1) Pick your measurement and weighting

Use dB(A) for general environmental noise and dB(C) when low‑frequency content matters (e.g., live music, machinery).

2) Measure or enter levels

• Single source: Enter the level in dB, choose distance if supported.
• Multiple sources: Enter each level; the calculator performs logarithmic addition.

Tip: Two equal sources add +3 dB, not +6 dB.

3) Account for distance

Sound in free field drops ~6 dB per distance doubling. If a source is 90 dB at 1 m, it’s ≈84 dB at 2 m and ≈78 dB at 4 m.

4) Time weighting / LAeq

For varying noise, use LAeq to compute an equivalent continuous level over a set period.

Worked examples

• Two fans at 70 dB: Result ≈ 73 dB combined.
• Leaf blower at 90 dB @ 1 m, listener at 4 m: ≈ 78 dB.
• Office background 55 dB + conversation 60 dB: ≈ 61 dB total.

Safety quick reference

At 85 dB, NIOSH recommends about 8 hours; every +3 dB halves the safe time. Wear hearing protection for prolonged exposures.

5) Calibration Tips

For casual checks, a phone app is fine; for decisions, use a calibrated meter.

• Field check: If you have a 94 dB or 114 dB calibrator, verify before/after a session.
• Orientation: Point the mic toward the dominant source unless your meter specifies otherwise.
• Wind: Use a windscreen outdoors; even a light breeze can add 5–10 dB spikes.

6) Weighting & Time Settings

A‑weighting approximates human hearing; use it for environmental noise. C‑weighting keeps more low‑frequency content for machinery or live music. Time response: Fast for transient changes, Slow for steadier displays. Use LAeq to average over minutes or hours.

7) Combining Sources: The Actual Math

To combine N sources at levels Lᵢ (dB): convert each to linear power, sum, and convert back.

Pᵢ = 10^(Lᵢ/10)   →   P_total = Σ Pᵢ   →   L_total = 10·log₁₀(P_total)

Rules of thumb: two equal sources add ≈ +3 dB; add a source that is 10 dB quieter → effect is < 0.5 dB.

8) Distance & Environment

• Free field (outdoors): −6 dB per distance doubling.
• Rooms: reflections reduce loss; expect −3 to −6 dB per doubling depending on absorption.
• Directional sources: Levels fall faster off‑axis; verify with a few angles.

9) Exposure Estimation (Rule of 3 dB)

A common guideline: 85 dB for 8 hours; each +3 dB halves allowed time.

When in doubt, wear hearing protection and take quiet breaks.

10) Measurement Checklist

• Pick weighting (A or C) and time response (Fast/Slow).
• Note the distance and environment (outdoor/indoor).
• Take multiple readings (center and edges) and log the max and LAeq.
• Document source details (model, speed, number of units).
• If combining, record each source separately before running the math.

11) Scenario Walkthroughs

Two box fans, each 70 dB @ 1 m

Equal sources: 70 dB + 70 dB → 73 dB combined.

Lawn mower 90 dB @ 1 m, listener @ 4 m

Distance loss (≈ −12 dB): ≈ 78 dB at 4 m.

Office background 55 dB + conversation 60 dB

Combine: 60 dB dominates; total ≈ 61 dB.

12) Troubleshooting

• Numbers jump wildly: switch to Slow response, shield mic from wind.
• Too low/high: check weighting; C often reads higher for bass‑heavy sound.
• Meter button didn’t scroll: ensure the homepage has an element with id="meter" (already added).

Downloadable Cheat Sheet

Copy the “Rules of thumb” and “Exposure table” into your classroom or shop. A one‑page PDF can be generated on request.

Use consistent mic positioning

When you compare two noise sources or room setups, try to keep the microphone in the same place each time. Marking a spot on a desk or tripod can reduce guesswork so you are not accidentally measuring a quieter corner on one day and a louder one on another.

Log context, not just numbers

A reading such as “72 dB” becomes much more useful when you note what was happening at the time: number of people present, type of activity, windows open or closed, and the distance to the main source. Simple notes like these help you understand why a space feels different on two days with the same average level.

Look for trends over time

Instead of chasing perfectly accurate single snapshots, pay attention to trends. If your typical evening listening level slowly creeps from the mid‑60s to the high‑70s dB over a few months, that is a gentle warning sign that habits are changing—even if your phone or laptop mic is not perfectly calibrated.

Chasing single-number perfection

It is tempting to keep re-measuring until two tools display the same value, but that pursuit rarely helps for everyday use. Small differences between devices are normal. Focus instead on consistent procedure and clear before-and-after comparisons.

Measuring from unrealistic positions

Some people hold the microphone directly against a speaker or stand in a location they would never actually occupy while listening. Try to measure where your ears are, at the height and distance you usually spend time. That makes the results more actionable.

Ignoring how long the sound lasts

Numbers alone do not capture duration. A short burst at a high level is very different from hours at a moderately elevated level. When you document your readings, note whether the sound was continuous, intermittent, or just an isolated peak.

When you show someone a reading from the meter, include a short description of how you measured it: where you were standing, how long you observed, and what was happening in the space. That context makes the information easier to understand and reduces the chance of defensiveness.

It can also help to lead with your experience—how the sound affects your focus, comfort, or sleep—rather than treating the number as a verdict. The meter becomes a neutral reference point you are both looking at together, instead of something you use to prove a point.

A quick sound check before a gathering, rehearsal, or recording session can prevent problems later. Take a short reading at the loudest point you expect, then decide whether you need to adjust placement, add treatment, or remind participants about volume. A few minutes of preparation often saves you from distractions or fatigue halfway through.