the six point test data for the same ob server . The individual slope score was also obtained fram the srume least square fitting. These two dependent scores, af ter correction for small deviations from the standardized background levels (10~

=

47.5, L02 = 54.5, 103 = 61.5 and Lo4 = 68.5) were then used to examine the s~gni­ ficance of trends due to treatments 10 (background level) and T (signal duration) .

First the overall effects of 10 and T and the interaction effects between these was explored, based on a randamized block factorial design. Table 1 shows the 35 corrected single scores obtained by the individual observers for 12 treatment combinations of background level and signal duration. The analysis of variances is then carried out (see Ref. 10) by first completing the 1 0,

+

summary table

(TabIe II) and then determining the sum of' squares partitioning and the M-S and FOBS values in Table lIl. Based on the tabulated F values (see Ref'. 10) at the

0.05

level of signif'icance it is seen that the FOBS values exceed the f'ormer f'or both the background level treatment (Lo) and the interaction of' Lo and

T

ef'f'ects, but not f'or duration

(T)

treatment ef'f'ects separately. Since the interaction eff'ects are signif'icant a more detailed analysis of' simple main ef'f'ects is indicated. Thus the sum of' squares f'or d.eviations due to background noise ef'f'ects and signal duration ef'f'ects and their

interactions are f'urther subdivided in Table·rv. Here the partitioned sums of' squares f'or the background noise ef'f'ects (at each level of' signal dura-tion) and the sums of squares f'or the signal duration ef'f'ects (at each level of' background noise) are given together with the appropriate degrees of' f'reedom, the MS values, and the calculated FOBS ratios. Based again on the tabulated F values, Ref. 10, at the 0.05 level of' signif'icance the f'ollowing conclusions are reached:

(i) The inf'luence of the background noise on the stibjective scores has statistical significance, at the

0.05

level, at signal duration values

(T)

of' 22 and

44

seconds. The inf'luence of' background noise at

T

=

88

seconds is not statistically signif'icant, at the

0.05

level, based on present test data.

(ii) The inf'luence of the signal duration

(T)

is statistically signif'icant at the lowest and highest background levels investigated but not at the middle background levels.

As a corollary to these findings it is noted that the trend analysis and regres sion data already presented show that the ef'f'ects of' background level at signal durations of T = 22 and T =

44

seconds are such that increasing background levels yields·a reduced subjective response (regression

coéf'f'i-cient of' Lo negative). At T

= 88,

however, the regression coef'f'icient

associated with Lo changes sign and becomes positive (but small) (see

equations of' Fig.

4).

The statistical analysis now conf'irms that the small positive trend with Lo is not statistically signif'icant (at the

0.05

level) based on existing test data.

In connection with the ef'f'ects of' signal duration T, which are statistically signif'icant at Lo

=

47.5

and Lo

=

68.5,

it is noted that these background conditions correspond to conditions of' large ~ signals and small ~ signals respecti vely, on the noise tapes evaluated by the jurors. (Figure

8

shows the distribution of' ~

=

_{(Lp-Lo) values used on} the jury noise tapes for the lowest background, Lo =

47.5

dBA, and f'or the highest background, Lo

=

68.5

dBA, and f'or all f'our backgrounds.) The

stibjective score trends with signal duration at Lo =

47.5

(Table II, Column 1) can now be compared with the variations of' LNP (f'or any of' the pulse shapes) plotted in Fig. 2 associated with the duration variable x f'or large y (~)

values, y ~ 1.5 and greater. It is seen that in both cases the dep ende nt variable passes through a maximum near the middle range values of' the duration variable. However, when ~ is reduced (y

< 1 approximately),

corresponding to the Lo

=

68.5

data, the averaged subjective score data (Table II, Column

4)

shows a statistically signif'icant monotonic increase .with T (f'ixed Lo). The same variation is noted f'or the LNP variation with

x at f'ixed y values, see Fig. 2, f'or values of' y

<

1 (approximately). The variation of' the averaged stibjective score with sIgnal duration at constant background levels of'

54.5

dB and

61.5

dB, see Table II, Columns 2 and

3,

duration range covered. However, these smaller variations with signal duration, are not statistically significant, see Table IV. It thus follows that same of the important trends implicit to the LNP index, for single noise events, are faithfully reproduced by the significant subjective score results obtained from the present jury testing.

The individual slope scores have been processed similarly, with individual slope scores given in Table V, the T, Lo slope sunma.ry data given in Table VI, and analysis of slope variances given in Table VII. It is seen that the interaction effects are again significant at the

0.05

level so that analysis of simple main effects at specific treatment levels is again required. This main effects analysis is carried out in Table VIII. It is seen that the variation of the s~ope scores with signal duration (at fixed background levels)

is significant only at the highest background level condition employed, Lo

=

68.5

dBA. Similarly, the slope score variations due to background level variations (at fixed signal durations) is not statistically significant at a signal dur a-tion of T

=

22,

is marginally significant at a duration of T

=

44,

and is clearly significant at the longest duration of T

=

88

seconds.

