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Boom Mic Distance Calculator

Enter the source and boom-mic distances to see the level change and the recommended mic placement.

How it is calculated

Both distances are measured from the sound source (the actor's mouth) in inches. d1 is the reference distance and d2 is the boom mic distance you are considering. By the inverse-square law, the level at d2 compared with d1 changes by ΔdB = 20 × log₁₀(d1 ÷ d2), rounded to one decimal. A positive number means louder (the mic is closer than the reference), a negative number quieter. The distance ratio shown is d2 ÷ d1. Every doubling of distance costs about 6 dB. The recommendation looks only at d2: between 12 and 36 inches (1 to 3 ft) it says that range is ideal, outside it suggests moving the boom into 12–36 inches. Both distances must be above zero, otherwise no result is shown.

Worked example

Your reference distance is 48 inches and you can bring the boom down to 24 inches. The ratio d1 ÷ d2 is 48 ÷ 24 = 2, and log₁₀(2) = 0.301, so ΔdB = 20 × 0.301 = 6.0 dB (louder). The distance ratio is d2 ÷ d1 = 24 ÷ 48 = 0.50×. Because 24 inches lies inside the 12 to 36 inch band, the note reads "Closer is cleaner — 1–3 ft is ideal". Starting from 24 inches and pushing the boom out to 72 inches would instead give -9.5 dB, and the tool would suggest moving it back to 12–36 inches.

Try this example →

Common mistakes

  • Typing the distances in feet or centimetres. The fields are inches, so 3 ft must be entered as 36; otherwise the 12 to 36 inch check judges the wrong number.
  • Swapping the two distances. The sign flips: 48 to 24 inches gives 6.0 dB, but 24 to 48 gives -6.0 dB.
  • Measuring from the boom pole or the camera instead of from the mouth. The inverse-square law uses the distance between mic and source.
  • Expecting the dB change to model room reverberation. The law assumes a free field; in a reflective room the level falls by less than 6 dB per doubling and the balance of direct sound to reverb gets worse.
  • Treating the dB figure as the whole story. It ignores the microphone's pickup pattern, so a mic pointed away from the mouth loses level on top of the distance loss.

About this calculator

Sound pressure level follows the inverse-square law — every time you double the distance from a sound source, the level drops by about 6 dB — which makes microphone placement on a boom pole a precise, calculable decision rather than guesswork. This calculator finds the dB change when a boom mic moves from one distance to another using ΔdB = 20·log₁₀(d₁/d₂); enter both distances in inches.

Moving a mic from 24 inches (2 feet) to 48 inches (4 feet) away from a speaker's mouth drops the level by about 6 dB — enough to noticeably hurt the signal-to-noise ratio in a room with background hum or hiss. That's why boom operators aim to hold the mic as close as the shot allows, typically 12–36 inches (1–3 feet) from the actor's mouth while staying out of frame.

Boom operators and production sound mixers use this relationship to judge how much headroom they're trading away every time a wide shot forces the mic further from the actor than the ideal working distance.

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Comments (1)

  • Editorial team

    The moves that cost the most are not always the obvious ones. Going from 24 inches out to 36 inches, still inside the recommended band, costs 3.5 dB, while going from 24 out to 96 inches costs 12.0 dB, which the tool flags with a suggestion to come back in. Use the first distance as the level you set on the recorder and the second as the shot's limit. What is the widest frame you have to cover on your shoots?

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