Noise Articulation Index Calc

92455EnvironmentalEffectsNoise

ArticulationIndex

Preparedfor

Dr.ColinNovak

FaisalSIDDIQUIStudentID101963673

3rdyearCandidateforBASc.MechanicalEngineeringDepartmentofMechanicalAutomotiveandMaterialsEngineering

1

Table of Contents Abstract ........................................................................................................................................... 2 Introduction to Articulation Index .................................................................................................. 2 How is Articulation Index calculated ............................................................................................. 3 Articulation Index in different contexts.......................................................................................... 7

Open Plan Office......................................................................................................................... 7 Classrooms.................................................................................................................................. 8 Medical Decisions....................................................................................................................... 9

Conclusion .................................................................................................................................... 10 References..................................................................................................................................... 11 Appendix....................................................................................................................................... 12

Raw Data................................................................................................................................... 12 Calculations............................................................................................................................... 13

List of Tables

Table 1: Frequency and Weighting Factor for Articulation Index Calculation .............................. 4 Table 2: Octave Frequency and Upper and Lower level A-weighted Sound Pressure Level......... 5 Table 3: Articulation Index, Privacy Index and Subjective Impressions........................................ 8 Table 4: Articulation Index of Teacher's voice in Untreated and Treated Classrooms with Loud and Quiet Ventilation Units ............................................................................................................ 9 Table 5: Data for Figure 1............................................................................................................. 12 Table 6: Data for Figure 2............................................................................................................. 12 Table 7: Data for Figure 3............................................................................................................. 12 Table 8: Data for Figure 4............................................................................................................. 12 Table 9: Data for Figure 5............................................................................................................. 12 Table 10: Calculation for Figure 1................................................................................................ 13 Table 11: Calculation for Figure 2................................................................................................ 14 Table 12: Calculation for Figure 3................................................................................................ 14 Table 13: Calculation for Figure 4................................................................................................ 15 Table 14: Calculation for Figure 5................................................................................................ 15

List of Figures

Figure 1: Articulation Index of a person (AI=1 or 100%).............................................................. 5 Figure 2: Articulation Index of a person (AI=0 or 0%).................................................................. 6 Figure 3: Articulation Index of a person (AI=0.97 or 97%)........................................................... 6 Figure 4: Articulation Index of a person (AI=0.94 or 94%)........................................................... 6 Figure 5: Articulation Index of a person (AI=0.91 or 91%)........................................................... 7

List of Equations

Equation 1: Articulation Index........................................................................................................ 4 Equation 2: Privacy Index............................................................................................................... 8 Equation 3: Total A-Weighted Sound Pressure Level dB(A)....................................................... 13 Equation 4: Articulation Index...................................................................................................... 13

Abstract

In this paper the concept of Articulation Index will be introduced. The Articulation Index is a

scale for measuring the intelligibility of a sound transmission system. The index has a

tremendous importance in many different aspects of daily life such as architectural design, and

medical decision making etc. There are many different methods of calculating Articulation

Index. But complex methods of calculations have stifled the use of Articulation Index as many

medical practitioners and dispensers do not prefer to use complex equipments to calculate the

index. This paper will discuss a simple method of calculating the index using the lower and

upper level A-weighted sound pressure level dB(A). This paper also looks at the use of

Articulation Index as an indicator of Architectural design criterion and medical decisions.

Introduction to Articulation Index

The Articulation Index (AI) is one of the earliest attempts to measure the intelligibility of a

sound transmission system with the aid of a machine. The concept of Articulation Index was

developed by the Bell Telephone laboratories in 1940's.4 The intelligibility of a speech pertains

to the accuracy with which a speech or phrase is understood by the listener.7 The Articulation

Index is the measure of speech intelligibility under a wide variety of communication situations,

such as noise, filtering, transfer through telephony, reverberation, etc.5 The index is defined by

numerical values ranging from 0 to 1. An Articulation Index of 0.1 is quite low and indicates that

very little if any conversation will be intelligible to the listener if a screen was to be placed

between the voice source and the listener. An AI of 0.6 would on the other hand, indicate poor

speech privacy.9 The Articulation Index is influenced by noise, interference, and distortion and

can vary significantly.