On the basis of the test data summarized in the statistical tables i t is straightforward to calculate the change in peak signal level required to evoke equal subjective response when the aircraft is heard without background

(minimum) and when it is heard with an arbitrary mean background level. Assuming that the data obtained with the minimum background level used

(47.5

dBA) is a conservative estimate of the response to be expected without background, the increase in peak signal level for equal stibjective response which is due to the background, is plotted in Fig.

9.

The ordinates in this figure are obtained from the averaged score data, and the averaged slope data in Tables II and VI respec-tively. Thus, typically, for a mean background level shift above the minimum of

21

dBA (maximum available herein, fram

47.5

dBA to

68.5

dBA) and T =

22,

we obtain:

Change in peak ,signal lev~l for equal stibjective response for 61,0 =

21

dBA, T =

22

[ Row I, Column

135

Row I, Column IV

J

Table II

} =

-[ Row I, Column V ] Table VI

₃₅

x

4

= (

204.6 - 167.3 ) ( 35

x

4 )

'

35

32.173

=

4.7

dBA

Repeating the above calculations for T =

44

seconds an effective signal level change of

5.5

dBA is obtained for a background level increase af

21

dBA. Additional values of the ,signal level changes associated with reduced mean background level changes (for T

=

22

and T

=

44

seconds) are plotted in Fig.

9.

The data plotted in Fig.

9

are in good agreement with earlier ,similar results reported in Refs.

3

and

5;

however, considerable discrepancy is noted with the data reported in Ref.

4.

The present

testing appears to most closely match the procedures and results of Powell and Rice (Ref.

5).

In the work of Powell and Rice the role of the test signal duration was not explicitly examined, a single test signal duration value of about

60

seconds being apparently utilized.

In

the present testing the total time

allowed f'or each aircraf't mEnt, to, was held f'ixed at 110 seconds, so th at the ratio of' signal time to judgement time, T/to ' was 0.20, 0.40 and 0.80 f'or the three signal durations studied. In the work of' Powell and Rice it appears that this ratio (T/t_{O )} was ab out 0.70 and their results, quantitatively, show good agr.e.ement wi th the present data (as to the signal level changes to be expected f'or equal annoyance) f'or T/to

=

0.20 and 0.40 only. At T

=

88 seconds (and T/to = 0.80) the present data show no statistically signif'icant trend with background level at all. In the limiting case T = to, the role of' the

back-ground noise is altered and the trend indicated by the present results (at T =

88

seconds) appears valid. However, the cases of' practical interest are expected to lie near the other limit with T/to probably conf'ined to the range

o

:s

T/tO

:s

0.25.

3.4

Session Results and Analyses

Trend analyses carried out with the subjective scores recorded f'or complete session exposure (Parts B and C of' the "Jury Instructions") using several sets of' regres sion variables produced disappointingly weak correla-tions. Correlations obtained were consistently lower than those with the subjective scores recorded f'or the single event judgements. Trend analysis results were also inf'erior to those obtained in earlier jury assessments of' extended duration random noise traf'f'ic signals (Ref's. 11 and 12), carried out at the Institute. In the earlier studies the noise signals had durations of' approximately 20 minutes, exceeding the present session times (10 minutes) by a f'actor of' two. An apparently signif'icant dif'f'erence in the two noise judge-ment studies, in addi tion to their signal durations, is that .in the present

noise judgement study, the jurors were required to f'irst evaluate individual sections of' the complete session bef'ore attempting to judge the complete session as a single noise event. This f'irst evaluation task appears to have had a marked and deteriorating inf'luence on the second task of' evaluating the entire session as a single entity. In the earlier study, ho wever , the jurors were required to carry out a single overall judgement of' the complete noise session. This sim-plif'ied judgement task appears to permit a noticeably improved score consistency and the def'inition of' appropriate and significant trends. It is hypothesized that in the process of' correctly evaluating each of' the f'lyover noise events, indi vidually, the observer is f'orced to "clear his memory" of' all earlier noise events. Each event must be seen as a f'resh judgement task with minimum carry-over f'rom the previous event. If' this "clearing" process is a necessary one f'or valid single event judgements (or even only partly so), it f'ollows that it may well be prohibitively dif'f'icult to simultaneously assess both the individual

sections of' a longer duration noise signal ·and the complete signal as a single entity during one single exposure.

In the present series of' session judgem.ents, the best session corre-lations were obtained using an averaged score f'rom results of' Part A (single event judgement) together with regression variables Leq and CT, evaluated f'or

the complete session. The averaged score used was obtained as the arithmetic average of' all six single event scores obtained by the same juror in the given session. Regression of' this derived session score with Leq and session variables showed a correlation of' 0.75 over all 12 test sessions.

The session correlations achieved and the session trend identif'iable with the present session results are noted to be signif'icantly weaker than those reported in Ref'.

