Inverse Square Law / SPL Calculator

Free SPL distance calculator for live sound engineers, AV technicians, and event planners who need an early check of point-source sound pressure level at a listener distance. Enter the loudspeaker sensitivity basis, amplifier power, listener distance, equal-level source count, and local environment row; the calculator applies 20×log10(distance) free-field distance loss and 10×log10(N) ideal source gain.

This is a preliminary planning calculation, not a system-design program. It does not model line arrays, coverage angles, directivity, delay zones, phase summing, comb filtering, atmospheric absorption, wind, ground effects, room reverberation, audience absorption, limiter behavior, thermal compression, or manufacturer maximum-SPL ratings.

Hearing-safety output is intentionally bounded. The app flags modeled levels near OSHA/NIOSH context, but it does not compute A-weighted time-weighted exposure, noise dose, hearing-protector attenuation, OSHA compliance, NIOSH REL compliance, or noise-ordinance status. Use calibrated measurements and qualified audio/acoustics/safety review before operational decisions.

Pro Tip: Verify the speaker data-sheet basis before using the result. A 1 W / 1 m sensitivity value, a 2.83 V / 1 m sensitivity value, a peak maximum-SPL value, and an in-room marketing rating are not interchangeable.

Check projection throw-ratio and brightness prompts for video

Projection Throw Ratio & Lens Calculator →

Size temporary power distribution for your event

Event Power Distribution Calculator →

Check worker noise dose before hearing-program review

Noise Dose & TWA Calculator →

Read the guide on SPL distance planning boundaries

SPL Distance Guide →

How It Works

Enter the Speaker Rating Basis

Input the sensitivity value you intend to calculator, normally a manufacturer 1 W / 1 m value. Do not mix sensitivity, peak maximum SPL, 2.83 V ratings, and in-room marketing values without checking the data sheet.
Enter the Listener Distance

Input the straight-line distance from source to listener in feet or meters. The app converts feet to meters and applies a local 20×log10(distance / 1 m) point-source loss.
Set Equal-Level Source Count

Use the source count only as ideal energy summing, 10×log10(N). Real phase, delay, spacing, aiming, and room/audience effects can add or subtract level.
Review Warnings Before Use

Read the OSHA/NIOSH and manufacturer-data warnings. The result is not a calibrated SPL measurement, safe-exposure decision, ordinance check, or final sound-system design.

Built For

Live sound crews doing a first-pass point-source level check before measurement and tuning
AV technicians comparing speaker sensitivity and amplifier power assumptions during planning
Event planners documenting why measured SPL, qualified audio review, and hearing-safety review are still required
Facility teams screening whether a simple loudspeaker assumption is clearly too low before vendor design

Features & Capabilities

Point-Source Distance Loss

Applies SPL2 = SPL1 - 20×log10(D2/D1) from a 1-meter reference and shows the local loss at the listener distance.

Equal-Level Source Gain

Uses 10×log10(N) for ideal equal-level energy summing. It does not predict coherent addition, cancellation, comb filtering, or array behavior.

OSHA/NIOSH Boundary Warnings

Separates OSHA 90 dBA 8-hour PEL table context from the 85 dBA OSHA action level and NIOSH REL context, and reminds users that measured A-weighted exposure is required.

Source Pointer Export

Report and PDF output include source pointers and warnings so the calculation is not detached from its assumptions.

Frequently Asked Questions

How much does sound level drop with distance?

For the local point-source calculator, level changes by 20×log10(distance ratio), which is about 6 dB per distance doubling. That simple row is not a complete outdoor propagation, indoor room, line-array, or directivity model.

Does this calculate coherent SPL addition?

No. The app uses 10×log10(N) equal-level energy summing. Coherent pressure summing, cancellation, comb filtering, delay, and array behavior require geometry, frequency, phase, and measurement data outside this calculator.

Is 85 dB an OSHA exposure limit?

Not as a generic PEL. OSHA 1910.95 Table G-16 lists 90 dBA for 8 hours, while 85 dBA is the hearing-conservation action level. NIOSH uses 85 dBA as an eight-hour recommended exposure limit with a 3 dB exchange rate. The app output is modeled dB SPL, not measured dBA TWA or dose.

Can this be used for noise permits or hearing protection?

No. Noise ordinance, OSHA, NIOSH, and hearing-protector decisions need calibrated A-weighted measurements, exposure duration, dose calculations, local rules, and qualified review.

Disclaimer: This screen applies local point-source SPL arithmetic for planning only. It is not ISO 9613-2, AES2 measurement verification, room acoustics, line-array prediction, calibrated SPL measurement, OSHA/NIOSH compliance, hearing-protector selection, noise-ordinance review, or final sound-system design.

Learn More

Live Events

SPL Distance Planning Boundaries

How to use point-source SPL distance arithmetic while keeping speaker-rating, OSHA/NIOSH, measurement, and design limits visible.

Read Guide →

Live Events

Temporary Event Power Distribution

How to size generators, feeder cable, and company switches for live events with 3-phase load balancing across audio, lighting, video, and motor loads.

Read Guide →

Related Tools

Live Events Live

Projection Throw Ratio & Lens Calculator

Calculate projector throw ratio, lens type, and screen brightness in foot-lamberts for AV installations.

Launch Tool →