The Articulation Index in an open office is the reflector of the extent to which intruding speech

from adjacent work stations exceeds ambient sound pressure level at the listeners ear. The sound

pressure level of the intruding speech and therefore the Articulation Index depends on various

factors.5

3

These include:

The voice effort of the intruding speaker. The locations, positions and bearings of the intruding speaker with respect to the listener. The dilution of intruding speech over a particular distance. The dilution of intruding speech due to the presence of barriers and screens. The reinforcement of speech due to reflections from surfaces.5

Articulation Index is of particular importance of in an open office environment because it

correlates well with the portion of population not satisfied with speech privacy. The AI is also

important measuring scale in many other different spheres of life such as in communications

between passengers in an automobile and in decision making to procure a hearing aid for hearing

impaired patients.

The short time Articulation Index is a procedure for time varying Articulation Index from data

on a block by block basis. The short-time AI is useful to provide a running measure for speech

intelligibility for adaptive noise cancellation system as it converges. The classical Articulation

Index calculation is useful for examining a stationary system as it provides a single number

based on long term noise power spectrum measurements. However this calculation fall short of

correctly predicting the sound intelligibility for an adaptive system which is changing with time.

Due to this reason short-time AI can be used with the index being calculated every few fractions

of a second. The short-time AI considers the effects of noise intensity and noise spectrum to

determine the quality of time varying voice communication systems and can serve as a criterion

for the degree of processing necessary to achieve the desired level of speech intelligibility.6

How is Articulation Index calculated

There are several different methods for calculating Articulation Index. These methods of

calculating Articulation Index vary from being very simple to very complex. While the complex

methods provide for greater accuracy they require complex algorithms and machinery and

infrastructures that are not readily available, the simpler methods require less calculation and

infrastructures while compromise some accuracy.10 Until recently the clinical use of AI has been

4

held back due to lack of easy to use and understand dB HL calculation method. Some simpler

methods of determining the Articulation Index has been resulted from research on AI. Their

work has led to modifications and simplifications. These days computer programs and probe

microphone units are capable of performing AI calculations. However simpler methods are

generally preferred by clinicians and dispensers. 10 In this report some simple methods for

calculating AI will be discussed.

The first calculation method to be discussed is based on calculations of some signal to noise

ratios in five octave bands with centre frequencies of 0.25, 0.5, 1, 2, and 4 kHz. The calculation

is based on only these frequencies rather than 1/3rd octave band sound pressure level (which

provides greater accuracy) due to the fact that the later requires greater knowledge of speech and

noise spectrums. Since speech level usually refers to long term AI, the octave spectra consisting

of these five frequencies is usually sufficient and do not cause great loss of accuracy.7

Articulation Index is calculated using the following simple steps:

1. Measure the effective signal to noise ratio for each octave band

2. Apply weighting factor to each ratio and clipping to ensure maximum contribution at +18dB

and minimum at -12dB.

3. Add these results and calculate the average value.

These steps are summed up by equation 1 and table 1: 7

Equation 1: Articulation Index

( )5[ ]1

1230

ii i

i

GAI Lsa Lna dB

dB == +

Where

[ ]

Articulation Index Weighting factor for each octave bandi

AIG

==

Table 1: Frequency and Weighting Factor for Articulation Index Calculation

Frequency (Hz)

Weighting Factor ( [ ]iG )

250 0.072 500 0.144 1000 0.222 2000 0.327 4000 0.234

5

Another simple method of calculating Articulation

Index results from the use of the lower and upper level

A- Weighted sound pressure level dB(A). Table 2

and the following simple steps illustrate this method:1

1. If A-weighted 1/3 octave level lies between upper and

lower limits then it will be a linear value between 0 and 1.

2. If value falls above the upper limit then result =0 for

that particular 1/3 octave band.

3. If value falls below the lower limit then result =1 for

that particular 1/3 octave band.

4. Multiply all of the calculated values by the AI

weighting and sum all the values to get the AI in

percentage terms.1

In this method the upper and lower A-weighted sound

pressure levels are the sound pressure levels a speech needs to have for a person to listen the

speech or voice accurately. This method of calculating Articulation Index is used in automotive

industry as wind noise metric.1

The following are some plots and their respective Articulation Index generated. To see the data

and calculations for these plots please refer to the appendix (table 5-9).

Figure 1: Articulation Index of a person (AI=1 or 100%)

Figure 1 shows that this test subject was

able to hear all the words, syllables etc.

correctly at a sound pressure level which

was lower than the lower level A-

weighted sound pressure level for each

octave frequencies in this method.