5

by Powell and Rice. In th at ref'erence, an extremely high

correlation is reported (correlation index of

0.99)

utilizing the same derived session score (an averaged event score) and the LNP index (LNP

=

Leq + Krr) calculated for the complete session. In order to identify possibly significant differences in these two nominally similar test series, the range of test

signal conditions used in both test series is summarized below.

Reference 5

{Powell

&

Rice~ Present Tests

L eq' dBA (max) 53'.2 80.0

L _eq' dBA (nün) 52.2

71.7

cr, dBA (max) 10.2 12·3

cr, dBA (min)

4.4

4.7

Duration (min) 12.0 10.0

In attempting to campare (and possibly extend) the session results of these separate tests, the following factors must be carefully considered:

(i) While the range of standard deviations used and total duration of the test sessions are seen to be very comparable, the Leg range . covered by the testing of Powell and Rice is quite restricted. (This limitation has already been clearly identified by the authors.)

(ii) The present testing has been conducted in a less well-controlle~more

reverberant, but probably more realistic listening environment than the tests of Powell and Rice.

(iii) In both tests, results with the actual Subjective scores for the complete sessions, as a single noise event, were disappointing, leading to weakly defined or insignificant trends. (This has led to the use of derived session scores with much improved correlations resulting.) The explana-tion advanced by Powell and Rice was that jurors were not forewarned of the requirement for an overall session judgement at the out set . Since this condition does not apply to the present test series, we are forced to offer the "memory clearance" concept associated with individual event judgements, described above, as a more probable explanation of the diffi-culties experienced in both test series wi th sessional evaluations.

4 .

CONCLUSIONS

The effects of traffic background noise on the judged noisiness'of aircraft noise events has been further examined in the present study. The aircraft noise events had varying durations and peak levels. The primary conclusions reached on the basis of this investigation are as follows:

(i) The presence of a steady traffic background noise reduces the perceived noisiness of aircraft flyover noise events provided the durations of the events above the background level is short enough in relation to the total judgement period available. When the duration of the aircraft event

increases, to occupy most of the judgement period available, this

(ii) If aircraft f1yover events are judged together with a substantial1y 10nger duration traffic background noise having a mean level equal to

(iii)

(iv)

(v)

(Vi)

the peak indoor aircraft level, the subjective response to the f1yover noise is equivalent to th at obta.i.ned without background noise (background noise suppressed 21 dBA or more, re1ative to the signal peak) and a peak aircraft level whicl1 is 5---6 dBA lower (at least). This conclusion is restricted to conditions where the peak aircraft level (indoor) and the associated mean background level lie in the approximate range:

45 < L (dBA) _< 68

- p

45< Lo (dBA) ::; 68

as determined by range of background conditions used in the present tests. At peak aircraft event levels (indoors) above 68-70 dBA the influence of the mean background level can be at least as great as that indicated in

(ii) above. (Thus an increase in background level of 21 dBA is still

equivalent subjective1y to a decrease in peak level of 'approximately

5-6 dBA.) In fact, for these higher peak event levels the interaction

of the baCkground noise is probably even larger since larger (Lp-Lo) values (in excess of the 21 dBA used herein) are then quite realistic and there is no indication that higher mean background levels than those used in the present testing (maximum 68 dBA) will not extend the favourable trends already measured.

Subjective responses obtained for single aircraft events (averaged over 35 jurors) with differing background levels and event durations did not

correlate nearly as strongly with Leq and cr (as implicit to Robinson' s

LNP index) as wi th the simpler

Lp

and Lo variables .

The best regression of the single event subjective response data over all signal durations and mean background levels studied was obtained

using regression variables ~ ~ Lp - Lo, and Lo in the form Lo + 1.10

(Lu-Lo)' 'Covering 12 test sessions (72 aircraft signals), and including

data for 35 observers in each session, a correlation coefficient of

R

=

0.941 was obtained using the above index. Higher correlations were

noted using the same index form:_{Lo +

keLp -

Lo)} for the short er signal

duration response data, individually.

Corre1ations obtained using the complete session'response data

(approxi-mate1y 10 minutes duration) were always ,found to be significantly lower

than those obtained using the individual aircraft event response data (approximately 1.5 minutes duration). The best session correlation

achieved using regression variables Leq and cr showèd a maximum value af

R ; 0.747. This was achieved using a derived session response óbtained by averaging all the single event scores for a given session. The

difficulties experienced in identifying significant trends for the longer session exposures is tentatively ascribed, in part, to the test procedure utilized.

