OHTA503Tools

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IEH OHTA 503

IEH OHTA 503 Student Tools

Use these interactive tools to practise common calculations used in occupational noise assessment, including logarithmic decibel calculations, task-based exposure assessment, daily exposure normalisation and hearing protection estimates.

Learning note: These tools are for student practice and training support. For workplace compliance work, always refer to the applicable legislation, recognised standards, calibrated instruments and competent professional judgement.
Basic sound calculation

Decibel Addition Calculator

Use this calculator to combine unrelated sound levels. Decibels are logarithmic, so values must be added by energy, not by simple arithmetic.

Example: 85, 89, 90
Method: Ltotal = 10 log10(Σ 10^(Li/10))
Basic sound calculation

Decibel Average Calculator

Use this calculator to find the logarithmic average of repeated sound level readings. This is useful when several measurements are taken at the same position or for similar conditions.

Example: 81, 86, 82, 84
Method: Lavg = 10 log10[(1/n) × Σ 10^(Li/10)]
Basic sound calculation

Decibel Subtraction Calculator

Use this calculator to estimate the remaining sound level when one known source is removed from a measured combined sound level. Decibel subtraction must be carried out by subtracting acoustic energy, not by simple arithmetic.

Example: total measured level from two or more sources.
This value must be lower than the combined level.
Method: Lremaining = 10 log10(10^(Ltotal/10) − 10^(Lknown/10))
Exposure assessment

Task-Based Daily Noise Exposure Calculator

Enter the sound level and duration for each task. The tool estimates the normalised daily exposure level, LAeq,8h.

Task or activity LAeq,T dBA Duration Unit Remove
Method: LAeq,8h = 10 log10[(1/8) × Σ ti × 10^(LAi/10)], where time is expressed in hours.
Exposure normalisation

LEX,8h / LAeq,8h Normaliser

Use this calculator when you already have an equivalent continuous A-weighted level for a known exposure duration.

Method: LEX,8h = LAeq,Te + 10 log10(Te / 8)
Exposure time planning

Maximum Exposure Time Calculator

Estimate the maximum exposure duration for a selected criterion level and exchange rate. Students may compare the 85 dBA / 3 dB approach with the 90 dBA / 5 dB approach used in some jurisdictions.

Select 85 dBA for the 3 dB equal-energy approach, or 90 dBA for OSHA-style examples.
A 3 dB exchange rate halves allowable time for every 3 dB increase. A 5 dB exchange rate halves allowable time for every 5 dB increase.
Method: T = 8 × 2^((Criterion − L) / Exchange Rate), where T is in hours.
Frequency analysis

Octave-Band Overall Level Calculator

Enter octave-band sound pressure levels and select A, C or Z weighting. The calculator applies the selected weighting correction to each band and then combines the bands logarithmically.

Leave any octave band blank if it was not measured.
Octave band centre frequency Measured band level, dB A correction, dB C correction, dB
16 Hz-56.7-8.5
31.5 Hz-39.4-3.0
63 Hz-26.2-0.8
125 Hz-16.1-0.2
250 Hz-8.60.0
500 Hz-3.20.0
1000 Hz0.00.0
2000 Hz+1.2-0.2
4000 Hz+1.0-0.8
8000 Hz-1.1-3.0
16000 Hz-6.6-8.5
Method: Overall level = 10 log10(Σ 10^((Li + correctioni)/10)). For Z-weighting, the correction is 0 dB for each entered band.
Hearing conservation

Hearing Protection Estimated Protected Level

Estimate the sound level at the ear after applying a simplified hearing protector rating. This is a learning estimate only; actual protection depends strongly on fit, training, maintenance and wearing time.

Simple learning method: Protected level = Measured noise level − (Rating × Derating factor). For formal assessment, use the rating method required by the relevant standard or regulation.
Hearing conservation

Hearing Protection Calculators

Use these tools to practise common hearing protector calculations. They are designed to help students understand estimated protected level, wearing-time effects, dual protection and required attenuation. Actual protection depends on protector fit, training, maintenance and correct use throughout exposure.

Hearing protection

Estimated Protected Level

Estimate the sound level at the ear after applying a hearing protector rating and an optional derating factor.

Simple learning method: Protected level = Noise level − (Rating × Derating factor)
Hearing protection

Wearing-Time Effect Calculator

Show how removing hearing protection for short periods can significantly reduce the effective protection achieved over a shift.

Method: Leffective = 10 log10[(tworn × 10^(Lprotected/10) + tremoved × 10^(Lunprotected/10)) / (tworn + tremoved)]
Hearing protection

Dual Protection Estimate

Estimate protection when earplugs and earmuffs are worn together. A common training approximation is to use the higher rating plus an additional 5 dB, before applying any chosen derating factor.

Training approximation: Dual rating estimate = max(Earplug rating, Earmuff rating) + 5 dB
Hearing protection

Required Attenuation Calculator

Estimate the minimum effective attenuation needed to reduce a measured noise level to a selected target level.

This estimates what labelled rating may be needed if only part of the rating is achieved in practice.
Method: Required effective attenuation = Noise level − Target protected level

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