Therefore resulting in AI of 100%

Table 2: Octave Frequency and Upper and Lower level A-weighted Sound Pressure Level 1/3 Octave

Centre Frequency

Hz

AI lower level

dB(A)

AI upper level

dB(A)

AI Weighting

200 23.1 53.1 1 250 30.4 60.4 2 315 34.4 64.4 3.25 400 38.2 68.2 4.25 500 41.8 71.8 4.5 630 43.1 73.1 5.25 800 44.2 74.2 6.5 1000 44 74 7.25 1250 42.6 72.6 8.5 1600 41 71 11.5 2000 38.2 68.2 11 2500 36.3 66.3 9.5 3150 34.2 64.2 9 4000 31 61 7.75 5000 26.5 56.5 6.25 6300 20.9 50.9 2.5

6

Figure 2: Articulation Index of a person (AI=0 or 0%)

Figure 3: Articulation Index of a person (AI=0.97 or 97%)



not able to hear any words, syllables etc.

correctly below the upper level A-

weighted sound pressure level for each

octave frequencies in this method.

Resulting in AI of 0%





weighted sound pressure level for all

octave frequencies except 3150Hz in this

method. Since sound pressure level

required was 44.2 dB(A), was between

lower 34.2dB(A) and upper 64.2 dB(A),

The Articulation Index dropped linearly.








required was 54.2 dB(A), was between

lower 34.2dB(A) and upper 64.2 dB(A),

The Articulation Index dropped linearly.

7


Hence, from the figures above it can be seen that if the Aweighted sound pressure level dB(A)

required by the intruding sound for a person exceeds the upper level for this method his/her

Articulation Index drops by the entire weight assigned to that octave frequency. On the other

hand if the Aweighted sound pressure level dB(A) required by the intruding sound for a person

is below the lower level for this method his/her Articulation Index retains the full weight

assigned to that octave frequency. For all other Aweighted sound pressure level dB(A) required

by the intruding sound the Articulation Index is linearly interpolated.

Articulation Index in different contexts

Open Plan Office In an open plan office the concept of speech privacy is a major concern. It is related to the extent

of speech disturbance between two individuals who are not in a conversation with each other,

one of whom is talking and the other is listening. This is a of concern to both individuals since

the listener would find the speech intrusive as the speech is not of any importance to him/her at

that point of time. On the other hand the speaker will be frustrated by the poor speech privacy as

the speech might be of personal or confidential in nature. An alternative single number rating for








required was 64.2 dB(A), equal to the

upper 64.2 dB(A), The Articulation Index

was reduced by the entire weight

assigned to 3150Hz.

8

speech privacy is called the Privacy Index (PI) and it is related to Articulation Index by the

following expression: 5 Equation 2: Privacy Index

( )1 100%PI AI=

Where

Privacy IndexArticulation Index

PIAI

==

Also the Articulation Index and Privacy Index and the related Subjective Impression are

provided in table 3:

Table 3: Articulation Index, Privacy Index and Subjective Impressions

Articulation Index

Privacy Index (%)

Speech Privacy Conditions

Communication Conditions

1.0 0 0.9 10 0.8 20 0.7 30

Excellent

0.6 40

Nil

Good 0.5 50 0.4 60 Very Poor Fair

0.3 70 0.2 80 Poor Poor

0.1 90 Acceptable Very Poor 0 100 Excellent Nil

To make the open office plan more favorable to speech privacy, the major vertical surfaces such

as walls need to be sound absorptive and sufficiently away from each other. Also the distance

between individual has to be sufficient and their sitting orientations have to be facing away from

each other.2

Classrooms While Architects and facility planner regularly specify appropriate lighting, required ventilation,

and environmental temperature levels for classrooms, they often overlook the issue of poor

acoustics. Poor acoustical designs of classrooms include noisy ventilation units, reflective walls,

floors, and roofs etc. For a student to hear the teacher and make sense of his/her speech and the

9

complex academic subject matters, an Articulation Index of 0.7 or more is required. But this is

typically not achieved due to the poor acoustics of the classrooms. The Articulation Index in the

center of a room 9 feet high by 20 feet by 15 feet (constructed with one glass window wall, three

gypsum board walls, a vinyl tile floor, and a painted concrete ceiling.) in eight different

conditions is summarized in the following table.3

The first condition assumed installation of the "loud" ventilation unit. The second condition replaces the "loud" unit with the "quiet" unit. The third and fourth conditions were the same ventilation units as the first and second.