(vii) Although the regressions obtained with the noise po~~tion index, LNP'

... - - - -- - - , 5. 1-2. 3· 4. 5. 6. 7. 8. 9· 10. 11. 12.

than the simpler N.., and LO variables , the score data did show a nuniber of'

signif'icant trends which are also associated with the LNP index variations f'0f single noise events. Thus, at low background values where generally

high values of' ~

=

Lp -

Lo were used in the test sessions, increasing

signal durations f'irst produce an increasing subjective score and f'inally at large durations a decreasing subjective score. This same f'eature is

noted in the computed variation of' the LNP index at large val.ues of' /5L

f'or a general trapezoidal shaped noise event superimposed on a longer duration steady background level. Addi tional.ly, at the highest value of'

background used in the testing and the associated lower val.ues of' /5L,

increasing signal. duration al.ways produced an increasing subjective score. This f'eature is again evident in the computed variation of' the LNP index,

at low ~ values, f'or a general trapezoidal shaped noise event superimposed

on a longer duration steady background level. REFERENCES Robinson, D. W. Rosenblith, W. A. stevens, K. N. Pearson, K. s. Nagel, D. G. Parnell, J. E. Parry, H. J. Powe11 , C. A. Rice, C. G. Robinson, D.

w.

Robinson, D. W. Robinson, D. W. Kryter, K. D. Kirk, R. E. Johnston, G. W. Carothers, R. G. Johnston, G. W. Carothers, R. G.

"An Outline Guide to Criteria f'or Limi tation of'

Urban Noise". NPL ARC CP 1112, 1970.

BBN Handbook of' Noise Control, II. "Noise and

Man", Report WADC TR-52-204, 1953.

"The Ef'f'ects of' Duration and Background Noise Level on Perceived Noisiness". FM Technical

Report ADS-78

(AD

646 025), 1966.

"The Ef'f'ects of' Background Noise Upon Percei ved Noisiness". FM Technical Report os-67-22, 1967.

"Judgements of' Aircraf't Noise in a Traf'f'ic Noise Background". Journal. of' Sound and Vibration, Vol. 38(1), 1975.

"The Concept of' Noise Pollution Level". NPL Aero Report AC 38, 1969.

"A New Basis f'or Aircraf'tNoise Rating". NPL Aero Report AC 49, 1971.

"Towards a Unif'ied System of' Noise Assessment". Journal of' Sound and Vibration, Vol. 14, 1971.

"The Ef'f'ects of' Noise on Man". Academie Press,

New York, 1970.

"Experimental Design Procedures f'or the Behavioral

Sciences 11 • Brooks and Co1e, 1968.

"Annoyance Measurements Related to Urban Traf'f'ic

Noise Exposure 11 • Research Report 13, 1973, Univ.

of' Toronto/York Univ. Joint Program in Transportation. "Urban Traf'f'ic Noise Annoyance Measurements and

Derived Indices". Research Report 24, 1974. Univ.

~

r,

7;L

_L

_1i

_L

,

,..-;

,

Loq..:'

f f

2

LOl

Loa

LC3

Lt.P4

Lel

Lo:l.

o~

Lo/l

lOl

jkS1k ( jkSjk)j jk

88°l.. 8 °3._

22.0 22.0 22.0 22.0 44.J 44.U 44.û 44.U 88.0 .IJ b.U tib.Ll

47.5 54.5 61.5 68.5 47.5 54.5 61.5 68.5 47.5 54.5 61.5 68.5 4.61 4.80 5.11 4.21 6.74 6.89 4.82 2.30 5.96 6.32 5.94 5.79 63.4-8 335.81 5.21 5.01 4.31 5.83 5.84 5.90 4.99 5.37 5 -33 6.48 4.61 4.48 63.37 334.63 6.25 4.81 4.73 4.11 6.81 5.61 6.68 5.93 5.94 5.45 5.03 5.52 66.87 372.63

~

~

H 6.56 5.69 6.89 5.11 6.94 6.82 5.51 3.54 7.50 7.43 5.45 4.83 72.27 435.24 6.78 5.69 6.48 5.59 7.35 6.73 6.08 4.85 6.83 6.17 5.61 5.13 73.29 447.59 6.76 6.14 6.82 5.68 7.49 6.14 5.76 4.76 6.52 6.78 6.11 5.24 74.18 458.55 5.88 5.35 6.15 5.83 6.7(,. 5.67 5.50 4.51 6.62 5.92 4.61 4.18 66.97 373.72 5.97 5.30 4.98 3.20 6.54 5.79 5.32 4.53 5.47 5.57 5-11 5.61 63.39 334.82

6

<:..J. 6.48 6.05 4.60 3.11 6.2(" 5.91 5.39 4.83 5.65 4.81 5.11 4.98 63.17 332.55 4.92 5.19 6.31 7.45 5.37 5.87 4.51 5.09 5.49 5.94 5.95 5.48 67.59 3!jO.70 5.80 5.49 5.38 l~. 78 5.83 5.03 5.15 4.25 4.15 3.74 4.61 5.49 59.70 296.99 w~ " 5.54 3.97 5.62 4.07 7.43 6.96 4.96 3.47 7.34 7.20 6.61 6.62 69.81 406.10 5.97 5.70 6.01 6.25 7.28 6.23 6.00 5.40 6.32 7.67 6.78 6.58 76-.19 4~3.70

~

~

~

..

