| Scenario | Source @ Ref | Distance | Attenuation | Penalties | Background | Predicted | Limit | Impact |
|---|---|---|---|---|---|---|---|---|
| Generator near homes (night) | 90 dB(A) @ 1 m | 30 m | Ground 2, Barrier 5, Air 0 | Tonal 2, Impulse 0, Intermittent 0 | 45 dB(A) | ~49–55 dB(A) | 45 dB(A) | Moderate to Major |
| Workshop (day) | 85 dB(A) @ 1 m | 50 m | Ground 3, Barrier 0, Air 1 | Tonal 0, Impulse 0, Intermittent 0 | 50 dB(A) | ~42–48 dB(A) | 55 dB(A) | Negligible |
This calculator applies a screening propagation model using spherical spreading from a measured reference level:
- Lp_single = L_ref − 20·log10(distance / d_ref) − A_ground − A_barrier − A_air
- Lp_multi = Lp_single + 10·log10(N)
- Lp_character = Lp_multi + (tonal + impulse + intermittency)
- Lp_total = 10·log10(10^(Lp_character/10) + 10^(L_background/10)) (if enabled)
Impact category is based on exceedance: 0–3 dB Minor, 3–6 dB Moderate, >6 dB Major.
- Enter the measured or rated noise level at a known reference distance.
- Set the receiver distance and number of identical sources operating.
- Add realistic attenuation for ground, barriers, and air absorption.
- Apply character penalties only if clearly present at the receiver.
- Choose receptor type and period, or enter a custom limit.
- Submit to view predicted levels and exceedance above the form.
- Export a CSV or PDF report for documentation and review.
1) What does “source level at reference distance” mean?
It is a measured or rated dB(A) level at a known distance, such as 1 meter from equipment. The calculator scales this level to the receiver using distance spreading and attenuation inputs.
2) Why does distance reduce noise so much?
For an ideal point source outdoors, sound spreads over a growing sphere. That produces a 20·log10(distance) reduction. Real sites may differ due to reflections, terrain, and wind.
3) How are multiple sources combined?
Decibels are logarithmic, so identical sources add using 10·log10(N). Two equal sources increase level by about 3 dB, and four equal sources increase it by about 6 dB.
4) Should I enable background combination?
Enable it when you want an overall ambient prediction at the receptor. Disable it when you need the project contribution only, such as compliance checks based on incremental noise criteria.
5) What are tonal and impulse penalties?
Tonal penalties address prominent hums or whines. Impulse penalties address bangs or impacts. These adjustments reflect higher annoyance compared to steady broad-spectrum noise at the same level.
6) Are the built-in limits legally binding?
No. They are typical screening values used for quick assessment. Always confirm your local jurisdiction’s criteria and use the custom limit field when you have a project-specific requirement.
7) What does the impact category indicate?
It indicates how far the predicted level is above the selected limit. Minor exceedances may be managed with operational controls. Major exceedances typically require engineering mitigation or redesign.
8) When should I commission a detailed noise study?
Commission a study for high-stakes sites, strong community sensitivity, complex terrain, multiple sources, or when predictions are near limits. Detailed modeling and measurements provide higher confidence and defensible reporting.