Table 4: Articulation Index of Teacher's voice in Untreated and Treated Classrooms with Loud and Quiet Ventilation Units

Normal Voice Effort from teacher

Raised Voice Effort from teacher

Loud Ventilation Unit 0.0 0.09 Untreated Classroom Quiet Ventilation Unit 0.56 0.74

Loud Ventilation Unit 0.16 0.37 Treated Classroom Quiet Ventilation Unit 0.85 0.94

It can be seen that with the quiet ventilator, speech intelligibility is good in the treated room and

fair in the untreated room. Also even with raised voice effort, speech intelligibility is poor in the

room with the noisier ventilation system. An acoustically treated room includes application of

sound absorbing panels on one wall and a suspended acoustical ceiling.3

Medical Decisions Articulation Index also simplify the clinical decision making process of recommending hearing

aid to individuals with hearing loss. A study was based on AI computations for a group of

patients who had previously purchased their first hearing aids. It was found that 96% of patients

purchased a hearing aid had an Articulation Index of 0.50 or less whereas only 4% of patients

having AI less more than 0.50 obtained a hearing aid. From this it could be concluded that an AI

of 0.50 or less can be an excellent predictor of the need for a hearing aid.8

10

Conclusion

The purpose of this report was to educate the reader about the Articulation Index (both classical

and short), how it is calculated and its usefulness in many different aspects of life such as

classrooms, and offices design and medical decision making. The Articulation Index is a useful

and excellent tool for measuring the intelligibility of sound transmission system and has a

numerical value between 0 and 1 inclusive, where 0 indicate no speech can be understood and 1

means 100% understanding. This index is influenced by noise, interference and distortion.

While classical Articulation Index provides useful basis for examining a stationary system, short

time AI correctly predicting the sound intelligibility for an adaptive system which is changing

with time. While there are many different methods of calculating Articulation Index this report

discusses in depth the use of the lower and upper level A-weighted sound pressure level dB(A) a

speech need to have for a person to accurately listen to the speech.

This report also discusses the use of Articulation Index in different context such as classrooms,

and offices design and medical decision making. It was found that offices and classrooms have a

poor acoustical design in general and this leads to loss of privacy in open office designs and poor

classroom instruction conditions. It was found that classroom and offices need to be designed

with quieter ventilation units and sound absorbing surfaces to increase Articulation Index. It was

also found that Articulation Index can be used to decide whether or not to recommend a hearing

aid to a hearing impaired patient. An Articulation Index of 0.5 or less is found to be an excellent

indicator in this decision making.

11

References [1] Dirac Delta Consultants Limited, (2006). Articulation Index. Retrieved July 1, 2007, from DiracDelta Science & Engineering Encyclopedia Web site: http://www.diracdelta.co.uk/science/source/a/r/articulation%20index/source.html [2] Hegvold, L.W. (1971, 07). CBD-139. Acoustical Design of Open-Planned Offices. Retrieved July 2, 2007, from IRC - Institute for Research in Construction Web site: http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd139_e.html [3] Erdreich, J. (1999, 06). TEACHING IN THE DARK. Retrieved July 2, 2007, from CEFPI, The School Building Association Web site: http://www.cefpi.org/pdf/issue9.pdf [4] Meyer Sound, (2007). Speech Intelligibility Papers - Glossary. Retrieved July 2, 2007, from Meyer Sound Laboratories Inc. Web site: http://www.meyersound.com/support/papers/speech/glossary.htm [5] Andersson, N. Chigot, P. (2004, 08). Is the Privacy Index a good indicator for acoustic comfort in an open plan area?. Retrieved July 2, 2007, from Ecophon Acoustic Bulletin Web site: http://www.acousticbulletin.com/FR/PRIVACY_INTERNOISE.pdf [6] Kates, J. M. (1987). The short-time Articulation Index. Retrieved July 2, 2007, from Rehabilitation RandD Service Web Site Web site: http://www.rehab.research.va.gov/jour/87/24/4/pdf/kates.pdf [7] Marsh, A. (1999). Speech Intelligibility. Retrieved July 2, 2007, from Department of Electronics and Multimedia Communications Web site: http://www.kemt.fei.tuke.sk/Predmety/KEMT320_EA/_web/Online_Course_on_Acousti cs/intelligibility.html [8] Roth, A. Langford, J. Meinke, D. Long, G. (2007). Using the AI to Manage Patient Decisions. Retrieved July 2, 2007, from ADVANCE for Audiologists Web site: http://audiology.advanceweb.com/Common/editorial/editorial.aspx?CC=10203 [9] Armstrong Australia/New Zealand, (2007). Glossary. Retrieved July 2, 2007, from Armstrong Australia/New Zealand Website: http://www.armstrong-aust.com.au/commclgpac/aus/ep/au/article16865.html [10] Mueller, G. (1990, 09). An Easy Method for Calculating the Articulation Index. Retrieved July 2, 2007, from Etymotic Research, Inc. Web site: http://www.etymotic.com/pdf/erl-0020-1990.pdf