7.03 6.1 7 5.96 5.54 6.51 5.61 6.24 4.64 6.11 5.65 6.11 5.77 71.33 424.00 6.44 6.28 5.31 5.91 7.09 7.17 5.99 6.92 5.86 6.94 6.86 6.39 77.16 496.16 6.50 6.76 5.99 5.54 7.65 6.94 6.32 6.14 5.38 6.53 6.61 6.34 76.71 490.34 4.41 5.49 6.68 4.32 5.64 5.60 5.40 5.94 3.30 4.98 4.77 5.16 61.69 317.16 5.79 5.69 4.78 4.54 5.64 4.78 4.85 4.04 5.19 6.39 4.44 5.55 61.67 316.89 5.92 4.87 4.32 3.83 5.39 4.79 4.54 4.13 4.84 3.92 4.36 5.28 56.20 263.23

I

5.68 5.78 4.22 3.71 5.82 5.76 5.62 4.89 4.58 3.80 5.36 6.20 61.41 314.31 6.69 5.37 5.43 4.17 6.80 5.78 5.23 5.40 4.10 5.95 6.94 7.20 69.05 397.30 6.86 7.33 5.99 8.12 6.80 7.50 7.70 8.63 3.46 4.04 5.61 7.43 79.47 526.30 6.13 6.52 4.98 3.83 5.28 6.69 6.76 6.43 3.19 2.38 6.11 7.45 65.76 360.39 7.10 6.85 6.16 7.45 5.2G 6.23 7.03 8.20 5.86 5.90 6.78 8.30 81.11 548.28 6.99 6.85 5.45 5.78 7.53 6.83 6.81 6.28 5.47 6.EH 6.28 7.22 78.29 510.81 6.20 5.69 6.03 5.30 6.70 5.68 5.23 5.53 5.73 5.74 5.11 4.75 67.70 381.93 6.02 6.19 4.25 2.16 5.77 5.64 5.27 4.67 5.30 5.46 5.28 4.99 60.98 309.92 2.32 3.35 4.09 3.02 2.43 2.21 4.95 5.26 2.92 2.78 3.11 6.00 42.43 15U.02 4.77 4.02 4.19 3.96 4.91 4.31 3.27 4.38 5.99 4.94 5.36 4.67 54.79 250.18 4.72 3.67 3.00 2.41 3.8G 3.34 2.90 2.65 3.41 2.15 2.61 3.68 38.40 122.89 4.69 3.51 3.37 2.78 4.32 3.93 4.12 2.68 3.39 3.42 3.61 3.98 43.81 159.93 6.04 4.81 4.63 4.91 ~.2(' '+.98 5.59 3.99 5.02 4.26 5.61 5.22 60.33 303.30 5.84 4.83 4.89 4.78

LOl

7i

204.602

1i.

211.880

7l

18 't. 7 21

~i~

601.204

(ELJ

3442.348 :SSfC3 SOURCE RLOCI<.S TR01NT TAU LO TAlJLO RF.S!OUAL TOTAL

L

_4~

_L

Lr

D~

<54-188.897 182.674 167.298 7l_t3.473 197.829 191.461 172.671 773.840 186.727 190.547 198.930 760.927 573.454 ?64.683 538.900 3131.897 3036.824 2765.837

TABLE II - L , T SUMMARY, PEAK SCORE

o SS

DF

Mi 278.506 34 8d91 49.837 11 4.5!U 3.318 2 1.6!39 B.861 3 6.287 27.659 6 4.610 253.662 374 0.678 582.005 419

*

SIGNIFICANT AT 0.05 LEVEL

TABLE 111 - ANALYSIS OF VARIANCE, PEAK SCORE

SO(/~Cé:"

s.s

.

,o

.

r.

_I1.S.

SS~ 3.318 2 1.65<;; 76)1.01 _{11.293 2 5.647}

'TlDLoit,.

1.978 2 0.989 7tD L CJ3 1.333 2 0.667

7wL

_o4 16.371 2 80186 SSLO 18.861 3 6.287

.0

ij)

r:

20.434 3 6.811 L~@ ?;.. 22.700 3 7.567

Lo

Ei>""~

3.31:l0 3 \ 1.127 TAULO 27.659 · 6 4.610 RES! DlJAL 253.662 374 0.678

*

SIGNIFICANr AT 0.05 LEVEL

2.-(E%.<+

39l_+8.229 .. ~71.3~1 4135.784 & ,

1;,6S.

12.077 2.446 9'.269 .. 6.797.

;;85,

2.446 80325" 1.458 0.983 12.069~ 9.269 ~ 10.042 f 11 ol56~ 1.661 6.797~

~

E;J <: t-t o c... -4 ~

_...

~

~

ro o

~

...

