A simple SPL distance screen can be useful during early audio planning, but it must stay inside its source boundaries. The local arithmetic starts with a loudspeaker sensitivity value, adds amplifier power gain, subtracts point-source distance loss, and optionally adds an ideal equal-level source count. That is not the same as a measured venue result or a complete sound-system design.
Real systems depend on speaker directivity, phase, delay, array geometry, limiter behavior, thermal compression, room reverberation, audience absorption, wind, ground effects, atmospheric absorption, and local noise rules. Use this guide to keep the Inverse Square Law / SPL Calculator as a first-pass estimate, not as coverage approval, OSHA/NIOSH exposure compliance, or permit documentation.
Point-Source Distance Arithmetic
The local screen uses SPL at distance = SPL at reference - 20 × log10(d/d_ref), where the reference is treated as 1 meter. This gives the familiar point-source free-field result of about 6 dB loss per doubling of distance.
That formula is a boundary, not a complete prediction. It does not include directivity, line-array behavior, near-field effects, room gain, critical distance, atmospheric absorption, wind, audience absorption, barriers, reflections, or equipment protection. Use it to see whether a simple assumption is plausible enough for more detailed design, measurement, or vendor review.
Inverse Square Law / SPL Calculator
Calculate sound pressure level at any distance from speaker sensitivity, amplifier power, array configuration, and environment.
What the Screen Does Not Model
Coverage is where simple SPL arithmetic can become misleading. A loudspeaker data sheet may publish nominal horizontal and vertical coverage angles, but usable coverage depends on frequency, mounting height, aiming, listener area, adjacent sources, room surfaces, and the selected product.
The ToolGrit screen does not calculate coverage angles, line arrays, delay zones, coherent pressure summing, cancellation, comb filtering, or directivity. Its source-count row is limited to 10×log10(N) ideal equal-level energy summing. Treat that as a screening assumption only.
Speaker Ratings and Power Basis
The screen adds amplifier power gain as 10×log10(watts / 1 W). That works only when the entered speaker rating is compatible with the wattage basis. Many products publish 2.83 V / 1 m sensitivity, maximum peak SPL, in-room values, or bandwidth-specific measurements that cannot be swapped blindly with 1 W / 1 m sensitivity.
Amplifier and loudspeaker decisions also need impedance, continuous and peak ratings, limiter behavior, thermal compression, distortion, warranty limits, product protection, electrical safety, and manufacturer instructions. The local screen does not approve amplifier selection or speaker protection settings.