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Appendix

Raw Data Table 5: Data for Figure 1 200Hz = 23.1 dB(A) 250Hz = 30.4 dB(A) 315Hz = 34.4 dB(A) 400Hz = 38.2 dB(A) 500Hz = 41.8 dB(A) 630Hz = 43.1 dB(A) 800Hz = 44.2 dB(A) 1000Hz = 44 dB(A) 1250Hz = 42.6 dB(A) 1600Hz = 41 dB(A) 2000Hz = 38.2 dB(A) 2500Hz = 36.3 dB(A) 3150Hz = 34.2 dB(A) 4000Hz = 31 dB(A) 5000Hz = 26.5 dB(A) 6300Hz = 20.9 dB(A) Table 6: Data for Figure 2 200Hz = 60 dB(A) 250Hz = 70 dB(A) 315Hz = 70 dB(A) 400Hz = 70 dB(A) 500Hz = 80 dB(A) 630Hz = 80 dB(A) 800Hz = 80 dB(A) 1000Hz = 80 dB(A) 1250Hz = 80 dB(A) 1600Hz = 80 dB(A) 2000Hz = 70 dB(A) 2500Hz = 70 dB(A) 3150Hz = 70 dB(A) 4000Hz = 70 dB(A) 5000Hz = 60 dB(A) 6300Hz = 60 dB(A)

Table 7: Data for Figure 3 200Hz = 23 dB(A) 250Hz = 30 dB(A) 315Hz = 34 dB(A) 400Hz = 38 dB(A) 500Hz = 41 dB(A) 630Hz = 43 dB(A) 800Hz = 44 dB(A) 1000Hz = 43 dB(A) 1250Hz = 42 dB(A) 1600Hz = 40 dB(A) 2000Hz = 38 dB(A) 2500Hz = 36 dB(A) 3150Hz = 44.2 dB(A) 4000Hz = 30 dB(A) 5000Hz = 26 dB(A) 6300Hz = 20 dB(A) Table 8: Data for Figure 4 200Hz = 23 dB(A) 250Hz = 30 dB(A) 315Hz = 34 dB(A) 400Hz = 38 dB(A) 500Hz = 41 dB(A) 630Hz = 43 dB(A) 800Hz = 44 dB(A) 1000Hz = 43 dB(A) 1250Hz = 42 dB(A) 1600Hz = 40 dB(A) 2000Hz = 38 dB(A) 2500Hz = 36 dB(A) 3150Hz = 54.2 dB(A) 4000Hz = 30 dB(A) 5000Hz = 26 dB(A) 6300Hz = 20 dB(A)

Table 9: Data for Figure 5 200Hz = 23 dB(A) 250Hz = 30 dB(A) 315Hz = 34 dB(A) 400Hz = 38 dB(A) 500Hz = 41 dB(A) 630Hz = 43 dB(A) 800Hz = 44 dB(A) 1000Hz = 43 dB(A) 1250Hz = 42 dB(A) 1600Hz = 40 dB(A) 2000Hz = 38 dB(A) 2500Hz = 36 dB(A) 3150Hz = 64.2 dB(A) 4000Hz = 30 dB(A) 5000Hz = 26 dB(A) 6300Hz = 20 dB(A)

13

Calculations Sample Calculation for table 10 Overall Level Equation 3: Total A-Weighted Sound Pressure Level dB(A)

10

1

23.1 30.4 34.4 38.2 41.8 43.1 44.2 44 42.610 10 10 10 10 10 10 10 10

41 38.2 36.3 34.2 31 26.5 20.910 10 10 10 10 10 10

10log 10

10 10 10 10 10 10 10 10 1010log 51.58 ( )

10 10 10 10 10 10 10

piLn

pti

L

dB A

=

= + + + + + + + + = = + + + + + + +

Equation 4: Articulation Index ( )

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

Articulation Index AI Weighting Linear Value

1 1 2 1 3.25 1 4.25 1 4.5 1 5.25 1 6.5 1 7.25 1

8.5 1 11.5 1 11 1 9.5 1 9 1 7.75 1 6.25 1 2.5 1 100%

= = + + + + + + ++ + + + + + + + =

Table 10: Calculation for Figure 1

1/3 Octave Centre frequency Hz

AI lower level dB(A)