I

r

LOl

22.0 47.5 0.21 0.20 0.15 0.17 0.20 0.23 0.19 0.27 0.26 0.31 0.27 0.19 0.27 0.21 0.21 0.24 0.16 0.28 0.23 0.14 0.22 0.21 0.27 0.14 0.25 0.20 0.22 0.09 Ö.22 0.18 0.21 0.19 0.22

r,

Loz.

L03

22.0 22.0 54.5 61.5 0.35 0.19 0.24 0.21 0.13 0.12 0.27 0.11 0.26 0.22 0.35 0.27 0.24 0.21 0.35 0.36 0.34 0.33 0.28 0.26 0.17 0.25 0.12 0.25 0.31 0.18 0.22 0.25 0.28 0.26 0.24 0.22 0.18 0.23 0.27 0.34 0.30 0.22 0.28 0.21 0.29 0.23 0.19 0.17 0.26 0.36 0.23 0.17 0.25 0.25 0.27 0.29 0.27 0.23 0.23 0.14 0.25 0.24 0.22 0.28 0.23 0.30 0.13 0.35 0.19

r:.

..

'Lol

L04

Lo-;.. Low

22.0 44.0 44.0 44.0 68.5 47.5 54.5 61.5 0.35 0.11 0.08 0.30 0.25 0.22 0.13 0.26 0.09 0.20 0.16 0.10 0.10 0.15 0.19 0.27 0.46 0.13 0.13 0.22 0.69 0.17 0.33 0.31 0.23 0.16 0.18 0.26 0.32 0.18 0.21 0.34 0.10 0.22 0.25 0.30 0.11 0.30 0.28 0.27 0.12 0.25 0.22 0.21 0.00 0.16 0.21 0.24 0.45 0.18 0.26 0.35 0.33 0.19 0.22 0.22 0.01 0.13 0.18 0.17 0.35 0.11 0.23 0.17

****

0.2G 0.23 0.17 0.33 0.26 0.22 0.27 0.23 0.20 0.15 0.25 0.34 0.20 0.17 0.24 0.26 0.14 0.22 0.30 0-13 0.14 0.18 0-12 0.25 0.33 0.29 0.23 0.11 0.28 0.26 Oell 0.12 0.12 0.31 0.29 0.58 0.18 0.29 0.30 0.23 0.22 0.33 0.32

****

0.16 0.15 Oel5 0.15 0.11 0.20 0.23 0.01 0.24 0.18 0.22 0.12 U.31 0.23 0.33 0.44 0.28 Oel9 0.23 0.12 0.23 0.24 0.20

7;L

....

,.

