SPL to Distance Calculator
This table will include key information, formulas, and rules of thumb to help you understand and calculate SPL changes with distance.
SPL and Distance: Everything You Need to Know
| Aspect | Description |
|---|---|
| Basic Relationship | SPL decreases as distance from the sound source increases |
| Inverse Square Law | Sound intensity decreases proportionally to the square of the distance from the source |
| 6 dB Rule | SPL decreases by 6 dB for each doubling of distance from a point source124 |
| Formula for SPL at Distance | p = pn + 10 × log(P) – 20 × log(d)1 |
| Where: p = SPL at distance d, pn = characteristic SPL, P = power in watts, d = distance in meters | |
| Distance Attenuation Formula | SPL2 = SPL1 – 20 × log(R2/R1)3 |
| Where: SPL1 and SPL2 are sound levels at distances R1 and R2 respectively | |
| Power and SPL Relationship | Doubling the power increases SPL by 3 dB1 |
| Perceived Loudness | A 10 dB increase is perceived as approximately twice as loud4 |
| Minimum Audible Change | The smallest change in SPL detectable by human ears is about 3 dB4 |
| Reference SPL | 0 dB SPL is the threshold of human hearing, referenced to 20 μPa4 |
| Pain Threshold | Approximately 120-130 dB SPL34 |
| Typical Environmental Range | 0 dB (threshold of hearing) to 140 dB (threshold of pain)4 |
| SPL Calculation | SPL (dB) = 20 × log(p/p0), where p is sound pressure and p0 is reference pressure (20 μPa)4 |
| Frequency Considerations | Low frequencies generally travel further than high frequencies |
| Environmental Factors | Humidity, temperature, and obstacles can affect sound propagation |
Key Takeaways:
- Use the 6 dB rule for quick estimations: SPL drops by 6 dB each time the distance doubles124.
- For precise calculations, use the distance attenuation formula: SPL2 = SPL1 – 20 × log(R2/R1)3.
- Remember that doubling the power only increases SPL by 3 dB1.
- A 10 dB increase in SPL is generally perceived as twice as loud4.
- Consider environmental factors and frequency when making real-world predictions.
This table provides a comprehensive overview of the relationship between SPL and distance, including key formulas, rules of thumb, and important considerations for acoustic calculations and estimations.