AI upper level dB(A) AI Weighting

dB(A) requirement for this person linear value

Weight x Linear Value

200 23.1 53.1 1 23.1 1 0.01250 30.4 60.4 2 30.4 1 0.02315 34.4 64.4 3.25 34.4 1 0.0325400 38.2 68.2 4.25 38.2 1 0.0425500 41.8 71.8 4.5 41.8 1 0.045630 43.1 73.1 5.25 43.1 1 0.0525800 44.2 74.2 6.5 44.2 1 0.065

1000 44 74 7.25 44 1 0.07251250 42.6 72.6 8.5 42.6 1 0.0851600 41 71 11.5 41 1 0.1152000 38.2 68.2 11 38.2 1 0.112500 36.3 66.3 9.5 36.3 1 0.0953150 34.2 64.2 9 34.2 1 0.094000 31 61 7.75 31 1 0.07755000 26.5 56.5 6.25 26.5 1 0.06256300 20.9 50.9 2.5 20.9 1 0.025

Overall Level dB(A) 51.58 Articulation Index 100%

14







200 23.1 53.1 1 60 0 0250 30.4 60.4 2 70 0 0315 34.4 64.4 3.25 70 0 0400 38.2 68.2 4.25 70 0 0500 41.8 71.8 4.5 80 0 0630 43.1 73.1 5.25 80 0 0800 44.2 74.2 6.5 80 0 0

1000 44 74 7.25 80 0 01250 42.6 72.6 8.5 80 0 01600 41 71 11.5 80 0 02000 38.2 68.2 11 70 0 02500 36.3 66.3 9.5 70 0 03150 34.2 64.2 9 70 0 04000 31 61 7.75 70 0 05000 26.5 56.5 6.25 60 0 06300 20.9 50.9 2.5 60 0 0

Overall Level dB(A) 88.28 Articulation Index 0% Table 12: Calculation for Figure 3






200 23.1 53.1 1 23 1 0.01250 30.4 60.4 2 30 1 0.02315 34.4 64.4 3.25 34 1 0.0325400 38.2 68.2 4.25 38 1 0.0425500 41.8 71.8 4.5 41 1 0.045630 43.1 73.1 5.25 43 1 0.0525800 44.2 74.2 6.5 44 1 0.065

1000 44 74 7.25 43 1 0.07251250 42.6 72.6 8.5 42 1 0.0851600 41 71 11.5 40 1 0.1152000 38.2 68.2 11 38 1 0.112500 36.3 66.3 9.5 36 1 0.0953150 34.2 64.2 9 44.2 0.6666667 0.064000 31 61 7.75 30 1 0.07755000 26.5 56.5 6.25 26 1 0.06256300 20.9 50.9 2.5 20 1 0.025


15







200 23.1 53.1 1 23 1 0.01250 30.4 60.4 2 30 1 0.02315 34.4 64.4 3.25 34 1 0.0325400 38.2 68.2 4.25 38 1 0.0425500 41.8 71.8 4.5 41 1 0.045630 43.1 73.1 5.25 43 1 0.0525800 44.2 74.2 6.5 44 1 0.065

1000 44 74 7.25 43 1 0.07251250 42.6 72.6 8.5 42 1 0.0851600 41 71 11.5 40 1 0.1152000 38.2 68.2 11 38 1 0.112500 36.3 66.3 9.5 36 1 0.0953150 34.2 64.2 9 54.2 0.3333333 0.034000 31 61 7.75 30 1 0.07755000 26.5 56.5 6.25 26 1 0.06256300 20.9 50.9 2.5 20 1 0.025

Overall Level dB(A) 55.89 Articulation Index 94% Table 14: Calculation for Figure 5






200 23.1 53.1 1 23 1 0.01250 30.4 60.4 2 30 1 0.02315 34.4 64.4 3.25 34 1 0.0325400 38.2 68.2 4.25 38 1 0.0425500 41.8 71.8 4.5 41 1 0.045630 43.1 73.1 5.25 43 1 0.0525800 44.2 74.2 6.5 44 1 0.065

1000 44 74 7.25 43 1 0.07251250 42.6 72.6 8.5 42 1 0.0851600 41 71 11.5 40 1 0.1152000 38.2 68.2 11 38 1 0.112500 36.3 66.3 9.5 36 1 0.0953150 34.2 64.2 9 64.2 0 04000 31 61 7.75 30 1 0.07755000 26.5 56.5 6.25 26 1 0.06256300 20.9 50.9 2.5 20 1 0.025


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Noise Articulation Index Calc