..

~~~(~~

L0

4

L~)/

L02.

03

L0

₄ 44.0 88.0 88.0 88.0 88.0 68.5 47.5 54.5 61.5 68.5 , . .J. ~k 0.14 0.14 1).rr 0.1)8 0.19 2.26 0.43 0.30 0.31 0.11 0.29 U.40 2.91 0.70 0.20 0.23 0.28 0.16 0.13 1.96 0.32 0.20 0.11 0.14 0.30 0.39 2.40 0.48 0.29 0.18 OelO 0.25 0.34 2.78 0.64 0.17 0.23 0.21 U.24 0.31 3.50 1.02 0.19 0.15 0.18 0.20 0.29 2.50 0.52 0.29 0.26 0.30 0.33 u.35 3.57 1.06 0.24 0.26 0.27 0.33 0.25 3.13

O.al

0.27 0.25 0.21 0.28 U.24 3.05 0.78

****

0.25 0.30 0.22 0.31 2.48 0.51 0.09 0.23 0-16 0.26 u.27 2.18 0.40 0.23 0.25 0.10 0.15 0.31 3.05 0.78 0.25 0.29 0-19 0.21 0.29 2.86 0.68 0.11 0.22 0.09 0.18 0.25 2.10 0.37 0.20 0.21 0.09 0.19 0.22 2.47 0.~1 0.16 0.20 0.11 0.11 0.24 1.84 0.28 I 0.25 0.23 0.08 0.19 0.19 2.90 0.70 0.24 0.23 0-14 0.10 0.20 2.50 0.52 0.18 0.24 0.23 0.24 0.28 2.75 0.63 0.14 0.29 0.13 u.16 U.20 2.~9 0.56 0.07 0.15 Od6 0.22 0.14 1.89 0.30 0.24 0.35 0.31 0.16 0.12 3.16 0.83 0.06 0.22 0.23 0.19 0.10 2.10 0.37 0.18 0.26 0.11 0.22 U.26 2.63 0.58 0.29 0.20 0.22 0.24 0.31 3.37 0.95 0.09 0.27 0.28 0.24 u.39 3.07 0.78 0.26 0.17 0.28 0.21 u.38 2.09 0.37 0.14 0.25 0.21 0.31 0.38 2.68 0.60 0.16 0.31 0.27 0.29 U.37 2.72 0.62 0.18 0.32 O.3u 0.26 U.40 3.19 0.85 0.22 0.35 0.37 0.28 0.33 3.38 0.95 0.28 0.25

z.

Lel

L

_o/'

L

_o~

₄₄

~T

_(Er%4

r,

7.406 8.540 8.624 7.603 32.173 7.393

'7f

7.035 7.530 8.494 6.555 29.t;,15 b.Z6~

13

8.469 7.093 7.750 9.587 32.899 7.731

~L.

_{22.911 23.162 24.869 23.745}

(LL;

4.999 5.109 5.890 5.370 as~~

TABLE VI - L 0 ' T SUMMARY, SLOPE SCORE

SOURCE SS OF MS

_.

_~B~

_.

BLOCKS 0.613 34 0.018 2.965 TREMNT 0.233 11 O.Ofl TAU 0.043 2 0.021 3.498

*

LO 0.022 3 0.007 1.190 TAULO 0.169 6 0.028 4.628 .. RESIOUAL 2.273 374 0.006 TOTAL :3 .118 419

*

SIGNIFICANT AT 0.05 LEVEL

TABLE VII - ANALYSIS OF V ARIANCE, SLOPE SCORE

SO(,/RCE.

S.S

nr:

,M.s.

~S.

SSr 0.043 2 0.021 3.498 ...

r.

LOl 0.032 _{2 0.016 2.604}

7'

ti)

L.oz-

_{0.031 2 0.016 2.590}

7tDLo'3

_{0.013 2 0_006 1.045}

7'eL:,4

0.135 2 0.068 .11.144* SSLO 0.022 3 0.007 1.190 Lofi>

r,

0.034 3 0.011 1.855

LD6)~

0.059 3 O.OlO 3.230

Lom

'3 0.098 3 0.033 5.361# TAULO 0.169 6 0.028 4.628* RESIDUAL 2.273 374 0.006

*

SIGNIFICANT AT 0.05 LEVEL

90 8D 70 60 5.0 3.0 T· 022 BO b. L.a47.!5 o L.-M.5 Rl.a41S = Q995 RL •• 54.S· 0995 RL ... S = 0.970 RL •• 6 I1.S • 0972 • L •• 61.5 • L. -68.5 90 S.S 95 100 90 T-044 B.O 7.0 6 5.0 40 30 BO L.=47.5 RL. '41S • 0977 RL.' SU • 094B RL. ... .s = 0931 RL.' &ell " 0.942 Lp - dB_A 4 L.-47.5 • La' 54.11 • L •• 61.5 OL. -68.& 90 95

FiQ. Ha) REGRE5510NS of MEAN SUBJECTIVE SCORES on PEAK SIGNAL LEVELS (Si;nal Duralion • 22 Seconds \ Tit.· 020)

FiQ. Hb) REGRESSION of MEAN SUBJECTIVE SCORES on PEAK SIGNAL LEVELS (SiQnaIDuration' 44 Second.\ Tit.' 040)

90 ao 70 S,SMEAN 60 5.0 4.0 30 T'OBB 2.0'L-_+-....L.. _ _ --'-_ _ ----''---'-_"''-_ _ -'-_ _ --' _ _ ---' 65

Fi;. I(e) REGRESSIONS of MEAN SUBJECTIVE SCORES on PEAK SIGNAL LEVELS (Si;nal Duralion ' BB Seeonds \ Til.' OBO)

.J

I

...

z ..J o ..J I CL z ..J 601- 501-40'

~f

60 50 40 Lewl

~

L.I ~~~ _-Time àL-30

/

20 ~ 10 0.6 08 T/to

F'I\j. 2(0) NOISE POLLUTION INDEX - TRIANGULAR PULSE

02 04

---

----

6L-30 -IT'I-Loj.~ I-=I.~ n ... _ - - - - -__ 20 15 5 0.6 08 T/to

-1.0 10

Fig. 2(c) NOISE POLWTION LEVEL-TRAPEZOIDAL PULSE ,~,-060

0 ..J I I! ..J 60

JiÇ+

1

