dB SPL Calculator
Estimate Sound Pressure Level at a distance.
What is Sound Pressure Level (SPL)?
Sound Pressure Level (SPL) is the objective measure of the "loudness" of a sound wave relative to the threshold of human hearing (20 µPa). Because the human ear has a massive dynamic range, we use the decibel (dB) log scale.
This calculator determines how loud a speaker will be at a specific distance, based on its manufacturer specifications (Sensitivity) and the amplifier power.
The Inverse Square Law
Sound spreads out as a sphere. As the radius of the sphere doubles, the energy is spread over 4x the area. This leads to the fundamental rule of acoustics:
Every doubling of distance = -6 dB drop in SPL
Calculation Formula
SPLdist = SPL1m - 20×log₁₀(Distance)
Where SPL1m is the SPL at 1 meter, calculated from the speaker's sensitivity and input power:
SPL1m = Sensitivity + 10×log₁₀(Power)
Practical Applications
- Concerts & Events: Audio engineers use this to calculate how many speakers and watts are needed so that people in the back row (50m away) can still hear clearly.
- Safety (OSHA): Determining if machinery noise levels at a worker's station exceed safe limits (85 dB).
- Home Theater: Calibrating speakers to "Reference Level" (usually 85 dB or 75 dB) at the listening position.
FAQ
Does doubling power double loudness?
No. Doubling the power (e.g., 100W to 200W) only adds +3 dB. To double the perceived loudness (which requires roughly +10 dB), you need 10x the power!
What is "A-Weighting"?
dBA or A-weighting is a filter that alters the reading to match human hearing. Our ears are less sensitive to bass and treble. This calculator assumes flat (Z-weighted) response, but dBA is used for safety/legal noise limits.
What is the "Threshold of Pain"?
Around 120-130 dB SPL. At this level, sound becomes physical pain and instant hearing damage can occur. A jet engine taking off is ~140 dB.