Speaker SPL at Distance Calculator (Inverse Square Law)
Calculate the sound pressure level (SPL in dB) at any distance from a speaker using the inverse square law (-6 dB per doubling of distance). Optional atmospheric absorption modeling for high frequencies (HF rolloff over distance). For live audio engineers, FOH operators, and AV designers.
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Last reviewed: April 2026Report an error
From spec sheet, typically 130-140 dB SPL @ 1m.
SPL at Listener
105.5 dB SPL
At 30m from a 135 dB @ 1m source, SPL drops by 29.5 dB to 105.5 dB SPL. Inverse square law: -6 dB per doubling of distance.
SPL @ Listener
105.5 dB
Total Attenuation
29.5 dB
OSHA 8hr Limit
90 dB
Source: ISO 9613-2 (free-field inverse square law). Assumes point source. Line arrays follow different rules in their near field.
SPL Drop Over Distance
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The Formula
- SPL(d) = Sound pressure level at distance d (dB)
- SPL(1m) = Speaker rated SPL at 1 meter (dB, manufacturer spec)
- d = Distance from speaker, in meters
- −6 dB = SPL drop per doubling of distance (the "rule of thumb")
How to Use This Speaker SPL Calculator
- 1Enter the speaker's rated SPL at 1 meter (manufacturer spec, 1W input).
- 2Enter the distance from the speaker to the listening position in meters.
- 3Optionally enable air absorption for outdoor/long-throw applications.
- 4Read SPL at that distance and view the curve from 1m to 50m.
Frequently Asked Questions
- Free-field sound pressure drops by 6 dB for every doubling of distance. So a speaker producing 100 dB at 1m produces 94 dB at 2m, 88 dB at 4m, 82 dB at 8m, etc. This assumes a point source in free space (no walls or ceiling reflecting energy back).
- No — line arrays are LINE sources, not point sources. Their near-field falloff is only -3 dB per doubling, which is why concert PAs reach the back row. The inverse square law applies in their far-field (typically beyond 30m) and to point-source speakers (single boxes, conventional setups).
- Reverberation builds the noise floor in indoor spaces, so SPL doesn't fall as steeply as in free field. In a typical reverberant room, SPL might drop only 3-5 dB per doubling of distance past the critical distance.
- For distances under 30m, air absorption is negligible. For outdoor stadium and festival applications (50m+), high frequencies (above ~4kHz) lose an additional 0.3-1 dB per 100m at typical humidity. Enable the option for those.
- OSHA permits 90 dB for 8 hours, with 5 dB exchange rate (95 dB for 4 hours, 100 dB for 2 hours, etc.). NIOSH is stricter: 85 dB for 8 hours, 3 dB exchange. Concerts often hit 100-110 dB at FOH — required hearing protection territory.
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