~'30 TiN 40 30 02 04 06 OB T/to

Fig. 2(b) NOISE POWJTlON INDEX - TRAPEZOIDAL PULSE - ,'re" • 0.30

o ..J I CL Z ..J 60 50 40 0.2

Lot~

_~~~ Q4 0.6 T/to TIme 0.8

Fig. 2(d) NOISE POLLUTION INDEX- SQUARE PULSE

1.0

40 30 1

~"I ~

7~4- 201-~,: I I nm. I OGO T/'.~ 10 0.. .-I 0.. Z ...J Ol 0.06 -10 002

--20 -30

Fig. 3(0) NOISE POLLUTION INDEX - TRIANGULAR PULSE

]

LaJ

T' ,

-rt)~

ror

TIm. ~ 10 0 ...J ~ I

1~1.h5==-

~ 0.. Z ...J

-lOl

~

0.02 -20 0.. .-I I 0.. 3.00 _z t.L/IO ...J 0-.-I I 3.00 _~ t.L/IO .-I 40

I

I--T'-t _ _ 301-

Lev-I

~

rt.,

, 20 10 I~ 1.00 -10 -20 -30 • Time 300 O~ t.L/IO 002

Fig. 3(b) NOISE POLWTION INDEX-TRAPEZOIDAL PULSE, T/T=0.30

30r- Level, 20 10 -10 -20

----'tI

I---f::-~. ~ 002 3.00 t.LlIO

10 8 70 T'22 Sec t •• 110 Sec +

SS-·-IO.8I+O.I83 {Lo +l25 (Lp-Lol}

R·Q983

80 90

Lo+k (Lp-.Lol

Fig. 4(01 SINGLE EVENT REGRESSION COLLAPSING La EFFECTS + 10 8 2 10 . T =44 Sec t. -110 Sec + 8 .... l5 6 ~ 0 .... (!)

"'

m:: 4 ~ + 2

S.S. --9.3O+QI66 {LO t l29 (Lp-LOl} R-Q948 70 T-88Sec t •• 110 Sec +. + + ~ + 70 80 Fig. 4(bl S.S '-15.5 t 0.262 {LO+Q92 (Lp-LOl} R' Q935 80 ·90 Lot k (Lp- Lo I

Fig. 4(cl SINGLE EVENT REGRESSIONS COLLAPSING La EFFECTS

90 100

Lo+k(Lp-Lol

SINGLE EVENT REGRESSIONS COLLAPSING Lo EFFECTS

100 (dBAl

"

10 8 6 4' 2 + + s. s. • -9.41 +0148 {Leq +3.80 CT} R -08n 80 90 100 (Leq+kCT) 110

FiQ. 5(0) SINGLE EVENT REGRESSIONS COLLAPSING La EFFECTS 10 8 LU a: 6 0 ~ 0 LU ~ a: 4 LU ~ 60 10 2 120 5.5. =-7.51+0.135 {Leq.3.17CT} R=0811 80 90 100 (Leq+ kCT) 110

Fig. 5(b) SINGLE EVENT REGRESSIONS COLLAPSING La' EFFECTS T"88Sec t. = 110 Sec + + + S. S. = -11.03 + 0205 (Leq+ 0.844 CT) R' Q921 70 80 (Leq + kCT) ++ + 90

FiQ. SIc) SINGLE EVENT REGRESSIONS COLLAPSING La EFFECTS

+ +

120 (dBAI

10 8 w ₆ cr:

8

Cl) w (!) ct cr: ₄ w ~ 2 + S. S = -12.24 + 0.210 { Lo + 1.10 ( Lp - Lo )} R

=

0.941 70 80 90

Lo+

kelp -L_o) 100

Fig. 6 SINGLE EVENT REGRESSIONS COLLAPSING Lo end T' EFFECTS

110 (dBA) 10 8 w 6 cr: 0 u Cl) 0 w (!) ct cr: 4 w ~ 2 70 S.S. = - 9.49 +0.169 (Leq + 1.99 cr ) R = 0.787 80 90 (L_eq + kcr) 00

Fig. 7 SINGLE EVENT REGRESSIONS COLLAPS! NG Lo end l' EFFECTS

110

~

_0/10

.IDa

0110

o

0lIO

I I I

10/20 20/30 30/40

(a ) All Background Levels.

~

10120 2

.L2'ZZl

20/30

o

30140 (b) High Background Level

~m.m.

10/20 20130 30140 (c) LDw Background Level

n

_{4O/0ver • {Lp - La}}

o

40i0v"er.

{Lp - La}

Km

4O/0ver • {Lp-La}

Fig. 8 DISTRIBUTIONS of NOISE EVENT EXCURSIONS ABOVE MEAN BACKGROUND ( Lp - Lo )

~

~

~~

ILIILI ;:»

ot:

..Ju ILIILI >-' lLIa:I ..J~ ." 8.0 ..J .... ~ ~ « 6.0 zl-'aI ~(/)"O (/)z o ~u

~~

4.0 Q.u..

z .

- 0 z ~

5

2.0

«P::: ILI~ P:::u u« ~a:I

o

T= 22 Sec

5

10 15

20

INCREASE IN BACKGROUND LEVEL. ~Lo. dBA ABOVE MINIMUM (47.5) dBA

Rg. 9 EFFECT of MEAN BACKGROUND NOISE LEVEL

on PEAK SIGNAL LEVEL for CONSTANT SUBJECTIVE RESPONSE

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1.0

0.6

"

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al

1.0

/

5 Hz RANGE

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50 Hz RANGE

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*

Time Interval to Within

/

0.5 dB of Final Value

/

3.0 ... ...,

...,

30

STEP VOLTAGE -llE (dB),(volts)

Fig. 10 STEP TI ME RESPONSE of LOG. CONVERSION UNIT

( H.

P.

MODEL 7562A)

50